Stem and Root Anatomy and Functions. Vegetative Propagation

What are root's functions? The three universal functions of all roots are anchorage, absorption and translocation of water with dissolved mineral nutrients. In many perennial and biennial species, roots are also sites for food storage. These food reserves keep the plant alive through the non-growing season, and are used to resume growth in spring or after cutting or grazing. Some species that store food in their roots are yams, alfalfa and red clover. Food storage organs of some vegetables (carrots, beets, and radishes) are actually a combination of root and stem tissues.

Types of root systems There are two major types of root systems: fibrous and taproot (left). Grasses have fibrous root system. Their roots are adventitious, arising from the lowest nodes of the stems. Species with a fibrous system are more shallowly rooted than plants with a persistent taproot. Most dicots have a taproot system. The taproot originates from the primary root (radicle) of the seed. The taproot may have many branches originating from it. Roots of legumes may also have root nodules, which are sites for nitrogen fixation .

Zones of the root A root can be divided into the mature zone, zone of maturation, zone of cell elongation, and the zone of cell division (the apical meristem) protected by the root cap (right). All of the root cells originate from the divisions of the cells of the apical meristem. These cells are small, thin-walled, and contain large nuclei. Root meristem is protected by a root cap. The root cap is a dynamic, multifunctioning organ. For many years it was believed that the root cap functioned solely to protect the apical meristem of the root. Recently, it was shown that the cells of root cap percieve both light and gravity. Root caps of both dicots and monocots produce large numbers of metabolically active root "border" cells, which are programmed to separate from the root into the surrounding soil. In soil, border cells play important roles in protecting the roots from the soil-borne diseases (Hawes et al, 1998).

What are the root tissues? The primary root tissues are the epidermis, the outermost layer of cells covering the root surface, the cortex that surrounds the stele, and the vascular tissue or stele, which occupies a central position.

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Stem and Root Anatomy and Functions. Vegetative Propagation

The root epidermis (1 on the cross-sections below) is usually a single cell layer that protects the root. The cells of epidermis can elongate to produce root hairs. These root hairs have larger surface area and are more efficient in absorbing water. Root hairs are also the sites of Rhizobium invasion of the legumes. Right: scanning electron micrograph of soybean root hairs.

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Legume-Rhizobium Symbiosis

Why are legumes important? Each year legume-Rhizobium symbiosis generates more useful nitrogen for plants than all the nitrogen fertilizers produced industrially -- and the symbiosis provides just the right amounts of nitrogen at the right time at virtually no cost to the farmer. This symbiotic nitrogen fixation is very beneficial for two reasons: ● it supplies the legume with nitrogen, ● it can significantly decrease spending on N-containing fertilizers for the subsequent crops. Symbiosis is defined as a mutually beneficial relationship between two organisms. In case of legume Rhizobium symbiosis, a legume provides the bacteria with energy-rich carbohydrates and some other compounds, while Rhizobium supplies the host legume with nitrogen in the form of ammonia. Unlike any plant, rhizobia (and some other microorganisms) can fix inert N2 gas from the atmosphere and supply it to the plant as NH4+ which can be utilized by the plant. Compare images on the left: a soybean plant inoculated with Bradyrhizobium japonicum (left), and a plant that wasn't (right). Un-inoculated plant shows signs of Nitrogen deficiency. Adding nitrogen fertilizer, on the other hand, suppresses N2 fixing symbiosis because the plants encounter enough nitrogen in the soil and don't need to expand energy to form the nodules and "feed" rhizobia inside the nodules. Let's briefly review the sequence of events leading to establishing a successful symbiosis. Rhizobial inoculum is usually added at planting as seed coating. Commercial formulations of inoculum, like the one we will use in today's lab, contain live bacteria. On the right is a scanning electron microscope image of the free-living cells of Bradyrhizobium japonicum which can form symbiosis with soybeans. You'll notice that the bacterial cells have flagella, thread-like organs that allow bacteria to swim and move in soils toward the host plants. Roots of legumes produce flavonoids, - chemicals that attract rhizobia. Different legumes produce different flavonoids to attract different rhizobia. On the left is a scanning electron microscop image of root hairs on soybean roots. Root hairs are extentsions of the root epidermal cells, they are the sites of rhizobial attachment and infection. When a plant senses Nod-factors (chemicals produced by rhizobia), a root hair curls (right). Rhizobium then invades the root cells. http://www.hcs.ohio-state.edu/hcs200/LegRhiz.html (1 of 9) [10/08/2001 09:57:23 a.m.]

Legume-Rhizobium Symbiosis

Inside the root, rhizobia invade expanded cells of cortex, and then bacteria differentiate into Nitrogen-fixing "bacteroids". On the left is microscopic picture of dissected nodules on the root of a cow pea. The effectiveness of a given nodule may be checked by cutting it open: an effective nodule should be pink (or purple) in color, while immature or ineffective ones are either green or white inside. Rhizobia inside the nodules, differentiated into "bacteroids", fix inert atmospheric N2 for the plants, and supply it in the water-soluble form for the plants. There are 12,000-14,000 species in the Legume family (alfalfa, clovers, soybean, lupin, vetch, and many other crops ). One should remember, though, that only certain species of Rhizobia can form effective symbiotic nodules with specific legumes. In other words, Rhizobia used to inoculate peas will not be effective in inoculating soybeans or alfalfa.

What is the Nitrogen Cycle? The Nitrogen Cycle is a microorganism-aided recycling of different forms of nitrogen in nature. Let's briefly review these biochemical conversions. Nitrogen gas (N2) is the most abundant gas in the atmosphere. However, it is inert and cannot be readily used by plants or animals. Symbiotic and non-symbiotic microorganisms have the ability to fix N2 and convert it into NH4+, a form that can be easily absorbed by plants. Nitrogen can also be fixed by industrial N2-fixation which requires high temperatures and catalysts. This "fixed" nitrogen, now in the soluble form, when applied to soil can be either absorbed by plants, lost with rainfall (leaching) or converted back to gaseous oxides of nitrogen or to N2 (denitrification). Ammonia (NH4+) and nitrate (NO3-) are the nitrogen forms that can be readily taken up by plants and used to build plants' own biological molecules (DNA, proteins, chlorophyll, vitamins, etc.). Animals and humans can thereby utilize plants as sources of nitrogen-containing protein and vitamins. As the plants and other soil inhabitants die, soil microbes break down decomposing organic matter and convert the nitrogen from the biological molecules into ammonia and nitrates. Some denitrifying microbes can sequentially convert various forms of reduced nitrogen back to gaseous forms, and nitrogen is therefore lost into the atmosphere. The sequence of events briefly discussed is usually called Nitrogen cycle. This is the way Nitrogen (and many other nutrients) cycles in nature.

Your group will have a choice of doing either Experiment A or Experiemnt B. Read below for instructions.

Experimental Design for Experiment A. (Legume-Rhizobium Symbiosis)

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Legume-Rhizobium Symbiosis

The hypothesis to be tested in this experiment is: Under the greenhouse conditions, Rhizobia can supply plants with sufficient available Nitrogen, and this will result in higher yield of green mass and higher chlorophyll content as compared with uninoculated plants. ●

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The dependent variables in this experiment are yield (fresh weight, and number of seeds), and chlorophyll content. The independent variable (the variable that elicits the response) is the inoculation (infection) of the plants with Bradyrhizobium japonicum.

We will use several controls in this experiment: 1) No nitrogen fertilizer, no inoculum. This treatment should have no effect on yield. 2) The application of urea CO(NH2)2 fertilizer (1/8 of a teaspoon per pot every other week) should cause plants to yield more green mass and have higher chlorophyll content as compared to "No urea, No inoculum" control. To randomize the treatments, place your pots in random order on the bench of the greenhouse (nevertheless, keep +INOCULUM treatments away from the other treatments to avoid contamination with Bradyrhizobium japonicum). Treatments set up by other teams will serve as replications. At the end of the experiment, we will compare the data obtained by different teams.

Protocol A. (Legume-Rhizobium Symbiosis) 1. Label each pot with the treatment, date, and your team number. Fill the pots with soil. 2. Apply 1/8 teaspoon of a fertilizer (0-26-26) to all pots. 3. Place five seeds of each species on the soil surface in the appropriate pots. 4. Moisten (do not saturate) the soil. Cover the seeds with soil except for +INOCULUM treatment. 5. Add 1/8 of a teaspoon of nitrogen fertilizer urea (46-0-0) to +UREA treatments. 6. Designate one person to inoculate +INOCULUM treatments. Inoculator: Bring your +INOCULUM pots to the inoculation area. Take a pinch of dry inoculum and sprinkle a little onto each seed. Then cover the seeds with soil. Wash your hands with soap immediately. Inoculum is safe to work with, but you MUST NOT allow it contaminate all of your treatments. Inoculate your "+Inoculum" treatments last. Inoculate in the designated area only. 7. Place +INOCULUM pots on a separate bench in the greenhouse.

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Legume-Rhizobium Symbiosis

Once you have collected the data, you will need to calculate variance and standard deviation. Every team member should record all data. 1. When the seedlings appear, thin the plants to two per pot. Keep the largest healthiest looking plants. 2. Add 1/8 teaspoon of urea to the +UREA treatments every other week. use only marked meter sticks to measure heights of the +INOCULUM treatments to avoid contamination of the "No inoculum" treatments with Bradyrhizobium japonicum. Contamination of other treatments with inoculum will make the collected data useless! 3. To measure height of soybeans, measure the distance from the soil surface to the apical meristem (the topmost bud) of the plant. 4. Measure the chlorophyll content of the first true leaf and the newest fully developed leaf of all your plants with the Minolta SPAD meter. In soybeans, the unifoliate leaf (not the cotyledon) is the first true leaf. At harvest (at the end of the quarter): 1. Carefully uproot the plants from their pots. Shake the roots. Rinse the soil from the roots. Briefly let the excess water dry off the plants by placing them for a moment on a dry paper towel. 2. Measure: the fresh mass of the plants, number of branches per plant, the number of pods per plant. 3. Calculate average fresh weight of above ground parts of the plants from each treatment, variability (s2) and standard deviation (SD). Complete the Data Sheets.

Experimental Design for Experiment B (Fertilizer Trial) The hypothesis to be tested in this experiment is: Under greenhouse conditions, vermicompost can supply adequate nutrition to plants and will result in a similar yield of green mass and chlorophyll content as compared to those plants receiving traditional garden fertilizer (12-12-12). Your group can decide which plant you prefer to use. You will be using seedlings of either sorghum, or sunflower.

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The dependent variables in this experiment are yield (fresh weight, height) and chlorophyll content The independent (the variable that elecits the response) is the fertilizer treatment (vermicompost or (12-12-12)-traditional garden fertilizer)

The treatments and controls include: 1. + vermicompost (15% of total volume)-treatment D

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2. + traditional fertilizer (12-12-12)-treatment E 3. control- no fertilizer- treatment F . There will be three replications of each treatment for a total of nine pots

Protocol B. (Fertilizer Trials) 1. Label each pot with the treatment, replication, date, and your team number. There will be a total of nine pots for each group (i.e. D1, D2, D3; E1, E2, E3; and F1, F2, F3.) 2. For the pots labeled D1, D2, and D3, mix in 15% vermicompost with the soil provided. Your group will need to figure out the volume of the pots first before adding the appropriate amount of vermicompost. Use your hands to mix thoroughly 3. Fill the remaining pots (treatments E and F) with the soil provided. Do not add vermicompost to these treatments. 4. Moisten each pot with water, do not saturate the soil. 5. Transplant one seedlings of the plant that your group chose to work with into each pot of all treatments. Be GENTLE and careful not do break the root system while transplanting. 6. Add the traditional garden fertilizer to those pots labeled E (ask your instructor about the correct application rate). 7. Do not add anything to those pots labeled F. 8. Place in random order on the bench of greenhouse. 9. Fertilize your E treatments every week until the end of the quarter

Observations and Data Collection Measure heights and chlorophyll contents of each of your treatments according to the class calendar. Once you have collected the data, you will need to calculate variability (s2) and standard deviation (SD).. Every team member should record all data. ●

To measure height of sunflower, measure the distance from the soil surface to the apical meristem (the topmost bud) of the plant. To measure height of sorghum, measure the distance from the soil surface to the end of the longest leaf blade.

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Measure the chlorophyll content of the first true leaf and the newest fully developed leaf of all your plants with the Minolta SPAD meter. In soybeans, the unifoliate leaf (not the cotyledon) is the first true leaf.

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At harvest (at the end of the quarter): 1. Carefully uproot the plants from their pots. Shake the roots. Rinse the soil from the roots. Briefly let the excess water dry off the plants by placing them for a moment on a dry paper towel. 2. Measure: the fresh mass of the plants, number of branches/nodes per plant, 3. Calculate average fresh weight of above ground parts of the plants from each treatment, variability (s2) and standard deviation (SD) Complete the Data Sheets.

Guidelines for writing the Lab Report Total 100 points For Experiment A. (Legume-Rhizobium) Your groups may chose to write either a report on Nutrient Deficiencies or on Legume-Rhizobium symbiosis. This is a group report, contributions of every team member will be evaluated by peers. The report should be typed, double-spaced and should contain the following sections: Introduction This section is usually 2-3 paragraphs long. It introduces the topic and provides background information on why the study was undertaken. Make sure you include objectives and hypotheses. Clearly define what symbiosis is and discuss the importance of legume-Rhizobium symbiosis in nature and agriculture (15 points). Materials and Methods Briefly (in one paragraph) summarize the protocol you followed. What tools did you use for measurements? Explain, why Bradyrhizobium japonicum, and not another Rhizobium species was used in this experiment (5 points). Results and Discussion This section is the "heart" of any report. It should be the longest part (2-3 pages + figures) of your report. Present data from the experiment in tables or graphs to support your conclusions. Title your figures. Titles are usually put at the top of tables and the bottom of figures in written documents. Refrain from using the laboratory data sheets to present data in your report (these data sheets are only guides for collecting information and lack the appropriate organization for a report). These questions will guide you in writing this section of the lab report. 1. Did you see any nodulation on the "NO INOCULUM" treatments? If yes, what happened? What did they look like?(5 points) 2. Which treatment(s) developed plants with the highest chlorophyll content, the most branches and pods, and highest mass? How variable were the results between replications What can you conclude from these observations?(15 points) 3. Using the data you collected, discuss chlorophyll content in old and younger leaves of the treatments: ● Is there a difference in chlorophyll content between older and younger leaves? What can you conclude from this finding? (10 points) ● Is there a difference in chlorophyll content between the treatment and the controls? What can you http://www.hcs.ohio-state.edu/hcs200/LegRhiz.html (6 of 9) [10/08/2001 09:57:23 a.m.]

Legume-Rhizobium Symbiosis

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attribute it to? (10 points) Did you expect inoculation with Rhizobium to have an effect on the chlorophyll content? Explain (5 points)

4. Do you think that chlorophyll content provide an accurate estimate of Nitrogen-status of the plant? (5 points). 5. Were there any confounding variables that might have interfered with the experiment? Would you set up the experiment differently? (5 points). 6. Attach Xerox copies of the completed data tables (10 points). 8.Include clearly labeled Figures and Tables (10 points) Literature Cited Include the list of the reference materials that you used to prepare your report. Cite only the materials that you have actually read (5 points) On a separate sheet of paper, evaluate contribution of each team member (including your self-evaluation) to this project. Evaluate contributions as percentages, rather then letter grades, i.e. if each member contributed equally, than each one gets 25%. Sign your name on the evaluation sheet. Turn in the evaluation individually. These evaluations will be confidential and will not be returned.

For Experiment B. (Fertilizer Trials) This is a group report, contributions of every team member will be evaluated by the peers. The report should be typed, double-spaced and should contain the following sections: Use the following guidlines: Introduction This section is usually 2-3 paragraphs long. It introduces the topic and provides background information on why the study was undertaken. Make sure you include objectives and hypotheses. Describe what is meant by inorganic and organic fertilizers. What is vermicompost and how is it produced? Briefly describe findings of other studies which have incorporated the use of vermicompost (15 points). Materials and Methods Briefly (in one paragraph) summarize the protocol you followed. What tools did you use for measurements? How did you fertilize your treatments? What was the experimental design?(5 points). Results and Discussion This section is the "heart" of any report. It should be the longest part (2-3 pages + figures) of your report. Present data from the experiment in tables or graphs to support your conclusions. Title your figures. Titles are usually put at the top of tables and the bottom of figures in written documents. Refrain from using the laboratory data sheets to present data in your report (these data sheets are only guides for collecting information and lack the appropriate organization for a report). These questions will guide you in writing this section of the lab report: 1. Which plants overall responded better to treatments? Which treatments developed plants with the highest cholorophyll content? (10 points) 2. Is there a difference in growth responses between treatments/controls? How can you account for these diferences?(10 points) http://www.hcs.ohio-state.edu/hcs200/LegRhiz.html (7 of 9) [10/08/2001 09:57:23 a.m.]

Legume-Rhizobium Symbiosis

3. Are there signs of deficiecies in any of the treatments. If so, can you narrow them down to specific nutrient deficiencies? Describe the symptoms. (10 points) 4. Do you think that chlorophyll content provides an accurate estimate of Nitrogen-status of the plant? (5 points). 5. How variable were your results betwen treatments? Were there any confounding variables that might have interfered with the experiment? Would you set up the experiment differently?(10 points) 6. In conclusion, which fertilizer out of the two would you recomend for other growers and why? Do you think the application rate of either the vermicompost or traditional fertilizer was effective or should a different recomendation be made? (10 points) 6. Attach Xerox copies of the completed data tables (10 points) 7.Include clearly labeled Figures and Tables (10 points) Literature Cited Include the list of the reference materials that you used to prepare your report. Cite only the materials that you have actually read (5 points) On a separate sheet of paper, evaluate contribution of each team member (including your self-evaluation) to this project. Evaluate contributions as percentages, rather then letter grades, i.e. if each member contributed equally, than each one gets 25%. Sign your name on the evaluation sheet. Turn in the evaluation individually. These evaluations will be confidential and will not be returned.

Guidelines for group Oral Presentations presentations will be given on the last day of lab (50 points) Each group will be expected to make an oral presentation to their lab section that lasts no longer than 15-20 minutes including questions and discussion. During this presentation, the group should present an introduction including objectives and hypothesis, materials and methods, results, and discussion. Visual aids should be used. Data should be presented in a visual form and be explained thoroughly. The discussion should include interpretations of data. If results did not comply with the original hypothesis, other possible explanations need to be addressed. Your grade is not contingent on whether your results complied with the hypothesis, but rather on the reasoning and explanations your group is able give to support or reject the hypothesis. All members of each group are encouraged to participate in the oral presentation, but the main presentation can be made by one or two persons as long as each has contributed equally. Contributions of every team member will be evaluated by the peers and will be incorporated into the final grade.

All materials on this website are for personal use only. Pictures, text or files cannot be legally reproduced or duplicated in any form. For commercial or instructional use of this website or materials from it, please contact Dr. P. McMahon or Max Teplitski.

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Legume-Rhizobium Symbiosis

©Copyright by M.Teplitski and P.McMahon, 1999

For more information, email us at [email protected], [email protected].

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Nutrient Deficiency Symptoms

Law of Minimum An important concept to remember is that one has to "feed" plants before the plants can provide us with food. As you have learned in the previous exercises, plant "food" consists of carbon dioxide and water (sources of C, H, O), and 16 elements (N, P, K, S, Mg, Ca, Fe, Mn, B, Cu, Zn, Mo, Na, Ni, Si and Cl). The 16 elements should be present in a water-soluble form so that a plant can take them up. The16 nutrients are divided into primary nutrients (N, P, K), secondary nutrients (S, Ca, and Mg) and micronutrients (Fe, Mn, B, Zn, Cu, Mo, Na, Ni, Si and Cl). Even if only one nutrient is missing from the soil (or hydroponic) solution the plant will not develop and produce normally. This notion was postulated by Justus von Liebig in his Law of the Minimum. The Law of Minimum maintains that yield is proportional to the amount of the most limiting growth resource. As you recall, such growth resources are nutrients, light, temperature, water and space.

Justus von Liebig

Deficiency Symptoms The corn plant on the left is nitrogen-deficient. It developed deficiency symptoms which include stunted growth, chlorosis (yellowing), and necrosis (death). Nitrogen is part of a chlorophyll molecule (right, below). As you recall, chlorophyll is the green pigment that plays an important part in photosynthesis. If nitrogen is limiting, chlorophyll molecules cannot be synthesized. The plant loses its green color, and can't photosynthesize As a result, the N-deficient plant does not produce required carbohydrates. Older leaves develop deficiency symptoms earlier, because N is translocated inside the plant from the older leaves to the younger ones. Below are several examples of nutrient deficiencies. Some of these minerals are involved in the formation of biologically active molecules, such as pigments (chlorophyll, carotenoids, etc.), nucleic acids (DNA and RNA), energy molecules (ATP, NADPH) and enzymes. All of these molecules have different important functions within a plant cell. Nucleic acids, for example, carry an organism's genetic information, ATP provides energy for the reactions within a cell, while enzymes catalyze the reactions.

chrolophyll

Let's briefly talk about enzymes. An enzyme is a protein (sometimes RNA) that functions as a biological catalyst.

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Enzymes are encoded by genes. Sequence of DNA in the genes codes for a sequence of aminoacids. Aminoacids are assembled together by ribosomes. When this amino acid chain is released from a ribosome, interactions between aminoacids cause unique folding of the protein.

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Nutrient Deficiency Symptoms

This uniquely folded protein, sometimes associated with co-enzymes and metals, functions as a biological catalyst. ● Enzymes are very selective in the substrates they act upon and in the kinds of the reactions they catalyze. Rubisco, an enzyme involved in photosynthesis, catalyzes the conversion of ribulose1,5-biphosphate to two molecules of 3-phosphoglycerate. Considering how many biological reactions take place inside an organism (bacteria, plant or human), you can only imagine how many different enzymes are present! The product of one enzymatic reaction is usually a substrate for another enzyme. This sequence of enzymic reactions in an organism is known as metabolism. If an enzyme (or any other important biological molecule) is not produced inside the cell due to a mineral deficiency, then the biological reactions catalyzed by this enzyme do not take place, the organism's metabolism is severely impaired, and deficiency symptoms develop. Nitrogen (N) deficiency N-deficiency is the most common nutrient deficiency. N is Leaf of a part of a chlorophyll molecule, aminoacids, proteins, and N-deficient many other important bioldogical molecules. Older leaves corn (top); of nitrogen- deficient plants are yellow from the tip N-deficient outside, plant is light green. Stalks of the N-deficient plants barley leaves, short and slender. Leaves drop. healthy leaf Excess N may cause K deficiencies. Potato, carrot, beet on the grown with excessive N, show prolific shoot growth with bottom small underground organs. Excess N leads to splitting of tomato fruits as they ripen.

P-deficient and healthy lettuce

Phosporus (P) deficiency Second to N, P is often the limiting element in soils. Older leaves of P-deficient plants are purple or dark green. Stalks short and thin. New growth is weak and stunted. Poor flowering and fruiting. Phosphorus is important in nucleic acids, and in energy molecules (ATP, NADP).

Potassium (K) deficiency Potassium is imporntant in many enzymes that are essential for photosynthesis. Like N and P, potassium is freely translocated inside the plant, so the deficiency symptoms first occur on the older leaves. Lack of potassium causes leaf margin chlorosis, followed by necrosis from outside to the midvein. K-deficient grasses are more prone to root K-deficient infections, and are easily bent to the ground (lodged) by rain or wind. Researchers from U. of corn (above), K-deficient Georgia suggest that K-deficient cotton plants are cucumber (right) more susceptible to fungal infections. They suggest split K applications (half at planting, half as

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Nutrient Deficiency Symptoms

side-dressing), and use foliar fertilization if the deficiency occurs.

Calcium (Ca) deficiency Calcium is often limited in acidic soils that recieve abundant rainfall. When calcium is deficient, terminal bud dies, young leaves are hooked, because Ca++ is not easily translocated inside the plant. Dying back Ca-deficient occurs at tips and margins, foliage may become distorted. Stalk dies off at the terminal bud. Root systems may be damaged by the root tip death. tomato Calcium is bound to enzymes, it also participates in cell wall formation. Calcium is required for cell division and is required for normal membrane functions. Excess Ca may cause boron or magnesium deficiencies.

Sulfur (S) deficiency Because enough sulfate is present in most soils, sulfur deficiency is fairly uncommon. S is not easily translolcated inside the plant, so sulfur-deficient plants develop interveinal chlorosis on younger leaves first. Necrotic spots are usually not present. Sulfur is essential for protein structure, it also occurs in vitamins.

S-deficient corn (right)

S-deficient cotton plant and healthy plants (left)

Magnesium (Mg) deficiency Mg is a part of the chlorophyll molecule, it is also important for activating some enzymes. Plants lacking magnesium have leaves with interveinal chlorosis. Leaves may redden, develop dead (necrotic) spots; tips and margins sometimes cup upward. Stalks are usually slender. Magnesium deficiency is rarely a problem in most soils. Excessive magnesium, on the other hand, can induce potassium deficiency due to interference with K uptake and utilization.

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Mg-deficient cucumber plants (right)

Nutrient Deficiency Symptoms

Iron (Fe) deficiency Iron often becomes poorly soluble and therefore limited in soils with neutral or basic pH. Fe-deficient plants develop interveinal chlorosis occuring first on younger leaves. In severe cases, younger leaves become white with necrotic lesions. Iron is important because it is a part of some enzymes. Its ability to undergo oxidations and reductions (Fe2+ Fe3+) is essential for electron transport in many biochemical reactions inside the plant.

A leaf of Fe-deficient peanut plant

Deficiencies making front pages... Here is how a recent journal PLANT PHYSIOLOGY desecribed its recent cover(right): the interveinal chlorotic sunflower leaves shown in the photograph suffer from Fe chlorosis. Fe chlorosis occurs mainly on calcareous soils with nitrate as the exclusive N form, and leaves are frequently chlorotic in spite of abundant Fe concentrations. Kosegarten et al. (pp. 1069-1079) have shown that pH of the intercellular space ("apoplast") regulates Fe3+ reduction and thus Fe2+ transport across the cell membrane. Microscope imaging combined with the fluorescence ratio technique revealed high apoplastic pH at cellular sites in the interveinal area of young leaves due to nitrate nutrition (see inset of the interveinal area). In the interveinal area, Fe3+ reduction was depressed at sites of high apoplastic pH, thus inducing leaf yellowing. In contrast, apoplastic pH in the xylem vessels (see related inset) was low even with nitrate nutrition, and, due to high rates of Fe3+ reduction at low apoplastic pH, the tissue around the leaf xylem remained green.

Deficiency symptoms could be sometimes confused with herbicide injuries. Refer to the following web pages for an illustrated list of some herbicide injuries on common crops: http://www.btny.purdue.edu/Extension/Weeds/HerbInj/InjuryHerb1.html For more information on plant mineral nutrition and role of various nutrients, visit: http://maine.maine.edu/~thomascb/nutri.html

Why do deficiency symptoms differ? The deficiency symptoms for any nutrient depend on two factors: ● the role of the element in the plant; ● whether or not the element is translocated from older leaves to younger ones. Ability of a nutrient to be translocated depends upon its mobility in the phloem. The mobility is determined by solubility of the chemical form of the element. Symptoms vary somewhat between species, and according to the severity of the problem, the growth stage, and complexities resulting from

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Nutrient Deficiency Symptoms

deficiencies of two or more elements.

Hydroponic production The first hydroponic systems were developed in France and England during the 17th century. Hydroponics is the technology of growing plants in a nutrient solution with or without the use of an artificial medium (vermiculite, sand, gravel, etc.) to provide mechanical support. Hydroponic systems are classified as liquid or aggregate, respectively. The vast majority of hydroponic systems are enclosed in greenhouses to provide temperature monitoring, reduce evaporation, and to protect the systems from unfavorable weather conditions. Several hydroponic techniques have been developed in the recent years: ● Nutrient Film Technique. A thin film of nutrient solution is driven by gravity through plastic-lined channels. The roots grow inside the channels and form a tangled mat. ● Floating hydroponics. Usually used to germinate seeds in beds floating on top of a nutrient solution. Lettuce is grown in this manner in 2.5 cm-thick plastic floats for 4-6 weeks. ● Aeroponics. Plants are grown in holes of expanded polystyrene panels. Plant roots are suspended in midair beneath the panel and enclosed in a spraying box. Aeroponics is valuable for the rooting of stem cuttings and in the production of leafy vegetables. Space is used more efficiently in this system. ● Aggregate hydroponics systems. A solid, inert medium provides support for the plants. As in liquid systems, the nutrient solution is delivered directly to the plant roots. Click here to obtain some practical advice on hydroponic production from Cornell scientists.

About the experimental setup In this exercise we will use an aggregate/wick hydroponics system. Solid medium (vermiculite) will provide support for the growing plants, nutrient solution will be driven into the medium by the capillary action. You will replace the mineral solution every week to compensate for the removal of the nutrients by the plants and pH changes resulting from this removal. Mineral solutions were prepared based on the Hoagland Mineral Solution No2 for Hydroponic Culture. The medium contains phosphates, which act as a buffer to prevent rapid pH changes in the solution. Chelating agents are added to the solution to prevent ions (mostly divalent metals) from precipitating. Click here to learn more about chelating agents and buffers. You may choose from -N, -P, -K, -Ca, -S and control solutions. You may also decide to work with tall fescue, lettuce, cucumber or a corn plant.

Protocol 1. Decide which crop and which deficiency your group would like to work with in this exercise. 2. Dilute the stock solution 5 times (i.e. 1 part of the stock per 4 parts of distilled water).

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Nutrient Deficiency Symptoms

3. Add the prepared mineral solution to the white bucket so that there is approximately 9 cm (3.5 inches) of liquid in the white bucket. 4. Place 2 sheets of cheesecloth inside the green pot. Pull the cheesecloth through the orifices in the green pot, so that when the green pot is inserted into the white bucket, cheesecloth is immersed into the mineral solution. 5. Fill the green pot with vermiculite. Wet vermiculite with the appropriate mineral solution. 6. Plant the seedling into vermiculite. 7. Place the green pot inside the white bucket with the mineral solution. 8. Clearly label the pot with your group number, date and treatment. Move the hydroponic assembly into the designated part of the greenhouse.

All materials on this website are for personal use only. Pictures, text or files cannot be legally reproduced or duplicated in any form. For commercial or instructional use of this website or materials from it, please contact Dr. P. McMahon or Max Teplitski. ©Copyright by M.Teplitski and P.McMahon, 1999

For more information, email us at [email protected], [email protected].

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Discussion questions Preparing for the class, let's all think about the social aspects of plant biotechnology. Here are some questions that have been igniting political debates recently: 1. Who owns the genes? Represenatives of Western companies travel to the developing countries to collect seeds of the local crop varieties. Commercial breeders work with these varieties and eventually protect them by their patents. Who do you think owns the rights to the crop varieties based on local "landraces". 2. Should you keep the "designer" genes from the wild relatives? Cultivated grasses easily and freely outbreed with their wild weedy relatives. Some breeders try to introduce herbicide-resistance genes into turf grasses using techniques described in this lab. What effects, do you think, introduction of herbicide-resistance genes into turf grasses will have on control of grass weeds? 3. As you'll learn in a couple of minutes, Russian botanist Nickolai Vavilov developed one of the first theories of crop origin. In the beginning of the 20th century, his studies of genetics and crop evolution clashed with the government's ideology. He was arrested and later died in Stalin's concentration camps. In your opinion, can government, society or interest groups impose their ideals on scientists? Can you think of other examples when different groups try to dictate their values to the scientists?

Frankenstein Foods or Crops for the Future? Genetic engineering more and more often becomes a front-page news in popular magazines. Crop breeders come up with new more productive crops that are stress-tolerant, disease-resistant, have higher qulatity yields and other superior traits. Corn and cotton plants were engineeried to carry genes of a bacterium Bacillus thuringiensis allowing the plants to fight off insects. RoundUp Ready soybeans are not destroyed by the herbicide which allows less expensive weed control. High-starch potatoes have higher starch content in their tubers and therefore are more nutritious. FlavrSavr tomatoes stay firm as they are stored and transported. Tobacco plants can synthesize vaccines and biodegradable plastics. Cotton, with genes from indigo plant, produce blue cotton fibers for natural, environment friendly denim. A variety of "decaf" coffee has been developed to produce naturally caffeine-free product. Rice, genetically engineered to synthesize β-carotene, made a front-page in TIME magazine (left). Click on the image (left) to read the article in TIME. According to a recent article in "Trends in Plant Science", scientists at Monsanto inserted a gene for b-carotene production in canola plants. Oil from this new canola variety contains b-carotene, which human body converts into vitamin A. One teaspoon of the oil could provide the daily recommended intake for an adult. In the same journal, they report that a Spanish scientist, Jesus Fernandez, has http://www.hcs.ohio-state.edu/hcs200/Breefrme.html (1 of 8) [10/08/2001 09:58:34 a.m.]

developed a variety of artichoke that grows ~12 feet (3 meters) high. Artichokes grow well in the infertile dry soils. The biomass of genetically modified artichoke is harvested and used for fuel. A factory was built to use up to 105, 000 tons of artichokes to produce 91.2 GW of electricity.

Crops: where did they come from? Crop domestication, a process of selection and adaptation of a wild species to cultivated environments, started ~9,000 years ago. People grew barley, wheat, bean, flax, yam, lentil, peas, and peppers as early as 7000-5000 b.c.e. Clover, forage grasses, oil palm, sugar beet, and strawberry were domesticated relatively recently (1750 c.e.-present). Planting, growing and harvesting the crops led to selection of types suitable to cultivation. Selection of plants with desirable traits was - for centuries - the only form of crop breeding. According to the Russian scientist Nickolai Vavilov, there were 12 centers of crop domestication around the world. Vavilov's theory has been modified since. Visit this nifty Crop Evolution Website with TONS of images and cool stories to lean about the revisions of the Vavilov's theory. What are the origins of the 10 crops we have mentioned during this quarter?

N. Vavilov

For additional information about the crops, click on the highlighted text above. Click here to learn more about Crop Genetic Diversity. You will also find out why the British are tea drinkers and why Boston basketball team is called Celtics. To learn more about life of N.Vavilov, click on his photograph (above right)

Brief history of crop breeding Crop breeding changed significantly since the discovery of inheritance and development of genetics. Gregor Mendel (left), in the 1850s made the first observations that plant traits are inherited. Mendel noticed that when green and yellow peas were crossed, all progeny seeds were yellow. When plants of this first hybrid generation (F1) were allowed to self-pollinate, the progeny (F2) segregated with one green seed per three yellow (right). Mendel experimented further, and cross-pollinated plants with green wrinkled and yellow smooth seeds (at the time, Gregor Mendel the talented scientist did not know that texture and color Click here of pea seeds are inherited independentenly from each other). In the first hybrid generation, F1, all seeds http://www.hcs.ohio-state.edu/hcs200/Breefrme.html (2 of 8) [10/08/2001 09:58:34 a.m.]

to visit MendelWebappeared yellow smooth (diagram below).When allowed

to self-pollinate, F1 plants produced segregating F2 progeny, with one green wrinkled seed, three yellow smooth seeds, three yellow wrinkled and nine yellow smooth seeds per each 16.

Based on the appearance of the seeds from F1 generation, one can conclude that the allele coding for yellow seed color is dominant over the allele coding for the green seed color; and smooth or round allele is dominant over the allele coding for wrinkled seed coat. In F2 generation, therefore some of the seeds that appear yellow and smooth still carry alleles coding for green wrinkled seeds. Note that in the F2 generation there are green smooth and yellow wrinkled seeds, a combination of traits that is different from both parents. These new traits arose due to an independent assortment of the alleles in meiosis. "Mendelian inheritance" assumes that genes are inherited independently from each other. In many cases, however, genes located close to each other on the chromosome are inherited together, and the simple segregation discussed above does not take place. Genes located on the same chromosome can be inherited separately due to an event known at "crossing-over". Crossing-over can occur during the first meiotic division. Crossing-over is the exchange of some of the corresponding parts of homologous chromosomes. Crossing-over leads to recombination of the traits. Barbara McClintock was one of the first people to study chromosome crossing-over in maize, she was awarded Nobel Prize for her studies and the discovery of the mobile elements in maize chromosomes. Click here to read an essay by D. Ardell on the fascinating life of B. McClintock

Brief review of genetic principles

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Barbara McClintock

Diversity among individuals is the raw material of genetics. Variation among crop plants is observed by breeders and farmers and allows them to select for the individuals with desired traits. Genetics studies the mechanisms by which traits are passed from one organism to another and how they are expressed. Here is a brief overview of some genetic principles.

Francis Crick

Each cell of an organism contains at least one set of basic genetic information. This set is called a genome. In a diploid organism, there is one set of chromosomes derived from one parent and one chromosome set derived from the other parent (that explains yellow wrinkled and green smooth seeds in Mendel's experiments). A chromosome is one long double-stranded molecule of DNA. The double helical structure of DNA was discovered by a British and an American scientists, J.Watson and F.Crick (left). For them, a clue about the structure of DNA came from X-ray photographs of DNA taken by Rosalind Franklin. Watson and Crick were awarded Nobel Prize for their discovery.

James Watson

Genes are the regions of a DNA molecule. A gene specifies the structure of a single protein. Each protein (enzyme) catalyzes a biochemical reaction within an organism that leads to formation of other biological molecules. Click here for an essay about life and Nobel Prize-winning discoveries of F.Crick and J.Watson.

Another genetic discovery: decoding of human genome is probably the most exciting scientific breakthrough of this year! What does it mean to the crop scientists? Genome of Arabidopsis thaliana, a weedy plant from the Mustard Family, is already sequenced. Genetic sequences of rice and Medicago truncatula (a relative of alfalfa) are on their way. Click on the image to the right to read the article in TIME magazine on sequencing of human genome. Haven't made up your mind on genetic engineering? Click on the highlighted question to read a great compilation of pro and con arguments (including the story on "crossing" tomato with cod)! Need to refresh your Genetics? Click here to review a Glossary of Genetic Terms.

Plant transformation So, how did they genetically engineer rice to synthesize β-carotene? Plant transformation (or genetic engineering) is the transfer of specific foreign DNA into a plant species. Transformation involves several steps: http://www.hcs.ohio-state.edu/hcs200/Breefrme.html (4 of 8) [10/08/2001 09:58:34 a.m.]

● ● ● ● ●

isolation of a useful gene; transfer of the gene into a plant cell; integration of the gene into the plant genome; regeneration of fertile plants through tissue culture; transmission of the transgenic (transformed) from generation to generation through cross pollination, as you will perform in today's lab. Let's review our "yellow rice" example (left). Scientist isolated a useful gene for β-carotene production from daffodil, and excised that gene (piece of DNA). The gene was then "glued" into a carriers (small loops of DNA called plasmids). Such plasmids are then introduced into plant cells, a new transgenic organism is then re-generated from a single cell.

There are several ways to introduce foreign DNA into a plant. In this Exercise, we will use the PIG, Particle Inflow Gun improved by the OSU scientists (Dr. J.Finer and colleagues). The gun is used to bombard (literally!) plant tissue with tungsten particles coated with DNA. DNA-coated particles are accelerated inside a chamber under pressurized helium and partial vacuum. DNA is later integrated into transformed cells' genome and transgenic plants are regenerated.

Review of flower anatomy and pollination Flowers are highly specialized reproductive organs, adapted for the entire range of reproductive functions: advertising, pollination, fertilization, seed development, and dispersal of seeds. Flowers can be male, female or both. By far the most common arrangement is having both male and female parts within each flower, otherwise known as perfect flower. Imperfect flowers have either male or female parts. Monoecious plants have male and female parts on the same plant (e.g., corn, cucurbits, birch, walnut). Dioecious plants have male and female flowers on separate plants (hemp, American holly, hazel nut). Complete flowers have all four parts (sepals, petals, stamen and pistil), while incomplete flowers are missing one or more of these parts. No two species of plants have identical floral anatomy, but the following diagrams illustrate "typical" flowers with both male and female parts.

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Apple (above) has a perfect flower. Green sepals (6) protect the bud before the flower opens. Petals (1) which people see as white, are highly visible to the insect pollinators. Male parts of the flower are called stamens, and consist of a filament (5) and anther (4). Pollen is produced in its anthers (4). When pollen grains mature, they land on the stigma (2), which is a receptacle for the style (a long tube that empties into the ovary (7)). The pollen grain then forms a pollen tube that grows down the style (3) and reaches the ovary (7), where it releases the male gamete. The gamete proceeds down the tube to fertilize an ovule in the ovary. The fertilized ovule develops into a seed and the ovary typically develops into the fruit. Sepals and petals in flowers of tulip (right), and its monocot relatives (lilies, daffodils, onions, etc) evolved into one organ, sometimes referred to as "tepal" (8, right). Flower parts of tulip are labeled similarly to the flower parts of apple.

Grasses are also monocots. You'll notice that flowers of grasses are less showy (eg. fescue flower, left). Grasses typically produce significant amounts of pollen in their anthers (4). Carried by wind, pollen lands on sticky feather-like stigma receptacles (2). Sepals and petals of grasses have evolved into three layers of protective bracts -glume, palea, and lemma (9).

Lab Activities 1. Study flower anatomy. Identify flower parts. 2. Cross-polinate tomato flowers according to the protocol below.

Tomato cross-pollination Tomato (Lycopersicon esculentum Mill.) is a highly self-pollinating species. Its flower is perfect, having male (anthers) and female parts. Four to eight flowers are borne on a compound inflorescence (right). A single tomato plant may produce up to 20 successive inflorescences during its life cycle. The cultivated tomato forms a tight protective anther cone that surrounds the stigma. Style elongation occurs within the anther cone and usually coincides with pollen release. Outdoors, wind aids in release of pollen with subsequent fertilization, but under greenhouse conditions, manual vibration of open flowers enhances effective pollination and fruit set.

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1. Select plump buds which are not yet open. The sepals can be separated but the petals are still closed. The outside of the petals should appear creamy white in color.

2. With clean fine-pointed tweezers, peel open the sepals and petals. The anther cone should be very pale yellowish-green and the petals should be pale yellowish-white. If the anther cone is yellow or the petals are yellow the flower is too old. With tweezers, remove all sepals. Take them off all the way down to the base of the bud. 3. Carefully remove all flower petals.

4. Completely remove anther cone by puncturing the base of the cone with tweezers, gently lifting upwards and away. This exposes the style and stigma of the flower. Emasculation for the purpose of cross pollination must be done approximately one day prior to anthesis (flower opening) to avoid accidental self-pollination. At this time, the sepals begin to change from light yellow-white to a dark-yellow. The stigma is fully receptive which allows for pollination immediately after emasculation. However, stigmas do remain receptive to pollen up to seven days. Under greenhouse conditions, hand-pollinated stigmas require no protection to prevent uncontrolled crossing, as would be the case under field conditions. 5. With your pollen source in hand, insert the stigma of the emasculate flowers into the pollen, making sure the stigma receives ample pollen. Gently snip off any immature flower buds located on the inflorescence. Under greenhouse conditions, hand-pollinated stigmas require no protection. In 4-5 days, if the fertilization was successful, the ovary will begin to show signs of swelling and enlargement as fruit development advances. Temperatures can influence the rate of ripening with optimal temperature for fruit maturation and color development between 20oC and 24oC.

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Techniques of plant transformation As you recall from our previous discussion of plant transformation, it is a rather time-consuming process. We will not have time to carry a transformation experiment all the way through. We will, however, learn some techniques of plant transformation. 1. Suppose we want to introduce a gene for RoundUp resistance into soybeans. 2. A gene for the herbicide resistance has already been isolated from another organism. This herbicide-resistance gene has been excised with special enzymes, working as biological "scissors". Another set of enzymes, working as biological "glue", inserted the gene of interest into the carrier plasmids. Your TA has coated gold particles with these prepared plasmids. 3. Your TA will demonstrate how to "shoot" these DNA-coated particles into plant tissue. Now it's your turn to play with the PIG. 4. Place bombarded tissue onto a regeneration tissue culture medium. It will take time to grow a plant from this tissue. When the tissue gives rise to a plant, it is time to test the plants for herbicide resistance. 5. Your instructor will spray seedlings of resistant and susceptible soybean seedlings with RoundUp.

Materials on this website are for personal use only. Text or files cannot be legally reproduced or duplicated in any form. For commercial or instructional use of this website or materials from it, please contact Dr. P. McMahon or Max Teplitski. ©Copyright by M.Teplitski and P.McMahon, 1999 For more information, email us at [email protected], [email protected].

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SCIENCE JULY 31, 2000 VOL. 156 NO.5

Grains Of Hope Genetically engineered crops could revolutionize farming. Protesters fear they could also destroy the ecosystem. You decide BY J. MADELEINE NASH/ZURICH

A Grain of Hope--and Fear: Ingo Potrykus had a simple idea: create genetically modified rice to feed the starving poor and give it away. Now, amid fresh protests against "Frankenfoods," his golden grain is caught in an increasingly polarized public debate Inside the Protest: Taking It to Main Street

How to Make Golden Rice Click here for full diagram

At first, the grains of rice that Ingo Potrykus sifted through his fingers did not seem at all special, but that was because they were still encased in their dark, crinkly husks. Once those drab coverings were stripped away and the interiors polished to a glossy sheen, Potrykus and his colleagues would behold the seeds' golden secret. At their core, these grains were not pearly white, as ordinary rice is, but a very pale yellow--courtesy of beta-carotene, the nutrient that serves as a building block for vitamin A. Potrykus was elated. For more than a decade he had dreamed of creating such a rice: a golden rice that would improve the lives of millions of the poorest people in the world. He'd visualized peasant farmers wading into paddies to set out the tender seedlings and winnowing the grain at harvest time in handwoven baskets. He'd pictured small children consuming the golden gruel their mothers would make, knowing that it would sharpen their eyesight and strengthen their resistance to infectious diseases. And he saw his rice as the first modest start of a new green revolution, in which ancient food crops would acquire all manner of useful properties: bananas that wouldn't rot on the way to market; corn that could supply its own fertilizer; wheat that could thrive in drought-ridden soil. But imagining a golden rice, Potrykus soon found, was one thing and bringing one into existence quite another. Year after year, he and his colleagues ran

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TIME.COM COVERAGE Search for TIME stories about the genetically modified foods POLL:Genetically Modified Foods Are you concerned about consuming genetically altered fruits, vegetables and grains? NEWSFILE: The Genetics Revolution Coverage of the new science set to profoundly change our lives WEB FEATURE: Visions of the 21st Century Find out if frankenfood will feed the world TIME ARCHIVES Make Way for Frankenfish! What Happens To These Ordinary

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into one unexpected obstacle after another, beginning with the finicky growing habits of the rice they transplanted to a greenhouse near the foothills of the Swiss Alps. When success finally came, in the spring of 1999, Potrykus was 65 and about to retire as a full professor at the Swiss Federal Institute of Technology in Zurich. At that point, he tackled an even more formidable challenge. Having created golden rice, Potrykus wanted to make sure it reached those for whom it was intended: malnourished children of the developing world. And that, he knew, was not likely to be easy. Why? Because in addition to a full complement of genes from Oryza sativa--the Latin name for the most commonly consumed species of rice--the golden grains also contained snippets of DNA borrowed from bacteria and daffodils. It was what some would call Frankenfood, a product of genetic engineering. As such, it was entangled in a web of hopes and fears and political baggage, not to mention a fistful of ironclad patents.

Salmon If The Genetically Modified Lunkers Ever Get Loose? MARCH 6, 2000

Who's Afraid of Frankenfood? So far, mostly just Europeans. But thanks to a little uncertainty and a lot of agitprop, that's changing NOVEMBER 29, 1999

Of Corn and Butterflies U.S. farmers are planting 20 million acres of bioengineered corn. Will it poison the monarchs? MAY 31, 1999

For about a year now--ever since Potrykus and his chief collaborator, Peter Beyer of the University of Freiburg in Germany, announced their achievement --their golden grain has illuminated an increasingly polarized public debate. At issue is the question of what genetically engineered crops represent. Are they, as their proponents argue, a technological leap forward that will bestow incalculable benefits on the world and its people? Or do they represent a perilous step down a slippery slope that will lead to ecological and agricultural ruin? Is genetic engineering just a more efficient way to do the business of conventional crossbreeding? Or does the ability to mix the genes of any species--even plants and animals--give man more power than he should have? The debate erupted the moment genetically engineered crops made their commercial debut in the mid-1990s, and it has escalated ever since. First to launch major protests against biotechnology were European environmentalists and consumer-advocacy groups. They were soon followed by their U.S. counterparts, who made a big splash at last fall's World Trade Organization meeting in Seattle and last week launched an offensive designed to target one company after another (see accompanying story). Over the coming months, charges that transgenic crops pose grave dangers will be raised in petitions, editorials, mass mailings and protest marches. As a result, golden rice, despite its humanitarian intent, will probably be subjected to the same kind of hostile scrutiny that has already led to curbs on the commercialization of these crops in Britain, Germany, Switzerland and Brazil. http://www.hcs.ohio-state.edu/hcs200/rice.html (2 of 3) [10/08/2001 09:58:41 a.m.]

WEB RESOURCES The Golden Age of Agriculture ó Grains A case study of golden grains by the Department of Natural Resources and Environment (NRE) of Victoria, Australia Future Foods Science Museum presentation about genetically modified foods, including real video on how to extract DNA from an onion Waiter, there's a Gene in my Food Introduction to issues and controversies surrounding genetically modified food by the Australian Broadcasting Corporation FDA Center for Food Safety and Applied Nutrition Contains information on biotechnology and

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The hostility is understandable. Most of the genetically engineered crops introduced so far represent minor variations on the same two themes: resistance to insect pests and to herbicides used to control the growth of weeds. And they are often marketed by large, multinational corporations that produce and sell the very agricultural chemicals farmers are spraying on their fields. So while many farmers have embraced such crops as Monsanto's Roundup Ready soybeans, with their genetically engineered resistance to Monsanto's Roundup-brand herbicide, that let them spray weed killer without harming crops, consumers have come to regard such things with mounting suspicion. Why resort to a strange new technology that might harm the biosphere, they ask, when the benefits of doing so seem small? Indeed, the benefits have seemed small--until golden rice came along to suggest otherwise. Golden rice is clearly not the moral equivalent of Roundup Ready beans. Quite the contrary, it is an example--the first compelling example--of a genetically engineered crop that may benefit not just the farmers who grow it but also the consumers who eat it. In this case, the consumers include at least a million children who die every year because they are weakened by vitamin-A deficiency and an additional 350,000 who go blind. MORE>> PAGE 1 | 2 | 3 | 4

Get the Magazine - Try 4 Issues Free IMAGE CREDITS | TIME DIAGRAM BY JOE LERTOLA SOURCE: DR. PERET BEYER, CENTER FOR APPLIED BIOSCIENCES, UNIVERSITY OF FREIBURG COPYRIGHT © 2000 TIME INC. I PRIVACY POLICY

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food

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Nikolai I. Vavilov (1887-1943) ---------------------------------------------------------------------------From : http://www.dainet.de/genres/vir/ (Russian Institute of Plant Industry )

Nikolai I. Vavilov was born into the family of a merchant in Moscow on November 25, 1887. In 1911, having graduated from the Agricultural Institute, Vavilov continued to work at the Department of Agriculture Proper headed by Prof. Pryanishnikov. In 1911-1912 Vavilov did practical work at the Bureau for Applied Botany and at the Bureau of Mycology and Phytopathology of the Agricultural Scientific Committee. In 1913-1914, Vavilov traveled to Europe where he studied plant immunity, mostly with Prof. W. Bateson, a co-founder of the science of genetics. In autumn 1917 the Head of the Bureau for Applied Botany Robert. E. Regel (1867-1920) supported the nomination of N.I.Vavilov, a young professor from the Saratov Higher Agricultural Courses, as Deputy Head of the Bureau. As Regel wrote in his reference letter, "In the person of Vavilov we will employ ... a talented young scientist who would become the pride of national science". Regel's prediction turned out to be true. Since then, all Vavilov's life and creative work have been inseparable from the world's largest crop research institute, into which he transformed the Bureau in the1920-30's. Vavilov continued his investigations in Saratov where he has awarded the title of Professor of the Saratov University in 1918. During the Civil War, from 1918 to 1920, Saratov became the scientific stronghold for the Department of Applied Botany (Bureau till 1917). In 1920 Vavilov was elected head of the Department, and soon moved to Petrograd (St.Petersburg now) together with his students and associates. In 1924, the Department was transformed into the Institute of Applied Botany and new Crops (VIR since 1930), and occupied the position of the central nationwide institution responsible for collecting the world plant diversity and studying it for the purposes of plant breeding. Vavilov is recognized as the foremost plant geographer of contemporary times. To explore the major agricultural centers in this country and abroad, Vavilov organized and took part in over 100 collecting missions. His major foreign expeditions included those to Iran (1916), the United States, Central and South America (1921, 1930, 1932), the Mediterranean and Ethiopia (1926-1927). For his expedition to Afghanistan in 1924 Vavilov was awarded the N.M.Przhevalskii Gold Medal of the Russian Geographic Society. From 1931 to 1940 Vavilov was its president. These missions and the determined search for plants were based on the http://www.hcs.ohio-state.edu/hcs200/vavilov.html (1 of 4) [10/08/2001 09:58:52 a.m.]

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Vavilov's concepts in the sphere of evolutionary genetics, i.e. the Law of Homologous Series in Variation (1920) and the theory of the Centers of Origin of Cultivated Plants (1926). N.I.Vavilov was a prominent organizer of science. In the period from 1922 to 1929 he headed the Institute of Experimental Agronomy (the former ASC) which developed in 1930 into the V.I.Lenin All-Union Academy of Agriculture; from 1930 to 1935 Vavilov was its first president. From 1930 to 1940 he was director of the Institute of Genetics. Vavilov organized and participated in significant home and international scientific meetings and congresses on botany, genetics and plant breeding, agricultural economy, and the history of science. All around the world N.I.Vavilov has gained respect and renown; he was elected member of many academies of sciences and various foreign scientific societies. Vavilov, the symbol of glory of the national science, is at the same time the symbol of its tragedy. As early as in the beginning of the 1930's his scientific programs were being deprived of governmental support. In the stifling atmosphere of a totalitarian state, the institute headed by Vavilov turned into a resistance point to the pseudo-scientific concepts of Trofim D.Lysenco. As a result of this controversy, Vavilov was arrested in August 1940, and his closest associates were also sacked and imprisoned. Vavilov's life ceased in the city where his star had once risen. He died in the Saratov prison of dystrophia on 26 January 1943 and was buried in a common prison grave. Nevertheless, the memory of Vavilov has been preserved by his followers. During that tragic period they kept on gathering Vavilov's manuscripts, documents and pictures. Since mid-50's, after the official rehabilitation of Vavilov, hundreds of books and articles devoted to his life and scientific accomplishments have been published. Memorial displays have been opened in Major N.I.Vavilov's Expeditions ---------------------------------------------------------------------------1916 Expedition to Iran (Hamadan and Khorasan) and Pamir (Shungan, Rushan and Khorog). 1921 Acquaintance trip to Canada (Ontario) and USA (New York, Pennsylvania, Maryland, Virginia, North and South Carolina, Kentucky, Indiana, Illinois, Iowa, Wisconsin, Minnesota, North and South Dakota, Wyoming, Colorado, Arizona, California, Oregon, Maine). 1924 Expedition to Afghanistan (Herat, Afghan Turkestan, Gaimag, Bamian, Hindu Kush, Badakhshan, Kafiristan, Jalalabad, Kabul, Herat, Kandahar, Baquia, Helmand, http://www.hcs.ohio-state.edu/hcs200/vavilov.html (2 of 4) [10/08/2001 09:58:52 a.m.]

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Farakh, Sehistan), accompanied by D.D. Bukinich and V.N. Lebedev. 1925 Expedition to Khoresm (Khiva, Novyi Urgench, Gurlen, Tashauz). 1926-1927 Expedition to Mediterranean countries (France, Syria, Palestine, Transjordan, Algeria, Morocco, Tunisia, Greece, Sicily, Sardinia, Cyprus and Crete, Italy, Spain, Portugal, and Egypt, where Gudzoni was explored by Vavilov's request) and to Abyssinia (Djibouti, Addis Ababa, banks of Nile, Tsana Lake), Eritrea (Massaua) and Yemen (Hodeida, Jidda, Hedjas). 1927 Exploration of mountainous regions in Wuertemberg (Bavaria, Germany). 1929 Expedition to China (Xinjiang - Kashgar, Uch-Turfan, Aksu, Kucha, Urumchi, Kulja, Yarkand, Hotan) together with M.G. Popov, then alone to Chine (Taiwan), Japan (Honshu, Kyushu and Hokkaido) and Korea. 1930 Expedition to USA (Florida, Louisiana, Arizona, Texas, California), Mexico, Guatemala and Honduras. 1932-1933 Trip to Canada (Ontario, Manitoba, Saskatchewan, Alberta, British Columbia), USA (Washington, Colorado, Montana, Kansas, Idaho, Louisiana, Arkansas, Arizona, California, Nebraska, Nevada, New Mexico, North and South Dakotas, Oklahoma, Oregon, Texas, Utah); Expedition to Cuba, Mexico (Yucatan), Ecuador (Cordilleras), Peru (Lake Titicaca, Puno Mt., Cordilleras), Bolivia (Cordilleras), Chile (Panama River). Brazil (Rio de Janeiro, Amazon), Argentina, Uruguay, Trinidad and Porto Rico. 1921-1940 Systematic explorations of the European part of Russia and the whole regions of the Caucasus and the Middle Asia. ---------------------------------------------------------------------------Major Collecting Missions Accomplished by N.I.Vavilov's Associates ---------------------------------------------------------------------------1922-1923 Expedition of V.E.Pisarev and V.P.Kuzmin to Mongolia. 1923 Expedition of E.I.Barulina to Crimea (Ukraine). 1924 Expedition of E.I.Sinskaya to Altai. 1925-1926 Expedition of S.M.Bukasov and Yu.N.Voronov to Mexico, Guatemala and Colombia. 1925-1926 Expedition of E.N.Stoletova to Armenia. 1925-1927 Expedition of P.M.Zhukovsky to Turkey. 1926 Expedition of N.N.Kuleshov and V.V.Pashkevich to Azerbaijan. 1926 Expedition of K.A.Flyaksberger to Azerbaijan and Russia (Daghestan). 1926 Expedition of N.N.Kuleshov and V.K.Kobelev to Uzbekistan. 1926 Expedition of K.A.Flyaksberger to Far East of Russia. http://www.hcs.ohio-state.edu/hcs200/vavilov.html (3 of 4) [10/08/2001 09:58:52 a.m.]

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1926-1928 Expedition of V.V.Markovich to Palestine, Pakistan, India, Java and Ceylon. 1926-1928 Expedition of S.V.Yuzepchuk to Peru, Bolivia and Chile. 1927 Expedition N.N.Kuleshov to Turkmenia. 1927 Expedition K.G.Kreier to Central and Western part of Siberia. 1928-1929 Expedition of E.N.Sinskaya to Japan. 1928-1932 Expedition of G.K.Kreier to Georgia and Azerbaijan. 1930 Expedition of E.A.Stoletova to Georgia (USSR). 1930 Expedition of G.K.Kreier to Kirgizia and Uzbekistan. 1933 Expedition of E.I.Barulina to Georgia (USSR). ----------------------------------------------------------------------------

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Barbara McClintock (1902 - 1992) Essay by David Ardell

Until recently, scientific research was considered beyond most women's abilities, despite notable historical exceptions - such as that of the great 19th century co-discoverer of radioactivity, Marie Curie. If a woman displayed natural talent in science and mathematics, the option to pursue her talents as a scientist was likely to be closed off in favor of more traditional roles: mother, wife, and homemaker. Sadly, this was true in America even as late as the 1950s. That is what makes Barbara McClintock and her lifelong achievements in genetics all the more notable. McClintock launched her scientific career at Cornell in1919 and, in the face of social adversity and tremendous intellectual challenges, established herself among the great geneticists of this century. At the time McClintock started her career, scientists were just becoming aware of the connection between heredity and events they could actually observe in cells under the microscope. McClintock pioneered the field of maize cytogenetics, or the cellular analysis of genetic phenomena in corn, which for the first time provided a visual connection between certain inheritable traits and their physical basis in the chromosome. McClintock rose to many challenges throughout her career - not only scientific but personal - from other scientists who felt intimidated or threatened by what one of her colleagues described as her "independence, originality, and extraordinary accomplishment." In the most notable case, Lowell Randolph, her advisor and colleague, became extremely irritated with McClintock's success in solving a problem he had spent his entire life working on. McClintock became the dominant member of his research team, and Randolph found this intolerable. McClintock soon departed, going on to greater things. For her ground-breaking work in the genetics of corn, Barbara McClintock earned a place among the leaders in genetics. She was elected to the prestigious National Academy of Sciences in 1944. Despite this, she still met with social adversity in her department at the University of Missouri and finally left there, too. She kept her next appointment at the Carnegie Institute at Cold Spring Harbor for the rest of her life. In 1983, Barbara McClintock was awarded a Nobel Prize in Genetics. To this day, her work is highly esteemed, still relevant despite the fact that much of it was completed over half a century ago, before the advent of the molecular era.

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Intrigued by B.McClintock? Click here to learn more about her discoveries.

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The Genetics Revolution

web resources

Monsanto Agriculture Press releases and news from the company on its biotech program The AgBio Forum A quarterly online magazine on the management of agricultural biotechnology International Center for Genetic Engineering and Biotechnology Italian institute promoting the safe use of biotechnology world-wide

interact POLL

Genetically Modified Foods: Are You Afraid of Eating Them?

newsfile subjects

Research The latest discoveries and the Human Genome Project Cloning Dolly was just the first. How long until humans follow? Plant & Animal Applications Why the farm will never be the same Human Applications Designer babies, maybe. But also designer

A genetically engineered tomato on the vine

The Killer Tomatoes

Somewhere, someone is crossing a fish with a tomato. Researchers are inserting an antifreeze gene from the winter flounder to produce a cold-resistant love apple, one that American consumers seem indifferent to but has Europeans taking to the streets to keep off their shelves. These are the front lines of the genetics revolution, the practical applications of the truly amazing discoveries of the past two decades. Here are miracles and wonders that could help feed an ever-more crowded world: extra-starch potatoes, coffee beans grown decaf right on the vine, low-sugar strawberries. Wonder Bread-quality wheat courtesy a plant with extra gluten built right in. Super high-protein grains that could be a boon to the developing world. And cotton and potatoes with herbicide-producing genes that could eliminate the need for toxic sprays. Here are dragons: Activists worry that plants with an innate herbicide might breed a new generation of resistant "super insects." Or that man-made seeds might cross-pollinate with other plant species, with unknown and potentially devastating results. Already, early studies show Monsanto's highly popular Bt corn could prove devastating to Monarch butterflies. Then there's the matter of intellectual property. To protect its billion-dollar investment, Monsanto hopes to introduce an

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treatments for your specific ailments Ethics What to do with our newfound knowledge Business The worth of the gene Timeline From discovery of the double helix to deciphering the human genome

elegantly malevolent technology, called "Terminator," that is a set of genetic instructions that render a seed sterile after just one planting -- thus enforcing the company's copyright. From a biotech standpoint, this is a marvel, what one scientist has called "the most intricate application of genetic engineering to date." From a human standpoint, it's a potential time bomb. The UN has already expressed concern that Terminator seeds could force farmers into total dependence on seed companies. Others are worried about possible cross-pollination that could render other plants sterile. Meanwhile, the U.S. Army War College is reportedly intrigued about the possibilities of technologies that could tell plants to commit suicide on demand. Which means the only certain thing is that there's a crop dustup in our future.

from TIME Will Frankenfood Feed The World? Genetically modified food has met fierce opposition among well-fed Europeans, but it's the poor and the hungry who need it most JUNE 19, 2000 Make Way for Frankenfish! What Happens To These Ordinary Salmon If The Genetically Modified Lunkers Ever Get Loose? MARCH 6, 2000

Who's Afraid of Frankenfood? So far, mostly just Europeans. But thanks to a little uncertainty and a lot of agitprop, that's changing NOVEMBER 29, 1999

Of Corn and Butterflies U.S. farmers are planting 20 million acres of bioengineered corn. Will it poison the monarchs? MAY 31, 1999

The Suicide Seeds Terminator genes could mean big biotech bucks--but big trouble too, as a grass-roots protest breaks out on the Net JANUARY 19, 1999

Brave New Farm Fears of "Frankenstein" food run deep, especially in Europe PHOTO: GERRY GROPP/SIPA

JANUARY 11, 1999

Copyright © 1999 Time Inc. New Media. All Rights Reserved.

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MAPPING THE GENOME JULY 3, 2000 VOL. 156 NO. 1

The Race Is Over The great genome quest is officially a tie, thanks to a round of pizza diplomacy. Yet lead researcher Craig Venter still draws few cheers from his colleagues BY FREDERIC GOLDEN AND MICHAEL D. LEMONICK

One day last April, Aristides (Ari) Patrinos, a scientist at the Department of Energy who directs that agency's share of the Human Genome Project, got a call from Francis Collins, director of the National Institutes of Health's National Human Genome Research Institute and the project's unofficial head. "Let's try it," said Collins--and at those words Patrinos knew that a longstanding scientific feud finally had a chance of being resolved. For months, Collins had been under pressure to hammer out his differences with J. Craig Venter, the prickly CEO of Celera Genomics, which was running its own independent genome-sequencing project--differences over who should get the credit for this scientific milestone; over whose genome sequence was more complete, more accurate, more useful; over the free exchange of what may be mankind's most important data versus the exploitation of what may also be its most valuable. The bickering had become downright nasty at times, upstaging the enormous importance of the project and threatening to slow the pace of scientific discovery. Therefore Patrinos had been lobbying his colleague to make love, not war, despite Venter's uncanny ability to get under the skin of Collins and other leaders of the U.S.-British genome project. So had Collins' counterparts at other NIH institutes. And so, most important, had President Clinton, who at one point scribbled a note to science adviser Neal Lane with the terse instruction: "Fix it...make these guys work together." Venter was clearly ready. His tactless rhetoric had http://www.hcs.ohio-state.edu/hcs200/timege.html (1 of 3) [10/08/2001 09:59:27 a.m.]

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lost him respect among his colleagues, and he recognized that more controversy could overshadow a historic moment in biomedicine. Beyond that, he'd taken a beating in the marketplace. After a joint declaration by Clinton and British Prime Minister Tony Blair in March that all genomic information should be free, the value of Celera stock plummeted from $189 a share to $149.25. So on May 7, over pizza and beer at Patrinos' Rockville, Md., town house, the two wary antagonists sat down in a deliberately casual setting to work out their differences. In an exclusive conversation with Collins, Venter and TIME correspondent Dick Thompson last Thursday night, Patrinos recalled, "I don't think I've ever seen them as tense as they were that day." Yet despite mistrust on both sides, Collins and Venter met a second time and a third. And finally they came, if not to a meeting of the minds, at least to a workable understanding--and a framework for this week's joint announcement. After more than a decade of dreaming, planning and heroic number crunching, both groups have deciphered essentially all the 3.1 billion biochemical "letters" of human DNA, the coded instructions for building and operating a fully functional human. It's impossible to overstate the significance of this achievement. Armed with the genetic code, scientists can now start teasing out the secrets of human health and disease at the molecular level--secrets that will lead at the very least to a revolution in diagnosing and treating everything from Alzheimer's to heart disease to cancer, and more. In a matter of decades, the world of medicine will be utterly transformed, and history books will mark this week as the ceremonial start of the genomic era. But while the announcement has been exquisitely choreographed to make the two scientists look like equals, it's clear to insiders that Venter's project is a lot further along. HGP scientists may have decoded 97% of the genome's letters--the remaining 3% are generally considered unsequenceable and irrelevant--but they know the order of only 53% of them. It's as if they've got the pages in the so-called book of life in the proper order but with the letters on each page scrambled. "It's going to take us a couple of years to put this together," Collins told TIME. Celera, by contrast, has not only the pages but all the words and letters as well--though neither side can yet say what most of these words and letters mean. And while the HGP boasts that it has done its sequence nearly seven times over to guarantee accuracy, Celera has gone over its own almost five http://www.hcs.ohio-state.edu/hcs200/timege.html (2 of 3) [10/08/2001 09:59:27 a.m.]

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times. Moreover, the company came up with a new technique that made its sequencing rate, already the fastest around, even faster. In addition, Venter claims that by the end of the year, he'll have sequenced the genome of the mouse--whose 2.3 billion letters contain enough similarities to ours to make it vitally important to scientists tracking down human gene function. Given this remarkable record, why are so few of Venter's fellow scientists trumpeting his success? Or talking him up for a Nobel Prize? Why, in fact, is this cherubic-looking, blue-eyed ex-surfer hated by so many colleagues, who have called him everything from a greedy megalomaniac to a Hitler? Forget about easy explanations, such as his outsize ego (yes, one of the samples he is analyzing is rumored to contain his own DNA) or his penchant for doing science by press release (yes, he keeps his door open to reporters) or his tendency to do not science but, as pioneer DNA mapper James Watson sneered, tedious assembly-line labor on machines that "could be run by monkeys" (yes, most of Celera's analysis was done by robot gene sequencers and high-speed computers). MORE>> PAGE 1 | 2 | 3 | 4

Get the Magazine - Try 4 Issues Free

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Biochemistry: Proteins

Plant Biochemistry: Proteins Proteins are long chains of amino acids linked together by peptide bonds. ● All enzymes are proteins, not all proteins are enzymes. ● Some are parts of membranes (channels and gates). ● Some are structural and/or storage units. There are 20 common amino acids. All amino acids have a carboxyl (COOH) end and an amino (NH2) end. This is the first time we have seen where N is a major component of a structure. The peptide bonds form a backbone with the unique portion of the amino acid attached to the backbone.

These amino acids are arranged in very specific order for each different protein. There can be 100,000's per molecule. They are what gives a protein it's specific role as an enzyme. The aminoacid sequence causes the protein to coil up in a very specific, convoluted (folded) form. The form is what determines if it is active or inactive many times. Only a slight conformational change is enough to activate or deactivate a protein. Adding or taking away even a single CH3 (methyl) from the entire molecule is enough to put it into or take it out of action. Other things can activate or deactivate. ● Kinases (enzymes that phosphorylate and de-phosphorylate a molecule using ATP as the P donor) need Mg+ to work. Without Mg+ the Calvin and TCA cycles shut down. Not good. Remember, all enzymes are proteins and an enzyme is needed for every single step of every single biochemical pathway - including protein synthesis. But not all enzymes are present in every cell all the time. They are synthesized as needed. Every cell has a complete set of genes. Proteins are synthesized when a gene is 'turned on'. Some proteins are soluble in H2O, some are not. The soluble ones can be transported to other cells in the plant. Remember, N is a mobile element, this is partly why. Two amino acids, methionine and cysteine also contain sulfur. Peanuts contain all the amino acids essential for human nutrition. The problem with peanuts is they also contain high amounts of lipids so they are high calorie. Some proteins help to make cellulose more rigid in the cell walls. These proteins are not mobile. Some proteins are a storage compound in legume seeds such as soybean, chickpeas (garbanzos),

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and lentils. These seeds are an important nutrient source for people in developing areas where the traditional primary diet is based on high carbohydrate seeds such as rice and corn.

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Index Page of HCS200

Class Schedule Syllabus Week week 1

Lectures Overview of Crop Science Plant morphology and anatomy

week 2 week 3

Environmental factors affecting crop growth and development. Light, water, heat Environmental factors cont'd. Soil/media, nutrients, atmospheric gases

week 4

Plant physiology and biochemistry

week 5

Transpiration, photosynthesis and respiration

week 6

Crop growth and development

week 7

Crop breeding (genetics, reproduction and improvement)

week 8

Cropping systems, Agroecology

week 9

Group Reports

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Labs Introduction

Index Page of HCS200

All materials on this website are for personal educational use only. We ask you not to reproduce any files, texts or figures without our permission. We are gratefull to Dr. M.Knee, Dr. X.Wei, American Society of Plant Pathology, PLANT PHYSIOLOGY journal, TIME magazine, Liebig Museum, Nobel Prize Archives, and Vavilov Research Institute for allowing us to use their copyright images. We thank Dr. D. Bauer, N. Cavender, G. Glaunsinger, T. Mangen, H. Brown, and J. Schmoll for contributing their ideas and suggestions. We are indebted to our students and colleagues for their constructive criticism and help in designing the website. Development of this website was supported, in part, by the Faculty Innovator Grant (2000) to Dr. P.McMahon. Copyright by M.Teplitski and P.McMahon, 2000

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HCS 200 - Winter Quarter 2001

Syllabus for CROP SCIENCE Horticulture and Crop Science 200 Winter 2001

Instructor: Dr. Joe Scheerens Columbus Office: 232 Kottman Hall Columbus Phone (work): 614-247-6859

Wooster Office: 213 Williams Hall Wooster Phone (work): 5-3826 from Campus

E-mail Addresses: [email protected] [email protected]

Wooster Phone (work): 330-263-3826 Wooster Phone (home): 330-264-4930 Wooster Fax: 330-263-3887

Teaching Assistants: Ms. Nicole Cavender [email protected] Kottman Greenhouse Supervisor: Mr. Harold Brown 144 Kottman Hall [email protected]

Ms. Gitta Glaunsinger [email protected] Administrative Assistant: Ms. Regina Vann 216 Howlett Hall Phone: 614-292-3866

Course Description: Study of environmental, genetic and cultural factors which influence plant productivity

Lecture: Discussion: Labs:

M,W TBA TBA

10:00 - 11:30 AM TBA TBA

Final Examination: Monday, March 12, 2001, 9:30 -11:18 AM.

References: Required Text; Plant Science Barden, Halfacre and Parish McGraw Hill, Publ.

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164 Howlett Hall TBA 334 Kottman Hall

HCS 200 - Winter Quarter 2001

Lab Manual; http://hcs.ohio-state.edu/hcs200 Lab Worksheets; Available at Cop-EZ

Lecture Notes: http://hcs.osu.edu/hcs200/notes1.html

Supplementary; Placed on reserve in Agric. Library

Purpose: This class give students interested in the production of plants and crops for food, fiber, ornamental, and recreational use the basic understanding of how environmental, cultural and genetic factors influence crop productivity. Students are introduced to contemporary issues surrounding plant agriculture and to the current concepts and techniques for improving crop productivity. Students are encouraged through interactive discussions and hands-on projects to develop skills needed to make informed decisions about the growing, production, and utilization of plants and crops. In addition, students develop an appreciation for the contribution that cultivated plants make to the environment and humanity.

Goals: Class goals for Winter 2001 will be determined by the class.

Lecture Schedule and Content: The majority of lecture topics that will be covered in H&CS 200 are listed below. However, several class periods (exact number to be determined collectively by students) will be devoted to exploring student-relevant topics or issues. Students will be involved in the development and perhaps, the presentation of these issues.

Topic 1. The origins of crop agriculture, the history of crop improvement, the importance of genetic diversity and the consequences of an agrarian society

Topic 2. Crop classification and diversity

Topic 3. Crop growth and development Topic 3a - Crop growth and development (continued)

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HCS 200 - Winter Quarter 2001

Topic 4. Environmental factors (light, heat, soil/media, water, nutrients, atmospheric gasses) affecting crop growth and development through modification of crop physiology and biochemistry ● Light ●

Heat

●

Water

●

Nutrients 1

●

Nutrients 2

Topic 5. Crop products and their relationship to our daily lives

Topic 6. Cropping systems at all levels of technology

Topics 7-? Additional topics to be determined by class SPECIAL NOTES NOTES 1 - Plant Cells

Lab Schedule and Content: See lab manual and accompanying materials

Discussion Section Schedule and Content: A portion of each discussion period will be devoted to clarification of lecture material if necessary or for pre-examination reviews . However, most of the discussion classes will be devoted to exploring individual crops (history, production, use, etc.) of importance to the world or of particular interest to students. Assignments in discussion sections will accomplished individually or in teams. For the most part, activities in discussion sections will be student-directed and interactive. This is your chance to be creative, productive and to have some fun at the same time.

Evaluation Methods: The relative importance of class activities and how and in some instances, by whom they are graded was determined by the class. The results are as follows

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HCS 200 - Winter Quarter 2001

Activity Two Midterms + Final* Labs Discussion Projects

Percent of Grade 50 30 20

Evaluator Instructor TAs To Be Determined

*Each test will be worth 25% of the class grade - the lowest score on the three tests will be dropped.

Grading Scale: A = 94-100 points C = 73-76 points A- = 90-93 points C- = 70-72 points B+ = 87-89 points D+ = 67-69 points B = 83-86 points D = 60-66 points B- = 80-82 points E < 60 points C+ = 77-79 points

Midterm Examinations: Midterms will be given during lecture periods and will be announced at least 5 days before being given. There will be ample opportunity for review prior to each examination. Examinations may contain objectively graded questions (e.g., matching or one word answer), but most assuredly will contain short essay questions. Students will always have a choice as to which short essays they write (i.e., students do not answer all questions that are posed, only those for which they have the most complete understanding of the subject).

Final Examination: A final examination will be given on the date/time listed previously. The structure (style) of the final exam will be similar to that used for midterms.

Second Chance Examinations: Students will have the opportunity to turn into the instructor (within an agreed-upon time frame) revised answers to any questions for which they lost points. The final score for each question that has an improved answer will be the average of the old and new score for that question. Students will not be penalized if they change an answer incorrectly. For the second chance exam, students can use any source or reference (except the instructor, teaching assistants, guest lecturers or classmates) to determine the appropriate answer. Second chance examinations for the final exam will be offered only if time permits.

Make-up Examinations: A full credit, written make-up midterm exam with a second chance will be given to students who notify the instructor or TA's ahead of time of their absence from the exam. There must be a verifiable, reasonable excuse (e.g., field trip, illness, transportation problems, family emergencies, etc). An unacceptable excuse would be any excuse that indicates a lack of responsibility on the part of the student. A student who has missed a midterm exam without an excuse has the option of taking a full-length, written exam http://www.hcs.ohio-state.edu/hcs200/syllabus.htm (4 of 5) [10/08/2001 10:01:02 a.m.]

HCS 200 - Winter Quarter 2001

worth 75% of the original points with no second chance exam option. Failure to attend the final exam will be adjudicated on a case by case basis. Attendance: Students are encouraged to attend class regularly. Material presented in lectures may or may not be found in the text book. Detailed lecture notes will be posted upon the completion of each topic at the web site indicated above. However, these notes are made available to students so as to provide best possible opportunity for students to listen and think as lectures are being delivered. They are not be designed to act as comprehensive web-based learning materials on their own. Because much of discussion and lab activities are team-based and interactive, failure to attend either will result in the inconvenience of others and the loss of experiences important to the educational process.

Class Participation: Although the instructor and TA's assume responsibility for most of the instruction in this course, each student brings to class, relevant personal experience that will relate to the subject matter. Students are asked to share this experience with their classmates, if they feel comfortable doing so. Students who enroll in this course come from a diversity of backgrounds and personal skills. The sharing of knowledge or insight with others is encouraged as a means to enrich the experience for all.

Effort: It is understood that individuals within the class will have other commitments (educational and personal) that he/she must fulfill. Moreover, because students in this course are diverse, it is unlikely that all will be able to devote equal amounts of time or effort to performing assignments in this class. However, the instructor and TA's ask that students work as diligently as possible to complete the activities in this course to the best of their abilities. A portion of the lab and discussion section grades will result from an assessment of effort. If students are experiencing difficulty (i.e, a crisis has arisen) please let the instructor or TA's know as soon as possible.

Code of Conduct: In H&CS 200, courtesy and respect for others will be given by all participants, including the instructor, teaching assistants and guests, in the class at all times. An environment that fosters free, non-confrontational expression of ideas will be maintained. When working on teams, each team member will assume full responsibility for their role as a member of that team. Academic misconduct or suspected academic misconduct will be handled according to policies of the Code of Student Conduct in the Student Handbook or Faculty Rule 3335-5-487.

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Horticulture and Crop Science 200 Winter Quarter 2001

Lecture Topic #1: Crop origins, crop development and the effect of crops and crop science on human life

References:

Brownowski, J. 1973. The harvest of the seasons. In: The ascent of man. Little, Brown Inc., Boston, MA.

Chandler, R.F. 1992. The role of the international agricultural research centers in increasing the world food supply. Food Tech. 46(7):86.

Council for Agricultural Science and Technology. 1985. Plant germplasm preservation and utilization in U.S. agriculture.

Goldblith, S.A. 1992. The legacy of Columbus, with particular reference to foods. Food Tech 46(10):62-85.

Hanson, H., N.E. Borlaug and R.G. Anderson. 1982. Wheat in the third world. Westview press, Boulder, CO.

Harlan, J.R. 1992. Crops and man (2nd ed.) Amer. Soc. Agron., Madison, WI.

Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant Science (2nd ed..). Prentice-Hall, Englewood Cliffs, NJ. http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (1 of 17) [10/08/2001 10:01:07 a.m.]

Hawkes, J.G. 1990. The potato: evolution biodiversity and genetic resources. Belhaven Press. London.

International Potato Center. 1984. Potatoes for the developing world. International Potato Center, Lima, Peru.

Metcalf, D.S., and D.M. Elkins. 1980. Crop production principles and practices (4th ed.) MacMillan Publishing Co., New York, NY.

National Academy of Sciences. 1972. Genetic vulnerability of major crops. NAS, Washington, D.C.

Niderhauser, J.S. 1992. The role of the potato in the conquest of hunger and new strategies for international cooperation. Food Tech. 46(7):91-95.

Zohary, D., J.R. Harlan and A. Vardi. 1969. The wild diploid progenitors of wheat and their breeding value. Euphytica 18:58-65.

http://www.ars-grin.gov/npgs/ http://www.cgiar.org/ http://www.state.oh.us/agr/97AnnlRpt/97SUMMAR.HTM

Quotation:

"Man during his history in all parts of the world has used for food more than 3000 species of plants. Of these, only some 150 parts have ever been extensively cultivated and only about dozen are important from the standpoint of the energy which they contribute." (Paul S. Mangelsdorf) http://www.hcs.ohio-state.edu/hcs200/topics/topic1.htm (2 of 17) [10/08/2001 10:01:07 a.m.]

Outline:

1. Definitions for "agriculture" and "crop"

The field of agriculture is diverse and not easily defined. A crop could be defined as a cultivated plant that yields an economically-valuable product (other definitions are valid). Crops are genetically distinct from their wild relatives.

2. The change in human society from that of "hunter-gatherer" to "agriculturist" is recent and irreversible.

The neolithic revolution (the dawn of agriculture) began about 10,000 years ago, corresponding with the end of the last ice age. There is evidence to suggest that plant agriculture was "invented" in various areas of the world independently. The changes to both man, animals and plants resulting from this invention were gradual and promoted a mutual dependency between man and agriculture.

Agriculture is a recent invention. About 90% of the humans who have ever lived made their living as hunters-gatherers, 6% were agriculturists and only 4% were urban dwellers.

3. What happened?

A. Ecological prospective-biological vs. agricultural fitness- general characteristics of potential domesticates.

A natural ecosystem includes the interrelated factors of: climate, soils, man, and other animals, and plants.

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Natural ecosystems contain a diverse number of species. The diversity of niches and organisms to fill them makes the system relatively stable and resistant to change. There is no net yield. All the energy arriving to the system via the sun is utilized by members of the ecosystem. Successful plants in the first ecosystem are those which are biologically fit (i.e. produce the greatest number of offspring). Plants in the community are subject to natural selection.

An agricultural ecosystem includes the interrelated factors of: climate, soils, man as the manipulator, crop plants, and domestic animals.

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Agricultural ecosystems contain a select number of species (few). The number of niches in very finite so the system is not very stable (i.e. vulnerable to change). There is no net yield (i.e. something to store or sell). The ecosystem outperforms the needs of its members. Successful plants in the second ecosystem are those which are agriculturally fit. Plants in the community are subject to natural selection and to the active or passive selection pressures for agricultural fitness by man.

The transition from biological fitness to agricultural fitness involves genetic changes in the organism.

The characteristics of potential domesticates are that:

-they produce a useful product -they are adapted to grow in disturbed soils (agricultural fields) -they exhibit high levels of genetic diversity

Weedy species often exhibit these traits.

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Morphological and physical changes in species undergoing domestication include:

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gigantism of horticultural/agronomic yield components (e.g. the development of corn ear from a small terminal inflorescence bearing a few kernels). loss of speed dispersal mechanisms (e.g. passive selection for non-shattering wheat rachis) loss of delayed seed germination (e.g. hard seed coat in wild beans absent from domesticates) loss of bitter or toxic substances (e.g. deleterious fats- canola: cyanogenic glycosides- canola and cassava: antagonists to digestion- lima and other legume crops; bitter steroids- squashes and melons; alkaloids-potato) changes in photoperiodic responses (e.g. development of day neutrality in cotton) changes in floral structures or pollination schemes (e.g. multiple petals- rose: increased self-pollination - chili) changes in flowering cycle (e.g. biennial bearing and development of tap root-carrot) synchronous tillering (e.g. rice amenable to single harvests) diversity of form (e.g. the multiple forms of Brassica oleracae - cabbage, cauliflower, broccoli, kohlrabi, kale, Brussels sprouts, etc) mechanisms to protect against predators (e.g. pendant rather than upright fruit in chili protecting from predatory birds; the corn husk)

Genetic mechanisms effecting (causing) these changes include:

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mutation- Mutations are sudden heritable changes in a gene. In wild populations, the natural mutation rate is about 10-6 (a low frequency) and unless they offer a strong reproductive advantage over the original gene, these mutant alleles remain at low frequency in the population.

However, under selection for agricultural fitness by and for man, the new trait may become fixed rapidly (e.g. non-shattering rachis in wheat). Therefore, emerging crops and their wild and weedy relatives began to diverge (separate).

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human migration-As man moved into new areas, his crops went with him. Planting a crop in a new area has several consequences including the passive or active selection pressure to adapt to a new environment (e.g. short day cottons into northern areas with long summer days) and new contacts with compatible weedy species.

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introgression- Introgression is the transfer of small amounts of genetic information from one

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species to another. The initial step in this process is a chance interspecific hybridization between an emerging crop (e.g., AA) and its relative (BB). Although the resulting hybrid (AB) is mostly sterile (i.e., chromosomes from the crop fail to pair with those of the related species so the meiotic process in the hybrid is hampered), sometimes a few viable gametes will be formed. With repeated backcrossing to the crop, the fully-fertile crop type can be recovered. However, a small number of useful genes from the related species will now be incorporated (AA B). "It is the genetic support of their companion weed races" (Jack Harlan). Stephens demonstrated the effects of introgression using two species of cotton -- upland cotton (Gossypium hirsutum) and sea island cotton (G. barbadense). Sea island cotton, a short day plant (SDP) that initiates flower buds as the days grow shorter, was crossed to an SDP segregate of upland cotton, normally day-neutral (DN).

Gossypium hirsutum X Gossypium barbadense F1 Hybrid (genes are ½ Gh and ½ Gb)

The F1 hybrid was backcrossed to Gossypium barbadense for 11 generations. With each successive generation, the percentage of Gh genes decreased and the percentage of Gb increased. After 11 backcrosses, there were few Gh genes left, but enough to demonstrate a high level of variability in flowering times among BC11 progeny.

Weeks to flower among individuals in two Gossypium barbadense populations. Weeks to flower G. barbadense introgressed with G. hirsutum genes G. barbadense (control) 11 2 0 12 4 3 13 17 2 14 33 0 15 48 0 No flowers 138 0

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Polyploidization- Polyploidization is also initiated by the chance hybridization between an emerging crop (AA) and its relative (BB). However, an additional event also occurred- a chance doubling of chromosomes in the hybrid resulting in an AABB individual with twice as many genes as either parent. Polyploidization may increase hybrid vigor through complementary gene action, a dosage effect or due to greater tolerance for mutant alleles). Polyploidization, in some instances, conferred new traits to crops also.

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All of these genetic mechanisms played major roles in the development of modern wheat.

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wild einkorn- (AA, brittle rachis) to cultivated einkorn (AA, durable rachis)- a major step in this process involved the incorporation of the mutation for non-shattering.

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migration of einkorn from cultivation in the Zagaros Mtn. Foothills to the Fertile Crescent. Growth of a crop innew environment (i.e., new selection pressures).

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cultivated einkorn (AA) crossed with wild emmer (BB, wild relative with brittle rachis). Chance doubling of chromosomes in the hybrid to form tetraploid cultivated emmer (AABB). Emmer was adapted to a much broader range of soil types and environments than was einkorn. Emmer became a crop of commerce and traded throughout the region. Emmer is the forerunner to the modern durum or pasta wheats.

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cultivated emmer brought to Iran (another migration) where chance crossing and polyploidization with a third species (DD) resulted in formation of the hexaploid bread wheats (AABBDD). The addition of the gene D genome did two important things-first, the seed storage proteins of emmer were highly modified. New wheat seed storage proteins were high in gluten, a protein complex with highly elastic properties which are responsible trapping yeast-derived CO2 in bread dough causing it to rise. Second, the adaption range of wheat was greatly increased again allowing for its cultivation in colder and drier climates. Eventually wheat culture was spread worldwide.

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in addition, there is ample evidence that wheat gathered genetic material from many other species as it evolved through the process of introgression, bringing disease resistance and additional useful traits.

Why did human kind domesticate plants and animals? What conditions might have promoted the origin of agriculture?

-Greek and Roman mythology suggest that agriculture was a gift from the gods to save the human race from savagery.

-Judeo-Christians believe that man was forced to till the soil as punishment for sins committed in the Garden of Eden.

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-Modern scholars (within the last 100 yrs or so) have put forth many theories concerning why hunter-gatherer societies began to domesticate the plants and animals they used. Theories that supposed that agriculture was "invented" out of desperation by starving people have been more or less dismissed as inaccurate. There is ample evidence to evidence to suggest that hunter-gatherers had a relatively stable economy and ecosystem, had a fair amount of leisure time (i.e., they supposedly worked about 15 hrs per week) and enjoyed a well-developed society as evidenced by the art they left behind. The exact reasons and methods of domestication are lost in antiquity. Moreover, as domestication occurred in many different places throughout the world about the end of last ice age, these methods and reasons may have varied from group to group. However, Carl Sauer (one of the domestication gurus) suggested some conditions which were necessary for the domestication of plants to occur.

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the domesticating society must already have a flourishing economic base- starving people are not innovative and they can't afford to experiment. the domesticating society must be oriented to food gathering as a way of existence (most likely this was accomplished by females whereas males hunted) the domesticating society must be partially sedentary the domesticating society must live in areas (such as woodlands) where the soil is tillable using crude implements the society must be relatively safe from natural disasters which would discourage settlement. The overall climatic situation was improving greatly at this time. there must be a wide diversity of plants and animals to exploit. This condition is certainly true with modern-day hunter-gatherers. African h-gs have been found to collect 60 species (ssp) of grains, 50 ssp of legumes, 90 species of root and tuber-bearing plants, 60 ssp of oil seeds, 500 species of fruits and nuts , and 600 ssp of vegetables and spices. Their North American Indian counterparts have been shown to collect over 1000 species of plants from 400 genera and 120 families of plants.

In 1926, N.I. Vavilov published a teatise stating that diversity in plant species is not evenly distributed. Crops were likely to have been developed in these Centers. See lecture outline for a map of the Centers of Diversity (Fig. 4.1).

C. What happened to human society as a result of adopting an agricultural way of life?

Essentially, like the Greeks and the Romans believed, we domesticated ourselves as well.

1. Increased carrying capacity of the land

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Carrying capacity for human habitation under several cultural systems Cultural system Land capacity (people/mile2) Food gatherers Higher hunters and fishers Simple cultivators Pastoralists and nomads (possessing domesticated animals) Advanced cultivators 21st Century man

2 20 50 100 150 ???????

2. Formation of sedentary societies 3. Development of technology (e.g., serrated scythe, plough, wheel) 4. Development of crafts-job diversity 5. Development of new products 6. Emergence of the concept of property and ownership 7. Development of complex distribution system for goods and services 8. Formation of trade centers and trade routes 9. Development of a legal code-especially laws controlling water rights 10. Advent of architecture for storage and protection of property 11. Urbanization

The net results of the domestication process were

That plants and animals that were domesticated underwent significant and irreversible genetic change (i.e. from biological or natural fitness to agricultural fitness) which makes them solely dependent upon us for survival.

And, conversely, that humankind underwent significant and irreversible cultural changes (i.e., from

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hunter-gatherer to urbanized (civilized) society) which makes them solely dependent upon domesticated plants and animals (i.e., agriculture) for survival.

6. Plant improvement and consequences

A. Formation of land races

Prior to modern breeding efforts crop varieties were land races. These land races were formed primarily by the practice of saving seed for planting from year to year by farmers.

Land races of self-pollinating crops (individuals breed true) were mixtures of pure lines. Land races of cross-pollinated crops (individuals do not breed true) were composed of heterogeneous populations with each plant possessing a unique genotype.

Land races had the following characteristics:

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they were endemic to a specific area or region they were extremely well-adapted to the area because... they were composed of a mixture of plant genotypes

DIVERSITY=STABILITY (remember our models of agricultural vs. natural ecosystems?)

The use of land races is relatively "safe" (for an ecological ecosystem) because the variability within the variety buffers against biotic and abiotic stresses/hazzards thus, avoiding potential disasters. Land races aren't particularly high yielding by today's standards, but when crop failure means starvation, a yield every year is preferable to high yield one year and none the next

B. Modern plant breeding and genetic vulnerability

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The scientific age for plant breeding starts in the late 1800's. For most crops, this process resulted in the gradual and systematic decrease in variablity (and genetic diversity). Many successful land races were abandoned/lost.

For self-pollinated crops-methods included pure line selection and pedigree breeding (developing new pure lines by inbreeding after crossing).

For cross-pollinated crops the method of choice was mass selection-formation of very successful open-pollinated varieties such as Krugs Yellow Dent-improvement by mass selection is a slow process with potentially diminished returns per cycle of selection.

To continue, the discussion will focus on corn (Zea mays), a cross-pollinated crop. However, before it does, a few definitions must be given:

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inbreeding depression - the loss of general adaptation and reproductive capacity associated with the accumulation of homozygosity. Plants are weak, highly subject to environmental stress, and are poor seed producers. Cross-pollinated crops suffer inbreeding depression, self-pollinated crops do not!!!!

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heterosis - the increased general adaptation and reproductive capacity associated with the accumulation of heterozygous loci following the cross of two unrelated inbreds (i.e., the opposite of inbreeding depression).

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combining ability - a relative measure of heterotic response through the combination of any two inbreds.

There are two theories why heterosis occurs:

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The dominance theory suggests that a hybrid resulting from a cross between unrelated inbreds displays heterosis because it possesses at least one dominant allele at a maximum number of loci.

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The overdominance theory states that a hybrid resulting from a cross between unrelated inbreds displays heterosis because it is heterozygous at a maximum number of loci. This explanation

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presumes that heterozygosity is superior to either homozygous condition. Most cross-pollinated crops suffer inbreeding depression. Understand the consequences of inbreeding (self pollinating) a cross-pollinated species by considering the fate of heterozygosity at a single locus. Notice that ½ of the heterozygosity in the population is lost with each successive generation of self pollination.

Decrease in heterozygosity at a single locus as affected by inbreeding. Generation Frequency of Frequency of Frequency of Frequency of parental heterozygous homozygous homozygous genotypes offspring dominant recessive offspring offspring 0 1.0 Aa 1 2

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1.0 Aa 0.50 Aa 0.25 AA 0.25 aa 0.25 Aa 0.375 AA 0.375 aa 0.125 Aa 0.4375 AA 0.4375 aa 0.063 Aa 0.469 AA 0.469 aa 0.031 Aa 0.484 AA 0.484 aa

0.50 Aa 0.25 Aa

0.125Aa

0.0625 Aa

0.031 Aa

0.016 Aa

0.25 AA 0.125 AA 0.25 AA 0.063 AA 0.375 AA 0.031 AA 0.438 AA 0.016 AA 0.469 AA 0.008 AA 0.484 AA

0.25 aa 0.125 aa

Frequency of homozygous individuals in population 0 0.50 0.75

0.25 aa 0.063 aa 0.875 0.375 aa 0.031 aa 0.938 0.438 aa 0.016 aa 0.969 0.469 aa 0.008 aa 0.984 0.484 aa

The progeny of inbreds, i.e., F1, hybrids, usually display a great deal of heterosis, especially when they are relatively unrelated. In other words, unrelated inbreds exhibit good combining ability because their offspring possess a high level of dominant alleles or heterozygous loci (depending on what theory you support.

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Even though the phenomenon of heterosis was known, it was not exploited in corn or other cross-pollinated crops because F1 seed (the seed for sale) would have been produced on a very weak, low-yielding inbred plants.

Until...D.F. Jones 1917 created the double cross below

Inbred A x Inbred B = Hybrid C

Inbred D x Inbred E = Hybrid F

Inbred C x Inbred F = Hybrid G

Seed of the Hybrid G born on Hybrid C (maternal parent) ears was what was sold to the farmer. Seed on yield on Hybrid C plant exhibited heterosis.

Immediate increases in yield of over 25% were realized through the use of these double-cross hybrids!! Later, as inbreds improved, F1 hybrids were produced directly which maximizes heterotic response. . The consequences of the use of F1 hybrids include:

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yield and acreage increased (see original handout) dependence on high yield dependence on uniformity- increased mechanization, consumer demand for uniform product. Note that the hybrid progeny of two inbreds are all genetically identical. the loss of diversity. Land races and open-pollinated varieties which held considerable genetic diversity were being abandoned. Within each field genetic diversity was essentially non-existent as each plant is genetically identical.

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Scientists began to worry about the loss of diversity as early as the 1930's. Then in the 1960's the FAO began cataloging variability in major crops, but no collections were made.

The triggering event in 1970 was an outbreak of Southern Corn Leaf Blight in the US caused by the fungus Helmenthosporium maydis. About 15% crop losses, primarily in southern states. Because of the method in which hybrid corn was produced, almost all corn in US was uniformly susceptible. This could have been a disaster.

The epidemic and near disaster sparked a flurry of scientific and political interest to collect and preserve plant germplasm, especially close crop relatives. In the 1980's combating the genetic vulnerability of crops became a national priority.

C. Loss of diversity in natural communities

The loss of natural habitats for plants (and animals) due to human development is a process that has been occurring throughout our history as cultivators. Ohio, after all, was not originally covered with monocultures of corn (Zea mays) and soybeans (Glycine max), but rather with hardwood and white pine forests. Clearing land for agricultural production and other uses, even if buffer zones of diversity are left in tact, has major consequences on gene pools.

In our lifetimes, perhaps the most notable examples of wholesale habitat destruction is occurring in Africa and South America. Deforestation is occurring in rainforests and in other areas as well at an alarming rate. These events certainly have caused the loss of important germplasm and may be effecting our global weather patterns (i.e., global warming through the greenhouse effect). It is beyond the scope of this course to delve into this controversial subject deeply, but for those who are interested, I urge you to explore the topic on your own.

See Fig. 1.1 and Table 1.2 in your lecture outline.

D. Efforts to preserve germplasm

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"To feel a world population growing by up to 160 people per minute, with >90% of them in developing countries, will require an astonishing increase in food production...Access to a range of genetic diversity is critical to the success of breeding programs. The global effort to assemble, document and utilize these resources is enormous, and the genetic diversity in the collections is critical to the world's fight against hunger." (Hoisington et al., 1999).

Potentially useful genetic resources for combating genetic vulnerability include: ● •current varieties ● •obsolete commercial varieties ● •breeding lines ● •induced or natural mutations in breeding lines ● •old land races ● •primitive forms of the crop ● •related weed races ● •related wild races Collections for individual crops should focus upon material in their Center of crop origin/diversity (especially for disease resistance genes).

In-situ vs. ex-situ collections and their maintenance.

"The conservation of germplasm can be managed according to two models: in situ, in its place of origin, or ex situ, outside its place of origin, as in zoos, botanical gardens, and germplasm banks. In situ conservation, clearly the more complex of the two attempts to protect species under the natural conditions in which than are normally found, be they pristine or anthropogenic habitats. In contrast with ex situ conservation, which saves germplasm under artificial conditions, in situ conservation seeks to maintain the genetic diversity of the species under the conditions in which it evolved so as to allow the process of adaption to continue". (B.F. Benz).

National/international efforts to combat the problem include:

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http://www.ars-grin.gov/npgs/

CGIAR -visit this web site to learn morehttp://www.cgiar.org/

FAO Seed and Plant Genocide Resources Service -AGPS - visit these web sites to learn morehttp://www.fao.org/ag/AGP/Welcome.htm http://www.fao.org/ag/AGP/AGPS/prg/global.htm

7. Summary of crop domestication effects

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•There was a gradual change in way of life from hunter-gatherer societies to agrarian societies. •Cultivation brought about new selection pressures (active or passive) on emerging crops. •Emerging crops underwent significant genetic changes to become "agriculturally" fit. In the beginning, genetic variability increased as crop-weed complexes interacted. •Domestication was irreversible. •Domestication occurred most often in Centers of Diversity. •Domesticators had broad-spectrum economy. They were not starving. •Origin of agriculture caused an irreversible cultural revolution in human society. Sedentary life greatly increased the carrying capacity of the earth and the complexity of civilization. •Agriculture as it evolves continues to both solve problems and, at the same time, create others such as the example given above with F1 hybrid corn.

8. Crop Science- its role and challenges in 2000 and beyond?

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•Solving problems •Reducing chemical inputs •Reducing risks for and instances of environmental degradation •Devloping new commodities-value added •Maintaining profitability in a global economy •Feeding an ever-increasing world population

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Horticulture and Crop Science 200 Winter Quarter 2001 Lecture Topic #2: Crop classification References: Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant science growth, development and utilization of cultivated plants. Prentice Hall,Inc., Englewood Cliffs, NJ. Outline: Botanical classification by binomial nomenclature There are over 500K species of plants - classification and naming system is important to be able to communicate about plants and to show relationship between them. Classification of plants was first attempted by Theophrastus, the "father of botany", in the 3rd Century BC. He based his classification schemes primarily on plant form, growth habit and differences in flower structures. Today, we actually use many different classification systems in everyday communication (see below), but perhaps botanical classification (the binomial nomenclature) system used by scientists is the most " information-rich" and least ambiguous of these naming systems. This system was developed by Carlus Linnaeus in the 18th Century AD. His was also based primarialy on flower morphology. Living organisms were divided into groupings (taxa) at many different levels of complexity. The first division, " Kingdom" is the most general (refer to Table 3-1 from Hartmann et al in handout); with each subdivision thereafter, the descriptions of members in the taxa are more specific and the number of members within the taxa decreases until at the species level, an individual plant with unique characteristics is identified. Today this system also considers other factors (e.g., genetic evidence) to distinguish one species from another. Note: the classic definition of species presumes that members of the species can freely interbreed and that member of different species can not, but in the case of plants, this is not clearcut. In terms of crops Members of the Plant Kingdom are thought to have some common characteristics: they are stationary, http://www.hcs.ohio-state.edu/hcs200/topics/topic2.htm (1 of 5) [10/08/2001 10:01:10 a.m.]

contain chlorophyll and photosynthesize, they have cells with rigid walls made of cellulose,and continue to grow throughout their life cycle. However, there are organisms that are considered plants which do not conform to one or more of these characteristics. I can't think of any crops that are not considered to be in the Plant Kingdom. Although we do use products derived from bacteria (genetically engineered or otherwise), we commonly don't think of production of this type as "cropping". Almost all of the crops that we study will be in the Division of Spermatophyta - seed - bearing. Mushrooms(edible) and ferns(ornamental) are two exceptions. Moreover, most crops that are grown are in the Class Angiospermae - plants that produce seeds inside ovaries. A notable exception to this statement, of course, is the production of conifers ( Members of the Gymnospermae - plants that bear naked seeds) as ornamental or industrial(forest) crops. Order, Family, Genus and Species will vary from crop to crop. Genus and species names are either underlined of italicized to indicate that they are in Latin. The former is capitalized while the latter is not e.g.,Agrostis stolonifera - creeping bent grass. Note that the species name is often descriptive - ie.,stolonifera referring to the fact that the plant produces lateral above ground stems called stolons. Question: Can you identify some of the important families which contain crop plants? What are some examples of crops (genus and species) that belong in these families? Do they have some characteristics in common? cultivar - a name derived from the term "cultivated variety". Cultivars describe a subject of plants within a species which demonstrate some recognizable uniformity in traits. This uniformity results primarily from mans efforts through breeding and selection, even though the genetic path by which uniformity is achieved and maintained varies depending on whether the plant is cross pollinated, self pollinated or asexually reproduced (discussed in detail in a later lecture). Cultivar identities are extremely important to producers because indicate what to expect in term of performance in the field(growth rate, flowering time , potential yield, etc.), resistance to diseases and other pests, and crop quality factors, etc. Confusion about what cultivar is being planted may lead to cropping disasters - consider your chagrin when you discover that your field of peppers is yielding chilies instead of bell peppers - the crop you were contracted to grow. This mix - up actually happened and, of course, resulted in some serious litigation. Cultivar designations are made in one of two ways: E.g.,Jubilee sweet corn should be designated as Zea mays ' Jubilee'. Note that the cultivar name is always capitalized and never italicized or underlined. - botanical variety - Botanical varieties also describe subspecies with specific traits. The difference is that botanical varieties are wild segregates. For instance in Aesculus parviflora,(a type of Buckeye tree) there is a botanical variety called serotina, which blooms several weeks later that its partent species. It is designated as Aesculus parviflora var. serotina.

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- group - Group is another subspecies classification. In a species with great diversity of form, the group designation literally "groups" cultivars with characteristics. E.g.,Brassica oleraceae Italica = broccoli, Gemmifera = Brussels sprouts, Capitata = cabbage, Botrytis = cauliflower, Gonglylodes = kohlrabi, Acephala = kale and collards. Roses would be another example of a species with groups. -hybrid (interspecific) - Interspecific hybrids are example of how the "species" designation can get somewhat "muddy" when considering plants. Case in point, Fragaria chiloensis ( the beach strawberry) was isolated from Fragaria virginiana ( the Virginia strawberry )in the wild, separated by 1500 miles of prairie, mountains and deserts between the Mississippi River and the Pacific Coast. However, when brought in close proximity to each other in the 18th century botanic gardens of Europe, these two " species" hybridized readily to form Fragaria X ananassa the cultivated strawberry of commerce. The latter is a "species" formed by a planned interspecific hybridization, therefore to designate it as such , there is an X between its genus and species names. -the problem with common names Consider a home owner entering a nursery and asking to jasmine (see list on handout). If you were an employee of this nursery, would you know what to get him/her? You might be in trouble even if they asked specifically for "star jasmine" because several species are commonly referred to by that name. In this case a single common name is used to designate several species. Can you think of a similar example? The other possibility is that a single species is known by several common names. Often these names are specific to regions. My ex-father-in-law, a native Ohioan, called bell peppers "mangos" his entire life as did many others in SW Ohio. The first time he referred to this, I presumed he meant the fleshy tropical fruit that I know by that name. This problem is not confined to reference to horticultural crops - If you refer to alfalfa in many other countries of the world, they won't know what you are talking about - they call that crop "Lucerne". In many regions of Africa, ground nuts are an extremely important food crop providing protein and energy. One of our ex-Presidents was a ground nut producer at one point in his life, but he called them peanuts. Some of his fellow Southerners might also refer to this food as "goober peas". A complex example of this problem involves the term "corn". In this country, corn means the grain from Zea mays. The same grain in England is called maize, and if you say corn, they think you are referring to wheat or barely. Classification by production - There are obviously many different ways to classify crop plants in addition to their botanical classification using binomial nomenclature. For instance, plants could be grouped as temperate or tropical, annual, biennial or perennial, etc. Some useful classifications for out purposes are discussed below: One very useful scheme is to consider our overall use of the plant/or in other words, how much of the http://www.hcs.ohio-state.edu/hcs200/topics/topic2.htm (3 of 5) [10/08/2001 10:01:10 a.m.]

plant do we produce. To develop such a scheme, one might consider data on either land area devoted to producing each crop or to their overall yield (tonnage produced). Table 1.1 on your handout classifies crops as either edible or industrial, then within each of these groups separates species by their overall yields. Notice that of the five crops the world relies upon for food, four of them are grain crops (sort of --- look at the footnotes in the Table --- one might argue over their definition of "food crop"). Classification by nutritive value = One might also consider classifying crops by the nutritive value they deliver. Certainly, in the grand scheme, hunger in the world is a matter of protein-calories malnutrition (See Table 1.2 on your handout). Note that there are some crops in this Table that are a fair source of both. However, other crops are also important for nutritive reasons, especially those which provide vitamins, minerals, dietary fiber, and other compounds that promote human health. Crops that produce secondary plant products that improve or maintain health (i.e., anticancer compounds, compounds that effect mood or performance) have been recently referred to as nutraceuticals. Documentation concerning the effectiveness of these secondary products varies tremendously from crop to crop. However, in general, these crops enjoy limited production and high profit margins (e.g.,ginseng). 4.Classification by crop use - perhaps the most useful (Class - derived list) Grains-corn,wheat,sorghum,oats,rice,spelt,rye,tritical, millet Pulses- (beans) common bean, soybean,cowpeas,chickpeas,fava beans,peas Oil crops- canola,safflower,peanuts,olives,coconut, sunflower,flax Forages - clovers,alfalfa, timothy,birdsfoot trefoil Fiber crops-cotton,flax,coconut,hemp,sissal Sugar crops-cane,sugar beet, corn(various corn syrups) Medicinal crops-marijuana,Echinacea,ginseng,Ginko biloba Herbs, spices and stimulants - tobacco,cinnamon, sage Vegetables- cabbage, zucchini, peppers, tomato, pumpkin, watermelon Fruits- strawberry, blueberry, peach

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Ornamental crops - red maple, dogwood, parsley, gourds, cabbage, pumpkins Turf- tall fescue, Kentucky bluegrass, Zoyzia, Bermuda, bentgrass Industrial crops- soybeans, pulpwood, rubber, southern yellow pine Note that many crops can be fit in multiple categories.

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Horticulture and Crop Science 200 Winter Quarter 2001 Lecture Topic #3: Crop Plant Morphology References: Text = Chapter 3 Campbell, N.A. 1996. Biology. Benjamin Cummings Publ. Co., Menlo Park, CA = Chapter 34. Copeland, L.O. and M.B. McDonald. 1985. Principles of Seed Science and Technology. Burgess, Publ. Co., Minneapolis, MN. Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant science - growth, development and utilization of cultivated plants. Prentice Hall, Inc., Englewood Cliffs, NJ = Chapter 2. Pollock, B.M. and V.K. Toole. After-ripening, rest period and dormancy. In. Seeds - 1961Yearbook of Agriculture. U.S. Govt. Printing Off., Washington, DC. Raven, P.H., R.F. Evert and S.E. Eichhorn. 1999. Biology of plants. W.H. Freeman and Co., New York, NY = Chapters 23-27. Toole, E.H. and V.K. Toole. 1961. Until time and place are suitable. In. Seeds - 1961Yearbook of Agriculture, U.S. Govt. Printing Off., Washington, DC. Quotation: ".......plants and their features can be identified and appreciated from their external structure, but their internal structure and function are often overlooked. The beauty of an orchid blossom is greatly admired, but just as impressive are the parts of a cell as recorded with a scanning electron microscope"...... Hartmann et al., 1988. Outline: 1. Crop Life Cycles (in brief) A crop's life cycle is determined by the seasonal pattern it exhibits between seed germination and the http://www.hcs.ohio-state.edu/hcs200/topics/topic3.htm (1 of 11) [10/08/2001 10:01:19 a.m.]

development of mature seed for the next generation. As you may guess, crops vary tremendously in this respect and the definition of "crop" life cycle is confounded significantly when one considers crops that are typically asexually reproduced (e.g., chrysanthemum). However, even in the latter case, we can still consider the "seed to seed" model with respect to traditional crop breeding. Most agronomic crops and quite a few horticultural crops are considered to be annuals. That is, they complete the crop life cycle in a single season [i.e., it germinates, grows, flowers, fruits, matures seed then senesces (dies)]. Almost all of them are herbaceous (non-woody). The annual life cycle begins with the germination of the seed and emergence of the new plant (see diagram in handout) which is usually a relatively rapid process. The rate of seed germination is species specific and can be highly influenced by a number of environmental factors (see detailed discussion below). During germination and for the first few days after emergence, the new plant is nourished by stored reserves present in the cotyledons or endosperm of the seed. As these reserves are depleted, newly developed leaves begin the photsynthetic process and newly developed roots begin to supply water and nutrients to the growing plant body. For a period of time, the plants develop vegetatively (i.e., their "growing tips" and "buds" produce only new leaves, stems or roots. The length of the vegetative phase of the annual life cycle varies per crop and may be as short as a few weeks (e.g., certain members of the Brassicaceae or cabbage family) or may last up to nearly a year (e.g., banana). However, at some point, one or more vegetative shoot growing tips or buds undergoes a transformation (floral initiation) which re-programs it to produce flowers and fruit. To ensure that flowering occurs at the most opportune period for plant survival and/or agronomic fitness, floral initiation is often triggered by an environmental trigger, such as the day length (see discussion below). Floral development progresses over time and when its development is visually obvious, it can be said to have emerged. The floral development process continues for a period of time before the flower is ready to open. During this period, pollen and egg cells are typically developing and are usually fully formed (or nearly so) at the time of flower opening (anthesis). Flowers vary tremendously with respect to the exact timing of pollen shed or stigma receptivity; in some species floral structure, pollen shed and stigma receptivity favor self-pollination of the flower (e.g., pea) whereas with others, these phenomenon are arranged to promote cross-pollination (e.g., corn). Pollen tube growth through the style is usually a rapid process requiring from 1-3 days to complete. The period following fertilization is marked by development of both fruit and seed structures in a set pattern which varies with species (see discussion below). During this period, much of the energy produced by the plant and the mineral nutrients it acquires from the soil/media are devoted to the fruit and seed maturation process. Therefore, fruit and seed development accounts for much of the addition of dry weight to the plant during this period. Some annuals have distinct vegetative and flowering phases (e.g., cereal grains) and are said to be determinant, whereas others are indeterminant and continue to grow vegetatively while flowers are periodically produced (e.g., some types of beans and tomatoes). Biennial plants require two seasons to complete their life cycle (e.g., carrots and onions), although in some cases we crop them for only one season because the yield component of interest is not the seed. Biennials are typically plants with a rosette form (i.e., vegetative shoots are extremely short and leaves appear to be in a whorl pattern). Floral initiation occurs during the first season of growth but is arrested early in its development, resuming only after receiving an appropriate environmental signal. In temperate crops, this signal is a period of chilling requiring temperatures from 1-7° C (34-45° F). The process of chilling is called vernalization. Once vernalized, floral development advances with the formation of a

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blooming stalk (typically attaining heights much in excess of the leaf canopy) and a "seed head" or flower. After seed is matured, the plant usually dies. In the case of carrots and onions, the root or bulb that we eat serves as a storage of food reserves that are almost entirely consumed by the plant in order to flower and mature seed. Herbaceous perennials (e.g., tulips, chrysanthemums, etc.) annually produce aerial vegetation and flowers from perennial plant parts [crowns (stem bases), rhizomes (underground stems) or bulbs]. The patterns of above-ground growth, flowering, seed maturation and senescence vary dependent upon species. Woody perennials produce top growth over a period of years, adding new stems, leaves, flowers and fruit every year while typically increasing the girth (thickness) of stems and roots produced in earlier seasons. Growth therefore is cumulative. Annual growth often occurs in flushes followed by sessation and the "setting" of a terminal bud. Many hardwoods (e.g., oaks) have only one growth flush, others (e.g., some pines) exhibit recurrent growth flushes throughout a season, whereas others exhibit sustained growth throughout the season. Optimum conditions must be maintained during the production of woody perennials, because growth flushes can terminate prematurely if stressed by unfavorable environmental conditions.

1. Seed Germination "One for the buzzard, One for the crow, One to rot, and One to grow!" (Fay Yauger) "In many ways, the seed is a microcosm of life itself. The seed is a neatly wrapped package containing a living organism capable of exhibiting almost all of the processes found in the mature plant." (Copeland and McDonald, 1985). "A seed is essentially a young plant whose life activities are at a minimum" (Toole and Toole, 1961). "The [biological] function of a seed is to carry its embryonic plant through the hazzards of time and space to a time and place where the new plant can grow, flower, and in its turn, produce seeds" (Pollock and Toole, 1961) Crop life cycles often begin with the germination of seeds. Each seed contains the following: a) an embryonic plant that has a radicle (embryonic root) and a plumule (embryonic shoot); one or two cotyledons that are used as a food source by the embryonic plant until it is able to photosynthesize on its own; (NOTE: in moncots, this function is also performed by the endosperm, a storage tissue for starch and other compounds) and c) a method of protecting the embryonic plant (seed coat or fruit structures). Shown in your original handout are the first phases of the lives of the quintessential monocot (corn) and

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the quintessential dicot (bean). Notice some of the similarities and the differences in their overall structure. As in all other phases of a crop plant's life, environmental conditions have a profound effect on plant performance. The exact conditions necessary for optimum seed germination are specific to each crop species. However, in general seeds often germinate best when the following requirements are met: ●

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Adequate soil or media mosture content. Seeds will not germinate in dry soil or media. Likewise they will not germinate under waterlogged conditions. Certain types of rice and aquatic species represent notable exceptions to the latter for they will not germinate unless they are under water. Proper temperature (15-26°C or 59-79°F common) Adequate soil or media aeration Soil or media free of diseases and other pests Soil or media with low salt concentrations

In addition, some seeds require light where others require darkness to germinate. A seed is said to be quiescent (resting) if it fails to germinate unless the above mentioned conditions are met. The quiescent seed is physically and physiologically ready to germinate, but awaits the proper conditions before doing so. A seed is said to be dormant if it fails to germinate even though the above mentioned conditions are met. Dormant seeds are not yet physically or physiologically ready to germinate no matter what environmental conditions are present. There are several common forms (types) of seed dormancy; a few are listed below:

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Hard seed coat (a physical dormancy) - the seed coats of some species (most notable examples are in the Fabaceae, the bean family) are either highly lignified or covered with waxy or oily substances (cutin and/or suberin) so as to be impervious to water and or gasses. Germination can only occur after the seed coat has been ruptured or breached. In nature, the disruption can result from conditions brought about by heavy rains (abrasion), fire, or consumption by birds or other animals (acid digestion). Embryo dormancy (a physiological dormancy). In many temperate zone species, seeds physically mature on the plant, but are physiologically unable to germinate until exposed to cold temperatures over a prolonged period of time. There is evidence to suggest that during the cold period, levels of a growth-inhibiting hormone (abscisic acid) decrease while levels of growth promoting hormones (gibberellins and cytokinins) increase. Similarly, in some species (e.g., Cucurbitaceae, the squash family) allowing physically mature seeds to "after-ripen" in detached fruit will increase their germinability.

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Rudimentary embryos (a physical and perhaps physiological dormancy). Some species (e.g., holly,

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magnolia) shed their fruit before fully maturing the seed. The seed continue to develop in or outside the fruit until competent to germinate. ●

Chemical inhibition (physiological dormancy). Chemical inhibitors to germination (e.g., caffeic acid, coumarin) can be present in the embryo itself, in the seed coat or in the fruit tissue surrounding the seed. These compounds must be metabolically inactivated, leached, degraded or removed in some other way before germination can occur. For instance, the gelatinous material surrounding a tomato seed contains an inhibitor which prevents the seed from germinating inside the fruit. This inhibitor must be removed prior to germination.

Under natural conditions, dormancy is an important phase of a seed's life as it often ensures that the seed does not germinate inside the fruit (vivipary) or does not germinate when environmental conditions are unfavorable. Delayed and staggered germination is a undoubtedly a selective advantage in a natural ecosystem, but it is not a trait commonly associated with agricultural fitness. See discussion of the difference between natural and agricultural fitness in Topic 1 notes. As agriculturists, we often "process" seed in order to overcome dormancy using a variety of techniques. Hard seededness is often alleviated through various scarification (scratching) methods using abrasives and mechanical devises to move seed across abrasive surfaces. Hot water treatments are also sometimes used as are acid scarification treatments using concentrated sulfuric or hydrochloric acids (these are somewhat dangerous). The exact timing and conditions of these treatments necessary for optimum success vary tremendously with species (of course). Embryo dormancy can be overcome by stratification, a process which can be done outside under "natural" conditions, but is more commonly practiced under controlled conditions. The critical factors in the stratification process include: ●

chilling temperatures - (1-7°C or 34-45°F). The physiological processes necessary to alter hormone levels progress under these conditions. If the temperature is below freezing or above critical temperatures, the processes are delayed or halted

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Moisture - Seeds are usually soaked prior to stratification and then placed in moist sand or paper to keep them moist (but not immersed) throughout the stratification procedure.

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Oxygen - Oxygen is necessary for continued respiration which keeps the seed viable and physiologically active. Therefore, stratification procedures should not be conducted in air-tight containers or under water-saturated conditions.

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Time - The period of time necessary to complete the stratification process varies tremendously with species and must be determined experimentally. However, 30-90 days is a typical time frame.

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Chemical inhibition may be overcome in a variety of ways depending on the inhibitor and on whether or not the inhibitor is internal or external to the seed. When extracted from the fruit, the gelatinous matrix surrounding tomato seeds must be "fermented" (removed) in order to remove it and the inhibitor it contains. In other species, inhibitors may be overcome by leaching (continued washing). Seed viability vs. maturity A seed which has reached physiological maturity when it has reached maximum dry wt (typically 5-20%). Other conditions which act as indicators of maturity include the sessation of nutrient importation and the formation of abcission layer at hilum (area where seed is connected to ovary tissue by a "stalk" called the funniculus). Most seeds viable before they are mature. For example, weed seeds (colonizing species) especially adept at producing new plants even when seeds are not fully ripened on the plant or under environmental situations that are not suitable for the germination of seed from truly wild (feral) or cultivated crops. For the seedsman, it is important to determine when maximum seed maturity is reached so that the seed they sell will be highly vigorous. The physiological steps in the seed germination process. ●

The imbibition of H2O. Water is taken up by the seed throughout the germination process in three distinct phases (see diagram in handout). The first "log" phase of imbibition is passive (i.e., it does not require the espenditure of the seed's energy) and relatively rapid. The rate of water uptake is determined by the difference between:

- The matric and osmotic potentials (pulling forces) in the soil/media as determined by the type of media and the level of dissolved salts that it contains and. - the osmotic potential (pulling force) and turgor pressure (pushing force) of the seed's cells. In order for seeds to imbibe water, their osmotic potentials must be greater (more negative) that the soil forces combined (i.e., the seed wins the tug-of-war for the water in the environment). If water in the soil remains adequate, the seed will continue to imbibe water until cells are fully hydrated. At that point turgor pressure will be great enough to prevent further movement of water into the cells (i.e., the beginning of the lag phase shown in the handout diagram). The rate of uptake in this phase is influenced by the composition of the seed (protein-rich seed usually imbibes water faster than starchy seeds), and seed coat permeability

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An environmental trigger? As stated above, some seeds require light in order to germinate. The compound in plants that senses light and the duration of light and dark periods is called phytochrome. Phytochrome, in its active form, promotes membrane permeability, and stimulates enzymatic and metabolic activity (see below). Phytochrome-mediated triggers often act in concert with or can be complicated by temperature factors. For more on phytochrome, see discussion on its effects upon the flower initiation process (daylength sensitivity).

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Enzymatic and metabolic activity. As the first log phase of imbibition ends, a "lag" phase begins, characterized by a greatly diminished rate of water uptake (see diagram in hand out). This period corresponds with an acceleration of metabolic and enzymatic processes within the seed as it prepares for growth. In this period, membrane-bound enzyme systems are activated and active transport (ATP-requiring) transport of ions and solutes across membranes is promoted. Gene expression occurs. Enzymes are also synthesized -- especially hydrolytic enzymes that control the glycolytic process (metabolism of sugars for the production of energy). Hormonal contents of seeds may also be altered so as to favor growth promoting substances over inhibitors.

Some aspects of cereal crop (e.g., corn, barley) seed germination illustrates how some of these processes are coordinated within the germinating seed. In cereals, the first step in the process of enzymatic stimulation is based upon the synthesis of gibberellic acid (GA3) in the scutellum (cotyledon) and its subsequent transportation to the protein-rich cells of the aleurone layer cells (i.e., the outer layer of the endosperm or storage tissue). The GA3 acts as a messenger to the aleurone cells, "informing" them that the conditions are now adequate for germination to occur. Peleg and coworkers demonstrated the necessity of the GA3 as a messenger in barley seeds (see figure in handout). If the embryo of barley is removed (i.e., including the scutellum), hydrolysis of starch in the endosperm does not occur. However, if it is exogenously-treated with GA3, the breakdown of carbohydrate progresses rapidly. Thus, the identity of GA3 as the messenger is confirmed. Exogenous application of GA3 breaks dormancy and/or stimulates germination in many species (both monocot and dicot) and many species have been shown to produce GA3 during the lag phase of the germination process. In other species, including most dicots, the stimulation of metabolic processes by hormones is much more complex and is based upon a balance of promoting and inhibiting substances. ●

Initiation of growth. The cell division and elongation necessary to form the new plant begins during the lag phase as metabolic and enzymatic activity progress. During this process, storage tissues decrease in dry weight while tissues in the embryo increase in dry weight.

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Protrusion of the radicle. In most instances, the protrusion of the radicle is the first physical sign of germination and is an indication of the seed's viability. However, at this stage, many "slings and arrows of outrageous fortune" (sorry Will) may still prevent the ultimate establishment of the new plant. The protrusion of the radicle also signals the beginning of the second log phase of water uptake. Rapid growth of both the root and shoot systems depends upon the rate of cell division and cell elongation which, in turn, requires optimum cell turgor pressure (pushing forces on cell walls and membranes caused by water uptake).

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Emergence and seedling establishment. Emergence is the process wherein the shoot of the new plant breaks through the soil/media surface and becomes aerial. The factors which promote or inhibit this process (e.g., whether or not the soil surface is crusted) are numerous and primarily soil/media dependent. There are several classic categories of emergence based primarily upon the relative position (above or below ground) of the cotyledons and other seed tissues. See any plant science text book, if you are interested in learning about these - we won't consider them further here).

As the embryonic plant begins to grow, it undergoes a planned (genetically programmed) sequence of tissue development which it continues throughout its life. Although there are obviously some major anatomical and physiological differences among higher plants, there is also substantial commonality in the types of tissues that are present. 3. Meristems All higher plants have meristems. Meristematic regions are composed of undifferntiated, parenchymatous cells which, when active (not dormant) are rapidly undergoing cell elongation and cell division. Meristematic tissues give rise to permanent tissues (containing mature, often specialized cells) which comprise the bulk of the plant body. Meristems can be found in various places on the plant. One might argue that the most obvious and logical place for a meristem to be is at the growing point (tips) of shoots and roots. It is so, and these meristems are referred to as apical meristems. Apical meristems of above-ground shoots give rise to cells that will eventually become the shoot epidermis, cortex, primary xylem and phloem and central pith. Some shoot apical meristems remain vegetative throughout their life while others undergo a transition to a flowering meristem in response to internal dictates and/or environmental cues. Some shoot apical meristems experience several seasons of growth punctuated by periods of dormancy. Apical meristems are also the source of axillary buds which, when allowed to develop, form new shoots (branches), inflorescences or both. Axillary bud growth is often suppressed by plant hormones produced by the apical meristem resulting in the phenomenon of apical dominance. Root tips also have apical meristems that give rise to the various tissue systems of the root, the stele, the root vascular system, the pericycle, the endodermis, the cortex and the epidermis. Shoot apical meristems also give rise eventually to other meristematic regions such as subapical (axillary) and lateral shoot meristems. Sub apical meristems are located just "underneath" the apical meristem. Some plants grow vegetatively following a "rosette" growth habit where internodes are very short and leaf petioles are in a compact bunch close to the crown of the plant. If such plants also have a terminal flowering habit, like carrots, for instance, one might expect the flower to also be very close to the ground. However, in these instances, after the terminal meristem has already transitioned to a flowering meristem, the subapical meristem produces the cells necessary for the development of an inflorescence or bloom stalk.

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Lateral meristems refer to cell layers in stems that give rise to new xylem and phloem members (the vascular cambium) or to new bark (the cork cambium). The vascular cambium in woody plants is cylindrical and the development of new xylem elements inward results in increased girth and the development of annual growth rings due to differential rates and cell sizes of xylem production throughout the season. Phloem gets produced outward from the cambium but as the season progresses, older phloem members get crushed and obliterated. Herbaceous stems have vascular cambiums as well, but these meristems are arranged with vascular tissue in "bundles" (i.e., not in a continuous cylinder). Intercalary meristems are meristems that have been separated from the shoot terminal meristem by intervening mature tissue. One good example of an intercalary meristem is that which is associated with the lower regions of a grass leaf sheath. Grass blades grow from this meristem rather than from a terminal meristem. I.e., they elongate from the base of the blade, not the tip of it. 4. Primary and secondary development of stems Stems and branches are the scaffolds which support leaves, flowers, fruit and other above-ground plant organs. A typical shoot (Figures 2-6, 26-3 and 26-7) has the following tissue groups: epidermis, cortex, primary xylem and phloem and central pith. It is punctuated in its growth by the development of nodes. Nodes typically contain a leaf supported by a petiole and an axillary bud which possesses a dormant, flowering or vegetative meristem of its own. A repeating stem unit containing a leaf, node, internode and axillary bud is called a phytomere. Each node (leaf axil) must be supplied with a vascular trace. In stems that are young, the vascular system is arranged in bundles which are located just interior to the cortex. The arrangement of these vascular bundles is well ordered but complex. Three typical arrangements are shown in Figure 26-7. Many dicot stems (e.g., basswood) have vascular bundles that more or less form a ring around the pith (Fig. 26-7 a), whereas others (e.g., elderberry) have more descrete vascular bundles that have wide interfascicular regions (spaces) between them (Fig. 26-7 b). Monocots (e.g., corn) and some herbaceous dicots have vascular bundles scattered throughout the central cylinder. Secondary growth occurs primarily in woody perennials. It can be defined as an increase in girth (thickness) of stems or roots in regions where individual cells are no longer dividing or elongating. In the case of stems, this growth is characterized by presence and activity the vascular cambium, a lateral meristem. The progression of from primary growth to secondary growth in elderberry is illustrated in Fig. 27-6. Note that in secondary growth, the interfascicular regions disappear and the vascular cambium forms a complete cylinder around the xylem and pith. The vascular cambium continues to produce xylem and phloem tissues and also a system of vascular (fluid conducting) rays which connect (radially) the various layers of xylem and phloem produced in successive growth phases. The vascular cambium increases in girth by anticlinal (lateral) cell division. What we commonly refer to as wood is secondary xylem. Secondary xylem that is still functional is called sapwood whereas that which no longer conducts is called heartwood. The transition from sapwood to heartwood often involves the loss of food reserves and the infiltration of oils gums and resins and tannins which give woods their characteristic color and odor. In a given season, new xylem members that

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formed early are wider, thinner-walled and less densely packed than those which are formed in late season. This pattern coupled with periodic yearly activity of the cambium results in "annual growth rings" which give wood its characteristic grain and arguably, its beauty. Any tissue located to the "outside" of the vascular cambium is considered bark. Bark includes operational and defunct phloem, periderm if present and epidermal-derived tissues. As girth increases, older phloem members are crushed and there is a tremendous stress on outer layers of bark resulting in its characteristic irregular surface. This material eventually sloughs off as new phloem are formed in subsequent seasons. Common products that we obtain from secondary phloem growth include bark mulches, maple syrup (tapped from active phloem members nearest the cambium - for an instructional website visit http://www.mi-maplesyrup.com/howto.html), and cork. 5. Primary and secondary development of roots Root systems have five functions: to anchor the plant, to absorb water and nutrients, to conduct water and nutrients to aerial portions of the plant, to synthesize plant hormones (primarily cytokinins) and to act as a storage organ for carbohydrates. Like the shoot or stem, primary root growth is a function of the root apical meristem and, in turn, tissues derived from this meristem develop into primary meristems, primary tissues and eventually, secondary growth. In some species, a quiescent center with reduced cell division forms within the meristematic region which may play a role in the organized development of root tissues. The apical meristem is protected by a rootcap; root cap cells are scraped off as the root penetrates the soil/media and mucigel, a "slimy" substance associated with the cap helps to lubricate the entire process. The region of [cell] elongation, typically only a few mm in length, constitutes an area of the new root where pith, vascular, cortical and epidermal tissues are beginning to mature. Water and nutrient uptake, however, occur most readily in the region of maturation characterized by the development of root hairs (see below). Tissue systems within this region are as follows: ●

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vascular cylinder - composed of differentiating xylem and phloem and associated parenchyma cells pericycle - a root tissue system meristematic region that gives rise to new vascular tissue, new endodermal tissues and adventitiously to branch roots.

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endodermis - the boundary layer between the vascular cylinder and thr root cortex. This tissue system includes a specialized layer of cells which are surrounded by a suberized (oily) substance called the casparian strip. The casparian strip serves a very important function - it prevents the free movement of solutes (nutrients) from the soil solution (water + dissoved nutrients) to the vascular cylinder. Therefore, in order to enter the vascular cylinder, solutes must first enter a living cell which is bounded by a cell membrane. The cell membrane is selective allowing only certain solutes to enter. It also prevents solutes that have entered from effluxing (escaping) back out into the soil solution due to osmotic potential.

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cortex - The cortical tissue system is composed of apoplastic (non-living intercelluar spaces) and symplastic (living cortical cell) regions. Movement of the soil solution is virtually unrestricted in

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this region. Cortical cells are interconnected by plasmodesmata and are a primary sites of nutrient assimilation. Assimilation by cortical cells is affected by the environmental parameters of temperature (assimilation generally increases up to 40 C, then declines) , soil aeration, light (shading of leaves affects CHO movement to roots restricting their energy levels), pH (because it affects membrane Ca content), and the relative conc. of ions in the soil solution. ●

epidermis - the primary functions of the epidermis are that of uptake and to protect cortical cells from the soil environment. Root hairs develop from tricoblasts (specialized epidermal cells) in the region of elongation. Root hairs are short-lived and are continually renewed. The function of root hairs is to increase surface area of the root which increases contact with the soil solution. It was estimated that a 4 month old rye plant root system contained 14 billion root hairs constituting 400 m2 of surface area and that if placed end to end, would stretch 10 thousand kilometers. Root hairs are especially important for the acquisition of phosphorus.

Some species (a few of them are crops) do not develop root hairs. Often, these plants have co-evolved with species of mycorrhizal fungi capable of forming a symbiotic relationship wherein fungal hyphae function similarly to root hairs. Secondary growth in roots is similar in its characteristics to those exhibited by stems. Although roots that have undergone secondary growth are not actively absorbing water and nutrients, they are involved with aeration and gas exchange through lenticels (pores).

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Horticulture and Crop Science 200 Winter Quarter 2001 Lecture Topic #3a: Crop Plant Morphology (continued) References: Text = Chapter 3 Bernier, G., J.M. Kinet and R.M. Sachs. 1981. The physiology of flowering. Vols. 1-2. CRC Press, Boca Raton, FL. Buban, T. and M. Faust. 1982. Flower bud induction in apple trees. Hort Rev. 4:174-203. Campbell, N.A. 1996. Biology. Benjamin Cummings Publ. Co., Menlo Park, CA = Chapter 34. Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant science - growth, development and utilization of cultivated plants. Prentice Hall, Inc., Englewood Cliffs, NJ = Chapter 2. Pratt, C. 1988. Apple flower and fruit: morphology and anatomy. Hort Rev 10:273-308. Raven, P.H., R.F. Evert and S.E. Eichhorn. 1999. Biology of plants. W.H. Freeman and Co., New York, NY = Chapters 23-27. Salisbury, F.B. and C.W. Ross. 1992. Plant physiology. 4th ed., Wadsworth Publ. Co., Belmont, CA. Westwood, M.N. 1978. Temperate zone pomology. H.W. Freeman and Co., San Francisco, CA Quotations: "It has been said that an oak is an acorn's way of making more acorns. Indeed, in a Darwinian view of life, the fitness of an organism is measured only by its ability to replace itself with healthy fertile offspring .... These two developments, pollen and seeds, are among the most important adaptations of plants to life on land." Campbell "Due to its tremendous agricultural and economic importance, reproduction has perhaps been one of the most studied processes in plant development." Scheerens (PhD Dissertation, 1985)

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Outline: (Continued) Previously we discussed 1. Crop Life Cycles 2. Seed Germination 3. Meristems 4. Primary and Secondary Development of Stems 5. Primary and Secondary Developmetn of Roots See Topic 3 Handout and Lecture Notes to review these concepts. 6. Leaves Leaf structure Leaf structures vary considerably with respect to size and shape. For instance, some species have simple leaves consisting of a single leaf blade or lamina (e.g. oak, corn) whereas others develop compound leaves that are comprised of several "leaflets" (e.g., tomato, rhododendron). Further, compound leaves are either palmately compound where all leaflets are joined at a central point or pinnately compound where leaflets are attached to a rachis in some organized fashion (usually two by two). Leaf size also varies greatly among species; consider the size difference between a Blue Spruce "needle" and a banana leaf. Please review Lab 1 for some details. Moreover, structural and morphological variations in leaves often can be understood in relation to differences in environmental adaptation among species. For example, leaves on desert species are often small or in other ways highly modified to protect against water loss. Cacti are, of course, an extreme example of modification for environmental stress as leaves have been "replaced" by a photosynthesizing plant body. Despite their differences, leaves typically share some general morphological features and functions (Figs 2-33 and 2-34). ●

Epidermis - Upper and lower surfaces of the leaf blade are formed by a single layer of parenchymatous cells which comprise the epidermis. The epidermis provides strength and some rigidity to the blade. Often, epidermal cells are covered by a cuticle (waxy material) which further protects the leaf from damage and water loss. The leaf epidermis also contains a group of specialized cells called Guard cells which flank (surround) the stomates (pores) through which water vapor and atmospheric gasses enter and exit the leaf. Because guard cell shape fluctuates over time in rapid response to environmental ques, guard cells can act as gate keepers, allowing gaseous interchange between the interior of the leaf and the surrounding atmosphere only when it is to the plant's advantage (see discussion below). Stomate size, shape (Figs. 3.18 and 3.19), density, order (random or ordered in rows) and position varies substantially among crop plants. Stomates are often more prevalent on the lower surface of the leaf, but this is by no means, universal. The stomates of aquatic plants (e.g., water lily), for obvious reasons, are primarily found in the upper epidermis. In some species, epidermal cells also give rise to trichomes or hairs (collectively called pubescence) that perform a number of important functions (see below).

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Spongy mesophyll and palisade layer - The spongy mesophyll and palisade layers of the leaf are composed of parenchymatous cells, both of which are present in many dicot leaves. As they contain chloroplasts, the double-membraned organelles that house pigments and enzymes responsible for photosynthetic processes, they are the "work horse" cells of the leaf. The cells in the spongy mesophyll are loosely and irregularly arranged resulting in relatively large intercellular spaces. Especially evident in some species are the large intercellular chambers that are associated with stomatal openings. Intercellular spaces enhance the process of gas exchange (primarily CO2, O2 and H2O) with the atmosphere. In contrast, palisade layer cells are more highly organized and contain minimal intercellular spaces. However, because they have expanded surface areas that are 2 to 4 times as extensive as those of the spongy mesophyll, they carry on the bulk of photosynthesis in most dicot leaves. In some leaves, the palisade layer is more than one cell thick.

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Vascular bundles - Vascular bundles distributed throughout the leaf contain both primary xylem (usually oriented toward the upper surface of the leaf) and primary phloem (usually oriented toward the lower surface of the leaf) elements. Larger vascular bundles are often called veins. Visually, venation appears to be netted (dicots) or parallel (monocots) in organization, but in every arrangement, vascular systems are continuous and connect to the stem through the midrib. The midrib of the leaf acts as the principal vascular conduit of the leaf and because it contains some secondary growth (lignification) the midrib adds rigidity to the leaf (i.e., it acts as a "main support beam").

Note 1: lignin is a polyphenolic material that is deposited in secondary cell walls. It is extremely resistant to degradation and is responsible for the durable characteristics of wood. If you witness the leaf decomposition process you will note that the midribs remain long after the rest of the leaf blade has disintegrated. Note 2: The midribs of simple leaves are continuous with the petiole or "leaf stem" which attaches to the stem at the nodes. In compound leaves, each leaflet possesses a midrib which is attached to the petiole by a petiolule, in pinnately compound leaves the leaflets are attached through the petiolule to a continuation of the petiole called the rachis (See lab #1). Sorry -- natural variation sometimes makes naming structures somewhat complicated. A bundle sheath, a tightly organized group of parenchymatous cells surrounds each vascular bundle. This tissue acts to prevent direct access of atmospheric gasses to the vascular system of the plant and insures that all compounds entering the vascular system from the "outside" must pass through cellular membranes which discriminate against potentially harmful substances. In most plants, these cells do not contribute much to the photosynthetic capacity of the plant as they contain relatively few chlroplasts. However, there is an important group of plants, C4 plants, in which the bundle sheath cells are extremely important for the photosynthetic process (see below). ●

Guard cell function - As stated above, act as gate keepers, allowing gaseous interchange between the interior of the leaf and the surrounding atmosphere only when it is to the plant's advantage (i.e., when photosynthesis is likely to take place). Guard cells open and close stomates by virtue of their ability to rapidly change shape in response to turgor pressure (the pushing force that the cytoplasm and cell membrane exerts on the cell wall). At a given moment, the turgor pressure results from the relative concentration of solutes (dissolved materials) in the cell and the effect they have on the importation of water into the cell. Teliologically, nature tends to want to increase the distance between molecules of dissolved solids so that their concentration (weight/volume) is at a minimum (one of the laws of

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thermodynamics). In aqueous systems such as the cell cytoplasm, nature does this by adding water. Remember, the plant cell membrane is permeable to water molecules; therefore, if the concentration of solutes on the inside of the cell is greater than on the outside of the cell, water will move into the cell to reduce solute concentration by a process called osmosis (see any biology text for a review of this phenomenon). As the quantity of water inside the cell increases, the turgor pressure increases exerting more force on the cell wall. Turgor pressure is maximized, of course, when the tensile strength (pulling forces) in the cell wall will not allow it to be stretched further. Otherwise the cell would burst. Guard cells that are fully turgid are open; those that are flaccid (the opposite of turgid) are closed (see a and b in handout) Guard cell turgor pressure is affected by several main controlling elements: light, CO2 concentration, temperature and water concentration of the leaf (Fig. 4-11). In most plants, stomates are closed at night (see exceptions below). When light strikes a leaf surface, photosynthesis commences causing the production of ATP (energy), decreases in CO2 levels, and increases in the concentration of sugar and other solutes such as the malate -2 ion. Note: malic acid is a commom organic acid containing 4 carbon atoms; its anion is called malate. Because it is associated with the Calvin (tricarboxyllic acid) cycle of respiration, it is ubiquitous and essential to all higher forms of life.) Then, the guard cell membranes open channels that permit the influx of K+1, and Cl-1 through active transport (energy requiring) mechanisms from the surrounding cell wall and intercellular spaces. The influx of these materials along with sugar and other cellular components increases the solute concentration and osmotic potential of the guard cell. Water then enters the cell by osmosis and the turgor pressure increases, "inflating" the guard cells and opening the stomates. This whole process can be reversed by increases in ABA (which stands for abscisic acid, a plant hormone that usually inhibits metabolic processes) concentrations. When water availability is limited (a function of soil moisture levels, temperature and relative humidity), ABA concentrations in the leaf are increased by synthesis in mesophyll cells or importation from the plant roots. Elevated ABA causes the efflux of solutes and water out of the guard cell, thus, closing the stomates to protect against wilting or in extreme cases, leaf death.

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Trichome function - Trichomes or hairs (collectively called pubescence)are specialized epidermal cells that perform a number of important functions. Because they increase the surface area of the epidermis, they aid the leaf in dissipating heat and retarding water loss. Some trichomes secrete oily resins which also help maintain leaf water balance. Trichomes may also protect the plant by discouraging insect predation or ovipositioning (egg laying) by a phenomenon known as antixenosis (xenos is Greek for stranger or guest; antixenosis literally means repelling guests). In simple terms, the antixenotic response occurs because insects simply do not prefer "hairy" leaf surfaces as they have to expend more energy to eat or lay eggs there than on glabrous (non-hairy) leaf surfaces. Trichome (pubescence) density, color and position varies, of course, with species and in the case of ornamental crops (e.g., african violets, lambs ear) can be one of their most attractive features.

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C3 VS. C4 Leaf anatomy and function - Most crop plants capture CO2 by incorporating it into a 5-carbon sugar phosphate (ribulose 1,5-bisphosphate) to form a transient 6-carbon compound that almost immediately disintegrates to for 2 molecules of a 3-carbon compound (3-phosphoglycerate). The enzyme that catalyzes this reaction is "nicknamed" rubisco (i.e., ribulose 1,5-bisphosphate carboxylase/oxygenase).

C5 + CO2 C6 C3 + C3 catalyzed by rubisco Thus these plants are called C3 plants. The fate of the two C3 molecules is as follows: Five of the six carbon atoms are used to regenerate the initial C5 compound while the other carbon atom is used in the synthesis of a glucose (simple sugar) molecule. C3 + C3 C5 + C used for glucose synthesis This complex and cyclic process is called the Calvin Cycle (after the person who figured it out experimentally). Obviously, since glucose contains six carbon atoms, the cycle must turn six times in order to fix the carbon from six CO2 molecules to one molecule of glucose. As we will discuss in detail in Topic 4, this process takes energy and requires the addition of electrons (i.e., it is accomplished via chemical reduction). Although most of our crop plants are C3 plants, a number of notable exceptions have an additional scheme to trap CO2. In these species CO2 can be added to a 3-carbon compound (PEP or phosphoenolpyruvate) to form a 4-carbon structure (oxaloacetate). The enzyme that catalyzes this reaction is called PEP carboxylase. C3 + CO2 C4 catalyzed by PEP carboxylase Thus, these plants are called C4 plants

The fate of the 4-carbon product is as follows: Three of the four carbon atoms are used to regenerate the initial C3 compound while the other carbon atom is passed to the Calvin cycle to be used for glucose synthesis in a process identical to that in C3 plants. C4 C3 + CO2 passed to Calvin Cycle where it is used for glucose synthesis This complex and cyclic process is called the Hatch-Slack Cycle (again after the researchers who figured it out experimentally). Again this process requires energy and electrons.

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Although this additional system in C4 plants seems to add unnecessary metabolic complexity to the capture of CO2, it has some real physiological advantages do to the nature of the two enzymes involved. PEP carboxylase has a greater affinity for CO2 than rubisco does so photosynthesis rates are high in C4 plants even when CO2 concentrations are limiting. The operation of the Hatch-Slack pathway in C4 plants feeds carbon (CO2) directly to the Calvin Cycle keeping it functioning at more optimum rates. If CO2 levels are low and oxygen levels are high, rubisco (Calvin Cycle enzyme) adds oxygen to the C5 starting sugar which is the beginning of another cyclic phenomenon called photorepiration. We will not discuss photorespiration in detail in this course except to say that it is a rather futile cycle which uses oxygen and releases CO2 and seems to waste energy and accomplish nothing (i.e., its positive attributes, if any, are not well understood). In C3 plants, photorespiration rates may be relatively high under certain conditions so that as much as 50% of the carbon fixed by photosynthesis is reoxidized and released as CO2. In C4 plants, rates of photorespiration are much lower because rubisco has a constant supply of CO2. C3 and C4 plants differ with respect to how photosynthetic rates are affected by light intensity. C4 plants continue to respond to higher light levels long after C3 plants have reached their maximum photosynthetic rates (see Topic 4 notes). C4 plants exhibit greater water use efficiency than C3 plants (see below). C4 metabolism has been observed in 19 plant families and may be active in thousands of plant species. C4 metabolism is perhaps most common in the Poaceae (grass family) which includes notable examples of crops such as corn (maize), sorghum, sugarcane, millet and bermudagrass and of weeds such as crabgrass and bermudagrass. The leaves of C4 plants function a little differently than do those of C3 plants. Most notably, CO2 is originally captured by the Hatch Slack pathway in the mesophyll cells and then is transferred to the Calvin Cycle which operates primarily in the bundle sheath cells. The bundle sheath layer is more highly organized in C4 plants (see Fig 26-26) and resembles a "wreath". Kranz is German for wreath and this arrangement in C4 plant leaves is called Kranz anatomy. In C3 plants, the bundle sheath cells contain few chloroplasts and contribute little to photosynthetic output. In C4 plants, the reverse is true, bundle sheath cells contain well developed chlorplasts that are highly active (Calvin Cycle). ●

CAM plants - Crassulacean Acid Metabolism or CAM is a notable variation of C4 metabolism was first witnessed in stonecrop an ornamental succulent in the Crassulaceae family. Thereafter, it was found to be prevalent in a number of xerophytic (desert-dwelling) species, especially succulents and cacti. In these species, stomates are opened at night when temperatures are relatively cool. At night, CO2 is fixed via the Hatch Slack Cycle and stored as 4-carbon compounds in mesophyll cell vacuoles. During the day, in the presence of light, these stored compounds are remobilized and further metabolized to sugar

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via the Calvin Cycle. Since the carbon supplied to the Calvin Cycle was previously fixed, stomates may remain closed during the day, which drastically improves water use efficiency. Metabolic Scheme

Water Use/CO2 Fixed (g/g)

C3

400-500

C4

250-300

CAM

50-100

Information from Raven et al., 1999

CAM metabolism is perhaps more widely spread than C4 metabolism since it is present in 23 families. The pineapple is probably the quintessential example of CAM crop plant; prickly pears (a minor crop grown for fruit or pads "leaves") also exhibit CAM metabolism. CAM metabolism is also active in many ornamental species including wax plant, snake plant (mother-in-law tongues), bromiliads, cacti and euphorbs Flowers The diversity among species with respect to flower structure is as vast as the diversity among leaf types or any other plant organ. As stated in Topic 2, differences in floral structure is one of the primary keys we use to classify plants and to determine phylogenetic (evolutionary) relationships among species. As with other organs, floral structure influences function and as such may influence how a crop is cultured. Last, but not least, floral diversity among species provides us with a stunning array of ever-changing beauty (sorry - had to wax poetic). Flowers are attached to an inflorescences or flower stalk by means of a pedicel, which in turn is attached to the stem. As with leaves, the vascular system of a flower is continuous with that of the stem. Inflorescences can be simple (bearing a single flower) or extremely complex (see Lab 1 for some details). ●

An Apple Flower - An apple flower (Fig. 2-39) is a good "typical" flower as it is simple and complete (contains all possible flower parts). All flowering meristems are the result of transitions in previously vegetative meristems. Thus, in some ways, flowers can be considered as modified leaves and stems. Typically, flower parts are arranged in whorls. The outermost whorl contains the sepals (collectively the calyx). Sepals are usually green in color but may also pigmented in a manner similar to that of the petals. In many species, the sepals surround and protect the other floral parts during flower bud development, but "peel back" or separate as the flower reaches anthesis (e.g., the transition from rose bud to open rose flower). In others, portions of the calyx remain joined even after the flower opens (e.g., petunia, carnation). The next outermost whorl is composed of the flower petals (collectively the corrolla). Flower petal color extremely diverse among and within species and is mediated by at least three different pigment classes (chlorophylls, carotenoids and anthocyanins). In many wind-pollinated grasses, flowers are green in color and not usually conspicuous whereas in crops that require pollination by insects or animals, flowers are often colored and showy (e.g., hummingbirds are attracted to red). In addition to color, flower fragrance resulting from essential oils in the petals also attract certain pollinators; some of

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these fragrances are extremely strong (e.g., lilac, orange, viburnum); some are somewhat ethereal or subtle (e.g., apple). Some fragrances are pleasing to humans whereas others are decidedly not (i.e., some insects are attracted to smells reminiscent to us of rotten meat -- yuk!) Note: nectars from nectaries or nectriferous glands also attract insects, bats and birds, as well as pigments in other flower parts. For instance, the yellow carotenoid pigments in most anthers reflects ultraviolet light which can be seen easily by bees. In most simple flowers the petal number and sepal number are the same, but this is not always the case. The inner most two whorls of the flower contain the sexual organs. The male sexual organ, the is called the stamen (collectively the androecium). Stamens each have two parts, an anther, which is the site of male gametogenesis, and a filament or stalk upon which the anther rests. The innermost whorl of the flower contains the female sex organ, the pistil (collectively the gynoecium). Each pistil is composed of three parts, the stigma, the style and the ovary. The stigma is composed of a relatively shallow tissue group and is the site of pollination and pollen germination (i.e., its where the pollen grain lands and begins to grow). The style is a columnar shape tissue group through which the germinated pollen grows, moving its male gametes toward the female gamete located within an ovule of the ovary. The ovary is the site of female gametogenesis and contains one or more ovules; each ovule contains an embryo sac (see below) containing the female gamete, the egg. In some fruit, ovaries can be subdivided into chambers called carpels, each of which may be serviced by its own stigma and style. In an apple flower, there are typically five stigmas and five styles. The apple ovary is divided into five carpels, each with two ovules that when pollinated, for two seeds. In many fruits (ripened ovaries), the ovary wall develops into the pericarp, which is sometimes edible (e.g., pea pods, outer surfaces of the tomato fruit, the flesh of a peach) and sometimes not (the peel of an orange, the shell of a nut, and the outer pit of a peach) The fleshy portion of the apple which we consume is actually derived from the hypanthium, an accessory structure that surrounds the ovary, whereas the pericarp is located in the portion we commonly call the core. Flower structure often reflects a species' preferred pollination scheme. Flower structures which are open at the time of pollination (chasmogamous; e.g., apple) invite cross pollination. Outcrossing species often bear flowers that are wind pollinated. Cross-pollination can also be promoted if the pollen of an individual flower is shed before the stigmatic surface is receptive (protandry) or if the reverse is true (protogeny). Species that are monoecious, bearing unisexual flowers on the same plant (e.g., corn, pecan) dioecious species that bear male and female flowers on different plants (e.g., hemp, fig, date) are outcrossing species. Species that produce sticky pollen that adheres to the body of insect pollinators are also often cross pollinated. Outcrossing species often develop showy fragrant and nectar-producing flowers in order to attract the appropriate pollinators. In contrast, self pollinating species often produce flowers which are not conspicuous (e.g., wheat). Flowers which are closed (cleistogamous; e.g., pea) when pollen is shed are obligatorily self pollinated. Flowers which are pendulous (hang down) with stigmatic surfaces below the anthers (e.g., tomato, some peppers) are often self pollinated, with gravity being the pollinating force. Self or cross incompatibility are additional mechanisms that promote outcrossing or self-pollination, respectively. Examples of species that employ incompatibility mechanisms can be found in almost every plant family.

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Incompatibility refers to a chemically-based recognition system wherein proteins excreted by the pollen grain interact with specialized receptor proteins in the cell walls of the stigma. Both stigma and pollen proteins are coded for at a single locus - the S locus. The S locus of most species has many potential alleles. That is, most species have the potential of producing a whole series of different S proteins; each stigma (2n) has the potential to produce two protein types and each pollen grain (n) will produce only one type depending upon what alleles are present within each genotype. The case of self incompatibility is illustrated below: Pollen Grains Stigma

S1

S2

S3

S1S2

In this situation, because the genotype of the stigma is S1S2, it will recognize any pollen grains that are either S1 or S2 as being produced by itself. The recognition event will trigger the production of ribonucleases (enzymes) in stigma cell which are released at the S1 or S2 pollen grain, destroying its RNA and effectively neutralizing it. If a pollen grain from a different plant lands on the stigmatic surface, chances are its genotype holds a different allele at the S locus (e.g., S3). If so, the stigmatic recognition system will not detect it and it may germinate and grow unheeded, eventually effecting fertilization. Note: In class, we discussed the topic of self and cross incompatibility under the section on fertilization and embryo growth. I have moved it here, as this is where I had originally intended to present this material ●

Types of flowers - We have actually been discussing types of flowers since the beginning of this section, but there are two additional sets of terms that you may encounter at some point in your career. They are:

Complete flowers vs. incomplete flowers. This pair of terms refers to whether or not all of the whorls of a flower are present. A complete flower contains sepals, petals, an androecium and a gynoecium. An incomplete flower lacks one or more of these whorls. Perfect flowers vs. imperfect flowers. This pair of terms refers to whether or not both sexual whorls of a flower are present. Perfect flowers contain both an androecium and a gynoecium. Imperfect flowers are unisexual; when they contain only an androecium they are called staminate and when they contain only a gynoecium they are called pistillate. ●

Flower bud initiation as controlled by daylength and other factors. Flower bud initiation is the point in time when a vegetative meristem is transformed irreversibly to a flower meristem. For each species, the timing of flower bud initiation is obviously quite important for the successful maturation of the fruit under optimum environmental conditions and for survival of the seed. Flower bud initiation is definitely under genetic control and as all other phenomenon we have studied, the exact timing varies tremendously from species to species.

As well as being genetically controlled, flower bud initiation is often triggered in response to some environmental que. One of the most studied of these ques is that of daylength. Some examples of daylength

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control of flower initiation are listed below. LDP - long day plants, species in which flowering is triggered by long days (e.g. chrysanthemum) SDP - short day plants, species in which flowering is triggered by short days (e.g. hibiscus) IDP - intermediate day plants, species which flower at median daylengths (e.g. coleus) DNP- day neutral plants, species in which flowering is unaffected by daylength.(e.g. cucumber) In daylength sensitive plants, the length of darkness is actually the important factor! The controlling or triggering mechanism is mediated by phytochrome, a ubiquitous plant pigment that controls a number of other functions as well as flower initiation (e.g., the germination of some seeds, tuberization in potatoes, leaf coloration in the fall, the onset of dormancy in temperate perennials just to name a few). A symplistic explanation of how phytochrome controls plant function is illustrated in Figures 29-16 (legend in bottom right corner) and 29-17 in your Topic 3a handout. Phytochrome exists in two forms, one which is sensitive to red light (Pr) at 660 nanometers and one which is sensitive to far-red light (Pfr) at 730 nanometers. Note: a nanometer equals 10-9 meters; a wavelength of 660 nm is 0.000000660 meters long. In darkness, most of pigment will be in the Pr form. When light containing wavelengths of 660 nm strikes Pr, it is almost instantaneously converted to the Pfr form. When light containing wavelengths of 730 nm strikes Pfr it is reconverted back to the Pr form. Note: For those of you who are biochemically inclined the actual chemical change that occurs in the molecule when it is converted involves a shift in the double bond preceeding the 4th (right most) heterocyclic ring in Fig. 29-17 from the trans to the cis isomer. This, of course drastically changes the conformational shape of the pigment and thus its function. For those of you who are not biochemically inclined, just remember that the pigment's shape changes. In sunlight, which contains both red and far-red light, an equilibrium between the forms will be established. In the absence of light (i.e., darkness, night), pigment in the Pfr form will slowly be reconverted to Pr even though no far-red light is present. This slow change is called dark reversion and it is the mechanism by which a plant can measure daylength or nightlength. The longer the night, the greater the extent of dark reversion. For most functions, the Pfr form of phytochrome is the one that elicits a biological response. LDPs require phytochrome to be in the Pfr form for an extended period in order to initiate flowers. However, the converse is true for SDPs, which rely on the absence of Pfr for an extended period before flowers are initiated (i.e., lots of dark reversion during long nights).

Experimental evidence proved that the phytochrome-mediated floral response is dependent upon the dark reversion process. For instance, when SDPs were grown under inductive conditions (i.e., long nights), they http://www.hcs.ohio-state.edu/hcs200/hcs200top3a.htm (10 of 17) [10/08/2001 10:01:32 a.m.]

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flowered as expected. But when the long nights were interrupted by a very brief burst of light (termed a night break), flowering was inhibited. Presumably the night break phenomenon resulted from the instantaneous conversion of Pr to Pfr during the light burst. Flowering in response to daylength is obligatory in some species (i.e., they will not flower unless a critical daylength is supplied) where as in others it is quantitative (i.e, flowering occurs more readily and abundantly when the critical daylength is supplied, but some flowering may occur at other times as well). The phytochrome-mediated response can be highly specific and highly sensitive. For example, rice is a SDP that can be planted at various times throughout the year in the tropics. Before it will flower, two criterion must be met. First, the plant must be physiologically "ripe to flower" which basically means that undergoes a basic vegetative phase before it is ready to receive a floral stimulus. Second, the daylength must be less than some minimum threshold (exact photoperiod is variety-dependent) before flowering will commence. If rice is planted from Aug - Dec, there is sufficient time to meet the requirement for the basic vegetative phase while the photoperiod is inductive (i.e., less than about 11.5 h Sept-April). Therefore, after the requirement for the basic vegetative phase has been met, flower induction will occur. However, if the crop is planted in January, the photoperiod will be too long by the time the basic vegetative phase is completed. Therefore, the plant will remain vegetative (flowering will be inhibited) until the following Sept. when the next inductive photoperiod occurs. Rice varieties can be extremely sensitive to the critical photoperiod. For the cultivar Siam 29 the critical photoperiod is just under 12 h. When this cultivar was planted in Malacca Malaysia in Sept, the crop cycle (planting to harvest) was 161 days; when it was planted in January, the crop cycle was 329 days. Since Malacca is only 2 north of the equator, daylengths on June 21 and Dec 21 (the solstices) differ by only 14 minutes! The expression of photoperiodicity can be highly influenced and in some cases overridden by temperature effects. Most commercial strawberry cultivars are SDP that initiate floral buds in the fall. In temperate regions like Ohio, these initiated buds remain dormant until the following spring, then flower. Flowering is relatively synchronous, and in Ohio that means that only one inflorescence/year (one flowering cycle/year) is produced from each plant. The fruit is ripe by June - hence the name Junebearing strawberries. However, the flowering response to daylength can be overridden in strawberries if temperatures are cool (especially night temps). California production illustrates how daylength and temperature interact to control flowering in strawberries. In California, there are two coastal regions of production, one centered near Ventura just north of Los Angeles, and the other located in Salinas, somewhat south of San Francisco. Production of strawberries in Ventura occurs from Feb - June (i.e., floral induction occurs from Jan - May). During this period, photoperiods are short enough and temperatures are cool enough that multiple cycles of induction occur. That is, the strawberry plant undergoes several flowering cycles per year instead of just one like they do in Ohio. As summer advances, both the LD photoperiod and the higher night temperatures shut down floral induction so production ceases. Production in Salinas occurs from late March - November. Early in the season, both SD photperiod and low temperatures promote floral induction. However, unlike production in Southern California, plantings in Salinas continue to flower throughout the summer when photoperiods are too long to promote flowering. Why does this occur? It occurs because the ocean moderates summer temperatures so that nights stay cool, and it is the

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cool nights which override the the effects of an unfavorable photoperiod. Again several cycles of induction and fruiting occur. The net result of these two interactive factors allows California growers to typically harvest around 30 tons/acre/year of fruit whereas the rest of us do well to harvest around 5 tons/acre/year. As stated above, phytochrome-mediated control of flowering is obviously an adaptive advantage in natural communities which forces synchronous flowering at a time when the probability of fruit set, development and maturation will be maximized. Plants within species display phytochrome-mediated responses in relation to their specific area of adaptation. For example, soybeans (a SDP) also respond to daylength in accordance with their region of development. Some soybean varieties are so sensitive, that they flower at the correct time for maximum yield only when cropped within a N-S band 40 miles N or S (i.e., 80 miles thick) from where they were developed. As with rice, soybeans must undergo an obigatory vegetative phase before they will recognise the photoperiodic flowering stimulus. However, if they have met this requirement, they will be induced to flower at some point after mid-July as daylengths are getting shorter. When `Lincoln' soybeans (adapted to Urbana, IL) were planted in mid-May at various locations from north to south, the following harvest dates were observed. Locations from N-S Harvest date Madison Wisconsin Oct 2 Dwight, Illinois Sept 27 Urbana, Illinois Sept 17 Eldorado, Illinois Sept 8 Sikeston, Missouri Aug 30 Stoneville, Mississippi Aug 12 Obviously, as one goes south, the critical photoperiod is reached at an earlier date, so the crop matures earlier. In northern locations, the obigatory vegetative phase is met long before the inductive photoperiod so that plants waiting to be induced go through an additional vegetative phase. During this extra phase the plants are storing carbohydrates and mineral nutrients which will be used later during fruit (sink) development. That is, this extra vegetative phase maximizes yield. However, northern-adapted soybeans are planted by southern farmers as a double-crop with winter wheat. Although the yields are diminished, these farmers can make money by harvesting two crops off the same field within a year. The nitrogen-fixing capacity of soybeans is also a plus in this cropping system. ● Flower bud development (FBD)

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Flower bud differentiation can be rapid, but it can also be a protracted process requiring several months to complete. In addition, in temperate zone plants that initiate fall flowers, the process can be interrupted by winter and completed in the following spring. In any event, the differentiation pattern is sequential - from outside to inside - with calyx and petal whorl primordia being developed prior to stamens and pistils. Once all structures are finally formed and fully developed, the reproductive cells are formed through the process of meiosis. The entire process of FBD ends at anthesis. The following time line describes this sequence for apple flowers. Flower bud initiation June 15-30 Calyx primordia formed early July Petal primordia formed early to mid July Anther primordia formed mid to late July Pistil primordia apparent mid August Ovarian cavity formed late September Meiosis in megaspore mother cells late September? Rest subject to chilling requirement November - March Meosis in pollen mother cells March Ovule and pollen differentiation April Anthesis May Note that flower bud initiation for the next season is occurring simultaneously with fruit set of this year's crop. Both floral initiation and fruit set depend upon critical levels of available energy (carbohydrates) and hormonal balance. Overall plant vigor is extremely important. If the plant is weak or has set too many fruit, carbohydrates available for floral initiation will be limiting and fewer flower buds will be formed for next year. If the reduction in flower initiation is severe enough, the tree enters an "alternate bearing" cropping cycle in which commercial crops are produced every other year. Alternate bearing is difficult to correct culturally once it is initiated and it has disastrous economic consequences for the orchardist. The length of the rest period is controlled by the plant's chilling requirement. The chilling requirement is defined as "the cumulative number of hours below 7 C (45 F) needed to satisfy the rest requirement and break dormancy in vegetative and floral buds." In some species, the chilling requirement for vegetative buds is less than that for floral buds. In other species such as apple, the converse is true. Note that the temperature range that satisfies chilling requirement is identical to that which satisfies vernalization and stratification requirements. Chilling requirements are a selective advantage and confer adaptation to specific growing regions. Many perennial crops fail in temperate growing regions not because they cannot withstand midwinter cold, but because their low chilling requirement allows them to break dormancy during the first warm spell of spring. Peaches and some other stone fruits are not well adapted to Ohio because they flower too early; their flowers are damaged by late spring frosts. Conversely, oaks and maples never leaf out until May, regardless of warm April temperatures.

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●

Gametogenesis

The formation of the male gametophyte (pollen grain) occurs in the anther. A typical anther consists of four sporangia or pollen sacs. These sacs contain sporogenous cells or microsporocytes which will undergo meiosis to form pollen grains during anther development and nutritive cells, collectively called the tapetum. During the process of meiosis, each microsporocyte produces four microspores, each containing ½ of the number of chromosomes present in the mother plant Note: If you are fuzzy about the process of meiosis, I urge you to review it in any biology text. It is an extremely important concept to understand. Once meiosis is complete, each of the microspores undergoes mitosis to form two cells within each pollen grain: a generative cell and the tube cell. The tube cell nucleus is responsible for controlling cellular activities as the pollen germinates on the stigmatic surface and grows through the style toward the embryo sac. The generative nucleus will mitotically divide a second time to form two sperm nuclei. In some species this is completed prior to pollination whereas in others it occurs after pollen germination on the stigmatic surface. Pollen grains are enclosed within very resistant outer and inner walls. The inner wall (the intine) is composed of pectin and cellulose as are many primary cell walls, whereas the outer wall (the exine) contains a very resilient material comprised of carotenoid polymers called sporopollenin. The outer walls of the pollen grain are "sculpted" differently in each species in such a way that they can serve as a "fingerprint". Not only are these patterns aesthetically pleasing and interesting scientifically, they also serve as a means to archaeologically verify plant use by indigenous people and infer evolutionary relationships among plant species in the fossil record. Pollen grains vary in size from 20 microns to 250 microns. Note: a micron or µ is equal to 10-6 meters. The formation of the female gametophyte occurs within the ovule. Each ovule contains a megasporocyte which undergoes meiosis to form four cells which contain ½ the chromosome number of the mother plant. One of these cells (usually the one distal to the micropyle or ovule pore) survives while the other three disintegrate. The process from megasporocyte to surviving megaspore is termed megasporogenesis. Megagametogenesis begins with the mitotic of the megaspore (three divisions in all) and the formation of eight genetically identical nuclei. These nuclei are specifically arranged within the embryo sac so as to perform specific functions. Membranes form around these nuclei to form 7 cells within the embryo sac. The three cells distal to the micropyle are called the antipodals (function obscure) and the three cells near the micropyle form the egg apparatus consisting of one egg and two synergids. Synergids are important in guiding the sperm nuclei to the embryo sac. The egg, upon fertilization will become the embryo. The remaining two nuclei are positioned near the center of the embryo sac. These nuclei will also be fertilized by one of the sperm nuclei to form the endosperm. The process of megasporogenesis and megagametogenesis shown here is typical but there are many variations of these schemes among plant species.

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Fertilization and Embryo Growth

Pollination is perhaps the first step in the process of fertilization. When an anther and the pollen grains it contains are mature, the anther wall dehisces (ruptures), releasing pollen into the environment. Pollen can be transferred from the surface of a dehisced anther to the stigmatic surface of the same or different flowers by wind, gravity, insects, or a variety of animals (birds, bats, etc.) including humans. The stigmatic surface in many species is "sticky" because it is coated with a sugar-containing solution secreted by glandular cells within the stigma. Climatic factors which either influence the activity of pollinators (e.g., bees don't fly when its cold or rainy) or the status of the stigmatic surface (e.g., extreme wind, rain, heat, etc.) can affect the transfer of pollen and its adherence to the stigma. If the pollen is compatible with the stigma upon which it has landed, it will "germinate". A pollen tube then begins to grow through the stigma and into stylar tissue, a process which is controlled by the tube nucleus. In some species, the pollen tube grows through a channel within the stylar tissue whereas in others it penetrates through the style's intercellular spaces (i.e., cell walls and middle lamella). In the latter case, tube growth is directed to the embryo sac via specialized cells which form tissue transmitting strands. The two sperm nuclei traverse the style through the pollen tube. In some species, the mitotic division of the generative cell forming two identical sperm cells occurs in the style whereas in others, it precedes pollination. As the pollen tube nears the embryo sac, one or both synergids located near the micropyle begin to disintegrate. Disintegration of synergid cellular membranes release Ca+2 into surrounding tissue which acts as an attractant to the growing tip of the pollen tube. As the tube enters the embryo sac through the micropyle, it releases the two sperm nuclei. One of the sperm nuclei fertilizes the egg cell to become the zygote, whereas the other fuses with the two polar to form the endosperm nucleus through a process called double fertilization. Typically, the processes of pollination and double fertilization take about 24-48 hours. Once double fertilization is complete, embryogenesis and seed development commences. In many species, endosperm development precedes embryo development. In the early stages, the endosperms of monocots and dicots develop similarly. First, the endosperm nucleus undergoes an extensive series of mitotic divisions, resulting in a multinucleate "super cell". At this point the endosperm is without internal structure. However, eventually, each nucleus in the super cell is surrounded by a cell membrane and wall and the endosperm starts to develop into a recognizable tissue group. A some point endosperm development patterns in monocots and dicots diverge. In monocots, the endosperm continues to enlarge and in the mature monocot seed, it is the principle storage organ for starch and other potential nutrients that will be needed for seed germination. The cotyledon in monocots aids in regulating seed metabolic processes and acts as a conduit of energy from the endosperm to the developing new plant. On the other hand, in dicot species, the endosperm is utilized during the development of the cotyledons so that in the mature dicot seed, little if any endosperm tissue is left. The zygote undergoes its first mitotic cycle, forming two distinct cells: the basal cell and the terminal cell. The basal cell further divides transversely creating a stalk-like structure called a suspensor. The suspensor suspends and anchors the developing embryonic plant in the ovule and connects it to the ovule integuments (rudimentary wall-like structures) through an attachment of the basal cell. At the same time that the suspensor is forming, the terminal cell undergoes several cycles of cell division in order to form a spherical mass that will

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eventually differentiate into primary meristematic regions or tissues (i.e., protoderm, ground meristem and procambium). Notice that similar tissue groups are also formed from apical meristems of the root and shoot. As the embryo develops root and shoot axes are formed, each with their apical meristems. Cotyledon tissue gains prominence and in the case of dicot seeds, the cotyledons will form the bulk of the seed dry weight. The ovule integuments develop into the seed coat. ●

Fruit set and fruit development

A fruit is a ripened ovary or group of ovaries. The characteristics and morphology of fruits of course varies in accordance with the flower and inflorescence structures which precede them. You will discuss this variation in an upcoming lab, so I won't belabor the point in this lecture. The early life of a fruit (i.e., shortly after ovule fertilization) is somewhat precarious. There are many physical and physiological changes that must take place. If internal or external conditions are not adequate, the newly formed fruit will abscise (drop off). Of course, sacrificing newly formed fruit in order to preserve maternal plant health may be of selective advantage to perennial plants as there will be additional chances to produce offspring in subsequent seasons. However, for annual plants, fruit drop is somewhat of a disaster biologically. Fruit set occurs when this early critical period has passed; fruit which have set enjoy a good chance that they will reach maturity. Several factors affect fruit set including: Successful embryo development - competent embryos which develop normally produce hormonal signals (usually mediated by auxin or gibberellins) to ovary tissue, stimulating it to grow and enlarge. In some crops, horticultural treatments using natural and synthetic growth hormones have been developed to enhance fruit set or to limit fruit set. Fruit set and subsequent development of seedless fruit (e.g., bananas, seedless grapes) results from the action of the same hormones, but, in this case, they (the hormones) are produced in sufficient quantities by fruit tissues themselves. The process of setting fruit without seed development is called parthenocarpy. Carbohydrate reserves - See discussion above about alternate bearing Competition - Many crops will drop fruit if fruit set is extremely high primarily due to competition for nutrients and energy. Other stress factors (e.g., heat, drought, low light intensity, cold weather etc.) can also result in fruit drop. Fruit growth is characterized by abundant gas exchange and rapid and extensive increases in H2O and overall dry weight. It is also controlled by hormonal balances. Early growth of all fruits results from cell division and elongation enhanced by the presence of auxin and giberellins. The relative level of these compounds determine the fruit's ultimate shape. Therefore, horticultural practices, such as treating 'Thompson Seedless' grapes with giberellin to elongate the berries and the rachis (fruit stem), have been developed and routinely practiced.

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Fruits can be classified into two groups, depending primarily on hormonal changes (primarily ethylene, a gasseous hormone) that occur as the fruit ripens. Climacteric fruits exhibit rapid rises in respiration and in ethylene generation which signals the onset of the ripening process (i.e., softening, changes in color, sugar content, etc.), whereas non-climacteric fruits seem to ripen without fluctuations in ethylene evolution. In crops with fleshy fruits, whether or not a fruit is climacteric affects when it is harvested, and how it is stored and how long its shelf life might be. Biotechnologically enhanced tomatoes (a climacteric fruit) have been produced through the incorporation of an Arabidopsis gene coding for defective counterparts to enzymes that responsible for ethylene production. The lack of ethylene production in these recombinants greatly increases the shelf life of this product over that of common fresh market tomatoes. Conversely, fruits that are climacteric can be ripened artificially by treating them with ethylene gas or products that evolve ethylene (e.g., banana, tomato, etc.) Fruits such as apple are stored in chambers designed to limit respiration and ethylene evolution (i.e., in controlled atmospheric storage chambers), which greatly prolongs their storage life. As you might expect, environmental factors can affect fruit growth rate and there is considerable variation in the time necessary for fruits to ripen (i.e., the obligatory time necessary to progress from pollination to fruit maturation (harvest or abscission). However, there are really only two fruit growth patterns: sigmoid growth curves and double sigmoid growth curves (Fig 9-2). In the double sigmoid pattern, fruit growth is retarded for a period during mid-season to allow rapid growth and development of seeds. In fruits that follow a sigmoid pattern (e.g., pecan), seed maturation often occurs in the latter stages of fruit development, or about the time when fruit development slows (see Table 1 and its associated graph).

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Light

Horticulture and Crop Science 200 Winter Quarter 2001 Lecture Topic #4A: Radiant Energy and Its Effect on Crop Growth - Part 1- Light.

References:

Text = Chapters 7 and 8

Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant science, growth, development and utilization of cultivated plants. Prentice Hall, Inc., Englewood Cliffs, NJ. = Chapter 10

Janick, J., R.W. Schery, F.W. Woods and V.W. Ruttan. 1981. Plant science, an introduction to world crops. H.W. Freeman and Co., San Fransico, CA. = Chapters 10 and 11.

Raven, P.H., R.F. Evert and S. E. Eichhorn. 1999. Biology of plants (6th Ed.). W.H. Freeman and Co., New York, NY = Chapter 29.

Quotation:

"... Although a small amount of the energy to power civilization comes from the interior of the earth and more is contributed by atomic fission, our most abundant source of energy is the sun"..... " The total incoming solar energy reaching the outer edge of the earth's atmosphere averages 1.94 cal/cm-2/min-1, a value known as the solar constant. We can put this in perspective by noting that in 1`0 days, the energy arriving at the periphery of the earth's atmosphere is equal to the total known fossil fuel reserves." from Text.

"It has been estimated that about 1.4 x 1014 kg of carbon from carbon dioxide in the air is converted to carbohydrates each year by the green plants that live on the land and in the oceans, seas and lakes. A number of this magnitude is beyond our comprehension. To put it another way, assume that the 1.4 X 1014 kg of carbon is

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Light

converted entirely to an equivalent amount of coal, which would be 1.4 X 1011 MT. Assume further that a standard-size railroad car holds 45.5 MT; then the carbon fixed annually by plants would yield enough coal to fill 97 cars every second of every hour of every day all year long." from Hartmann et al.

Outline:

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What is radiant energy.

Radiant energy - radiant energy is that which is derived from the sun. It has a unique feature in that it behaves as both a particle (photon - a descrete unit of radiation) and a wave. We typically measure the amount of radiation striking or reaching a given area in photons but we measure the strength (energy level) of those photons in terms of wavelengths. Short wavelengths are very powerful while longer wavelengths are less so. In other words 100 photons of radiation at a 800 nm wavelength has only half the energy of 100 photons of radiation at a 400 nm wave length. The entire range of wavelengths reaching the earth's outer atmosphere is called the electromagnetic spectrum (see diagram in handout). Notice that visible light (wavelengths from about 400 - 700 nm) comprises only a small portion of this spectrum. Radiation at the highest energy level exhibits extremely short wavelengths. The highly energetic radiation of X-rays and rays can cause serious damage to biological systems because when they hit organic constituents in cells, "knock" electrons out of their orbits, thus creating ions -- hence their alternate names, cosmic or ionizing radiation. Although less dangerous, ultraviolet light is also somewhat ionizing and is the chief culprit causing sunburn in humans and other animals. Prolonged exposure to high levels of ultraviolet light is also linked to various types of skin cancer. Radiation at wavelengths longer than 700 are more or less undetectable by the human eye, and those that are longer than 760 nm but less than about 10,000 nm are responsible for what we commonly refer to as "heat". Electromagnetic radiation of extremely long wavelengths (>100,000,000 nm) comprise radio waves. Wavelengths between heat waves an radio waves are considered to be microwaves (useful for cooking and communication).

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Some definitions

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•radiation = the movement of energy without physical connection (e.g., light through space)

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•conduction = the movement of energy through one body to another (e.g., heat from electric stove element to kettle bottom, light through a fiber-optic cable)

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•convection = the movement of energy by (air) currents (e.g., heat from gas furnace flame to upstairs bedroom via forced air )

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•insolation = solar radiation striking the earth's surface

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•diffuse radiation = radiation that has been scattered or reflected by clouds or atmospheric particles. The amount of diffuse radiation is dependent on cloudiness, latitude, season, time of day and elevation

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•radiant flux density = number of photons/cm2 surface area

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•foot candle (lumen) = quantity (intensity) of light which falls on a 1 ft2 surface area generated from a candle that is 1 foot away.

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•lux = lumens/m2 1 lumen = 10.76 lux

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•Einstein = energy in one mole of photons.

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•microEinstein = energy in 1 µmole of photons.

At noon on a summer's day, insolation is roughly equal to about 108 K lux, 10,000 ft. candles or 1800 microEinsteins.

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What happens to the radiant energy arriving at the earth?

About 20% of the light arriving at the earth's outer atmosphere penetrates directly to the earth's surface, about 25% of it is scattered in the atmosphere and reaches earth as diffuse radiation, about 20% of it is absorbed by atmospheric particles and about 35% of it is deflected back out into space without ever entering the atmosphere.

Other than the fact that we receive enough radiation to make life as we know it possible, there are are several important consequences to this scheme that bear some discussion

First, light scattering in the atmosphere is a function of particulate matter such as dust, smoke and water droplets. These large particles scatter all visible wavelengths of light in equal proportion so that on a cloudy or hazy day, the sky appears to be white and on a smoggy or dusty day it appears to be brown, the color of the polutants. However, smaller particles such as atmospheric gases scatter shorter visible wavelengths while allowing longer ones to pass through without incident. That's why on a clear and dry day the sky appears to be blue.

Radiant energy that is absorbed by the atmosphere before it reaches earth's surface is comprised mainly of wavelengths that are shorter than those in the visible spectrum. Ozone and oxygen are primarily responsible for absorbing much of the ultraviolet rays which might otherwise have drastic consequences (mutations, cancer, etc.) on terrestrial life forms. The depletion of the ozone layer by chlorofluorocarbons (freon), methyl bromide (a fumigant) and other such compounds became a matter of concern to scientists and then to enviromentalists and now to the public at large. There is still great controversy as to how large of a problem we have created for ourselves and whether or not the steps we have taken to correct it will be effective.

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Of the direct and/or diffuse radiant energy that reaches the earth, about half is in the visible range. This fact has undoubtedly affected the evolution of both plants and animals. Those animals that had "sight" (i.e., keenly sensed radiant enery in the 400-700 nm range), or those plants who were strong photosynthesizers had a selective advantage over those that didn't. The relatively unrestricted penetration of visible light is called the window effect. (Note: glass is impervious to ultraviolet light --- that's why you will never tan while working in a greenhouse.

Once reaching the earth, only about 2-3% of solar radiation is utilized directly by plants in the process of photosynthesis. Much of the light striking the earth's surface is radiated back into the atmosphere as heat (longer infrared wavelengths). This longer wavelength radiation has far less of a chance of passing out of the atmosphere than light has of entering it. Atmopheric gases such as CO2 from combustion of carbon-based fuels such as wood, coal and gasoline impede the escape of heat further. The lack of energy balance (i.e., more light energy enters than heat energy escapes) results in the "greenhouse effect" which is now a common concern among scientists, politicians, enviromentalists and the public at large. The increased retention of heat in the atmosphere due to man's activities within the 20th Century may be radically warming our atmosphere (i.e., global warming), again with some potentially nasty side effects such as the melting of the polar ice caps, massive flooding, increased frequency and intensity of violent storms, catastrophic climatic changes, just to name a few. As with the depletion of the ozone issue, the extent of global warming and its consequences are still a matter of controversy that fosters continued debate worldwide.

Of the 2-3% of radiant energy utilized by plants for the photosynthetic process, much of it absorbed by plankton, algae, etc. in aquatic communities (Table 11-1). Cultivated land accounts for only about 5% of net production and only about 0.4% of world biomass accumulaion yearly.

Some climatic and geographic factors that affect the path of radiant energy in the atmosphere (besides those mentioned above) include lattitude, season, time of day (all which affect the angle of incidence (obliqueness) with respect to the earth's surface and thus, the amount of atmosphere traveled through prior to terrestrial contact. Elevation affects the intensity of sunlight (greater at higher elevations) and the ability to lose heat (also greater at higher elevations). Therefore, although higher elevations receive more of the sun's radiation, they loose heat easily and are often cold.

4. Plant growth and development as affected by light

A. Photosynthesis The primary light harvesting molecules (pigments) of plants are of course, chlorophyll a and chlorophyll b. If you are interested in the exact chemical structure of these molecules, you will easily be able to find them in many of the plant science texts. However, for our discussion, remember that they each are composed of a

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tetrapyrrole or porphyrin ring ( a complex ring structure containing four N atoms exposed to the ring's center. A Mg+2 ion is coordinately held by these four N atoms comprising the "business end" of this pigment. Electrons within the ring can be excited (i.e., bumped to a higher orbit) after intercepting a photon of light. When they return to ground state, three possible events may occur:

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the energy can be converted to a combination of heat and fluorescence (light of longer wavelengths) the energy, but not the excited electrons can be passed directly to another chlorophyll molecule, exciting its electrons, in turn while its own return to ground state. This is called resonance energy transfer. the energy and excited electrons can be passed on to enzymes responsible for ATP and NADH synthesis characteristic of the light reactions of photosynthesis. This leaves an "electron hole" in the chlorophyll molecule that must be filled with the addition of electrons through oxidation of a suitable substrate (see discussion below for clarification).

Note: Various carotenoids serve as additional or "accessory" pigments involved in the light harvesting process. Radiant energy captured by these pigments must be transferred to chlorophyll prior to its use in the photosynthetic process

Chlorophylls absorb light only in two regions of the visible spectrum (Figure 7-8) in the blue-violet range (i.e., 420-460 nm) and in the red range (630-660 nm). THESE WAVELENGTHS COMPRISE THE PHOTOSYNTHETICALLY ACTIVE RADIATION or PAR. Notice that chlorophyll absorbs very little light of wavelengths from 500 to 540 nm (i.e., the green region), but reflect it instead. This is why we "see" plants as being green. It's also interesting to note that carotenoid (accessory) pigments, do absorb some light in the green region. Although light harvesting by carotenoids may offer a selective advantage, the primary function of carotenoids is as antioxidants protecting the chlorophyll molecule from light induced oxidative degradation.

The effect of PAR can be demonstrated by examining the rate of photosynthesis and the rate of growth (height) of plants grown at a series of monochromatic wavelengths (Figs. 7-6 and 7-7). In these examples, bean plants photosynthesized most actively and grew tallest when grown using light of red and blue wavelengths.

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Photosynthesis Basics

The basic reaction of photosynthesis is 6 CO2 + 12 H2O C6H12O6 + 6 H2O + 6O2. Glucose

The carbon in CO2 is "fixed" within the glucose molecule via a series of enzymatic reactions within the chloroplast known as the Calvin cycle. As we studied earlier, CO2 is first combined with a C5 compound called http://www.hcs.ohio-state.edu/hcs200/light.htm (5 of 14) [10/08/2001 10:01:43 a.m.]

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ribulose bis phosphate to form an unstable C6 intermediate (catalyzed by the enzyme rubisco). The C6 intermediate is almost immediately cleaved to for two C3 compounds. Several reactions later, one carbon atom is used in the formation of glucose while the other five are rearranged to reform ribulose bis phosphate, completing the cycle. Therefore it takes six turns of the cycle and six CO2 molecules to form one molecule of glucose.

In order for the Calvin Cycle to work, the carbon atoms of CO2 (oxidation state +4) must be reduced (have electrons added to them) in order to be transformed into the carbon atoms of glucose (oxidation state average of 0). To reduce molecules in a biological system almost always requires two things --- Energy in the form of ATP and a source of electrons carried by NADPH. To build a glucose molecule via the Calvin Cycle, it requires the energy stored in 18 ATP molecules and 24 electrons delivered by 12 NADPH molecules. Ultimately light energy (24 photons) will be used to garner both of these required "building" materials via the energy transduction or light reactions of photosynthesis catalyzed by membrane bound enzymes within the chloroplast. The source of the needed electrons is water. In the light reactions, 12 H2O molecules are broken down to their constituents 6O2 and 24H+. Notice in this reaction that each oxygen atom went from an oxidation state of -2 in water to an oxidation state of 0 in O2. Hence the oxygen of water was oxidized (electrons were taken away).

Diagrams 7-13 and 7-14 illustrate how all of this works. The process starts with the harvesting of light energy by Photosystem II. Photon energy may be captured by any chlorophyll molecule. Electrons within the porphyrin ring are first excited and then return to their ground state passing the captured energy to another chlorophyll molecule in the process (see above). Eventually, the energy is transferred to a chlorophyll a molecule in a specialized reaction center. This also results in the excitation of the electrons in the chlorphyll molecule of the reaction center. However instead of returning to ground state. The energy along with the excited electrons are passed to an electron acceptor which is part of an electron transport chain of pigment molecules. The excited electrons with the energy they hold are passed down this chain from pigment to pigment in a series of energy favorable reactions forming an ATP molecule in the process. Finally the electrons and the residual energy they hold are passed to a chlorophyll a molecule at a reaction center of Photosystem I. Again an excitation event occurs and the excited electrons are passed along to another electron acceptor in yet another membrane bound electron transport chain. The net product of energy and electron movement down this chain is the formation of an NADPH molecule.

This process leaves the entire system two electrons short (i.e., the reaction center chlorphyll a molecule in Photosystem II is missing two of its electrons. They are replaced by the cleavage of water and the oxidation of the oxygen molecules within as described above.

One additional option worth mentioning here is that ATP may also be formed in an alternate Photosystem I scheme by a process called photophosphorylation.

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The Effect of Light Intensity on Photosynthetic Rate

The effect of light intensity on net photosynthesis is depicted in Figure 7-8. The light compensation point is the amount of light necessary to stimulate a level of photosynthesis in plants that is equal to their level of respiration. A typical light compensation point might be reached at about 2% full sunlight or about 40 microEinsteins. Notice that net photosynthesis is zero at that point. The Light saturation point occurs at the light intensity level which saturates the photosynthetic mechanisms. I.e., for a given set of conditions (CO2, temperature, water availability etc.), the photosynthetic process is operating at a maximum rate - light intensity is no longer the limiting factor

Values for light compensation and light saturation points vary tremendously among plant species, but is mainly dependent on dark reaction mechanisms (i.e., C3 , C4 , and CAM metabolism). A typical C3 plant will reach its light saturation point at around 800 microEinsteins (less than ½ of full sunlight on a cloudless day). A typical C4 plant exhibits a much higher light saturation point than the typical C3 plant -- as much as 2X higher. Thus, C4 plants have a definite advantage in environments that are usually cloudless because they can more efficiently use the solar radiation provided to them.

Factors which affect light intensity (the number of photons) reaching leaf surfaces, affect photosynthetic rates including: ● ● ● ● ● ● ●

time of day season of the year lattitude elevation the level of atmospheric pollution cloud cover atmospheric moisture

Additional factors which may affect photosynthetic rates include

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temperature nutritional status water status genetics (species and cultivar differences) leaf age Atmospheric CO2 concentration

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Light saturation points also vary among shade tolerant (100 microEinsteins) and shade intolerant species (500-800 microEinsteins) (Figure 12-4). Berry and his coworkers conducted an interesting experiment wherein they collected three plants from their native habitat: Tiderstromia oblongata, a C4 plant from Death Valley, Atriplex hastata, a C3 plant native to the Pacific Coast, and Alocasia macrorrhiza, a rainforest floor species native to Queensland. (Note: The arrows on each data line indicate the typical light levels of the species' native habitat). They then subjected these plants to various levels of light intensity and measured photosynthetic output.

Alocassia behaved like a typical shade tolerant plant because:

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It outperformed all others at very low light intensities, It exhibited a very low light compensation point, and It became saturated at very low light intensities so that increased PAR had no effect on photosynthetic rate.

The morphological and physiological adaptations shade tolerant plants have undergone to survive on the forest floor typically render these plants in capable of taking advantage of full sunlight. They survive, but grow slowly.

Tidestromia behaved like a typical C4 plant because:

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It outperformed all others at very high light intensities It exhibited a light compensation point similar to sun tolerant C3 and C4 plants, and

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It did not reach a light saturation point at full sunlight or beyond

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These species are best capable of taking advantage of their typically sunny environments. Growth rates are usually very rapid.

Atriplex behaved like a typical C3 plant because:

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It's performance at very high and very low light intensities was intermediate between sun-loving C4 and shade tolerant plants It exhibited a light compensation point similar to sun tolerant C3 and C4 plants, and

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It reached it's light saturation point at light intensities much less than full sunlight (typically one-fourth to one-half full sunlight).

These plants typically do not capitalize on all of the available sun light they receive. Their typical growth rates are much faster than shade-tolerant species, but not nearly so rapid as C4 plants. Remember, however, there is great diversity among C3 plants with respect to light saturation. Peanut and sunflower are examples of C3 plants whose light saturation points are near full sunlight.

Can sun-loving and shade-loving plants be "re-conditioned" to survive in the alternate environment?

Those of you who will go on to take H&CS 310 will likely have a whole section on acclimatization of indoor foliage plants to low levels of light. Sun-grown plants vary tremendously with respect to their tolerance of being placed in the shade (genetic limits) and of course, leaf morphology and physiology at maturation is influenced by the light levels present during leaf development (see below). However, some degree of acclimatization is possible.

Representative plants of two clones of Solidago virgaurea were collected, one from a sunny location and the other from a shaded area of the forest floor. Representatives from the sunny location and representatives from the shady location were cultured under both high and low light intensities and later measured for their response to various irradiance levels (Figure 12-6 a,b).

Representatives from the sun clone exhibited the typical C3 pattern when grown at high light intensities (their natural condition). When grown at low light intensities the representatives of the sun-adapted clone tended to behave somewhat as a shade tolerant species in that both their light saturation and their light compensation points were reduced by exposure to low light culture. Thus, they had become somewhat adapted to the low light environment. However, light saturation points and photosynthetic maximums of the sun-adapted clone growing in the shade (Fig. 12-6 a) were lower than for shade-adapted clone growing in the shade (Fig. 12-6 b). In other words, although some acclimatization had taken place in the sun-clone during its growth at low light, changes in its physiological status did not render it as efficient at low light intensities as was its shade-adapted counterpart which was both physiologically and genetically suited to perform well in this environment.

Representatives from the shade clone exhibited a typical pattern for shade tolerant species when grown at low light intensities. However, unlike their sun-clone counterparts, they were entirely unable to capitalize on the additional radiant energy when cultured at high light intensities. Successful acclimatization of a shade plant to full sun is much less common than the reverse. B. Photoperiodism

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Photoperiodism, or crop development as a function of daylength (night length) is mediated by the pigment phytochrome (see previous lectures for details). Processes we have studied (or will study) which are photoperiodic include floral initiation, dormancy, cold hardiness, potato tuberization and membrane permeability.

C. Phototropism

Phototropism, or the orientation of plants toward light, can be transient or permanent.

Examples of transient orientation (alternate names: solar tracking, heliotropism) include: sunflower heads that change orientation throughout the day to follow the sun; leaves that change orientation throughout the day so that their upper surface is always perpendicular to the sun angle; and leaves that orient themselves to avoid direct sunlight during periods of drought.

Transient orientation results from osmotic changes in specialized cells near the base of the moving leaf or flower called pulvini. Because cell osmotic potentials (i.e., resulting from the relative concentration of solutes in and outside the cell) can be regulated by hormones and other membrane or cellular components (enzymes, etc.), changes in cell turgor and thus changes in orientation of the structure in question can be relatively rapid.

The permanent orientation of plants to light (e.g., shaded plants that "reach" for sunlight) occurs via a different mechanism. Well over 100 years ago, Darwin noticed that if oat seedlings were grown with a light source at one side rather than overhead, the coleoptile of the seedling would bend in the direction of the light (Figure 35-2). He also discovered that this would not happen if the seedlings apical meristem was damaged or removed. He and his son conducted a series of experiments to demonstrate the necessity of an operating meristem for phototropic response using decapitation and various types of transparent and opaque caps. They concluded that the meristem controlled the process, but the actual bending occurred somewhere below the meristem. They also concluded that the meristem must be sending some sort of signal to the cells below directing them to grow at a differential rate in order to bend the coleoptile. A little later, Boysen-Jensen confirmed that a signal was indeed being translocated from the meristem to the rest of the coleoptile using permeable and non-permeable blocks. Later F.W. Went experimented with this phenomenon further and in the process discovered the plant hormone, auxin (indoleaceticacid) (Figure 35-3).

Auxin is a growth promoting substance (usually) which is integral to cell elongation. It is produced in meristems, such as the apical meristem of an oat seedling. Auxin normally is translocated downward evenly throughout the coleoptile cylinder so that expanding cells are exposed to similar levels of this promoting substance. However, auxin is easily degraded by light. If one side of the cylinder is illuminated and the other shaded, auxin levels will be greater on the shaded side and thus cell elongation will be greater. THIS is the basis

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for permanent phototropism.

D. Photomorphogenesis

Hypocotyl elongation

Hypocotyl elongation in several species is controlled by phytochrome in the Pr form. Therefore, longer nights, or treatment with far-red light simulates their growth whereas long days and night breaks would inhibit it.

Seed germination

Seed germination of some species (e.g., lettuce) is controlled by phytochrome in the Pfr form. Therefore, continuous light or treatment with red light simulates germination.

Leaf thickness

Relative to their position in the canopy, leaves on a given plant may either develop in full sunlight or in various levels of shade. The light intensity available to a leaf as it develops often affects its morphology and its function when fully developed.

Shade leaves are usually larger than, but thinner than sun leaves. Shade leaves typically exhibit: ● a poorly developed palisade layer, ● large intercellular spaces and loose organization of the spongy mesophyll ● very thin (if any) cuticle layers Shade leaves often have higher chlorophyll contents (by weight) than sun leaves but less rubisco and other photosynthetic enzymes (both light and dark reaction enzymes). In other words, these leaves have invested more effort in producing pigments for harvesting light than for fixing carbon. This makes some intuitive sense in that the limiting factor for photosynthesis in these leaves will be light availability. These leaves are set up to be able to fix some carbon under low light intensities with minimum expenditures of energy to maintain the

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Calvin cycle and electron transport systems at levels appropriate for the amount of sunlight likely to be received. In other words, why develop a massive CO2 fixing capability if it is unlikely ever to operate at full capacity due to limited light.

Sun leaves typically exhibit:

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a well developed palisade layer which may be more than one cell thick, tight organization among cells of the palisade and/or spongy mesophyll relatively small intercellular spaces within the spongy mesophyll very thick cuticle layers

Since sunlight is not a limiting factor in their development, these leaves are seemingly set up to maximize carbon fixation rates.

Leaves developed in partial shade have characteristics between these two extremes

All of this notwithstanding, shade and sun leaves on a given plant may show a five fold difference in photosynthetic capacity.

5. Methods to control light

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Field orientation

Plant row east-west to minimize shading within the row.

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Plant spacing

In field, landscape and greenhouse situations, the amount of carbon fixed per unit land area will be proportional to the amount of the land area covered by leaves. For this reason greenhouse and container-grown materials are densely planted as seedlings and then repotted several times as their size increases during their production. This practice not only maximizes photosynthetic capacity/unit area, but also minimizes costs and maximizes profit.

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literature is replete with studies concerning the effects of plant spacing on yield and or product quality, so no example will be given here. If you want specific information about a species, it is probably available through many sources. For each species and in some cases cultivars, there is an optimum spacing.

The optimum spacing for a variety does not necessarily optimize the photosynthetic capacity of individual plants. Rather, it is the spacing at which the photosynthetic capacity of individuals is balanced against other limiting factors and production is maximized over the entire area.

If plants are grown at closer than optimum spacings, interplant competition for water, nutrients and sunlight will have a deterimental effect. Often this is a factor of within row spacing. In apples, a 2m X 10 m spacing will have a greater detrimental effect than a 4m X 5m spacing, even though these schemes both result in a plant density of 500 trees/HA. If plants are grown at wider than optimum spacings, individual photosynthetic rates may increase, but at the expense of overall production. In general, it is the balance of limiting effects that is of importance.

In general, plant spacing in field and landscape production is fixed at the time of planting. Therefore, until maximum canopy area is achieved, sunlight energy is being wasted. However, under certain conditions, (eg. high value crops) it may be advantageous to overplant the area originally, with the intent of removing "temporary plants" as permanent plants become mature.

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Leaf area index and leaf orientation

Leaf surface area is both a vertical and horizontal phenomenon. Leaf area index (leaf surface area (one side)/unit land area is affected by both. The vertical aspects of LAI affect the photosynthetic capacity through the effects of shading.

In general, about 70 percent of the light which strikes the leaf surface is absorbed. Therefore PAR rapidly decreases as light penetrates the leaf canopy. Shading can have a dramatic effect on ps rates of lower leaves. In general LAIs between 4-8 are optimal for most crop species. If the canopy is too dense (i.e., the LAI is too high) there will be many leaves which do not photosynthesize enough to counteract their respiratory activities. Under these cases overall yield will be reduced. Notice also that the optimum LAI is somewhat dependent on the average light intensity (see above right). For a given species, the optimum LAI will be less under environmental conditions where cloudy weather is the rule.

Leaf orientation also effects the optimum LAI. The shading effects of upper leaves is far greater in crops with planophile leaves than in those with erectophile leaves. This phenomenon is most evident in C4 plants because their light saturation point is high.

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Supplemental lighting - see additional handout distributed in class.

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Horticulture and Crop Science 200 Winter Quarter 2001 Lecture Topic #4A: Radiant Energy and Its Effect on Crop Growth - Part 2- Heat.

References:

Text = Chapters 7 and 8

Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant science, growth, development and utilization of cultivated plants. Prentice Hall, Inc., Englewood Cliffs, NJ. = Chapter 10

Janick, J., R.W. Schery, F.W. Woods and V.W. Ruttan. 1981. Plant science, an introduction to world crops. H.W. Freeman and Co., San Fransico, CA. = Chapters 10 and 11.

Raven, P.H., R.F. Evert and S. E. Eichhorn. 1999. Biology of plants (6th Ed.). W.H. Freeman and Co., New York, NY = Chapter 29

Quotations:

"All matter is composed of atoms that are in a state of vibration that depends on their relative heat. The temperature of a substance is a measure of the relative speed with which its atoms are vibrating. If they are vibrating fast, the temperature is high. Theoretically, at absolute zero (0°K, -273°C), all vibration ceases and atoms at that temperature are absolutely still" Janick et al., 1981.

"The ability of plant life to adapt to changing temperatures within the life range ...... is remarkable. The critical range varies widely from species to species. Banana, sweet potato, cucurbits and many tropical plants may be seriously injured by exposure, however brief, to temperatures below 4°C. A properly acclimated apple tree on the other hand, seldom suffers injury at -35°C" - Text

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Outline:

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Heat vs. temperature; temperature measurement

heat is a radiant energy form. It will move by conduction or convection from a warm body to a cold body

temperature is a qualitative measure of heat intensity but does not measure energy quantity directly (Note: see heat of fusion or heat of vaporization below, where energy is added or given off during a phase change, but temperature stays the same.)

Temperature can be measured using various instruments. Some of the common instruments include:

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•thermometers - thermometers are based on the fact that materials (most notably liquids and gases) expand when they are heated and contract when they are cooled. Common thermometers are constructed with a reservoir filled with either mercury or alcohol which is attached to a calibrated capillary column. As the temperature increases, the liquid in the reservoir expands and fills the capillary proportionally.

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•thermocouples - thermocouples are based on the fact that the electrical conductivity of metals is influenced by temperature. They are composed of two wires of different metals (usually iron and constantan) that are fused (arc welded) at their tip. As the temperature changes, the difference in relative conductivity of the two metals change. Conductivity differences are then measured electronically.

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•thermisters - thermisters are also based on the fact that the electrical conductivity of a metal is influenced by temperature. However, most thermisters are constructed of a single alloy which is extremely sensitive to changes in temperature. Changes in the electrical conductivity in proportion to temperature fluctuation are measured electronically. The advantage of thermisters is that they can be constructed to be very small, so they are great for measuring temperatures of very small or delicate items (e.g., the temperature of a bee, or the temperature of a seedling root).

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•infrared radiometers - infrared radiometers measure directly, the amount of infrared radiation being given off by a body (i.e., the heat escaping from the body). They are very useful for estimating the temperatures of large bodies (e.g., the temperature of a corn field).

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Some definitions

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•specific heat - the amount of energy required to change 1 g of a given substance by 1°C.

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See specific heats of various substances in Table 8-1. Notice that the specific heat of water is 1.00 and that it is relatively high in comparison to other materials. Another way of putting this is that water is slow to heat up and slow to cool down.

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•heat of fusion - the amount of energy required to change 1 g of solid to 1 g of liquid at the melting point

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•heat of vaporization - the amount of energy required to change 1 g of a liquid to 1 g of vapor at the boiling point

See heats of fusion and vaporization of various substances in Table 8-2. Notice again that the heat of fusion and the heat of vaporization of water are relatively high.

Figure 8-1 illustrates nicely the concepts of specific heat, heat of fusion and heat of vaporization. Starting at a temperature of -100°C, energy is applied to a 1 kg block of ice over time at a constant rate (i.e., 100 Kcals/min). As the specific heat of ice is 0.50 cal./g/°C (equivalent to Kcal./Kg/°C), it takes just ½ minute to raise the temperature of the block of ice from -100°C to 0°C. As additional energy is applied, the block of ice begins to melt. Since the heat of fusion of water is 80 cal/g (equivalent to 80 Kcals/Kg) it takes 0.8 minutes for the melting process to be completed. Since the energy being added during this time went into the melting process, temperature didn't change!!! Once the melting process was complete, the liquid water began to increase in temperature in response to the added energy in proportion to the specific heat of water, 1 cal./g/°C (equivalent to 1 Kcal/Kg/°C.) Therefore, in one minute, the temperature of the water went from 0°C to 100°C). Then it was time for another phase change. The transition from liquid to steam took 5.4 minutes to complete as the heat of vaporization of water is 540 cal/g (equivalent to 540 Kcal/Kg). Thereafter the temperature of the steam rose in proportion to the energy supplied and its specific heat.

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•calorie - a calorie is the amount of energy needed to raise the temperature of 1 g of water by 1° C.

Note: dietary calories (those we count as we eat a hot fudge brownie with ice cream, whipped cream and chopped nuts on top) are actually kilocalories (Kcals) = 1000 calories.

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•BTU - British Thermal Units (residential and commercial building industry measures heat using these units -- the output of your furnace will be expressed in BTUs). One BTU is the amount of energy needed to raise 1 lb. of water by 1°F. 1 BTU = 253 cals.

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Factors influencing temperature •Latitude and season

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Table 8-3 summarized latitude's effect on temperature for the Northern Hemisphere. No surprises here -however, please note that the temperature difference at the two solstices is almost nothing at the equator, but http://www.hcs.ohio-state.edu/hcs200/heat.htm (3 of 8) [10/08/2001 10:01:49 a.m.]

gets larger as one moves toward the north pole. For those who don't believe this, I suggest moving from Central Ohio to Central Michigan --- not a great distance north but the winters are much more brutal.

Differences in temperature with respect to latitude actually result from latitude's effect on sun angle and day length. Sun angle affects the relative intensity of radiation reaching the surface and it is 5.8 X greater at the equator than at the north pole. Likewise, day length flucutations are extreme at the poles and almost non-existent at the equator.

The effect of latitude on biological communities is illustrated in the diagram to the right.

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•Elevation

A general rule of thumb is that for every 100 m rise in elevation temperature decreases 0.6° C. Consider two cities that more or less are at the same latitude. Belan Brazil (19 m in elevation) has a mean temperature of 28°C whereas Quito Ecuador (3000 m in elevation) has a mean temperature of 13°C. The effects of elevation and latitude mimic each other (Figure10-2). Latitude and elevation may act in concert. A typical snow line in tropical regions is 4500 m where as in temperate regions they are only 3000 m.

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•Aspect or slope exposure

If you ever take a trip through mountains the effect of exposure (whether or not the slope faces N, E, S or W) on temperature will be made obvious by the differences in vegetation. In the west, it is not uncommon at all to see desert scrub on the south-facing slope while the adjacent north-facing slope supports juniper or pine. Crops also are affected by slope exposure. In general southern or western-exposed sites are warmer than eastern or northern-exposed sites.

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•Time of day

A substantial portion of the radiant energy that reaches earth's surface is converted to heat. Diurnal fluctuation in temperature is obviously a function of the varying amounts of incoming insolation at different times of the day, including the night when insolation is absent (See Figure 8-6). However, diurnal fluctuations in temperature typically lag behind the curve of radiant energy gain and loss throughout the day. Just after sunrise, the ambient temperature and the relative energy (light and heat) gained from the sun are at a minimum. As the angle of the sun becomes more direct as the day advances to noon, incoming energy increases. Surfaces (such as leaves) exposed to sunlight absorb heat and become hotter than the surrounding air. Eventually they begin to radiate that heat into the surrounding air. However, as it takes some time for this to occur so that the maximum temperature occurs in mid afternoon, several hours after the insolation peak at noon. After that point, the surrounding air also begins to cool, but is far more buffered than surfaces. After dark, surfaces are actually cooler that ambient air temperature. The same sort of phenomenon controls the relationship between daylength

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and seasonal temperatures (i.e., summer and winter start on their respective solstices because the earth temperature fluctuation lags behind changes in the duration or intensity of insolation.

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•Temperature inversions

Normally, the atmosphere on a cool night is layered such that the warmest air is nearest the earth's suface (Figure 11-13 A). However, if the nights are long, skies are clear, the air is dry and there is no wind, cold air can "drain" down-slope, setting up an inversion layer where the temperature gradient is reversed from normal. This phenomenon is extremely important to understand for both frost avoidance (i.e., plant orchards on the sides of hills) and frost control (i.e., using the inversion layer air to alleviate freezing conditions via wind machines).

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•Large bodies of water

Large bodies of water have a moderating effect on temperature and adjacent land masses often enjoy a milder climate than they otherwise might have. Figure 8-8 compares the seasonal fluctuation of monthly means in two cities - St. Louis and San Francisco. Both cities are approximately situated at the same latitude and both have a yearly mean temperature of 13°C. However, as San Francisco is a coastal city, their winters are warmer and their summers are cooler than those of St. Louis. St. Louis temps range from -1°C to 26°C whereas San Francisco's only ranged from 8°C to18 °C.

This phenomenon results from the fact that water heats up and cools down much slower than does air. The same situation is responsible for "lake effect" snow as cold air crosses a "still warm" Lake Erie, picking up moisture as it goes and then dropping it as it crosses land. The lake effect is also why it is possible to grow European wine grapes all around Lake Erie and why there is an extensive fruit growing region in Michigan near the eastern shore of Lake Michigan.

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Plant growth and development as affected by temperature

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•Cardinal temperatures -

One system of modeling crop growth involves the determination of cardinal temperatures. If one measures growth rate as a function of increasing heat, the first cardinal temperature one would reach is that of the cardinal minimum, or the lowest temperature at which growth will occur. Presumably increasing heat would accelerate growth in some sort of predictable way. Growth is accelerated primarily because the added heat increases enzymatic activity. The Q10 is a relative measure of enzymatic activity.

Q10 = the increase or decrease in the rate of enzymatic activity in response to raising the temperature 10 °C.

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When temperatures are moderate Q10s are typically about 2 but as temperatures reach extremes these values are much less. Presumably one could increase temperature and experience increased growth rate up to the point when any additional increases in temperature would result in decreases in both Q10s and growth rate. This temperature would constitute the cardinal optimum. Finally, if one continued to increase heat past the cardinal optimum, Q10s and growth rates would continue to drop until the plant ceased to grow thus reaching its cardinal maximum temperature.

Cardinal temperatures will be specific to cultivar, to stage of development being monitored , to plant organ of interest, and growing systems or conditions.

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•Degree days (growing degree days, heat units)

The calculation of degree days is yet another way to model crop growth and to predict maturity dates

In simple terms, a degree day is calculated as follows:

GDD = mean daily temperature - a crop-specific constant

The crop-specific constant is a base temperature for each crop which is experimentally determined.

Degree days are monitored daily and accumulated over time, presumably giving an estimate of how many additional degree days will be needed to reach maturity. If the mean daily temperature is below the crop specific constant, the GDD count for that day is defined as "0". In this modeling process, it is presumed that the relationship between growth and heat is linear, even though that probably is not true.

Corn has a crop-specific constant of 50°F. If the mean daily temperature on a given day was 80°F then the corn crop would have received 30 degree days for that day. If the crop needed 2400 degree days to maturity, then one would need 80 days worth of 30 degree days in order to harvest.

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•Onset of dormancy

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Temperate woody perennials often require a brief period(s) of cold weather in conjuction with receiving critical daylengths in order to "harden off" or to prepare for dormancy. Several light freezes prior to entering dormancy actually increases winter hardiness.

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•Cold requirements (i.e., vernalization, stratification, chilling requirement - see previous notes and handouts)

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•Heat stress

In latitudes from 20° to 40° N, midseason radiation = 400-500 cal/cm2

Since less than 5% of that insolation is used for photosynthesis, the rest is essentially converted to heat.

Remember that only 1 cal of heat is necessary to raise 1 g of water by 1°C. Since a 1 cm3 leaf volume contains less than 1 g of water, heat build up is possible. In mild cases, heat stress can cause midday wilt. It can also cause dehydration, denaturation of enzymes and metabolic imbalances in photosynthesis, respiration and photorespiration.

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•Cold stress

Chilling injury - read second quotation on front page

Freezing injury - results from the formation of ice crystals (water expands when it freezes).

Intracellular events cause cell rupture and death; intercellular ice crystals cause tissue damage (tearing etc.) which may disrupt the vascular system of flowers or new leaves during spring frosts.

No time to discuss it, but read about ice nucleation sometime - its kind of a neat phenomenon.

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•Frost tolerance

There are two types of frost tolerance to consider - tolerance to severe midwinter cold and tolerance or avoidance to spring frosts. Species and cultivars differ with respect to both types of tolerance. Of the two, http://www.hcs.ohio-state.edu/hcs200/heat.htm (7 of 8) [10/08/2001 10:01:49 a.m.]

spring frosts have probably caused more economic losses over time than winter kills have (my opinion).

Read more if you have time.

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Horticulture and Crop Science 200 Winter Quarter 2001 Lecture Topic 4B: Soil and Water and Their Effect on Crop Growth

References:

Text = Chapters 7 and 8

Hartmann, H.T., A.M. Kofranek, V.E. Rubatzky and W.J. Flocker. 1988. Plant science - growth, development and utilization of cultivated plants. Prentice Hall, Inc., Englewood Cliffs, NJ. = Chapter 10.

Janick, J., R.W. Schery, F.W. Woods and V.W. Ruttan. 1981. Plant science, an introduction to world crops. H.W. Freeman Col., San Francisco. = Chapters 10 and 11.

Raven, P.H., R.F. Evert, and S. E. Eichhorn. 1999. Biology of plants (6th Ed.). W.H. Freeman and Co., New York = Chapter 29.

Quotations:

"To many people, soil is merely dirt. From a plant's perspective, howver, soil is crucial for survival because it provides support, water and a variety of elements essential for growth". (Raven et al., 1999)

"The importance of water for crop production cannot be overemphasized. Within a given temperature zone, the availability of water is the most important factor in determining which plants can grow and what their level of productivity will be". Text.

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1. What is soil and how is it formed?

"Soil is the unconsolidated, weathered, biochemically-modified portion of the earth's surface which is composed of organic matter, minerals, air, water and organisms".

"Soil is the portion of the earth's crust that has formed through physical, chemical and biotic forces, in which the roots of plants grow".

Parent rocks (igneous, sedimentary or metamorphic) are weathered to form soil parent material which is then further decomposed until it differentiates into distinct layers or horizons - see below.

The factors involved in soil genesis include climatic weathering agents (i.e., temperature extremes, water movement, ice, wind, and other physical forces), chemical weathering processes (i.e., hydrolysis, hydration, carbonation, oxidation etc. - see lecture handout for details), and biologic factors (plants, insects, worms, bacteria)

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Soil profiles

Soil profiles are composed of horizons

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•The O horizon, the top most layer is typically less than 1" thick. It is composed primarily of organic matter that is just beginning to decompose. - a litter layer or peat layer.

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•The A horizon is top soil (0-25" in depth) containing highly decomposed organic matter and highly weathered mineral elements. Top soil in Ohio typically contains 2-5% organic matter most of which is humus. Humus is highly decayed, colloidal organic matter that is chemically stable. Humus improves soil structure.

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•The B horizon is subsoil (25-36" in depth) containing less organic matter, but still showing significant weathering of mineral elements.

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•The C horizon is substratum (greater than 36" in depth) which may or may not include some parent material (rocks). The C horizon has no clay or organic material.

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•Parent Rock lies below the substratum.

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Soil texture

Soil texture refers to the size of mineral particles in the soil.

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•Gravel is > 2.0 mm = particles are visible to the eye •Sand is 0.05 to 2.0 mm = particles are visible to the eye •Silt is 0.002 to 0.05 = particles are visible with light microscopes •Clay is