Visible Light within the EM spectrum of the sun The visible spectrum is the EM radiation that can be detected by the human eye. A typical human eye has its maximum sensitivity at around 555 nm (540 THz), in the green region of the spectrum
Direct emission & indirect reflectance of light
Why do we have receptors that do not see active radiation from living beings (IR) but are honed to things hotter than coals (visible light emission) ? Creation 101
Our IR Vision We have no natural IR sensors that reach further than a few cm!
Visibility ≠ objectivity depends on the sensors (in animals these are all mutated forms of rhodopsin
What does the snake really perceive? The mouse better knew and so should you! You have to be warm-blooded animal to be detected. A coldblooded frog with wet skin is safe at night & daytime as long as it does not move. However, snakes can also see plants very well at night! What use is that? …. Choose your background well or be detected! Avoid moving in front of rocks, lakes, w. falls, glass facades, wet yourself or wear heavy insulation, blind the observer with flashlight or a hot foreign body.
Secrets of IR Vision What is clear in the visible spectrum is not clear in IR What does a snake see? also gun sights have IR sensibility there is no chance to approach at night or is there? (survival 101) You can bring a glass suit!
Jack R. White: The invisible world of the Infrared. Dodd, Mead & comp. NY 1984 (written for children)
Light absorption by Plants The absorption of light by leaves is mostly due to its pigments
Plants absorb Infra Red Leaves absorb & reflect light deep into the IR spectrum. They especially absorb low-energy IR except for 0.8 to 1.3 micrometer Whether this has a purpose we do not know.
There are plants that are adapted to bright light and there are shade plants
Shade plants reach optimal photosynthesis at low light levels, grow slower and are content with low light conditions. Sun plants can reach high photosynthetic effectiveness grow fast.
There are plants adapted to bright light & there are shade plants Sun leaves of oak are thicker, hairier and more deeply lobed than shaded leaves. Under equal illumination the temperature is 20 % lower.
Beach leaves
Oak leaves
Plant and light interaction
Morphogenetic = non-photosynthetic effects of light
Growing-up in the dark is a normal part of the upbringing of plants
Mustard & bean plants
Light and Plants - Phytochrome Phytochrome is a a pigment plants use to detect light in the red and far-red region of the visible spectrum. They use it to regulate (1) the time of flowering based on the length of day (photoperiodism) (2) to set their circadian rhythms (3) the germination of seeds, (4) elongation of seedlings, (5) the size, shape of leaves, (6) the synthesis of chlorophyll (7) the straightening of the epicotyl or hypocotyl hook of dicot seedlings phytochrome is a protein with a bilin chromophore.
Greenish
Blue
Light and Plants – Phytochrome for red light effects Phytochrome converts form Pr under red light to Pfr
Red –light effects are mediated by Phytochrome system •Phytochrome is a pigment sensitive to light in red and far-red region of the visible spectrum. It is found in the leaves of most plants. It is a protein with a bilin chromophore just like the phycoeryhtrin in red algae.
Phytochrome and germination of Lettuce seeds The phytochrome pigment was discovered by Hendricks and Borthwick (USDA) in the late 1940s to the early 1960s. Famous became their experiment with phytochrome induction of seed germination of lettuce seeds, some of the species which need light to germinate. The same is true and can be done with Arabidopsis seeds.
Phytochrome and germination of spring flowers Spring annuals in deciduous forests need warmth of spring + the red of full sun in order to have their phytochrome receptors give the signal to germinate
Light loving Seeds There are seeds of wild plants that absolutely need light to germinate. Even 5 mm below an uncovered soil surface light penetrates to a level of 5 to 20%. 1. Positively photoblastic seeds: need to light to germinate like grasses, carrot. Lettuce, mustard and celery. Need to be planted very shallow in the soil. 2. Photoblastic seeds last for many years. The red poppies of Verdun & many wild plants germinated after soil was turned over (artillery at Verdun) 3. Also, since antiquity some farmers plant seeds at night (at moonlight) to prevent weed seeds from germinating. Negatively photoblastic seeds: need absolute darkness to germinate like melon, pumpkin, cucumber and other wildflowers with larger seeds. Need to be planted deeper Caution: Seed quality changes all the time and the breeding companies try to eliminate all features that the wild species developed to protect its seeds from germinating under unfavorable conditions. Example: recent lettuce & mustard seeds do no longer require light to germinate
Which seeds need light in order to germinate? Plant them shallow, not much soil on top Annuals Begonias, Coleus, Impatiens, Portulaca, Lobelia, Scarlet sage, Snapdragons Antirrhinum, Sweet Alyssum, Strawflowers, Biennials. Bellflowers Campanula, English Daisy, Foxglove Perennials Chinese Lanterns, Primroses, Rock Cress, Edelweiss, Columbines, Chrysanthemums
Which seeds need darkness to germinate? Plant them deep into the soil
Many in the family Cucurbitaceae Cucumber Cucumis sativus , Pumpkin, Cucurbita pepo Melons Cucumis melo Perennials Centurea, Pansy Viola, Phlox
Growing-up in the dark is a normal part of the upbringing of plants
Mustard & bean plants
Other Phytochrome effects Plants use phytochrome to regulate (1) the germination of seeds, (2) elongation of seedlings, (3) the size, shape and number of leaves, (4) the synthesis of chlorophyll, (5) the straightening of the epicotyl or hypocotyl hook of dicot seedlings (6) the time of flowering based on the length of day & night (photoperidism)(7) and establish circadian rhythms
Photoperiodism and Thermoperiodism In nature animals and plants are well aware of circadian changes in illumination (light-dark light intensity, light quality color or wavelength) & temperature (relative day to night temperatures required, in a to induce growth, reproduction, or flowering of plants or animals). However the ratio of duration of the phases as day : night & warm : cold increases from winter to summer and then declines again. The duration of the dark or cold periods is easily measured by comparison of an internal rhythmic process – a biological clock
Maintaining the biological clock and adapting it to the prevailing photoand thermo-periods of the season depends both on red light (phytochrome)and blue light (cryptochrome)
Other Phytochrome effects: Shade avoidance The Shade-Avoidance Effect Natural sunlight contains more red (660 nm) than far red (735 nm). However, chlorophyll absorbs 660 nm light strongly, so that the light that filters through a canopy of foliage is enriched in far red light.
Other Phytochrome effects: Shade avoidance
Other Phytochrome effects The Neighborhood Watch: If you have a sun plant (not a shade plant) it will avoid to be out-shaded by a neighbor & increase its growth rate. (1) You can fool a plant to believe it has neighbors by increasing the FR:R ration shining FR red light onto the plant. It will grow taller (b). (2) You can prevent a plant from detecting its neighbors by increasing R:FR ration shining R red light onto the area. Competition suppressed!
Can plants learn? example 3 (1) If plants – like dandelions, creeping buttercups etc. are exposed to repeated mowing of the grass meadow (lawn) they are living in, they adopt to a stunted short size that enables them to flower & propagate under such harsh conditions (2) If a tobacco plant is repeatedly forage by tobacco leaf worms they will increase production of proteinase inhibitors which stops the digestion in the worms.
(3) If fast growing plants are exposed to increase DR/R ratio (which simulates the encroachment of other plant neighbors) it will increase its growth rate to outcompete them. Nagashima and Hikosaka manipulate Chenopodium album by lifting or lowering potted plants grown at a high density lifted plants reduce vertical growth rate.
Chrysanthemum pots
Blue light When is the sky blue? “ ..And why the sky is blue uhuh uhu (Amer song)
As the sun begins to set, the light must travel farther through the atmosphere before it gets to you. More of the light is reflected and scattered, especially blue. the sun appears less bright & its color appears to change to orange and then to red. This is because even more of the short wavelength blues and greens are intensely scattered. & only the longer wavelengths are left in the direct beam that reaches you.
Daily changes in wavelength Sunset and sunrise have the sun at an angle which increases the distance the light has to travel through the atmosphere to reach you blue gets scattered completely and left over is red The sun is in zenith at noon when the distance through the atmosphere to you is the shortest. The sun feels warm (red and IR) but what you see is actually the blue that is scattered by the particles in the atmosphere.
Can Plants see (you)? In all likelihood, no. Why should they care to? However they can detect light vs dark, differentiate between light colors, with specific pigments for blue and red. More so, they can identify the length of the day as the interval between periods of increased DR/R ratio (sunrise & sunset) As well as the time of the season: increasing daylength signifies spring & approach of summer (drought) Decreasing daylength signifies fall and approach of winter (cold)
Blue light Effects by phototropins
Blue-Light Photoreceptors: Phototropins Several plant pigments absorb in blue: e.g. chlorophyll + anthocyanins esp carotenes + flavines which made them targets of early hypothesis. Now identified three types: phototropins, phototropins phot1/phot2 Actions (1)phototropic bending (2)chloroplast movement
Chloroplast movement (blue light responses) Several plant pigments absorb in blue: e.g. chlorophyll + anthocyanins esp carotenes + flavines which made them targets of early hypothesis. Now identified three types: phototropins,
This picture shows an image created in live coleus leaf by light-induced chloroplast movements. The person appearing in the leaf is Norman E. Good (1917-1992),
Blue-Light chloroplast Movement – the experiment 1. Find a suitable leaf. Coleus leaves can be excellent as long as you can find a variety that doesn't have too much purple pigmentation (the anthocyanains absorb the blue light required to cause chloroplasts to move and can make seeing the effect difficult). Geranium leaves also work but they are quite think and it is more challenging to see the images. However, the thickness adds an interesting 3-D effect. •2. you need to prepare some templates. For this, you need black & white images with high contrast. To start, it is recommended that you use text until you have established that you leaves and lighting system will work. 3. Cut a leaf from the plant and place it on wet paper towel. Place the wet paper towel on the inside of the lid of a Petri dish & place the leaf on the paper, then place the template on the leaf. Cover it. 4. Shine a bright light source on the leaf. A slide projector works great for this. Illuminate the leaf for about 45 min. 5. Remove the leaf from the wrapping and view the leaf .Where the light was bright, the leaf should be more transparent than were the leaf was covered by the dark template.
Blue-Light Photoreceptors: Phototropins Chloroplasts and mitochondria are very mobile organelles within the plant cell. Why?
Blue-Light Photoreceptors Several plant pigments absorb in blue: e.g. chlorophyll + anthocyanins esp carotenes + flavines which made them targets of early hypothesis. Now identified : phototropins phototropins phot1/phot2 double m discovered in nph1 (non-phototropic hypocotyl) Arabidopsis plants= phot1 Proteins are voltage sensors in K channels in animals. bind FMN = flavin mononucletide with BL dependent autophosphosphorylation Actions phototropic bending similar to chloroplast movement
Growing plant shoots exhibit bending under the influence of light (phototropism) and gravity (gravitropism). Gravitropic recovery of horizontally placed radish seedlings
