Planta

Planta 140, 245-249 (1978)

9 by Springer-Verlag 1978

The Effect of Wavelength of Light on Stomatal Opening Susan Lurie Department of Agricultural Botany, Hebrew University, Rehovot 76 100, Israel

Abstract. The effect of broad band green, blue and

red light on stomatal opening of Vicia faba L. (broad bean) leaves was examined. In air, blue light caused greater stomatal opening than red light. In air with green light stomata were only slightly opened. In a nitrogen atmosphere red light caused greater opening than blue light, and green light caused only slight opening. Opening in air or nitrogen atmosphere in red or blue light was inhibited by the uncoupler CCCP, while the photosynthetic inhibitor DCMU inhibited opening in air but not in nitrogen atmosphere. We concluded that more than one light activated metabolic pathway can supply the energy needed to effect stomatal opening and that different pathways are operative under different conditions. Key words: Action spectrum - Ion uptake - Malate - Starch - Stomata - Viola.

Introduction

It has been shown that while the action spectrum of stomatal opening roughly follows that of photosynthesis (Kuiper, 1964; Kana and Miller, 1977), blue light is more effective than red light (Hsiao et al., 1973; Mansfield and Meidner, 1966). In certain cases the involvement of the phytochrome system in either stomatal opening or closing has been postulated (Haberman, 1973; Evans and Allaway, 1972). Blue light influences certain metabolic pathways other than the photosynthetic reductive pentose phosphate pathway. It may enhance activity of phosphoenolpyruvate carboxylase (Miyachi and Hogetsu, 1970; Tamos et al., 1970), oxidative respiration (Kowallik and Gaffron, 1967; Voskresenskaya, 1972) or starch breakdown Voskresenskaya, 1972). It seemed

possible that the effect of blue light on stomatal opening was due to the additive effect of photosynthesis plus one of the other pathways, while in red light only photosynthesis is involved. This paper attempts to determine what causes the differing extents of stomatal opening in red or blue light.

Materials and Methods The plants used were three week old Vicia faba L. Plants were kept in the dark for 24 h before each experiment. Lower epidermis was stripped and rolled following the technique of Allaway (1973), then floated on a solution of i0 m M KC1, 0.5 m M CaSO4. The epidermis was illuminated for 2.5 h in closed petri dishes with either air or nitrogen atmosphere and the stomatal aperture measured under the microscope. The air or nitrogen atmosphere was obtained by bubbling the solution with the proper gas for 5 rain. The solution was then transferred to the petri dishes and the epidermis was added. The petri dishes were then flushed 5 or 6 times with the appropriate gas and sealed. Illumination was through cellulose filters and was adjusted to give 20 btE m - 2 s - * as measured by a L a m b d a radiometer which is sensitive to wavelengths of 400 700 nanometers. The transmission characteristics of the filters are shown in Figure 1. In some experiments S6Rb + uptake and malate accumulation were determined. In these experiments each dish contained 20 cm 2 of epidermal tissue. The solution of KC1 contained 0.1 gCi S6Rb/ mol K. At the end of illumination the epidermis was extracted in 96% ethanol and the chlorophyll content determined by the method of Wintermans and De Mots (1965). There was 0.1 0.2 btg chl cm 2 epidermis. The tissue was extracted twice more with 70% ethanol and the extracts combined. Half was used to determine S6Rb uptake in a liquid scintillation counter and the other half was used to determine malate content using the enzymatic assay of G u t m a n n and Wahlefeld (1974). In the experiments where starch was determined, simultaneous light and dark samples were run. Each sample contained 20 cm 2 of peeled epidermis. At the end of 2.5 h light or dark stomatal aperture was checked and the epidermis was extracted in 96% ethanol and chlorophyll determined. The extraction procedure and the enzymatic assay of the glucose obtained from hydrolysis was according to M a c R a e (1971). D C M U was used at a concentration of 5 x 1 0 - 6 M and C C C P at 10-SM.

0035-0935/78/0140/0245/$01.00

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S. L u r i e : Effect o f L i g h t o n S t o m a t a l O p e n i n g

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