THE EFFECT OF SOME ENVIRONMENTAL FACTORS ON THE MOVEMENTS OF GUARD CELLS

Abstract

The effects of light, temp., and humidity on stomatal aperture were observed on leaves of potted specimens of Camellia japonica and Ligustrum japonicum growing out-of-doors. The stomates are affected by variation in temp., remaining closed at temp. of [long dash]4[degree]C or less. The guard cells respond slowly to light when the temp. is low. With temp. of 20 [degree]C or higher, the stomatal aperture is directly affected by variations in the light intensity. The effect of low relative humidity on stomatal aperture is comparatively slight at medium and low temp., but is more pronounced at high temp. An equation was derived from these data which describes the effects of light, temp. and humidity on the stomatal aperture of both species. The stomatal aperture of both cotton and tobacco decreased with decreasing temp. Photosynthetic measurements are reported for the plants whose stomatal apertures were also being detd. Fluctuations in the rate of photosynthesis do not appear to affect the stomatal aperture of Camellia and privet. The apparent photosynthetic rate of leaves of both spp. is affected by age differently than the stomatal aperture. The effect of chloroform is to inhibit apparent photosynthesis but not greatly to affect stomatal aperture. Guard cells containing non-fluorescent plastids on leaves devoid of chlorophyll exhibit light-induced movements. These results indicate that probably there is no causal relation between photosynthesis and stomatal opening. Stomatal behavior has been explained by turgor changes associated with changes in permeability, changes in enzyme activity and variations in colloidal hydration. It has been assumed that these changes are initiated by fluctuations in photosynthesis. None of these proposed theories is adequate to account for all of the observed facts concerning the movements of the guard cells.