PLANT PHYSIOLOGY , Vol 103, Issue 2 399-406, Copyright © 1993 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Circadian Rhythms in Stomatal Responsiveness to Red and Blue Light
H. L. Gorton, W. E. Williams and S. M. Assmann
Department of Biology, St. Mary's College of Maryland, St. Mary's City, Maryland 20686 (H.L.G., W.E.W.)
Stomata of many plants have circadian rhythms in responsiveness to
environmental cues as well as circadian rhythms in aperture. Stomatal
responses to red light and blue light are mediated by photosynthetic
photoreceptors; responses to blue light are additionally controlled by a
specific blue-light photoreceptor. This paper describes circadian rhythmic
aspects of stomatal responsiveness to red and blue light in Vicia faba.
Plants were exposed to a repeated light:dark regime of 1.5:2.5 h for a
total of 48 h, and because the plants could not entrain to this short
light:dark cycle, circadian rhythms were able to "free run" as if in
continuous light. The rhythm in the stomatal conductance established during
the 1.5-h light periods was caused both by a rhythm in sensitivity to light
and by a rhythm in the stomatal conductance established during the
preceding 2.5-h dark periods. Both rhythms peaked during the middle of the
subjective day. Although the stomatal response to blue light is greater
than the response to red light at all times of day, there was no
discernible difference in period, phase, or amplitude of the rhythm in
sensitivity to the two light qualities. We observed no circadian
rhythmicity in net carbon assimilation with the 1.5:2.5 h light regime for
either red or blue light. In continuous white light, small rhythmic changes
in photosynthetic assimilation were observed, but at relatively high light
levels, and these appeared to be attributable largely to changes in
internal CO2 availability governed by stomatal conductance.
