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THE BLUE LIGHT RESPONSE OF STOMATA: PULSE KINETICS AND SOME MECHANISTIC IMPLICATIONS *

Abstract— Intact leaves of Commelina communis irradiated with high fluence rates of red light, showed discrete increases in stomatal conductance in response to pulses (1‐100 s) of blue light (250 μmol m−2 s−1). Red light pulses were ineffective, indicating that the conductance increases were not mediated by photosynthesis and that they constitute a specific stomatal response to blue light. The response peaked 15 min after the pulse and was completed within50–60 min. Conductance increases were proportional to pulse duration up to about 30 s and saturated at longer exposures. The relationship between stomatal responses and pulse duration approximately fitted an exponential function, with a t 9s. Pulse responses at two different fluences indicated that reciprocity held. Responses to two consecutive pulses varied with time between pulses. A saturating pulse applied immediately after a preceding one induced no additional response; two saturating pulses 50 min apart caused two identical, consecutive responses. Total increases in conductance induced by two pulses separated by intermediate time intervals increased with time between pulses with a = 9 min. These results point to a blue light‐dependent photoconversion of a molecular form, with the activity of the photoconversion product decaying in a thermal reaction. Under continuous blue light, prevailing fluence rates and rates of the light and thermal reactions are postulated to determine steady‐state activities of the photoconversion product and proportional increases in conductance levels. These findings have implications for the environmental and metabolic roles of the stomatal response to blue light.