Contributions of cryptochromes and phototropins to stomatal opening through the day

The UV-A/blue photoreceptors phototropins and cryptochromes are both known to contribute to stomatal opening (Delta g(s)) in blue light. However, their relative contributions to the maintenance of g(s) in blue light through the whole photoperiod remain unknown. To elucidate this question, Arabidopsis phot1 phot2 and cry1 cry2 mutants (MTs) and their respective wild types (WTs) were irradiated with 200 mu mol m(-2) s(-1) of blue-, green- or red-light (BL, GL or RL) throughout a 11-h photoperiod. Stomatal conductance (g(s)) was higher under BL than under RL or GL. Under RL, g(s) was not affected by either of the photoreceptor mutations, but under GL g(s) was slightly lower in cry1 cry2 than its WT. Under BL, the presence of phototropins was essential for rapid stomatal opening at the beginning of the photoperiod, and maximal stomatal opening beyond 3 h of irradiation required both phototropins and cryptochromes. Time courses of whole-plant net carbon assimilation rate (A(net)) and the effective quantum yield of PSII photochemistry (phi PSII) were consistent with an A(net)-independent contribution of BL on g(s) both in phot1 phot2 and cry1 cry2 mutants. The changing roles of phototropins and cryptochromes through the day may allow more flexible coordination between g(s) and A(net).