Phototropins But Not Cryptochromes Mediate the Blue Light-Specific Promotion of Stomatal Conductance, While Both Enhance Photosynthesis and Transpiration under Full Sunlight        

Abstract

Leaf epidermal peels of Arabidopsis (Arabidopsis thaliana) mutants lacking either phototropins 1 and 2 (phot1 and phot2) or cryptochromes 1 and 2 (cry1 and cry2) exposed to a background of red light show severely impaired stomatal opening responses to blue light. Since phot and cry are UV-A/blue light photoreceptors, they may be involved in the perception of the blue light-specific signal that induces the aperture of the stomatal pores. In leaf epidermal peels, the blue light-specific effect saturates at low irradiances; therefore, it is considered to operate mainly under the low irradiance of dawn, dusk, or deep canopies. Conversely, we show that both phot1 phot2 and cry1 cry2 have reduced stomatal conductance, transpiration, and photosynthesis, particularly under the high irradiance of full sunlight at midday. These mutants show compromised responses of stomatal conductance to irradiance. However, the effects of phot and cry on photosynthesis were largely nonstomatic. While the stomatal conductance phenotype of phot1 phot2 was blue light specific, cry1 cry2 showed reduced stomatal conductance not only in response to blue light, but also in response to red light. The levels of abscisic acid were elevated in cry1 cry2. We conclude that considering their effects at high irradiances cry and phot are critical for the control of transpiration and photosynthesis rates in the field. The effects of cry on stomatal conductance are largely indirect and involve the control of abscisic acid levels.

Phospholipase D δ knock-out mutants are tolerant to severe drought stress

“…The differenes found between stomatal responses in isolated epidermal peels compared to intact leaves could result from the presence of the mesophyll in intact leaves. 27,28,29 In addition, wild-type and mutant plants showed the same stomatal index and stomatal density (data not shown). Thus, the drought tolerant phenotype of pldd mutants cannot be explained by means of water balance through stomatal pore width regulation.…”

A Dominant Mutation in the Light-Oxygen and Voltage2 Domain Vicinity Impairs Phototropin1 Signaling in Tomato

“…Since only a minor increase in stomatal conductance is observed in Nps1 under high-fluence BL, the participation of phot2 in this increase remains equivocal. At the same time, retention of the rhythm of stomatal movement in the Nps1 mutant implies that it is not affected in stomatal responses mediated by cryptochrome and phytochrome (Somers et al, 1998;McClung, 2001;Boccalandro et al, 2012). The Nps1 seedlings grown under omnilateral BL showed altered hypocotyl growth orientation very similar to that of the phot1 seedlings of Arabidopsis.…”

A proteome map of a quadruple photoreceptor mutant sustains its severe photosynthetic deficient phenotype

“…This altered growth and development of the quadruple mutant could be the consequence of a reduced photosynthetic capacity. Although photosynthesis is reduced in the phyB simple and cry1 cry2 double mutants (Boccalandro et al, 2009(Boccalandro et al, , 2012, detailed information about the processes that might affect them have not been described.…”