Phototropins and not cryptochromes mediate the blue light-specific response of stomatal conductance but both promote photosynthesis and transpiration under full sunlight in Arabidopsis

BOCCALANDRO HE; GIORDANO C; PLOSCHUK EL; PICCOLI PN; BOTTINI R; CASAL JJ

PLANT PHYSIOLOGY.

AMER SOC PLANT BIOLOGISTS

Año: 2012 vol. 158 p. 1475 - 1484

0032-0889

In arabidopsis mutants lacking either phototropins 1 and 2 (phot1, phot2) or cryptochromes 1 and 2 (cry1, cry2), leaf epidermal peels 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 could be involved in the perception of the blue light-specific signal inducing the aperture of the stomatal pores. In leaf epidermal peels the blue-light specific effect saturates at low irradiances and it is therefore considered to operate mainly under the low irradiance of dawn, dusk or deep canopies. Conversely, here 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 showed compromised responses of leaf conductance to irradiance. However, the effects of phot and cry on photosynthesis were largely non-stomatic. While the leaf conductance phenotype of phot1 phot2 was blue-light specific, cry1 cry2 showed reduced leaf conductance not only in response to blue light, but also in response to red light. The levels of abscisic acid (ABA) were elevated in cry1 cry2. We conclude that given 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 do not involve the perception of the blue-light signal causing a rapid aperture of the stomatal pore. Rather, the action of cry is more indirect and involves the control of ABA levels