Abstract
Guard cells undergo quick volume changes during stomatal movements. However, the contribution of aquaporins to stomatal movements has not been well understood. The plasma membrane aquaporin PIP2;1in Arabidopsis has been found to mediate abscisic acid-induced or flag22-induced stomatal closure. In this research, we investigated the role of PIP2;1 in light-induced stomatal opening by measuring the stomatal apertures of the pip2;1 mutant and PIP2;1 overexpression lines after light treatment. pip2;1 mutant exhibited a larger stomatal aperture, and the overexpression lines displayed a smaller stomatal aperture. It has been reported that the phosphorylation at Ser-280 and Ser-283 of PIP2;1 in rosette tissue increased in response to darkness, whereas osmotic water permeability (P(f)) in mesophyll protoplasts in darkness was lower than that under light, suggesting that phosphorylation at Ser-280 and Ser-283 of PIP2;1 affected P(f) in mesophyll protoplasts. Therefore, we obtained the pip2;1 mutant expressing phosphorylation-deficient (PIP2;1 AA) or phosphomimetic (PIP2;1 DD) forms of PIP2;1. The PIP2;1 AA lines exhibited a larger stomatal aperture as pip2;1 mutant, whereas PIP2;1 DD lines exhibited a smaller stomatal aperture as PIP2;1 overexpression lines under light. These results suggest that PIP2;1 plays a negative role in light-induced stomatal opening, and phosphorylation of PIP2;1 at Ser-280 and Ser-283 causes reduced water absorption in guard cells and decreased stomatal opening.