Roles of phosphoinositides in regulation of stomatal movements.

Guard cells sense various environmental and internal stimuli and, in response, modulate the stomatal aperture to a size optimal for growth and adaptation. Among the many factors involved in the fine regulation of stomata, we have focused our studies on the role of phosphoinositides. Our recent study published in the Plant Journal (52:803-16) provides evidence for an important role for phosphatidylinositol 4,5-bis-phosphate (PtdIns(4,5)P(2)) in inducing stomatal opening. Light induces translocation of a PtdIns(4,5)P(2)-binding protein from the cytosol to the plasma membrane and treatments that increase the intracellular PtdIns(4,5)P(2) level induce stomatal opening in the absence of light irradiation. Inhibition of anion channel activity, a negative regulator for stomatal opening, was suggested as a mechanism of PtdIns(4,5)P(2)-induced stomatal opening. We also reported that phosphatidylinositol 3-phosphate (PtdIns(3)P) and phosphatidylinositol 4-phosphate (PtdIns(4)P) regulate actin dynamics in guard cells. The effects of the phosphoinositides were specific, and were not induced by other lipids with similar structures. The roles of different interacting partners are likely to be important for these lipids to produce specific changes in guard cell activity.