Phosphatidylinositol 3-and 4-phosphate are required for normal stomatal movements

Phosphatidylinositol (Pl) metabolism plays a central role in signaling pathways in both animals and higher plants. Stomatal guard cells have been reported to contain Pl 3-phosphate (Pl3P) and Pl 4-phosphate (Pl4P), the products of Pl 3-kinase (Pl3K) and Pl 4-kinase (Pl4K) activities. In this study, we tested the roles of Pl3P and Pl4P in stomatal movements. Both wortmannin (WM) and LY294002 inhibited Pl3K and Pl4K activities in guard cells and promoted stomatal opening induced by white light or the circadian clock. WM and LY294002 also inhibited stomatal closing induced by abscisic acid (ABA). Furthermore, overexpression in guard cells of GFP:EBD (green fluorescent protein:endosome binding domain of human EEA1) or GFP:FAPP1 PH (Pl-four-P adaptor protein-1 pleckstrin homology domain), which bind to Pl3P and Pl4P, respectively, increased stomatal apertures under darkness and white light and partially inhibited stomatal closing induced by ABA. The reduction in ABA-induced stomatal closing with reduced levels of Pl monophosphate seemed to be attributable, at least in part, to impaired Ca2+ signaling, because WM and LY294002 inhibited ABA-induced cytosolic Ca2+ increases in guard cells. These results suggest that Pl3P and Pl4P play an important role in the modulation of stomatal closing and that reductions in the levels of functional Pl3P and Pl4P enhance stomatal opening.