By stomatal bioassay and measurement of endogenous nitric oxide (NO) level in guard cells, the interactions of NO and phosphatidylinositol 3-phosphate (PI3P) \[the product of phosphatidylinositol 3-kinase (PI3K)\] in UV-B-induced stomatal closure were studied in the epidermal strips of abaxial surface of broad bean(Vicia faba L.) leaves. The results showed that both the NO production in guard cells and stomatal closure induced by UV-B were significantly inhibited by PI3K inhibitors wortmannin (WM) and LY294002 (LY). Meanwhile, exogenous NO-releasing compound sodium nitroprusside (SNP) could completely reverse the inhibitory effect of LY and WM on the UV-B-induced stomatal closure, and WM and LY could not inhibit exogenous SNP-induced stomatal closure of broad bean. These results indicate that PI3P acts upstream of NO in the signal transduction pathway of UV-B-induced stomatal closure of broad bean.

phosphatidylinositol 3-phosphate; nitric oxide; UV-B radiation; stomatal closure; broad bean