Involvement of putrescine in osmotic stress-induced ABA signaling in leaves of wheat seedlings.

To elucidate one mechanism by which putrescine (Put) functions in plant signaling under osmotic stress, Put and ABA contents, and plasma membrane-NADPH oxidase (PM-NOX) activity were detected in wheat seedling leaves. Under osmotic stress, ABA and Put contents, PM-NOX activity, and PM-NOX-dependent O2.- production all increased. The inhibitor tungstate (T) of ABA bio-synthesis reduced the increases in ABA and Put contents under osmotic stress. The inhibitor D-arginine (D-Arg) of Put bio-synthesis didn't reduce osmotic-induced increase of ABA, but it inhibited the increases of PM-NOX activity and O2 . - production, and the inhibitory effects were reversed by exogenous Put. These findings suggested that ABA might regulate Put biosynthesis, and Put might regulate PM-NOX activity. Treatments with three inhibitors imidazole (I), diphenylene iodonium (DPI) and pyridine (P) of PM-NOX reduced significantly not only O2 . - production, but also the stress-induced increase of Put content, which indicated that O2 . - production might regulate Put biosynthesis. Treatments with EGTA (Ca2+ chelator), La3+ and verapamil (V) (Ca2+ channel blockers) reduced significantly the stress-induced increase of Put content, which suggested that Ca2+ might regulate Put biosynthesis. With these findings, it could be concluded that Put was involved in ABA signaling induced by osmotic stress via regulating PM-NOX activity in wheat seedling leaves.