The role and the interrelationship of hydrogen peroxide and nitric oxide in the UV-B-induced stomatal closure in broad bean

Previous studies have showed that UV-B can stimulate closure as well as opening of stomata. However, the mechanism of this complex effect of UV-B is not clear. The purpose of this paper is to investigate the role and the interrelationship of H2O2 and NO in UV-B-induced stomatal closure in broad bean ( Vicia faba L.). By epidermal strip bioassay and laser-scanning confocal microscopy, we observed that UV-B-induced stomatal closure could be largely prevented not only by NO scavenger c-PTIO or NO synthase ( NOS) inhibitor L-NAME, but also by ascorbic acid (ASC, an important reducing substrate for H2O2 removal) or catalase (CAT, the H2O2 scavenger), and that UV-B-induced NO and H2O2 production in guard cells preceded UV-B-induced stomatal closure. These results indicate that UV-B radiation induces stomatal closure by promoting NO and H2O2 production. In addition, c-PTIO, L-NAME, ASC and CAT treatments could effectively inhibit not only UV-B- induced NO production, but also UV-B- induced H2O2 production. Exogenous H2O2-induced NO production and stomatal closure were partly abolished by c-PTIO and L-NAME. Similarly, exogenous NO donor sodium nitroprusside-induced H2O2 production and stomatal closure were also partly reversed by ASC and CAT. These results show a causal and interdependent relationship between NO and H2O2 during UV-B- regulated stomatal movement. Furthermore, the L-NAME data also indicate that the NO in guard cells of Vicia faba is probably produced by a NOS-like enzyme.