Abstract:

Role and relationship of NO and H₂O₂ in light/dark-regulated stomatal movement in Vicia faba L. were investigated by epidermal strip bioassay and laser-scanning confocal microscopy. Results showed that the effects of exogenous sodium nitroprusside (SNP, NO-releasing compound) and H₂O₂ on stomatal closure were more significant in light than those in the dark. Dark-induced closure of stomata was largely prevented not only by 2,4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO), a specific NO scavenger and N^G-nitro-L-arg-methyl eater (L-NAME), an inhibitor of NO synthase (NOS) in mammalian cells that also inhibits plant NOS, but also by addition of ascorbic acid (Vc) and exogenous catalase (CAT), which are an important reducing substrate for H₂O₂ removal and an H₂O₂ scavenger, respectively. Experiments based on fluorescent probe DAF-2 DA and H₂DCF-DA showed that the level of endogenous NO and H₂O₂ in guard cells was greater in the dark than that in light. These results prove that light/dark regulates stomatal movement via influencing NO and H₂O₂ production. In addition, H₂O₂-induced NO production and stomatal closure in light were abolished partly by cPTIO and L-NAME. Interestingly, SNP-induced H₂O₂ accumulation and stomatal closure were reversed by Vc and CAT in light. These show that NO and H₂O₂ cross talk in light/dark-regulated stomatal movement. Furthermore, L-NAME could reverse stomatal closure and NO generation induced by darkness and H₂O₂ in light, we presume that the NO generation in guard cells of Vicia faba is likely related to NOS-like enzyme.

Key words: nitric oxide, hydrogen peroxide, light/dark, stomatal movement, Vicia faba