Nitric oxide is involved in the brassinolide-induced adventitious root development in cucumber (Cucumis sativus L.) explants

Abstract Background: Brassinolide (BR), as a new type of plant hormones, is involved in the process of plant growth and stress response. Previous studies have reported the roles of BR in regulating plant developmental processes and also response tolerance to abiotic stresses in plants. In my study, the main purpose is to explore whether nitric oxide (NO) is involved in the process of BR-induced adventitious root formation in cucumber (Cucumis sativus L.), and whether it plays a certain role. Results: Exogenous application of 1 μM BR significantly promoted adventitious rooting, while high concentrations of BR (2-8 μM) effectively inhibited adventitious rooting. NO donor (S-nitroso-N-acerylpenicillamine, SNAP) promoted the occurrence of adventitious roots. Simultaneously, BR and SNAP mixed treatment significantly promoted adventitious rooting and the promoted effects was significantly superior to the application of BR or SNAP alone. Moreover, NO scavenger (c-PTIO) and inhibitors (L-NAME and Tungstate) inhibited the positive effects of BR on adventitious rooting. BR at 1 μM also increased endogenous NO content, NO synthase (NOS-like) and Nitrate reductase (NR) activities, while BRz (a specific BR biosynthesis inhibitor) decreased these effects. In addition, the relative expression level of NR was up-regulated by BR and SNAP, whereas BRz down-regulated it. The application of NO inhibitor (Tungstate) in BR also inhibited the up-regulation of NR. Conclusion: BR promoted the formation of adventitious roots via inducing the generation of endogenous NO.