Nitric oxide contributes to methane-induced osmotic stress tolerance in mung bean

Background: Osmotic stress is a major abiotic stress limiting crop production by affecting plant growth and development. Although previous reports discovered that methane (CH4) has a beneficial effect on osmotic stress, the corresponding downstream signal(s) is still elusive. Results: Polyethylene glycol (PEG) treatment progressively stimulated the production of CH4 in germinating mung bean seeds. Exogenous CH4 and sodium nitroprusside (SNP) not only triggered nitric oxide (NO) production in PEGstressed plants, but also alleviated the inhibition of seed germination. Meanwhile, amylase activity was activated, thus accelerating the formation of reducing sugar and total soluble sugar. Above responses could be impaired by NO scavenger(s), suggesting that CH4-induced stress tolerance was dependent on NO. Subsequent tests showed that CH4 could reestablish redox balance in a NO-dependent fashion. The addition of inhibitors of the nitrate reductase (NR) and NO synthase in mammalian (NOS), suggested that NR and NOS-like protein might be partially involved in CH4-alleviated seed germination inhibition. In vitro and scavenger tests showed that NO-mediated S-nitrosylation might be associated with above CH4 responses. Conclusions: Together, these results indicated an important role of endogenous NO in CH4-enhanced plant tolerance against osmotic stress, and NO-regulated redox homeostasis and S-nitrosylation might be involved in above CH4 action.