Nitric Oxide Synthase-Dependent Nitric Oxide Production Is Associated with Salt Tolerance in Arabidopsis.

Nitric oxide (NO) has emerged as a key molecule involved in many physiological processes in plants. To characterize roles of NO in tolerance of Arabidopsis (Arabidopsis thaliana) to salt stress, effect of NaCl on Arabidopsis wild-type and mutant (Atnoal) plants with an impaired in vivo NO synthase (NOS) activity and a reduced endogenous NO level was investigated. Atnoal mutant plants displayed a greater Na+ to K+ ratio in shoots than wild-type plants due to enhanced accumulation of Na+ and reduced accumulation of K+ when exposed to NaCl. Germination of Atnoa1 seeds was more sensitive to NaCl than that of wild-type seeds, and wild-type plants exhibited higher survival rates than Atnoal plants when grown under salt stress. Atnoa1 plants had higher levels of hydrogen peroxide than wild-type plants under both control and salt stress, suggesting that Atnoal is more vulnerable to salt and oxidative stress than wild-type plants. Treatments of wild-type plants with NOS inhibitor and NO scavenger reduced endogenous NO levels and enhanced NaCl-induced increase in Na+ to K+ ratio. Exposure of wild-type plants to NaCl inhibited NOS activity and reduced quantity of NOA1 protein, leading to a decrease in endogenous NO levels measured by NO-specific fluorescent probe. Treatment of Atnoal plants with NO donor sodium nitroprusside attenuated the NaCI-induced increase in Na+ to K+ ratio. Therefore, these findings provide direct evidence to support that disruption of NOS-dependent NO production is associated with salt tolerance in Arabidopsis. [ABSTRACT FROM AUTHOR]