Deciphering the protective role of nitric oxide against salt stress at the physiological and proteomic levels in maize.

Saline stress is a major factor that limits crop yield. Nitric oxide (NO) is functional during plant growth, development, and defense responses. In the present study, the protective role of NO in alleviating saline stress in maize at the physiological and proteomic levels was examined. Our results showed that salt treatment quickly induced NO accumulation and addition of the NO donor S-nitroso-N-acetylpenicillamine (SNAP) efficiently eliminated the inhibitory effect of salt on shoot growth and photosynthesis and inhibited salt-inducible H2O2 accumulation. These effects could be reversed by NO metabolic scavengers and inhibitors. Further proteomic and Western blotting analysis revealed that NO induced G-protein-associated protein accumulation and antioxidant enzymes activities, in addition to activation of defense proteins, energy metabolism, and cell structure/division in salt-treated maize seedlings. Controlling the G-protein status with G-protein activators or inhibitors also affected NO generation and root and stem growth in maize seedlings after saline stress. On the basis of these results, we propose that NO enhances salt tolerance in maize seedlings by enhancing antioxidant enzyme activities and controlling H2O2 levels, and these effects are accompanied by diverse downstream defense responses. During this process, G-protein signaling is an early event that works upstream of NO biogenesis.