Exogenous Sodium Nitroprusside Improves Salt Stress Tolerance of Wheat (Triticum aestivum L.) via Regulating the Components of Ascorbate-Glutathione Cycle, Chlorophyll Content and Stabilization of Cell Membranes State

Application of nitric oxide (NO) has been shown to be effective in improving plant tolerance to various environmental stresses. The present study was carried out to investigate the protective role of exogenous application of sodium nitroprusside (SNP) (200 mu M) as a donor of NO in preventing the oxidative damage of salt stress on wheat (Triticum aestivum L.) plants. The results showed that salt stress decreased growth and chlorophyll content of wheat seedlings while it increased root electrolyte leakage (EL), malondialdehyde (MDA), reactive oxygen species (ROS) (i.e., O2- and H2O2), proline, and antioxidants, including reduced glutathione (GSH), ascorbic acid (AsA), glutathione reductase (GR), glutathione-S-transferase (GST), superoxide dismutase (SOD), and ascorbate peroxidase (APX) activities. Pretreatment with SNP stabilized stress-induced drop in GSH/GSSG ratio and AsA content, and resulted in additional proline accumulation. Meanwhile, it contributes to the reduction of ROS production by positive regulating the activity of SOD, APX, and GR. Particularly, an additional GR activation was found, which corresponds to the content of GSH in these plants. This was reflected in SNP-induced protective effects on the growth (root length, fresh and dry biomass) and leaf chlorophyll during stress and after the recovery period. Overall, SNP-pretreated plants showed the lowest MDA and EL under salinity, and the highest antioxidant activities, which were mainly involved in the ascorbate-glutathione cycle to maintain the balance between the ROS generation and scavenging. These results demonstrate that exogenous application of the SNP is useful in ameliorating the toxicity generated by NaCl stress on wheat plants.