Effect of exogenous application of nitric oxide on salt stress responses of soybean

• Induced long-term salinity stress in soybean led to increased cellular hydrogen peroxide H2O2 content.
• Application of nitric oxide donor (NO) (2,2′(hydroxynitrosohydrazono) bis-ethanimine) to salt stressed soybean improved various plant growth parameters.
• NO confers tolerance to salt stress through activation of ascorbate peroxidase activity.

Salinity stress is one of the major factors that reduce annual agricultural produce. This has led to numerous studies investigating means to improve tolerance to salt stress. Nitric oxide (NO) is a gaseous signaling molecule involved in the regulation of diverse processes in plants. Certain studies have demonstrated the role of exogenous application of NO in mediating responses to abiotic stress. We investigated the role of exogenously applied NO 2,2′(hydroxynitrosohydrazono) bis-ethanimine (DETA/NO) in ameliorating long term salinity stress on soybean. Long term salinity stress in the form of a final concentration of 80 mM sodium chloride (NaCl) over a 16 day period drastically affected the plants as indicated by decreased biomass of shoots, roots and nodules of soybean plants. In contrast, supplementation with 10 μM DETA/NO improved growth of soybean plants under NaCl as evidenced by increased shoot, root and nodule weights and nodule number. Further analysis showed that long-term salinity stress led to increased cellular hydrogen peroxide (H2O2) content and high levels of cell death in the soybean. Treatments with NO, either as DETA/NO alone or in combination with NaCl, resulted in reversal of H2O2 to basal levels. This study showed that application of DETA/NO resulted in increased enzymatic activity of ascorbate peroxidase (APX). We propose that the role of NO in increasing tolerance to salinity stress in soybean may result from either its antioxidant capacity by direct scavenging of H2O2 or its role in activating APX activity that is crucial in scavenging H2O2.