Nitric oxide improved salt stress tolerance by osmolyte accumulation and activation of antioxidant defense system in seedling of B. juncea (L.) Czern

The present manuscript elucidates the cytoprotective role of nitric oxide and its relation with ROS and antioxidants in minimizing the effect of salinity in B. juncea (Indian mustard) which is an important salt tolerant crop of arid and semi arid region. NO alleviates the adverse effect of salt on growth, biomass, relative water content and photosynthesis. At 50 mM NaCl concentration, rapid accumulation of NO was observed that is 2.02 folds higher in roots respectively while in leaves and roots insignificant changes were observed. At higher concentration of salt stress (70–100 mM NaCl), considerable rise in H2O2 content and membrane damage were documented which restrained by the application of 100 µM SNP. NO mitigates the salt stress by regulating the activities of nitrate reductase and other antioxidants. Reduction in NO content was observed in independent treatment of NaCl and SNP in comparison to combined treatment of SNP + NaCl (100 µM SNP + 50 mM NaCl). The different antioxidant enzymes show disparate behaviour with signalling molecule NO. The activity of catalase, guaiacol peroxidase and nitrate reductase were upregulated whereas ascorbate peroxidase was downregulated with NO. The elevated activities of antioxidant and NO accumulation might be responsible for detoxifying the detrimental effect of salinity in B. juncea. The current investigation emphasizes on the potential role of NO in salt stress tolerance by regulating antioxidative defense metabolism, cellular homeostasis and detoxification mechanism in seedlings of B. juncea. © 2019, Society for Plant Research.