Redox-active ash gourd extract mitigates salt-stress toxicity through modulation of primary metabolites in rice

Salinity stress is considered as one of the major detrimental stresses for reducing plant growth and crop productivity. Hence, concerted efforts are going on to develop sustainable solutions for reducing salinity-induced negative effects on crop productivity. Given this, the present study evaluated the potential of ash gourd extract (AGE; 0.9 mu g/mL) for ameliorating NaCl (100 mM) stress in rice, which is one of the major staple food crops worldwide. The differential phenotyping revealed growth reduction under NaCl treatment, as indicated by 0.27- and 0.36-fold decrease in survival and whole-seedling biomass, respectively, compared with those of control. In contrast, 24 h pre-treatment with AGE before NaCl exposure (AGE24h+NaCl) improved these growth attributes by 1.29- and 1.70-fold, respectively, compared with those of NaCl treatment. The differential phenotype of AGE was associated with its inherent ability to scavenge reactive oxygen species, which was equivalent to 0.08-fold of ascorbic acid. The higher accumulation of superoxide radicals and upregulated expression of stress marker genes including OsTSPO, OsCBS, OsHKT1;5, and OsNHX1 under AGE24h treatment also suggested AGE mediated priming effect. Under AGE24h+NaCl, the expression levels of these stress markers were either maintained or their extent of upregulation was further enhanced. In addition, the coordinated activation of antioxidant machinery and reduced Na-accumulation further supported stress amelioration under AGE24h+NaCl treatment. GC-MS-based metabolomics highlighted fatty acids, malic acid, myo-inositol, allose, trehalose, and L-oxoproline, as key metabolites, associated with AGE-mediated amelioration of NaCl stress. The foliar application of AGE increased seed yield and 1000 seed weight by 1.13- and 1.06-fold, respectively, compared with those of NaCl, validating its agronomic feasibility. Thus, the results highlighted the application of AGE, as a "green" bioregulator for ameliorating NaCl stress conditions in rice.