Pretreatment with Proline or an Organic Bio-stimulant Induces Salt Tolerance in Wheat Plants by Improving Antioxidant Redox State and Enzymatic Activities and Reducing the Oxidative Stress

In this study, the effects of seed soaking in proline (12mM) or Moringa oleifera leaf extract (MLE; 6%) on the biomass, yield, and the antioxidant systems were investigated using wheat plants grown under NaCl stress (120mM). Shoot fresh and dry weights, yield, K+ ion accumulation, K+/Na+ ration, soluble protein, photosynthetic pigment (that is, carotenoids and chlorophylls) contents, and efficiency (that is, Fv/Fm and performance index; PI) of wheat were decreased at salt-stress treatment. Salinity increased the activity of superoxide dismutase, ascorbate and glutathione peroxidases, and the content of malondialdehyde, H2O2, and Na+ and Cl- contents in leaf compared to control. Additionally, increased magnitudes of proline, soluble sugar, soluble protein, ascorbate, glutathione contents were more pronounced under 120mM NaCl than those under control. Proline or MLE ameliorated the inhibitory effects of NaCl stress to varying degrees, ensuring significant amelioration on biomass, yield, osmoprotectants and antioxidant systems. In comparison to proline, seed soaking with MLE was more effective in improving wheat growth and yield by mitigating the inhibitory effects of salinity stress. The presented results indicate that seed soaking with 6% MLE can contribute to protecting wheat seedlings/plants against NaCl stress by mitigating the oxidative stress.