Ascorbic and Salicylic Acids Vitalized Growth, Biochemical Responses, Antioxidant Enzymes, Photosynthetic Efficiency, and Ionic Regulation to Alleviate Salinity Stress in Sorghum bicolor

Ascorbic acid (ASA) and salicylic acid (SA) are well-known growth stimulators influencing various physiological and biochemical functions in plants. The present study aimed to examine the exogenous effects of ASA and SA on growth and physiological performance of Sorghum bicolor, under saline conditions. Plants were grown in netted greenhouse and sub-irrigated with Hoagland's nutrient solution containing 0- and 100-mM NaCl. Both sets (non-saline and saline) were provided with two concentrations (0.5 mM and 1 mM) of ASA and SA each, through rooting medium and the experiment was continued for 45 days. Salt stress adversely affected the growth, physiological, and photosynthetic attributes of S. bicolor. Salt stress inactivated the reaction centers of S. bicolor chloroplast and disturbed the structural stability of PSII. The changes in PSII caused the reduction in PIABS, Fv/Fm, and OJIP parameters. However, the application of ASA and SA effectively enhanced plant biomass, leaf pigments, photosynthetic efficiency, and enzymatic and non-enzymatic antioxidant activities under both saline and non-saline conditions. The most effective concentrations that significantly improved plant biomass, chlorophyll fluorescence, and eco-physiological responses of S. bicolor were 0.5 mM and 1 mM for ASA and SA, respectively. Both treatments strengthen plants by decreasing Na+ uptake and Na+/K+ ratio, while retaining more K+ in root and increasing K+ transport to shoot, under saline conditions. In addition, these treatments significantly reduced oxidative stress markers (MDA and H2O2) by increasing activities of enzymatic and non-enzymatic antioxidants and polyphenols, soluble sugars, and proline contents. Therefore, application of ASA (0.5 mM) and SA (1 mM) was turned out to be the effective remedy for improving salinity tolerance of Sorghum. This approach could be used to obtain significant biomass of a multipurpose crop from theoretically unproductive soils that will help to meet the basic necessities (like food, fodder, forage, and energy) of the ever-growing population.