Exogenous applications of ascorbic acid improve wheat growth, physiology and yield under salinity stress via a balance in antioxidant production and ROS scavenging

Ascorbic acid (AsA) improves plant tolerance against abiotic stresses, but key mechanisms of salt tolerance by its different application modes are obscure. In this study, 5 mM AsA was applied in seed priming (SP), foliar spray (FS) and medium supplementation (MS) modes to explore their comparative effectiveness in improving salinity (170 mM) tolerance in wheat (Triticum aestivum L. cv. Galaxy-2013). For SP, seeds were primed while FS and MS were administered at tillering. One set of plants was harvested 30 days after treatment to record data for growth, pigments, leaf gas exchange and water relations, as well as shoot and root osmolytes accumulation, antioxidative defence and ionic contents. Another set was harvested at ripening to measure grain yield (GY) components. Salinity stress reduced growth, photosynthesis, water relations, antioxidants defence, enhanced free amino acids, soluble sugars, free proline and glycine betaine, hydrogen peroxide and malondialdehyde. The correlations heatmap revealed positive associations among growth, physiological and GY; being stronger in MS mode. All AsA modes reduced salinity damage, but MS was highly promising. Conclusively, maintenance of a balance in reactive oxygen species dousing and antioxidant production following tissue absorption of AsA in diminishing oxidative damage is a plausible mechanism of wheat salt tolerance.