The protective effect of exogenous salicylic and gallic acids ameliorates the adverse effects of ionizing radiation stress in wheat seedlings by modulating the antioxidant defence system.

Plant growth regulatory substances play a significant role in maintaining developmental and physiological processes in plants under abiotic stress. Apart from traditional plant hormones, the phenolic acids, salicylic acid (SA) and gallic acid (GaA), are emerging players with pivotal roles in alleviating various environmental perturbations. The present study compared the stress alleviation effect of these two phenolic acids in wheat (Triticum aestivum L. 'Gönen-98') seedling whose seeds were used in this study pre-treated with increasing doses of gamma irradiation (IR, 100 > 400 Gy). Leaves from seedlings hydroponically grown for 10 days in medium containing 100 μmol/l SA and GaA were used in the measurements and determinations. Accordingly, exogenous treatment with SA and GaA significantly improved plant growth and photosynthetic activity and regulated stress-induced osmolyte accumulation against γ-irradiation. Treatments also led to significant reductions in TBARS and HO contents. Antioxidant enzyme activities were further stimulated by SA and GaA treatment in comparison to IR alone. The phenolic pool including phenolic acids and GSH content in whole seedlings were promoted by IR and further SA and GaA applications. Contents in phenolic acids liberated from soluble free, soluble ester-conjugated and soluble glycoside-conjugated SA and GaA contents in roots and leaves increased following SA and GaA treatments alone in comparison to the control and IR groups. The present results indicate that SA and GaA can alleviate the ameliorative effects of IR, leading to further oxidative stress, and can improve the tolerance of stressed wheat seedlings by stimulating enzymatic and non-enzymatic antioxidant defence system components.