Antioxidant Machinery and Glyoxalase System Regulation Confers Salt Stress Tolerance to Wheat (Triticum aestivum L.) Plants Treated with Melatonin and Salicylic Acid

Plant growth regulators melatonin (MT) and salicylic acid (SA) have potent roles in plant salt tolerance. However, only a few reports have studied the influence of their combined treatment on plant salt tolerance. The current study, as a first investigation, was aimed to evaluate the effect of MT and SA combined treatment on the antioxidant and glyoxalase defense machineries of salt-stressed wheat plants. In the present study, the potential role of 70 mu M MT and/or 75 mg l(-1) SA on mitigating salt injury (6.0 and 12.0 dS m(-1) salinity levels) was investigated in wheat (Triticum aestivum L. cv. Sids 14). Exogenously applied MT and/or SA improved the activity of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, glutathione peroxidase, and glutathione S-transferase, which effectively scavenged reactive oxygen species (ROS) in stressed plants. Excessive accumulation of the toxic methylglyoxal was reversed via the upregulation of the glyoxalase system (glyoxalase I and glyoxalase II) and the ascorbate-glutathione cycle. Foliar applications also reduced membrane damage by lowering lipid peroxidation and protein oxidation due to effective ROS detoxification by antioxidants such as ascorbate, glutathione, phenols, and flavonoids. Moreover, exogenous MT and/or SA applications increased endogenous MT and SA levels under both non-saline and saline conditions. The combined treatment of MT and SA yielded the best results. Overall, this combined treatment regulated the antioxidant machinery and glyoxalase system, suggesting a role for it in salt stress mitigation. Therefore, it can be considered as an effective method for reducing salt toxicity in sustainable agricultural systems.