The Impacts of Gallic Acid on Redox State of Antioxidants Related to Ascorbate–Glutathione Cycle in Wheat (Triticum aestivum) Grown Under Cadmium Toxicity

Abstract

This work was conducted to define the efficacy of gallic acid (GLA) on growth, water management, ROS content, the antioxidant capacity including ascorbate–glutathione cycle and their redox state and lipid peroxidation (TBARS) in wheat grown under cadmium (Cd) toxicity. Germinated wheat was hydroponically grown for 21 days (d) and was treated with the combination form and alone of GLA (25 and 75 μM) and Cd stress (100 and 200 μM) for 7 d. The findings revealed that the decrement on growth, water content and proline content was observed under stress. The decreases were reversed by GLA applications. Despite the increased superoxide dismutase (SOD) activity, stress caused an inactivation of catalase (CAT), peroxidase (POX), glutathione reductase (GR) and NADPH oxidase (NOX) but, only ascorbate peroxidase (APX) activity was induced. APX activity was not enough for scavenging of Cd-induced hydrogen peroxide (H2O2) content. Therefore, in stress-treated wheat, the enhancement in TBARS content was detected. After GLA applications to plants exposed to stress, the increased H2O2 content by the activation of SOD and NOX was eliminated by the activities of APX, GR, monodehydroascorbate reductase and dehydroascorbate reductase and glutathione (GSH) rather than CAT and POX enzymes. From this study, we conclude that 25 μM GLA was more effective in protection against the damages triggered by both Cd treatments by maintaining the pool of ascorbate and glutathione, decreasing TBARS levels and improving the scavenging activity of hydroxyl radical. The redox state of enzymes/non-enzymes antioxidants including ascorbate–glutathione cycle was also induced by 75 μM GLA under low Cd concentration.