Mitigation of Arsenic Toxicity in Wheat by the Exogenously Applied Salicylic Acid, 24-Epi-Brassinolide and Silicon

A greenhouse investigation was performed to examine the influence of salicylic acid (SA; 0, 0.5, and 1 mM), 24-epi-brassinolide (BR; 0, 0.5, and 0.75 μM), and silicon (Si; 0, 6, and 12 mM) in alleviating arsenic (As) toxicity in wheat under different As levels (0, 50, and 100 μM). Arsenic stress enhanced electrolyte leakage (EL), activities of some critical antioxidant enzymes, and the concentrations of malondialdehyde (MDA) and hydrogen peroxide (H 2 O 2 ) as well as raised the accumulation of key organic osmolytes in wheat leaves. Indeed, application of Si and also of SA and BR considerably elevated the activities of antioxidant enzymes and the concentrations of osmolytes, and decreased the levels of H 2 O 2 and MDA as well as EL in As-stressed plants. Arsenic toxicity resulted in reduced relative water content (RWC), photosynthetic rate, stomatal conductance, transpiration, and chlorophyll content of wheat. In contrast, Si, SA, and BR improved RWC and gas exchange characteristics under varying As regimes; however, the positive effects of SA and BR were high when applied with Si. The adverse effect of As on wheat was: root > leaf > grain. Under As-stress, supplementation with Si, SA, and BR applied separately or in combination caused a significant reduction in arsenic concentration in wheat, but the effect of Si + SA and especially of Si + BR was greater than that of Si, BR, or SA applied separately. Overall, SA, BR, and Si application proved to have a great potential in improving growth and quality of wheat and reducing As content in different parts of the wheat plant under high levels of As.