Silicon Alleviates Nickel-Induced Oxidative Stress by Regulating Antioxidant Defense and Glyoxalase Systems in Mustard Plants

Soil polluted with heavy metals is a continuous threat to global crop production. The present study deals with growth, biochemical attributes, photosynthetic pigments, antioxidant responses and gyloxalase systems of mustard plants under varying concentrations of nickel (Ni) stress. Ni stress (150 µM) reduced growth (shoot length by 34.46% and root length by 52.49%), chlorophyll (57.63%), gas exchange parameters (P_N by 36.84%, A by 55.61%), leaf relative water content (LRWC by 24.34%), and enhanced hydrogen peroxide (H₂O₂ by3.23 fold) malondialdehyde (MDA by 2.07 fold), and methylglyoxal (MG by 3.32 fold) content. Si (10^{− 5} M) application ameliorated the negative effects of Ni on growth, chlorophyll content, photosynthetic traits and also elevated the activities of antioxidant enzymes and enzymes associated with the ascorbate glutathione (AsA-GSH) cycle and glyoxylase systems. Nevertheless, Si application to Ni-stressed plants had an additive effect on the enzyme activities of antioxidants and enzymes of AsA-GSH cycle. Exogenous Si supplementation elevated endogenous Si content which decreased root to shoot Ni translocation and maintained optimum osmolyte and secondary metabolite accumulation. We conclude that Si-induced Ni stress tolerance in mustard plants could be correlated with the upregulation of enzymes associated with antioxidant defence, glyoxalase detoxification systems and sufficient primary and secondary osmoprotectant accumulation.