Temporal dynamics of sulphur mediated alleviation of lead toxicity in Brassica juncea

Sulphur amelioration effectively mitigated lead toxicity in Brassica juncea L. by reducing oxidative stress and enhanced antioxidant defense, photosynthesis by detoxifying the lead accumulation. The current study was conducted to study physiological, yield and redox regulation under exogenous effect of sulphur (S1; 100 ppm, S2: 200 ppm) in lead stressed (Pb1; 100 ppm, Pb2; 200 ppm, Pb3; 300 ppm) Brassica juncea L. (RH 749) at 30, 60, 90 days after sowing (DAS). Lead stress of 300 ppm increased malondialdehyde (MDA) by 30.93, 32.73, 34.82% and electrolyte leakage (EL) 204, 116, 94.3% at 30, 60, 90 DAS, respectively. Moreover Pb3 stress increased ascorbic acid (AsA), glutathione (GSH) and phytochelatins by 53.1, 27.96, 362.73% at 90 DAS, respectively. Lead stress decreased yield and physiological parameters, such as transpiration rate, photosynthetic rate and stomatal conductance, by 33.6, 20.76, 33.36%, respectively, at 90 DAS. Besides, S2 spray to Pb3-stressed plants decreased MDA 13.49 and EL by 18.62%, respectively, at 90 DAS. Exogenous sulphur treatment further steadied the cellular homeostasis by increasing transpiration, photosynthesis, oil content and yield. Under Pb stress sulphur assimilating enzymes ATPS and GST increased. As a result of S assimilation in plants AsA, GSH and phytochelatins synthesis also increased and detoxified the toxic Pb. Besides, transcriptomic studies of BjATPS increased under Pb stress and S spray almost doubled fold expression and provided resistance to the plant. The present study concludes that S application alleviates Pb stress in Brassica seedlings by regulating oxidative biomarkers and antioxidants thus improving yield constraints and suggests that S could be a suitable choice for farmers in mitigating Pb toxicity in Brassica, where S not only employs in defense mechanisms against metal stress, but also regulates plant growth and development.