Sulfur mitigates lead toxicity through phytochelatin-driven vacuolar sequestration and antioxidant defense in mustard (Brassica juncea)

Abstract

Lead (Pb) toxicity is a serious concern for edible crops, soil, and the environment. Therefore, an eco-friendly, cost-effective strategy is highly in demand to mitigate Pb toxicity in plants and provide health benefits for humans. This study aimed to explore the impact of exogenous sulfur (S) in mitigating Pb toxicity in mustard. Pb toxicity severely inhibited mustard growth, development, biomass yield, chlorophyll content, and photosynthetic attributes (Fv/Fm, Pi_ABS) in mustard. Interestingly, exogenous S considerably restored these morpho-physiological attributes in mustard. The concentration of S declined under Pb stress, and it was restored after exogenous S supplementation to roots and shoots, suggesting that S is actively involved in regulating Pb and S accumulation and homeostasis processes in mustard plants. Additionally, S supplementation in Pb-exposed plants induced the antioxidant activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), as well as the concentrations of glutathione (GSH) and phytochelatin (PC) in roots. Given the binding affinity of PC with toxic metals, the reduction of Pb in the aerial part may result from the vacuolar sequestration of Pb, mediated by elevated PC synthesis in the roots of mustard supplemented with S. These overall findings might be useful for oilseed crop breeders and farmers to apply S-amendments in Pb-free edible crop production.