The Mechanistic Basis of Sulfur-mediated Alleviation of Pb Toxicity in Wheat

Even though lead (Pb) poses a hazard to the plants, an eco-friendly strategy in reducing Pb toxicity in wheat has received little attention. The purpose of this work was to define the effect of sulfur (S), a critical nutrient element, in reducing Pb toxicity in wheat plants. S reduced the adverse effects of Pb on root biomass, cellular integrity, redox status and chlorophyll score. The exogenous S also restored the Fe status accompanied by the upregulation of TaNAS1 and TaDMAS1 genes in roots. The ICP-MS analysis revealed that Pb concentrations increased in the root, shoot, and vacuole but not in the cell wall subjected to Pb-toxicity compared to the plants cultivated without Pb and S. In addition, cysteine, glutathione, and phytochelatin were increased together with the induction of TaGST and TaPCS1 genes in roots subjected to the dual application of Pb and S. It implies that higher glutathione levels caused by S may allow phytochelatin to bind with excess Pb, resulted in the subcellular sequestration in the root vacuole. S can also stimulate the S‑metabolites in Pb-exposed wheat to restore redox equilibrium. These findings can be used to promote the usage of S and to develop Pb-free wheat through breeding and transgenic initiatives.