A glimpse into the effect of sulfur supply on metabolite profiling, glutathione and phytochelatins in Panicum maximum cv. Massai exposed to cadmium

Sugar, amino and organic acid, glutathione (GSH) and phytochelatin (PC) content in plant tissues can be altered by S nutrition, and these metabolites have the potential to lower a plant's susceptibility to cadmium (Cd) toxicity. In the current study, our aim was to analyze the effect of S nutrition on the metabolic profile and the synthesis of GSH and PCs in Panicum maximum cv. Massai (Massai grass) used for Cd phytoextraction, since this forage grass shows fast growth, high biomass production, and adaptation to soil and climatic adversities. We evaluated in a greenhouse combinations of three S (0.1, 1.9 and 3.7 mmol L-1) and two Cd concentrations (0.1 and 0.5 mmol L-1) in nutrient solution, within a single growth period. The tissues of plants exposed to Cd showed distinct responses related to the primary metabolism. Tryptophan, lysine, and histidine were more accumulated in all tissues when Massai grass was exposed to Cd and was grown with 1.9 and/or 3.7 mmol L-1 S, which indicates that these amino acids are probably involved in Cd accumulation and detoxification in this plant. Among the sugars and sugar derivatives detected, galactinol appears to be the most active in decrease Cd-induced oxidative stress. Although there was no effect of Cd/S combinations on the expression of the genes encoding GSH1 and PCS2, the levels of GSH and PCs were strongly increased by Cd, mainly in roots and samples comprising both stem and sheath material of Massai grass and independently of different metabolic changes occurring in these tissues. Synthesis of the majority of metabolites evaluated in this study was mostly induced when Cd-exposed Massai grass was supplied with 1.9 mmol L-1 S, but more studies in field conditions are necessary to define the optimal S concentration for the plants grown in soil.