Impact of different sulfur sources on cadmium accumulation and metabolic responses of glutathione and cysteine in peppers
Guilan Peng, Hongyan Liu, Yue Liu, Qun Zhao, Ghulam Rasool
Abstract
Sulfur (S) is essential for life while cadmium (Cd) is known to be both extremely toxic and ubiquitous in natural environments. Interactions between S and Cd from soil to plant could provide insights into the dynamics of environmental contaminants and the mechanisms of regulation. Geological sulfur from pyrite (FeS2) and atmospheric sulfur from coal combustion deposits (H2SO4) significantly affect soil acidification, potentially increasing the bioavailability of Cd. To investigate the influence of different sulfur sources on cadmium (Cd) uptake, transfer, accumulation, and the regulation of physiological responses in pepper, we conducted a controlled pot experiment. The study utilized yellow soil and 'Z2' line pepper (Capsicum spp.) as the test plant. We assessed the fresh weight, Cd concentration in various plant parts, and the levels of reduced glutathione (GSH) and cysteine (Cys) during the fruiting phase under varying concentrations of Cd. Under Cd stress, supplementation with FeS2 and H2SO4 markedly enhanced pepper growth, increasing biomass by over 30%. Among these, geological sulfur (FeS2) demonstrated a more pronounced effect compared to H2SO4. Overall, the cadmium content of each part of FeS2 treatment was lower than H2SO4 under cadmium-induced stress. And at medium cadmium level, a concentration of 100 mg/kg of FeS2 resulted in a 16.51% relative reduction in fruit Cd content from 2.12 mg/kg in the 1.5 mg/kg Cd treatment to 1.78 mg/kg. Both sulfur sources increased GSH and Cys content, particularly under high Cd stress, with FeS2 raising GSH and Cys levels by 3.33–61.87% and 43.29–71.94%, H2SO4 increased 15.65–66.43% and 48.02–74.58%, respectively (P ≤ 0.05). The highest GSH content occurred in leaves, whereas fruits had the highest Cys content. FeS2 and H2SO4 can promote pepper growth and enhancing the synthesis of GSH and Cys, which mitigates Cd toxicity. On the whole, the cadmium content of each part of FeS2 treatment was lower than H2SO4 under cadmium stress conditions.