Abstract
Supplying exogenous sulfur-rich compounds increases the content of glutathione(GSH) and phytochelatins(PCs) in plant tissues, enabling plants to enhance their cellular defense capacity and/or compartmentalize Cadmium(Cd) into vacuoles. However, the mechanism by which surplus S modulates tolerance to Cd stress in different tissues need further investigation. In the present study, we found that supplementing the tartary buckwheat(Fagopyrum tararicum) exposed to Cd with surplus S reversed Cd induced adverse effects, and increased Cd concentrations in roots, but decreased in leaves. Further analysis revealed that exogenous S significantly mitigated Cd-induced oxidative stress with the aids of antioxidant enzymes and agents both in leaves and roots, including peroxidase(POD), ascorbate peroxidase(APX), glutathione peroxidase(GPX), glutathione S-transferase(GST), ascorbic acid(AsA), and GSH, but not superoxide dismutase(SOD) and catalase(CAT). The increased Cd uptake in root vacuoles and decreased translocation in leaves of exogenous S treated plants could be ascribed to the increasing Cd binding on cell walls, chelation and vacuolar sequestration with helps of non-protein thiols(NPT), PCs and heavy metal ATPase 3(FtHMA3) in roots, and inhibiting expression of FtHMA2, a transporter that helps Cd translocation from roots to shoots. Results provide the fundamental information for the application of exogenous S in reversal of heavy metal stress.
Highlights
Cadmium (Cd) has become a primary heavy metal pollutant due to its increasing concentration in agricultural farmland, which, in turn, reduces crop production and threatens human health as it enters the food chain[1,2]
Treating tartary buckwheat with Cd promoted the production of O2− and H2O2, while net photosynthesis decreased compared to the control
CK: control plants without Cd or surplus S treatment; Cd: plants treated with cadmium; Cd + S: plants treated with cadmium and surplus sulfur
Summary
Cadmium (Cd) has become a primary heavy metal pollutant due to its increasing concentration in agricultural farmland, which, in turn, reduces crop production and threatens human health as it enters the food chain[1,2]. S is an essential nutrient element for cysteine (Cys), methionine, reduced glutathione (GSH), coenzyme A, sulfo-lipids, iron-sulfur (Fe-S) clusters, and the thioredoxin system, and plays a vital role in the stress tolerance of plants[9]. Preliminary experiments indicate that tartary buckwheat tolerates high concentrations of Cd (>200 mg·L−1 of CdCl2), and that exogenous S supplied at an appropriate concentration of 400 mg·L−1 plays an important role alleviating Cd stress. Previous studies have revealed the essential role of S in the biosynthesis of GSH, glutathione S-transferase (GST), and phytochelatins (PCs), i.e, which scavenge various ROS and/or chelate Cd to reduce the deleterious effects of Cd on plants, and decrease Cd transportation from roots to shoots[17,18,19,20]. The aim of the current study was to uncover the physiological and molecular mechanism associated with the effect of exogenous S on Cd accumulation and distribution in tartary buckwheat
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