Brassinosteroids alleviate cadmium phytotoxicity by minimizing oxidative stress in grape seedlings: Toward regulating the ascorbate-glutathione cycle

Brassinosteroids are widely used to combat several environmental factors, including heavy metal stress in plants, however the effects on alleviating cadmium (Cd) phytotoxicity in grape seedlings are unknown. This study was designed to investigate the effect of 24-epibrassinolide (EBR) on chlorophyll fluorescence, antioxidant system and gene expression in grape (vitis vinifera L.) plants under Cd stress. The grape seedlings were treated with half strength Hoaglands nutrient solution, 1 mM Cd2+ (CdCl2) and Cd2+ combination with EBR (0.05 mg/L, 0.1 mg/L, 0.2 mg/L). Oxidative stress caused by higher biosynthesis of reactive oxygen species (ROS) and malondialdehyde (MDA) damaged the morphological features and photosynthesis of grape seedlings under Cd toxicity. However, EBR treatment alleviated the Cd stress injury symptoms, increased the maximal photochemical efficiency of PS II (Fv/Fm), photochemical quenching coefficient (qP) and actual PS II photochemical efficiency (phi PSII), reduced the levels of superoxide anions (O-2(center dot-)), hydrogen peroxide (H2O2), and MDA, increased the contents of antioxidants and osmolytes and enhanced the activities of guaiacol peroxidase (POD), superoxide dismutase (SOD), and antioxidases involved in the ascorbate-glutathione (AsA-GSH) cycle. Furthermore, the expression levels of VvSOD, VvPOD, VvAPX, VvGR, VvDHAR and VvMDHAR genes were upregulated in EBR treated grape seedlings under Cd stress. Here, principal component analysis showed that amelioration of Cd-induced oxidative stress by EBR treatment in grapevine seedlings is mainly by regulating AsA-GSH cycle, and the Cd stress alleviation effect of EBR was more prominent at 0.05 mg/L than at 0.1 mg/L and 0.2 mg/L. Taken together, our results suggest that applying EBR can mitigate Cd toxicity in grape seedlings via ASA-GSH cycle and advocate a positive role for EBR in strengthening phytoremediation.