Exogenous 24-epibrassinolide alleviates zinc-induced toxicity in eggplant (Solanum melongena L.) seedlings by regulating the glutathione-ascorbate-dependent detoxification pathway

Excessive zinc (Zn) uptake is toxic to both plants and animals. 24-Epibrassinolide (EBL), a plant steroid hormone, plays a pivotal role in regulating plant resistance to various stresses. In this study, the effects of EBL on oxidative stress and components of the ascorbate-glutathione (AsA-GSH) cycle in the leaves of eggplant (Solanum melongena L.) seedlings were investigated under Zn stress. Exogenous 0.1 mu M EBL significantly alleviated the oxidative damage caused by Zn stress, as reflected by increased plant growth and decreased accumulations of Zn, hydrogen peroxide (H2O2), and malondialdehyde (MDA). In addition, components of the AsA-GSH metabolism cycle, such as the concentrations of reduced ascorbic acid (AsA) and glutathione (GSH), as well as the activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), and glutathione synthetase (GS), increased significantly in the presence of EBL under Zn stress. Moreover, exogenous EBL caused a significant increase in the levels of expression of the DHAR, MDHAR, GR, and GS genes in the AsA-GSH cycle during Zn toxicity, showing that EBL could regulate the regeneration of AsA and GSH at the transcriptional level. Taken together, the results of the present study suggest that exogenous EBL confers resistance against Zn-induced oxidative damage by enhancing the ASA-GSH cycle by up-regulating key gene expression and key enzyme activities.