24-epibrassinolide regulates oxytetracycline-induced phytotoxicity and its detoxification mechanism.

Oxytetracycline (OTC), a crop-absorbable antibiotic, poses a health risk to humans through the food chain. Conversely, 24-epibrassinolide (EBL), a plant growth hormone, mitigates the toxic effects of various pollutants on plants. However, the mechanism by which exogenous EBL affects the growth of rape seedlings exposed to OTC remains largely unknown. In this study, we found that environmental OTC concentrations significantly inhibited plant growth and metabolism, whereas exogenous EBL could restore plant growth characteristics. Exogenous EBL significantly decreased reactive oxygen species (ROS) accumulation, alleviating OTC-induced cell membrane lipid peroxidation. This was achieved by increasing the antioxidant capacity and secondary metabolism levels. Notably, our findings suggested that EBL stimulated glutathione S-transferase (GST) and glutathione reductase (GR) activities, enhancing reduced glutathione synthesis and participating in plant OTC detoxification. OTC residues in EBL + OTC-treated seedlings at 21 d were significantly reduced by 29 % compared with OTC alone. Further transcriptomic and metabolomic analyses revealed that the differentially expressed genes and metabolites in the EBL and OTC alone or combined treatment groups were primarily involved in the regulation of phenylpropanoid biosynthesis, glutathione metabolism, and lant hormone signal transduction pathways in response to phytotoxic effects and detoxification mechanisms, as compared to the control group.