Application of Brassinosteroid Mimetics Improves Growth and Tolerance of Maize to Nicosulfuron Toxicity

Pesticide residues, especially for herbicides, often damage crops, except for weeds, which results in reduced production or even death in agriculture. Brassinosteroids (BRs) can alleviate the injury from pesticide stress and enhance the growth of plants. However, the roles of low-cost BR mimetics in alleviation and protection from herbicide (nicosulfuron, NSF) stress in maize remain unclear. To investigate the effects of brassinosteroid mimetics on the growth of NSF-stressed plants, we treated maize seedlings with bikinin and brazide at 10 µM prior to NSF treatment, and epibrassinolide (EBL) as a positive control. The NSF treatment dramatically reduced the height, root length, and biomass of maize, and significantly influenced photosynthetic activity and pigments. Accumulation of reactive oxygen species (ROS) and membrane lipid peroxidation, enhanced activity of antioxidant, and detoxification-related enzymes were also observed under NSF stress. As compared to NSF-induced plants, foliar application of bikinin and brazide significantly increased biomass, photosynthesis, and antioxidant enzymes activities and decreased the ROS levels by more than 32.3%, the similar effects as EBL. The glutathione content genes ( GST1, ABC-2, ALS1) involved in detoxification in the BR mimetics + NSF-treated plants were higher than those of NSF alone. Reduced levels of NSF residues by more than 55% after 3 days were observed as a result of BR mimetics pretreatment. In summary, our results present a new pattern of roles of BR mimetics, which display the potential protection of plants under pesticide stress.