Multifaceted Mechanisms of Cyprosulfamide in Mitigating Mesosulfuron-Methyl Phytotoxicity in Maize Seedlings: GST Activation, Oxidative Stress Alleviation, and Target-Site Competition

Mesosulfuron-methyl (MS), a sulfonylurea herbicide used in wheat, poses significant residual phytotoxicity risks to subsequent maize (<i>Zea mays</i> L.) crops. This study evaluated the protective role of the safener cyprosulfamide (CSA) through physiological, biochemical, and molecular analyses. MS treatment drastically reduced maize shoot length and fresh weight by 80.74% and 74.24%, respectively, while CSA pretreatment significantly relieved these inhibitory effects, with the mitigation rates of shoot length and fresh weight reaching 66.3% and 63.57%, respectively. Physiologically, CSA alleviated MS-induced chlorophyll and carotenoid losses and reduced oxidative stress by lowering malondialdehyde (MDA) levels (23.39% at 6 days after sowing) while enhancing superoxide dismutase (SOD) and glutathione <i>S</i>-transferase (GST) activity. Molecularly, CSA upregulated nine GST genes, competitively bound to <i>ZmALS1/2</i>, increasing acetolactate synthase (ALS) activity by 70-146%, and reduced MS residues in shoots (4.02%) and roots (33.78%). These findings demonstrate CSA's multifunctional detoxification mechanism, combining gene activation, antioxidant regulation, and target-site competition, offering a viable strategy to mitigate herbicide carryover in crop rotations. CSA application could significantly reduce MS phytotoxicity, advancing sustainable herbicide management.