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 (Zea mays 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 S-transferase (GST) activity. Molecularly, CSA upregulated nine GST genes, competitively bound to ZmALS1/2, 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.