Integrated Analysis of Metabolites and Biological Endpoints Bring New Insights into Sulfamethoxazole Stress Tolerance in Ryegrass

Although metabolomics is widely used to assess the detrimental effects of antibiotics and characterize stress response, the relationships between metabolites and biological endpoints following antibiotics remain unknown. In our study, we exposed ryegrass seeds to sulfamethoxazole for five days. The results showed that sulfamethoxazole inhibited plant growth (by 12.90-85.83%). It also decreased chlorophyll content (by 35.40-93.32%), carotenoid content (by 32.76-90.18%), and root cell permeability (by 98.43-99.29%), but increased root reactive oxygen species (ROS) concentration (increasing rate: 11.32- to 137.36-times). Moreover, high sulfamethoxazole concentrations increased superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities. To elucidate the association between metabolites and biological endpoints, we conducted an orthogonal partial least squares analysis. The results showed that sulfamethoxazole significantly altered six metabolic pathways. Among the metabolites modulated by sulfamethoxazole, amino acids mainly affected root growth and ROS concentration, whereas carbohydrates were substantially associated with the effect of sulfamethoxazole on cell permeability. Many metabolites had contrasting effects. For example, some metabolites increased root fresh weight and improved cell permeability by decreasing ROS levels and SOD, POD, and CAT activities. By contrast, some metabolites negatively affected root fresh weight and cell permeability by increasing ROS levels and SOD, POD, and CAT activities. These observations bring new insights into ryegrass responses to sulfamethoxazole-induced stress.