Effects of quinolone antibiotics on spearmint (Mentha spicata L.) cuttings: Insights into growth, biological activity, and computational modeling perspectives

The increasing global consumption of quinolone antibiotics (QNs) has raised growing concern. However, research on the toxicity and quality-altering effects of QNs on medicinal plants remains scarce, particularly under combined exposure to QNs. In this study, spearmint ( Mentha spicata L.) was exposed to norfloxacin (NOR), ofloxacin (OFL), and combined NOR and OFL treatments for 45 d at three environment-related concentrations (0.01, 0.1, and 1 mg·L −1 ). The phenotypic, physio-biochemical, secondary metabolite indicators, and in vitro antioxidant capacity were determined. The results revealed a hormesis effect on plant height, root length, and leaf area. The combined treatments mainly showed antagonistic effects on the indicators and had a greater impact on phenotypic indicators. At the biochemical level, QNs exposure triggered oxidative stress responses. The content of total phenols and flavonoids in leaf extracts increased significantly, and the relative proportion of terpenes decreased slightly. The dose-/treatment-type dependent toxicities of QNs to spearmint and the antioxidant capacity of leaf extracts (free radical scavenging rate and ferric ion reducing antioxidant power) were evaluated comprehensively. Molecular docking and molecular dynamics simulations indicated that OFL treatment exhibited stronger binding affinity and enhanced stability with target protein receptors compared to NOR, for higher antioxidant capacity. Spearmint growth deteriorated more sharply than the increase in antioxidant capacity as antibiotic concentrations rose. Notably, there was no significant correlation between plant growth profiles and antioxidant capacity. These findings provide new insight into the changes in ecotoxicology and biological activities in medicinal plants caused by antibiotic pollutants. • Quinolone antibiotics exhibit dose-/treatment-type-dependent toxicity on spearmint. • Antioxidant capacity of the extract rises under individual and combined treatments. • Computational simulations reveal mechanisms of antioxidant capacity enhancement. • The growth has no significant relevance to antioxidant capacity by model analysis.