Polystyrene nanoplastics regulate flavonoid biosynthesis in Salvia plebeia through coordinated responses of plant physiology, rhizosphere microenvironment, and microbial communities

Abstract

Despite the increasing prevalence of plastic-derived nanoplastics (NPs) as emerging environmental stressors in agricultural systems, their impacts on bioactive compound production and quality formation in industrial medicinal crops remain largely unexplored. Salvia plebeia R.Br. (S. plebeia), a flavonoid-rich medicinal species with considerable potential as a high-value industrial crop for bioactive ingredient production, was used to investigate the effects of polystyrene NPs (PS NPs) on plant growth, secondary metabolism, and rhizosphere regulation. Confocal imaging revealed treatment-associated fluorescence in root and leaf tissues, suggesting the potential uptake and root-to-shoot translocation of fluorescently labeled PS NPs. PS NP exposure significantly inhibited plant growth and photosynthetic performance, with pronounced reductions in leaf biomass, leaf area, and net photosynthetic rate under high exposure levels. In contrast, moderate exposure (100 mg/kg) stimulated secondary metabolism, increasing total flavonoids by 46.3% and enhancing the accumulation of homoplantaginin, hispidulin, and nepetin. Antioxidant enzymes exhibited a hormetic response, with activation at low NPs concentrations (< 100 mg/kg) and inhibition under severe stress. Synchrotron radiation FTIR imaging revealed pronounced redistribution of organic functional groups across the root-rhizosphere interface. Rhizosphere bacterial communities were also significantly restructured (R² = 0.535, P = 0.006), demonstrating close association with antioxidant responses and flavonoid-related gene expression. This study reveals a multi-scale mechanism linking PS NP exposure with plant physiology, rhizosphere processes, and flavonoid biosynthesis, providing new insight into environmental regulation of medicinal quality and supporting the sustainable cultivation and industrial utilization of flavonoid-rich S. plebeia.