Morphological, physiological, and molecular responses of Perilla frutescens to copper stress alleviated by PVC microplastics.

Microplastics (MPs) and copper (Cu) are common co-pollutants in agricultural environments, yet their combined effects on plants remain poorly understood. This study investigated the individual and interactive impacts of Cu and polyvinyl chloride (PVC)-MPs on Perilla frutescens, a heavy metal hyperaccumulator and economically important crop, using hydroponic experiments. Low Cu concentrations (<2 mg L) promoted growth, whereas higher levels (>2 mg L) induced leaf chlorosis, curling, and root decay. PVC-MPs alone exhibited phytotoxicity only at high concentrations (>1000 mg L). In combined treatments, 10-100 mg L PVC-MPs alleviated Cu-induced chlorosis and increased leaf area, though higher MP concentrations suppressed root growth. Physiologically, Cu stress impaired photosynthesis, enhanced antioxidant enzyme activity, and increased osmoregulatory substance content. PVC-MPs counteracted these effects by improving photosynthetic efficiency, enhancing peroxidase activity, and reducing osmotic stress markers. Transcriptomic analysis revealed that PVC-MPs upregulated endocytosis-related genes while downregulating jasmonic acid (JA) biosynthesis and lipid metabolism pathways. ABC transporter genes were differentially expressed, functionally linked to these processes. We demonstrate for the first time that PVC-MPs mitigate Cu stress via three synergistic mechanisms: enhanced membrane trafficking (endocytosis activation), suppression of stress-signaling phytohormones (JA), and lipid metabolism reprogramming. These findings redefine MPs' dual role as both pollutants and unexpected alleviators of metal toxicity. While these findings reveal MPs' unexpected capacity to alleviate metal stress, their persistent environmental accumulation necessitates comprehensive risk-benefit analysis and long-term ecological monitoring-highlighting the imperative for science-based evaluation rather than promoting field applications of MPs as stress mitigants.