Combination of transcriptomics, metabolomics and physiological traits reveals the effects of polystyrene microplastics on photosynthesis, carbon and nitrogen metabolism in cucumber (Cucumis sativus L.)

Although microplastic pollution has been widely studied, the mechanism by which they influence plant photosynthesis and carbon and nitrogen metabolism remains unclear. We aimed to explore the effects of polystyrene microplastics (PS) on photosynthesis and carbon and nitrogen metabolism in cucumber using 5 mu m and 0.1 mu m PS particles. The PS treatments significantly reduced the stability of cucumber mesophyll cells and photosynthetic parameters and increased the soluble sugar content in cucumber leaves. The 5 mu m PS affected the photosynthetic pathway by changing the expression of enzyme genes required for the synthesis of NADPH and ATP, which decreased the photosynthetic capacity in cucumber leaves. However, 0.1 mu m PS altered the genes expression of phosphoenolpyruvate carboxykinase (PEPCK) and phosphoenolpyruvate carboxylase (PEPC), which affected the intercellular CO2 concentration and attenuated the negative effects on photosynthetic efficiency. Additionally, PS reduced the expression levels of nitrate/nitrite transporter (NRT) and nitrate reductase (NR), reducing the nitrogen use efficiency in cucumber leaves and mesophyll cells damage through increased accumulation of reduced glutathione (GSH), y-glutamylcysteine (y-GC), and citrulline. This study provides a new scientific basis for exploring the effects of microplastics on plant photosynthesis and carbon and nitrogen metabolism.