The multifaceted mechanisms of microplastic inhibition of tomato plant growth: oxidative toxicity, metabolic perturbation, and photosynthetic damage

The ubiquity of microplastics (MPs) currently endangers vegetation, ecological balance, and public health. Although biodegradable plastics (BP) are potential alternatives to conventional plastics, the mechanisms underlying their effect on plants remain unclear. This study investigated the effect of biodegradable MPs (BMPs) on tomato seedlings, focusing on oxidative stress, leaf metabolism, and photosynthetic pigment synthesis. BMPs (poly (butylene adipate-co-terephthalate) (PBAT) and polylactic acid (PLA)) had a significant negative effect on tomato seedling growth compared to conventional MPs (polyethylene (PE) and polypropylene (PP)). The findings indicated that BMPs could exert stronger toxic effects on tomato seedlings than conventional MPs, as demonstrated by integrated biomarker response indices. The high degree of oxidative toxicity severely disrupts leaf metabolism, particularly the amino acid, lipid, and tricarboxylic acid (TCA) cycle. Photosynthetic pigment synthesis was inhibited more by BMPs, with key gene expression in chlorophyll (Chl) and heme pathways down-regulated, decreasing the precursor content. Exposure to BMPs Chl a and b levels were reduced by 5.25 %-43.75 % and 24.74 %-56.25 %, respectively, compared with conventional MPs. Findings from this study enhance our understanding of food safety risks associated with BMPs.