Brassica chinensis L. response to polypropylene microplastics via photosynthetic and antioxidant systems: A combined analysis of transcriptomic and metabolomic.

Soil currently stores an estimated 20 %-42 % of the world's plastics. Microplastics (MPs) released during plastics decomposition are readily adsorbed by the soil because of their small size, large specific surface area, and other characteristics, potentially generating ecological risks. Recent studies have demonstrated that polypropylene microplastics (PP-MPs) in farm soils markedly alter plant growth and development. The present study combined transcriptomic and metabolomic analysis to clarify the defensive mechanism of Brassica chinensis L. to PP-MPs. PP-MPs notably decreased chlorophyll and carotenoid content, while showing no impact on biomass accumulation. Antioxidant enzyme activities (catalase (CAT) and superoxide dismutase (SOD)) markedly increased after 20 days and escalated with rising PP concentrations. CAT and SOD activities rose significantly by 28.10 % and 12.25 %, respectively, at 0.2 % PP, whereas malondialdehyde (MDA) content decreased by 4.28 %. Transcriptome and metabolome data revealed that PP-MPs influenced antioxidant-related genes and metabolites in B. chinensis. Among these, the gene encoding the enzyme aldehyde dehydrogenase (ALDH) and the metabolite phosphatidyl-1D-myo-inositol showed the most significant up-regulation, increasing by 31.3664 and 2.9366-fold, respectively, at 20 days compared to CK. PP-MPs altered pathways such as stimulus response and metabolic processes by inducing up-regulation. The differential expression of genes encoding the photosynthetic enzyme RuBisCO influenced chlorophyll content and photosynthesis directly or indirectly, with five and four genes exhibiting down-regulation at 20 and 40 days, respectively. Alterations in the energy transfer system supported both antioxidant activity and photosynthesis in rapeseed. These changes in pathways also regulated plant growth and development.