Buckwheat responds to co-exposure to PLA microplastics and Pb by regulating the synthesis of unsaturated fatty acids and jasmonates.

Polylactic acid (PLA) microplastics (MPs) and lead (Pb) co-contamination, an emerging co-contamination, may profoundly impact plant growth. We aimed to evaluate the effects of PLA-MPs and Pb on buckwheat growth and physiology and to elucidate the underlying molecular mechanisms through an integrated transcriptomic and metabolomic approach. PLA-MPs alone reduced buckwheat biomass by 26.0 %, while combined exposure to Pb and PLA-MPs (PLA-Pb) further exacerbated morphological impairments, decreasing biomass by 43.1 % and 50.4 % compared to the control. Antioxidant enzyme activities increased under Pb and PLA-Pb treatments. The analysis revealed 536 differentially expressed metabolites (DEMs) and 3229 differentially expressed genes (DEGs) in PLA-Pb vs. control, 168 DEMs and 1555 DEGs in PLA-Pb vs. PLA, and 196 DEMs and 4057 DEGs in PLA-Pb vs. Pb. Key DEGs involved in lignin biosynthesis, including caffeoyl-CoA-O-methyltransferase, cinnamoyl-CoA reductase, and catechol-O-methyltransferase, were upregulated, suggesting that buckwheat mitigates toxicity by enhancing cell wall modification. Similarly, DEGs and DEMs linked to jasmonate biosynthesis were enriched in the alpha-linolenic acid metabolic pathway, including allene oxide synthase, allene oxide cyclase, and 12-oxophytodienoate reductase, as well as methyl jasmonate. These results suggest that buckwheat counters PLA-MPs-Pb toxicity by enhancing oxidative stress responses and upregulating the synthesis of lignin and unsaturated fatty acids. In conclusion, this study provides novel insights into the molecular mechanisms of plant detoxification under PLA-MPs-Pb co-exposure, highlighting the need for ecological risk assessment of combined microplastic and heavy metal pollution.