Nanoplastics enhance tebuconazole toxicity in lettuce by promoting its accumulation and disrupting phenylalanine metabolism: Importance of Trojan horse effect

Nanoplastics (NPs) are ubiquitous in agricultural environments and may exacerbate environmental risks of pesticides. This study investigates how NPs influence the toxicity of tebuconazole in lettuce. In a hydroponic model, NPs (10 and 50 mg/L) enhanced tebuconazole accumulation in roots and exacerbated its toxicity. To elucidate the underlying mechanisms, a combination of in vivo, in vitro, and in silico models was employed. The results indicated that NPs were taken up by roots through apoplast pathway, predominantly accumulating in roots (35.6-40.7 %) due to aggregation in root sap and adhesion to cell wall. Tebuconazole adsorbs onto NPs with a high adsorption capacity (123.7 mg/g), enabling NPs to serve as carriers that facilitate tebuconazole entry into roots. Once in the root sap, tebuconazole desorbed from NPs and accumulated in cell walls, leading to higher residue in the roots (7.19-9.85 mg/kg). Furthermore, tebuconazole bound to key proteins involved in auxin biosynthesis (e.g., YUC) and signaling (e.g., TIR), thereby inhibiting tryptophan-dependent auxin biosynthesis pathway and disrupting TIR1/AFB-mediated auxin signaling. Additionally, tebuconazole suppressed the phenylalanine pathway, reducing antioxidant secondary metabolites such as flavonols. When NPs are present, co-exposure intensified the inhibition of auxin and phenylalanine pathways, thereby amplifying the toxicity of tebuconazole, as evidenced by impaired plant phenotypes (e.g., biomass, root tips) and disrupted antioxidant systems. This study reveals threats posed by NPs and tebuconazole in agricultural systems and highlights the novel carrier effect of NPs in enhancing tebuconazole toxicity, emphasizing the urgent need to assess the fate and toxicity of NPs and coexisting pollutants.