Unveiling Underlying Mechanisms of Root Uptake, Bidirectional Translocation, and Biotransformation of Tire Rubber-Derived 6PPD and 6PPD-Q in Wheat ( Triticum aestivum L.): Implications by Nontarget Screening, Transcriptomics, and Molecular Docking

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its derivative 6PPD-quinone (6PPD-Q) are emerging pollutants in the environment due to widespread usage of tire rubber-related products, yet their uptake, translocation, and biotransformation behaviors in plants remain elusive. Here, we systematically investigated the uptake, translocation, and biotransformation mechanisms of 6PPD and 6PPD-Q in wheat. Results demonstrated that 6PPD and 6PPD-Q could be taken up by roots via apoplastic and symplastic pathways. Transmembrane transport of 6PPD and 6PPD-Q was found to enter the vascular bundle in roots, which was mediated by water and anion channels for 6PPD, and anion channel and energy-dependent active transport for 6PPD-Q. Split-root experiments revealed the bidirectional translocation of 6PPD and 6PPD-Q between roots and shoots, and secretion back into the environment from roots. Furthermore, four degradation products, including 6PPD-Q, were detected for 6PPD via nontarget screening. Transcriptomic and molecular docking analysis consistently indicated that the aquaporins and NRT2 transporter participated in root uptake of 6PPD and 6PPD-Q, respectively, and the SWEET transporter mediated their translocation in shoots. In addition, CYP450 enzymes were involved in the biotransformation of 6PPD to 6PPD-Q. Our findings verify the bioaccumulation and biotransformation of 6PPD and 6PPD-Q in plants, which highlight attention to the transfer of tire antioxidants along the food chain.