Uptake, metabolism, and transcriptome responses to 6PPD-Quinone in germinating Ipomoea aquatica

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q), a transformation product of the widely used tire antioxidant 6PPD, has emerged as a ubiquitous environmental contaminant with potential risks to agroecosystems and food safety. This study systematically investigated 6PPD-Q uptake, translocation, transformation, and transcriptomic responses in the germinating leafy vegetable Ipomoea aquatica. In low, medium and high exposure groups, 6PPD-Q preferentially accumulated in roots, reaching concentrations of 17.8 ± 0.7, 55.3 ± 2.9 and 1414.5 ± 17.3 ng/g, respectively. High exposure to 6PPD-Q significantly inhibited seed germination and biomass accumulation, concomitant with the induction of oxidative stress. Nineteen 6PPD-Q transformation products were identified (e.g., C₁₈H₂₂N₂O₃, C₂₂H₂₇N₅O₉S, C₂₄H₃₄N₂O₇, C₁₂H₂₀N₂O, and C₇H₁₃NO₃), revealing novel metabolic pathways including glycosylation, methoxylation, glutathionylation, oxidization, and carboxylation. Notably, several transformation products (e.g., C₁₉H₂₄N₂O₂, C₁₈H₂₄N₂O) were predicted to be more toxic than the parent compound based on ECOSAR modeling, highlighting a potential secondary risk. Transcriptomic analysis suggested that the up-regulated genes encoding ABC transporters, cytochrome P450s, glutathione S-transferases, peroxidases, and UDP-glycosyltransferases likely played a role in the transmembrane transport and metabolic transformation of 6PPD-Q. Furthermore, the up-regulation of antioxidant genes and down-regulation of stress responsive genes indicated that 6PPD-Q exposure disrupted the balance between growth and stress defense. This study provides a comprehensive metabolic and molecular framework for understanding the fate of 6PPD-Q in an edible plant.