6PPD-Quinone Triggers Oxidative Stress, Metabolic Reprogramming, and Rhizosphere Microbiota Shifts in Wheat

The highly toxic tire-derived compound N -(1,3-dimethylbutyl)- N ′-phenyl- p -phenylenediamine-quinone (6PPD-Q) poses emerging environmental risks, yet its fate within the soil–plant system remains unclear. This study reveals that 6PPD-Q induces significant oxidative stress in wheat ( Triticum aestivum L.), increasing reactive oxygen species (ROS) by 259% in shoots and 217% in roots and malondialdehyde (MDA) by 57 and 59%, respectively, at a concentration of 200 ng/g compared to the control. This oxidative stress disrupted key antioxidant enzymes (SOD and POD) and reduced the uptake of essential nutrients (Fe, Cu, Mg, Mn, and P). Metabolomic analysis showed perturbation in central carbon metabolism, fatty acid turnover, and amino acid biosynthesis. 16S rRNA sequencing indicated reduced rhizosphere bacterial diversity and shifts in key phyla, linked to nutrient cycling. This work provides mechanistic insights into tire-derived contaminant toxicity in soil–plant systems and highlights the need for further ecological risk assessment.