Coexposure to 6PPD and Copper Induces Oxidative Stress and Physiological Damage in Wheat ( Triticum aestivum L.)

N- (1,3-dimethylbutyl) -N′- phenyl- p- phenylenediamine (6PPD), a tire antioxidant and a persistent environmental pollutant, and copper (Cu) co-occur in terrestrial ecosystems; however, their combined phytotoxic effects on crops remain inadequately elucidated. This study investigated the individual and combined impacts of 6PPD and Cu on wheat ( Triticum aestivum L.) under hydroponic conditions, employing an integrated approach of physiological, biochemical, and metabolomic analyses. Single exposures to 6PPD or Cu impaired wheat growth, whereas their coexposure exerted a synergistic toxic effect, severely inhibiting growth, reducing chlorophyll, inducing oxidative stress (elevated MDA and ROS), disrupting metal homeostasis, and altering amino acid and carbohydrate metabolism (e.g., TCA cycle, l -glutamic acid, and GABA) in a tissue-specific manner compared to the control group. These findings highlight the synergistic toxicity of 6PPD and Cu in wheat, offering critical insights for environmental risk assessment and the impact of tire-derived pollutants on agricultural systems.