Melatonin-mediated biochemical and redox adjustments alleviate polyethylene and polyvinyl chloride derived...

Microplastic (MPs) -induced stress poses an emerging threat to crop productivity; however, effective mitigation strategies remain limited. This study elucidated the physiological and biochemical impacts of polyvinyl chloride (PVC) and polyethylene (PE) microplastics and evaluated the potential role of melatonin (MEL) in alleviating MP-induced toxicity in maize (Zea mays L.). Five maize varieties (FH2018, Malka, FH1046, FH2335, R4040) were exposed to MPs (400 mg kg^-1 mixed in soil), followed by foliar application of MEL (5 mg L^-1, 21.5 μM). Exposure to both MPs significantly curtailed maize plant performance, intensified oxidative stress, and altered antioxidant enzyme activities. Conversely, MEL supplementation substantially enhanced biomass of shoot and root, particularly in FH1046 under PVC-stress, compared without MEL treated plants. The strongest melatonin-mediated recovery of photosynthesis was observed in FH2018 exposed to PE-stress, as indicated by increased Pn, E, gS, and total chlorophyll. MEL reduced lipid peroxidation and hydrogen peroxide levels in Malka plants treated with PVC and PE. Moreover, MEL increased superoxide dismutase and peroxidase activity by 60%, 70%, respectively in FH 2018. MEL also promoted the accumulation of ascorbic acid and total soluble sugars, total soluble protein, as well as glutathione dehydrogenase, glutathione and glutathione reductase activity. A rise in endogenous melatonin and H⁺-ATPase activity displayed enhanced cellular homeostasis. Multivariate analyses revealed distinct varietal response patterns, which, together with physiological and biochemical results, suggested comparatively greater resilience in FH1046 and FH2335, while R4040 showed greater sensitivity to MP stress. All these coordinated adjustments after MEL application curtailed MP-induced physiological and metabolic disruptions, stabilizing maize growth. This study highlights the potential of MEL as practical strategy for mitigating MP toxicity and improving crop tolerance to emerging environmental contaminants.