Melatonin alleviates lead-induced stress in rice through physiological regulation and molecular defense mechanisms

This study investigates how melatonin (Mel) supplementation mitigates Lead (Pb) toxicity in rice by evaluating plant growth, physiology, and molecular responses. Pb stress markedly reduced root and shoot lengths by 63% and 33%, respectively, compared to control plants; however, Mel supplementation effectively mitigated this inhibition, enhancing root and shoot lengths by 100% and 47%, respectively, relative to Pb-stressed plants after 10 days. Furthermore, prolonged Mel application under Pb stress sustained growth improvement, increasing root and shoot lengths by 36% and 35%, respectively, compared to Pb-stressed plants. We observed a 19.5% increase in plant height with Mel treatment, along with improvements in yield-related traits such as panicle length and seed weight. Beyond morphological traits, Mel reduced Pb-induced oxidative stress by decreasing, H₂O₂, and MDA levels by 36%, 26%, and 46%, respectively. Moreover, Mel modulated antioxidant enzyme activities in Pb + Mel-treated plants by decreasing ascorbate peroxidase (APX) activity and enhancing catalase (CAT) activity. Additionally, Mel regulated ion homeostasis, with K⁺ and Ca²⁺ contents increasing by 74% and 89%, respectively. At molecular level, Mel reduced OsMTP1 levels by 45% and increased OsPCS1 by up to 193%. Overall, Mel significantly alleviates Pb toxicity by enhancing growth, physiological traits, and stress resilience in rice plants, highlighting its potential as a sustainable strategy for improving crop performance under heavy metal stress and offering promising directions for future agricultural research.