Melatonin Alleviates Chromium Toxicity in Maize by Regulating Polyamine Metabolism and Enhancing Antioxidant Activity

Chromium (Cr) contamination leads to the accumulation of Cr in crops, thereby posing a significant threat to food security and human health. It is essential to comprehend the mechanisms underlying Cr toxicity and to develop effective mitigation strategies to ensure healthy crop growth. Melatonin (MT), a multifunctional regulatory molecule, plays a pivotal role in the response of plants to heavy metal stress. This study is designed to investigate the underlying mechanisms through which exogenous application of MT mitigates the toxicity of Cr stress in maize seedlings. The findings of the study indicate that under Cr stress conditions, treatment with MT significantly decreased the Cr concentrations in the roots and leaves of maize, with reductions of 22% and 28.5%, respectively. Concurrently, MT demonstrated effectiveness in alleviating the toxic effects induced by Cr exposure, as evidenced by substantial improvements in the leaf area, chlorophyll content, and photosynthetic rate, which increased by 40.3%, 47.7%, and 64.8%, respectively. This led to a 42.2% increase in the total dry weight of maize. Further analysis indicates that MT modulates the antioxidant system, thereby reducing the production of reactive oxygen species and reducing membrane lipid damage associated with Cr toxicity. Moreover, MT upregulates the expression and activity of enzymes involved in polyamine synthesis while simultaneously inhibiting the activity of polyamine-degrading enzymes, leading to a 38% increase in total polyamine content. This study has enhanced our understanding of the mechanisms through which melatonin alleviates chromium toxicity in crops and has provided a theoretical foundation for its sustainable application in agricultural production.