Melatonin in redox network and hormonal balance in mungbean seedlings due to fungicide-induced seed stress

Melatonin (N-acetyl-5-methoxytryptamine), a plant regulatory molecule, is currently under study for its potential as a biostimulant and protector against biotic and abiotic stressors by regulating the redox network and modulating primary and secondary metabolisms. This study’s aim is to analyze the possible protective effects on redox network of melatonin in mungbean seedlings obtained by priming Vigna radiata L. seeds with the broad-spectrum fungicide copper oxychloride and/or melatonin. The impact of melatonin and fungicide on seedling growth and redox parameters, including hydrophilic antioxidant activity, total melatonin content, H₂O₂ content, total carbonyl content and the activity of antioxidant enzymes: catalase, peroxidase, ascorbate peroxidase, polyphenol oxidase, superoxide dismutase, and glutathione-S-transferase, was evaluated. Additionally, the effect of exogenous melatonin on endogenous stress-related phytohormones, such as salicylic acid and jasmonic acid, was assessed both in the presence and absence of fungicide. The results reveal that melatonin, either alone or in combination with fungicide, maintained antioxidant parameters and reduced protein carbonylation induced by fungicide stress. Furthermore, melatonin restored the activity of antioxidant enzymes that had been disrupted by the fungicide. Both the copper fungicide and melatonin significantly affected the hormonal profile, specifically salicylic and jasmonic acids. Overall, melatonin improved plant tolerance, acting as a natural safener that enhanced plant resilience in the presence of copper oxychloride.