Interactive effects of salinity and melatonin on growth, antioxidant defense, and nutrient composition of radish microgreens

Background Enhancing the growth and nutritional quality of microgreen vegetables has gained increasing attention due to their significant health benefits. Sodium chloride (NaCl), acting as a chemical eustressor at low concentrations, can induce metabolic pathways that enhance plant secondary metabolites and antioxidant compounds. Melatonin, a multifunctional plant regulator, has recently been recognized as an elicitor capable of enhancing stress tolerance. Methods This study investigated the interactive effects of different salinity levels (0, 10, 20, 40, and 80 mM NaCl) and exogenous melatonin application (0, 100, 200 µM) on growth, photosynthetic pigments, bioactive compounds, antioxidant capacity, nutrient elements, and oxidative stress markers in radish microgreens. Results Low salinity (10–40 mM NaCl) enhanced growth, mineral nutrients (Ca, Mg, Mn, Zn), and antioxidant compounds without triggering oxidative stress. High salinity (80 mM NaCl) decreased growth, pigments, and vitamin C, and increased reactive oxygen species. Exogenous melatonin acted as an elicitor, mitigating salinity-induced damage by improving growth, pigments, phenolics, flavonoids, anthocyanins, vitamin C, antioxidant enzyme (CAT, POD and SOD) activities, and nutrient balance. Conclusions The synergistic effect of mild salinity and melatonin treatment enhanced bioactive compound accumulation and antioxidant capacity without compromising growth, suggesting a promising strategy to improve the nutritional quality and antioxidant compounds of radish microgreens.