Melatonin Enhances Growth and Glucosinolate-Associated Nutritional Quality of Mustard Sprouts Under Moderate Salinity Stress

Salt stress profoundly affects plant growth and metabolism, whereas melatonin has emerged as an effective regulator that modulates plant responses to abiotic stress. In this study, we investigated the interactive effects between salinity (80 and 160 mM NaCl) and exogenous melatonin (100 μM) on the growth, metabolism, and antioxidant capacity of mustard (<i>Brassica juncea</i>) sprouts. The results revealed a synergistic interaction in which melatonin effectively mitigated the inhibitory effects of salinity and optimized the balance between growth and defense metabolism. Under moderate salinity, the combined treatment (MN1) significantly enhanced biomass accumulation, soluble sugars, proteins, and glucosinolate retention, while markedly increasing ascorbic acid, total phenolics, and antioxidant capacity. Principal component and membership function analyses confirmed that the melatonin × salinity interaction improved overall physiological performance more effectively than either factor alone. These results demonstrate that melatonin effectively enhances stress resilience and nutritional quality in mustard sprouts, providing a promising strategy for improving the functional value of sprouting vegetables under salinity conditions.