Seed priming with melatonin enhances salt stress tolerance in triticale through coordinated regulation of antioxidant defense, osmotic homeostasis, and phytohormone signaling

BACKGROUND: Seed germination and early seedling establishment in triticale (×Triticosecale Wittmack) are highly vulnerable to salinity stress. Seed priming has emerged as a potent and cost-effective strategy to enhance salt tolerance during these critical developmental stages. However, the physiological mechanisms through which melatonin (N-acetyl-5-methoxytryptamine, MT) priming alleviates salt stress in triticale remain poorly understood. METHODS: In this study, four treatments were applied: CK (control), MT (melatonin priming without salt stress), S (non-primed seeds under salt stress), and MS (melatonin-primed seeds under salt stress). We comprehensively assessed the effects of MT priming on seed germination, seedling growth, photosynthetic performance, and key physiological indicators under saline conditions. RESULT: The results revealed that MT priming significantly increased the germination rate by 26.87% compared to non-primed seeds under salt stress. Moreover, seedling height and fresh weight in the MS treatment were significantly higher by 3.86% and 36.00%, respectively, than those in the S group. These enhancements were attributed to the upregulation of antioxidant enzyme activities, including superoxide dismutase and peroxidase, which effectively reduced reactive oxygen species accumulation and mitigated oxidative damage. Additionally, MT priming improved Na⁺/K⁺ homeostasis and stimulated the biosynthesis of osmoregulatory compounds such as soluble sugars and proteins. Notably, MT application also increased endogenous gibberellin levels while reducing abscisic acid content in both seeds and seedlings under salt stress. CONCLUSION: Melatonin alleviates the detrimental effects of salt stress on seed germination and seedling growth in triticale by modulating antioxidant defense, osmotic adjustment, and hormonal homeostasis.