Coordinated roles of melatonin and putrescine in modulating oxidative balance and gene expression during postharvest life of Alstroemeria hybrida

This study investigated the effects of preharvest foliar application of putrescine and melatonin on enzymatic and non-enzymatic antioxidant systems, as well as molecular responses, in cut Alstroemeria hybrida cv. Amatista during postharvest storage. The experiment was arranged as a factorial completely randomized design with three factors and three replications. Treatments consisted of putrescine at three concentrations (0, 1.5, and 3 mM), melatonin at three concentrations (0, 50, and 100 µM), and four sampling times (0, 5, 10, and 15 days) during the postharvest period. Evaluated parameters included total phenolic and flavonoid contents, antioxidant capacity determined by DPPH radical scavenging activity, activities of antioxidant enzymes (catalase, superoxide dismutase, guaiacol peroxidase, and ascorbate peroxidase), and relative expression levels of SAMDC and SPMS genes. The results demonstrated that preharvest application of putrescine and melatonin significantly enhanced phenolic and flavonoid accumulation, antioxidant capacity, and enzymatic antioxidant activities throughout postharvest storage. Among the treatments, the combined application of 1.5 mM putrescine and 50 µM melatonin consistently induced the strongest antioxidant responses. Gene expression analysis further revealed a marked upregulation of SAMDC and SPMS transcripts in response to these treatments. Overall, the findings highlight the synergistic role of putrescine and melatonin and suggest that the combined application of 1.5 mM putrescine and 50 µM melatonin represents an effective and practical strategy for improving oxidative balance and postharvest performance of cut Alstroemeria flowers.