Exogenous melatonin and gibberellic acid enhance postharvest quality of cut lotus flowers by improving water balance, antioxidant defense and anthocyanin accumulation

Lotus is an important aquatic ornamental flower, but its cut flowers senesce rapidly after harvest, limiting commercial value. Melatonin (MT) has exhibited potential in preserving fruits and some terrestrial cut flowers, yet its effects, alone or with gibberellic acid (GA3), remain unexplored in aquatic cut flowers. Following concentration screening, we investigated effects of 1 mM MT, 150 mg/L GA3 and their combination on postharvest quality in cut lotus flowers. These treatments significantly extended vase life, increased flower diameter, and maintained fresh weight, with the combination most effective. For water metabolism, GA₃ primarily promoted water uptake, MT effectively reduced water loss, and their combination optimally improved overall water balance. All treatments activated ascorbate-glutathione (AsA-GSH) cycle, as evidenced by higher AsA/DHA and GSH/GSSG ratios and increased ascorbate peroxidase and glutathione reductase activities, leading to lower malondialdehyde and hydrogen peroxide levels. Moreover, all treatments promoted anthocyanin accumulation and maintained petal color, associated with upregulation of dihydroflavonol 4-reductase and anthocyanidin synthase activities and gene expression. The combined treatment showed the strongest alleviation of oxidative damage and enhancement of anthocyanin accumulation. Two-way ANOVA further revealed significant MT × GA₃ interactions on vase life, fresh weight change rate, water balance, antioxidant indicators, anthocyanin content, and ANS activity. Collectively, exogenous MT and GA₃, particularly in combination, effectively delay senescence of cut lotus flowers through coordinated regulation of water balance, antioxidant defense, and anthocyanin biosynthesis. This study offers both a theoretical foundation and a practical preservation strategy for improving postharvest quality and commercial sustainability of aquatic cut flowers.