Melatonin enhances drought tolerance in Dendrobium ovatum: Insights into physiological and genomic adaptations

Melatonin, an evolutionarily conserved indoleamine, is increasingly recognized as a crucial regulator in plants, orchestrating diurnal rhythms, stress adaptation, and metabolic reprogramming. However, its integrative functions in epiphytic orchids, particularly Dendrobium ovatum, remain inadequately defined. This study explores melatonin’s role in enhancing physiological resilience, pigment homeostasis, metabolic stability, stomatal dynamics, and genomic integrity in D. ovatum, emphasizing its modulation of bioactive stilbenoids such as moscatilin. Melatonin supplementation significantly enhanced biomass accumulation, structural integrity, and root system proliferation, highlighting its potential for improving vegetative growth under nutrient and water limitations. Circadian-metabolomic analyses revealed melatonin-driven stabilization of endogenous melatonin levels, strategic redirection of tryptophan flux toward serotonin biosynthesis, and sustained diurnal modulation of moscatilin. Additionally, melatonin regulated stomatal behavior and epidermal development, thereby optimizing water-use efficiency and gas exchange. Metabolomic profiling demonstrated melatonin-induced osmoprotective adjustments through enhanced proline biosynthesis, sulfur metabolism, and glutathione-mediated redox regulation, underpinning its role in adaptive stress responses. Karyomorphological assessments have confirmed that melatonin affects chromatin condensation, decreases genome size, and increases mitotic activity, implying that epigenetic mechanisms support genomic stability and resilience. These results collectively emphasize melatonin's role as a crucial mediator of circadian regulation, metabolic balance, and genomic integrity in epiphytic orchids. This understanding offers new perspectives on their adaptive strategies and has implications for sustainable horticulture and conservation practices.