• Melatonin enhances biomass, root, and pseudobulb growth in D. ovatum . • It balances its rhythms, boosts moscatilin, and adjusts tryptophan pathways. • It stabilizes pigments, mitigates photodegradation, enhances photosynthesis. • It improves stomatal water efficiency & osmoprotection. • It reduces chromatin, lowers DNA content without changing ploidy, & boosts mitosis. 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. Melatonin functioned as a pivotal modulator in Dendrobium ovatum , orchestrating a complex network of physiological and biochemical pathways. This multifunctional phytoanticipin had been instrumental in enhancing growth parameters, cellular integrity, and defense mechanisms, thereby establishing itself as a crucial elicitor of moscatilin production, an auxin analog, and a chromatin modulator. The cascade of effects included elevated biosynthesis of flavonoids, serotonin derivatives, and curcuminoid compounds, along with increased antioxidant defenses and photosynthetic efficiency. Moreover, melatonin promoted lignin biosynthesis, thereby fortifying cell wall integrity, stomatal density, and mitogenic activity, ultimately driving biomass production and chromosomal stability. This dynamic regulation underscored melatonin's role as a critical agent in optimizing the growth and resilience of D. ovatum under varied environmental conditions.
Bargunam et al. (Sun,) studied this question.