Sucrose Regulates the Flower Color and Main Bioactive Components of Dendrobium thyrsiflorum

Abstract Sucrose signaling regulates plant growth, ornamental traits, and secondary metabolism. However, the systematic effects of exogenous sucrose on the interplay between ornamental traits and bioactive metabolite accumulation remain unexplored in the orchid Dendrobium thyrsiflorum. In this study, we applied exogenous sucrose (0–50 mmol/L) to D. thyrsiflorum and found that 30 mmol/L sucrose optimally enhanced morphological and floral attributes: corolla length, floral tube length, and flower diameter increased by 43.5, 36.3, and 13.5%, respectively. Petal redness decreased by 19.1%, while carotenoid (Car) and flavonoid contents rose by 12.0 and 9.8%, respectively; in contrast, anthocyanin synthesis declined by 70.7%. These changes collectively enhanced lip brightness, yellowness, and chroma by 17.9, 72.1, and 51.4%, respectively, resulting in a vivid yellow hue. Physiologically, 30 mmol/L sucrose elevated superoxide dismutase (SOD) activity and osmoprotectant levels, such as soluble sugars (SS), proteins, proline (Pro), with peak catalase (CAT) and peroxidase (POD) activities observed. On day 21, polysaccharide, polyphenol, and flavonoid concentrations peaked at 0.37, 0.91, and 4.08 mg/g fresh weight (FW), respectively, exceeding those of the control (P < 0.05). Collectively, this study provides the first systematic characterization of how exogenous sucrose concurrently modulates floral coloration, morphological traits, and bioactive metabolite accumulation in D. thyrsiflorum, thereby filling a critical gap in understanding sucrose-mediated quality regulation in this species.