Impact of Exogenous Sugars on the Potency of Selected Secondary Metabolites in Non-Starchy Amaranth (Amaranthus hybridus L.)

The biosynthesis of secondary metabolites plays a significant role in determining the value of medicinal herbs, with sugar metabolism frequently influencing overall metabolic processes. To investigate the regulatory mechanisms, exogenous sugars (sucrose, glucose, and fructose) were applied to the leaves of Amaranthus hybridus L., a highly valued and multifunctional vegetable plant, both individually and in combination (sucrose + glucose + fructose), along with a control (water). Our findings revealed that exogenous sugars enhanced the accumulation of starch and soluble sugars, while also increasing enzyme activities associated with carbohydrate assimilation. Additionally, plant biomass was significantly boosted by combined exogenous sugars, sucrose alone enhanced the photosynthetic rate, and the combined sugars accelerated the accumulation of phenols and flavonoids. Metabolomic analysis further confirmed that exogenous sugars increased the levels of phenolic and flavonoid compounds. The levels of UDP-glucose pyrophosphorylase (UGP) and hexokinase (HKX) were elevated by exogenous sugars and showed a strong correlation with their metabolic activities, which in turn stimulated the synthesis of specific secondary metabolites. These results provide valuable insights into the key factors contributing to the value formation of A. hybridus and suggest a potential approach to enhancing its quality.