## 3 Results and Discussion
### Influence of BTH Treatment on the Physicochemical Parameters of Cabernet Gernischt Grapes
#### 3.1.2 Total Soluble Solids and Reducing Sugars  
Total soluble solids (TSSs) not only affect the post-harvest flavor and overall sensory quality of grapes but also play a crucial role as signaling molecules in regulating gene transcription related to defense responses, metabolic processes, grape ripening, and the biosynthesis of secondary metabolites [24]. In this study, the levels of reducing sugars in grapes exhibited a consistent increase during the ripening process, while TSSs initially decreased and then subsequently increased. The TSS content increased rapidly during veraison, with the highest content in ripe grapes. BTH treatment resulted in a significant decrease in reducing sugars and TSSs in ripe grapes. Specifically, at the mid-ripeningstage (week 13), reducing sugars and TSSs were reduced by 16.50% (31.73 g/L) and 11.13% (2.30 \({}^{\circ}\)Brix), respectively, compared with the CK (Figure 1C,D). [PERSON] et al. [30] found that BTH treatment reduces the activities of sucrose synthesis enzymes (such as sucrose synthase and sucrose phosphate synthase) and the expression of key genes involved in sucrose synthesis (_VvSuS_, _VvSPS_). Conversely, BTH treatment increases the activities of sucrose invertase enzymes (e.g., cell wall-bound acid invertase, soluble acidic invertase, neutral invertase) and their relative gene expression levels. As a result, the sucrose content decreases, while the fructose and glucose contents increase [23]. Glucose can also be synthesized and catalyzed by glucose phosphoglucomutase to generate UDP-glucose and ADP-glucose, which serve as precursors for the synthesis of phenolics  
Figure 1: Physicochemical parameters of BTH-treated (BTH) and control (CK) Cabernet Gernischt grapes. Among them are the 100-berry weight (**A**), skin/berry ratio (**B**), reducing sugars (**C**), total soluble solids (**D**), titratable acidity (**E**), pH (**F**), total phenolics, (**G**) and total flavonoids (**H**). Data are expressed as means (\(n=3\)). Error bars represent standard deviation. Different uppercase letters indicate significant differences between BTH and CK (\(p<0.05\)), while different lowercase letters indicate significant differences within CK or BTH between different weeks of post-flowering (\(p<0.05\)). and starch, respectively [15]. Therefore, the results indicate that BTH promoted glucose metabolism by increasing phosphoglucomutase activity, resulting in a decreased glucose content and increased phenolic content. Genetic research has demonstrated significant associations between sugar and plant hormone signaling, with hexokinase (HXK) playing a crucial role as a glucose sensor [24]. Various signals from sugar activate multiple pathways, some of which depend on HXK, while others do not, and these pathways use different mechanisms to regulate transcription, translation, protein stability, and enzymatic activity [24]. HXK, phosphofructokinase, and pyruvate kinase (PK) are the three most important pacemaker enzymes in the energetic EMP pathway. In plants, HXK is responsible for catalyzing the metabolism of different hexoses, including fructose as one of its substrates. Phosphofructokinase is involved in the phosphorylation of fructose 6-phosphate, resulting in the formation of 1,6 fructose diphosphate. Pyruvate is a significant product of PK and the final product of the EMP pathway. It serves as a crucial precursor for the synthesis of organic acids and plays a role in various metabolic pathways, including sugar metabolism, fatty acid metabolism, and the tricarboxylic acid cycle. Additionally, pyruvate is involved in the respiratory oxidative energy supply and is closely associated with several important metabolic processes [24]. From our findings, with fructose and pyruvate as precursors, BTH could potentially regulate the synthesis of aroma substances by reducing the expression of _VvHXXK_ and _VvPK_ genes; inhibiting the activities of HXK and PK enzymes; and altering the levels of fructose (increasing) and pyruvate (decreasing).