## 3 Results and Discussion
### Soluble Sugars, Organic Acids Profiles, and Related Gene Expressions  
The soluble sugar and organic acid profiles of spine grapes are shown in Table 1. In grape berries, glucose and fructose are the main soluble sugars, and some table grape varieties do not contain any detectable sucrose [27]. The soluble sugar in grapes provides nutrients for the yeast, which can be converted into alcohols and esters by the yeast during the fermentation process, which affects the quality of the wine. The type and content of soluble sugar affect the fermentation process, which in turn affects the flavor quality of the wine [28]. The results of this study were consistent with previous research results, as only glucose and fructose were determined in the spine grapes. XZZ had the highest glucose and fructose content. G2 and G4 had the lowest fructose content. G4 and BY had the lowest glucose content. These results were consistent in that XZZ had the highest content of soluble solids, while G2 had the lowest. In general, the organic acids in grapes were mainly tartaric, malic, and citric acids, and these components play an important role in grape and wine quality [29]. The maturity and genotype of grapes affect the composition of these organic acids [29]. As shown in Table 1, malic acid was the main organic acid present in spine grapes and was detected in all varieties, while citric acid was only found in G2 and XZZ grapes. [PERSON] et al. [24] also reported that the malic acid content was significantly higher than that of citric acid in Cabernet Sauvignon grapes. However, the malic acid content in the spine grapes ranged from 3.13 g/L to 4.22 g/L, which was significantly lower than in Cabernet Sauvignon grapes (11.53-13.57 g/L) [24]. Citric acid can also affect the acidity of wines and inhibit the activity of yeasts during fermentation, therefore, a higher content of citric acid in wine indicates adulteration [30]. The malic acid can be transferred to lactic acid by lactic acid bacteria, therefor, the concentration of malic acid decreases during fermentation. Tartaric acid is an organic acid unique to grapes and wine [16]. The tartaric acid is the main source of the acid taste of wine and plays an important role in maintaining the chemical stability of wine and its color or taste [30]. XZZ and G4 had the highest tartaric acid content, while the lowest tartaric acid content was detected in G2. These results indicate that there were differences in soluble sugar and organic acid composition between spine grape varieties and _Vitis vinifera_ cultivars. The sugar in grape berries is transported in the form of sucrose from the source organs (leaves) through the phloem to the sieve element/companion cell (SE/CC) complex in the phloem of the fruit vascular bundle, and then unloaded from the sieve-companion cell complex and enters the sink cells [31]. The expressions of sugar unloading genes play a key regulatory role in the process of sugar transport. Thus, to further reveal the mechanism of the differences in varieties in soluble sugar profiles, the expression levels of six genes (_VdHT1, VdHT3, VdHT4, VdcwINV, VdGIN1_, and _VdGIN2_) involved \begin{table}
\begin{tabular}{c c c c c c} \hline
**Cultivars** & **Fructose** & **Glucose** & **Tartaric Acid** & **Malic Acid** & **Citric Acid** \\ \hline G2 & 64.31 \(\pm\) 2.04 c & 71.03 \(\pm\) 3.41 ab & 1.21 \(\pm\) 0.08 bc & 3.13 \(\pm\) 0.22 bc & 0.11 \(\pm\) 0.02 a \\ XZZ & 80.73 \(\pm\) 4.18 a & 75.89 \(\pm\) 8.51 a & 1.43 \(\pm\) 0.02 a & 4.22 \(\pm\) 0.20 a & 0.06 \(\pm\) 0.01 b \\ G4 & 65.42 \(\pm\) 0.61 c & 63.40 \(\pm\) 0.02 c & 1.42 \(\pm\) 0.08 a & 3.35 \(\pm\) 0.27 b & - \\ BY & 68.33 \(\pm\) 1.81 b & 63.59 \(\pm\) 1.98 c & 1.33 \(\pm\) 0.00 b & 3.17 \(\pm\) 0.12 bc & - \\ \hline \end{tabular} Note: All values shown are mean \(\pm\) SD, \(n=3\). Lowercase letters indicate significant (\(p<0.05\)); “-” means not detected; G2: Gaoshan #2; G4: Gaoshan #4; XZZ: Xiangzhenhu; BY: Baiyu.  
\end{table} 
Table 1: Soluble sugar and organic acid composition of Chinese wild spine grapes (g/L).