## 3 Results and Discussion
### Glycosidally Bound Volatiles and Related Gene Expressions  
The GBV profiles among the different spine grapes were determined, and the results are shown in Table 3. A total of 27 kinds of GBVs, including alcohols, monoterenes, esters, aldehydes, ketones, and phenolic acid, were identified in spine grapes. These GBVs could be converted to their free-form volatiles by enzymatic hydrolysis, and the bound volatiles could contribute to the aromatic characteristics of grapes and wines, especially the monoterenes, alcohols, and esters [40]. In the present study, BY had the highest monoterpene and alcohol content, followed by G4. The main monoterenes in spine grapes were \(\alpha\)-Terpineol, citronello, terpinolene, and linalool, while benzyl alcohol was the most abundant alcohol; these bound volatiles could give the grapes and their wines a more floral and fruitier aroma [41]. BY and G4 had higher \(\alpha\)-terpineol, citronello, terpinolene, and benzyl alcohol contents than G2 and XZZ. Geraniol was only detected in BY and G4. For esters, methyl salicate accounted for about 60%-80% of esters present, but no methyl salicate was detected in XZZ grapes. BY had the highest methyl salicate content, followed by G2. The ester content in XZZ grapes was the lowest among the four spine grape varieties. In addition, two ketone and phenolic acid-bound aromas were also detected in the tested grapes. No ketones were detected in BY, however, although mequinol was only detected in BY grapes. Overall, BY and G4 grapes had the highest bound volatiles content, while XZZ had the lowest. BY and G4 had rich bound volatiles, which might give the  
Figure 2: Expression levels of key genes involved in anthocyanin biosynthesis of spine grapes. Values presented are means \(\pm\) SD (\(n\) = 3). _VdGAPDH_ was used as reference gene. Different letters indicate significant differences among four spine grapes using [PERSON]’s test (\(p\) < 0.05). G2: Gaoshan #2, G4: Gaoshan #4, XZZ: Xiangzhenzhu, BY: Baiyu. grapes more aromatic characteristics [14]. The GBVs in ripe grapes might relate to the concentration of free volatiles, and more research is needed to reveal the relationships and impact factors for the profiles of free and bound volatiles [15]. Compared with _V. vinifera_ grapes, such as Cabernet Sauvignon, the spine grapes had a richer bound aroma, which might give the wine a richer aroma type, such as floral, fruity, etc. To analyze the expression patterns of key genes involved in the GBV biosynthesis pathway in spine grapes, the transcript levels of five genes (_VdGT5_, _VdGT6_, _VdGT7_, _VdGT9_, and _VdPNGer_) were determined. As Figure 3 shows, the expression levels of _VdGT5_, _VdGT9_, and _VdPNGer_ were higher in G4 grapes than in the other varieties. BY had the highest transcript level of _VdGT6_ but lower expressions of _VdGT6_, _VdGT9_, and _VdPNGer_. XZZ had the highest expression level of _VdGT6_ but the lowest expression levels of _VdGT5_ and _VdGT9_. The expression levels of _VdGT9_ and _VdGT7_ were the highest among the five genes in all spine grapes, especially in G4 and G2 grapes, respectively. The GTs (monoterpol \(\beta\)-p glucosyltransferase) proteins could catalyze the GBV biosynthesis in grapes [42]. Many studies have reported a positive correlation between the expression levels of _GT_s genes and the concentrations of GBVs [43; 44]. The difference in _VdGT_s gene expressions between varieties might be the main reason for variation in GBVs between varieties [43; 45].