## 2 Results and Discussion  
### Green Leaf Volatiles (GLVs) Profiling during Berry Development of Four Wine Grape Varieties  
Figure 1 displays a brief metabolic pathway graph, and the colored boxes represented the relative concentration of these compounds (red: higher level; blue: lower level). The data in each square of heat map were homogenized. Hexanal and (\(E\))-2-hexenal are two major C6 aldehydes and they are the most abundant volatile compounds in grapes as known [4; 7]. This investigation also revealed that the grapes had considerable concentrations of hexanal and (\(E\))-2-hexenal, and a relatively low level of (\(Z\))-3-hexenal (Table S1). (\(E\))-2-Hexenal roughly increased during early berry development followed by a decrease at late ripening stage. A similar (\(E\))-2-hexenal accumulating pattern was observed for these four varieties. This increase normally started at about 60 days after flowering (DAF) for Muscat Tchervine, Gewurztraminer and Chardonnay, but at about 45 DAF for Syrah berries in the 2010 vintage. On the contrary, Gewurztraminer berry started accumulating (\(E\))-2-hexenal in a much earlier stage than Syrah and Muscat Tchervine in the 2011 vintage. Generally both Syrah and Gewurztraminer presented more rapid accumulation of (\(E\))-2-hexenal than Muscat Tchervine. Regarding hexanal, its evolution pattern varied with varieties and vintages. The concentration of hexanal constantly increased during the developing stages of Syrah berries in both vintages. An upward trend was observed for hexanal during the berry development of 2011 vintage for both Muscat Tchervine and Gewurztraminer. However, the highest concentration of hexanal appeared at early stage in 2010 vintage for these two varieties, which was drastically different from other _Vitis vinifera_ cultivars such as Cabernet Sauvignon [4] and Riesling [7]. It was speculated that the accumulation of C6 aldehydes could be more dependent upon the environment in Muscat Tchervine and Gewurztraminer in comparison with neutral cultivars. As is known, the non-Muscat aromatic varieties contain higher level of terpen compared with neutral varieties, and this large accumulation of terpen is considered to be an essential signal with important evolutionary role in pest or disease resistances [24; 25; 26]. For neutral varieties, the relatively less variation during berry development observed in this study could indicate the indispensable role of hexanal as defense signals in the physiological point of view. The major C6 alcohols are direct products by alcohol dehydrogenase. These compounds provide green leaf odor for grapes and wines [4; 27]. Meanwhile, they are direct precursors for the formation of C6 esters in wines [5]. The ratio of C6 alcohols and aldehydes was used as a marker for grape aromatic maturity according to previous reports [4; 28]. In this work, both (\(Z\))-3-hexen-1-ol and hexanol were the most abundant among all C6 alcohols especially for 2010 vintage (Table S1). A certain level of (\(E\))-2-hexen-1-ol was also detected in various stages and varieties. This showed a little differences from a previous research speculation that little enzymatic activity in transforming (\(E\))-2-hexenal to (\(E\))-2-hexenal led to rather low level of (\(E\))-2-hexen-1-ol in Riesling and Cabernet Sauvignon grapes [7]. The most remarkable difference in the C6 alcohols accumulating pattern among varieties were observed in (\(Z\))-3-hexen-1-ol and hexanol. The concentration of (\(Z\))-3-hexen-1-ol gradually decreased in the development of Gewurztraminer and Chardonnay, which was in consistent with the pattern of Chardonnay in another study [29] and roughly correspondent with Riesling in a previous report [7]. However, this compound increased with berry development in Syrah and Muscat Tchervine grapes. Hexanol gradually accumulated in the process of berry development of Syrah, Muscat Tchervine and Gewurztraminer grapes, which validated the previously observed steady and significant increasing trend of hexanol of Cabernet Sauvignon and Riesling [4].