## 1 Introduction  
Volatile organic compounds are vital for the quality of grape berries and wines. They determine the aromatic quality and variety characteristics. Hundreds of volatile organic compounds have been identified and they are divided into several major families: terpenoids, fatty acids derived compounds, aromatic aldehydes and alcohols, thiols and methoxypyrazines [1]. The aromatic characteristics of each grape variety are due to its unique combination of these compounds. Among these volatile compounds, C6 aldehydes, alcohols and esters are named as Green Leaf Volatiles (GLVs) based on their odor description [2]. The C6 aldehydes are the most abundant volatile components in grape berry [3; 4]. In addition, C6 aldehydes and C6 alcohols are precursors of hexyl acetate in wines. Hexyl acetate in wines is found to be grape dependent and contribute to fruity character [5]. Hence, the level of C6 compounds in grape berries are closely related to odor sensory of the wines made from these fruits. The C6 volatile compounds of wines, except (\(Z\))-3-hexen-1-ol and (\(Z\))-3-hexenyl acetate,showed an increasing pattern with increasing sugar contents and delayed harvest dates of grape berries [6]. This pattern of C6 volatiles was in agreement with other grape volatile evolution during berry development [4; 7]. The C6 aldehydes are generally derived from linoleic acid and linoleic acid by grape lipoxygenase (LOX), hydroperoxides lyase (HPL) and (3_Z_)-(2_E_) anal isomerase. The aldehydes are then reduced by alcohol dehydrogenase (ADH) to form C6 alcohols, which can be esterified into acetates. Two _13-LOXs_ were cloned from Sauvignon Blanc and their transcript rapidly accumulated in response to mechanical wounding and the infection of _Botrytis cinerea_[8]. _VvHPL1_ and _VvHPL2_ were cloned from Cabernet Sauvignon berry and identified with different enzymatic functions [9]. Several VvADHs have been biochemically identified in grape berry [10]. There have been accumulating studies aiming at revealing the physiological functions of GLVs and the regulation of LOX-HPL pathway in plants [11; 12; 13; 14]. The biological significance of this pathway has been well demonstrated to date. The GLVs are thought to be signals released from plants under biotic or environmental stress [15]. Therefore, the GLVs are not only important aroma compounds for both grape berry and wine, but also act as efficient defense chemicals. Variety is considered to be one of the most important factors influencing grape and wine aromatic characteristics. The varietal aroma depends on the overall profile of odor-active compounds present in grapes and wines [16]. Wine grapes generally have been grouped into three categories based on the level of free monoterpenoids: Muscat varieties (high free monoterpene content), non-Muscat aromatic varieties (medium free monoterpene content) and neutral varieties (very low free monoterpene content) [7]. Terpenes and C13-norisoprenoids are demonstrated to be important contributors to the aroma of Muscat and non-Muscat aromatic varieties [17; 18]. More than 50 terpen have been identified as responsible for varietal flavor of Muscat grape varieties. In addition, C6 alcohols and C6 aldehydes are also considered as characteristic compounds of non-Muscat varieties such as Cabernet Sauvignon, Monastrell and Tempranillo [3]. Recently, C6 compound contribution to wine odor has been paid attention. For example, (_Z_)-3-hexen-1-ol and hexanol were considered as secondary sources of differences between young red wines from Grenache, Tempranillo, Merlot and Cabernet Sauvignon, and the byproducts of yeast amino acid metabolism were major different components [19]. A recent study compared the varietal differences between Shiraz and Cabernet Sauvignon grapes and wines with regard to volatile esters, and found that C6-acetates were the most importantly influenced compositions [20].