Multiple glucosyltransferase activities in the grapevine Vitis vinifera L

Abstract

The conjugation by glycosyltransferases of sugars to primary and secondary metabolites is widespread among plants and almost certainly a prerequisite for the accumulation of secondary metabolites at high levels. In the case of the grapevine, Vitis vinifera, modulating the levels of specific secondary berry metabolites is a desirable outcome for the development of wines with particular style characteristics. This can be achieved only by a thorough understanding of the processes underlying glucoside formation and accumulation during berry development. Using protein extracts prepared from leaves and berries of Vitis vinifera cvs, we show here that glucosyltransferase activities can be detected against a wide range of substrates. Among the substrates glucosylated were several classes of phenylpropanoids, including flavonols, anthocyanidins, flavanones, flavones, isoflavones, and a stilbene. Additionally, simple phenols and monoterpenes were glucosylated. Total soluble leaf proteins subjected to ion-exchange chromatography separated into fractions with differing glucosyltransferase activities. This provided strong evidence for the existence both of multiple distinct enzyme activities, and multiple isozymes catalysing identical reactions. Polyclonal antiserum raised to a V. vinifera UDP-glucose:anthocyanidin glucosyltransferase was used to demonstrate the existence of multiple glucosyltransferases in berries and leaves of the grapevine cvs Muscat of Alexandria and Shiraz, thereby confirming data obtained previously through biochemical analyses of recombinant glucosyltransferase.