Biosynthesis and genetic control of isovitexin 7-O-xyloside in the petals of melandrium album

Abstract

An enzyme was detected in petal extracts of Melandrium album which catalysed the transfer of the xylose moiety of UDP-xylose to the 7-hydroxyl group of isovitexin. Genetical analysis revealed that the presence of the dominant allele gx was necessary for enzymic activity. This activity was independent of the residual genetic background. Xylosyltransferase activity is also present in extracts of gGgx plants, in which the product of the enzyme is not detectable. Maximal activity was found between pH 7·0 and 7·5; MnCl2 inhibited this transfer. The enzyme had an ‘apparent Km' value of 1·0 mM for UDP-xylose and of O·04 mM for isovitexin.