Differential Regulation of Two Genes Controlling the Biosynthesis of Isovitexin 7-O-Galactoside in Silene Plants

The expression of the allelic isovitexin 7-O-glycosylation genes gG (transfer of glucose) and g X (transfer of xylose) was studied in cotyledons, rosette leaves, stem leaves and petals of Silene plants. These studies revealed that gG is expressed in all ontogenetic stages, whereas its allele g X is only expressed in the petals. In the vegetative parts of g X individuals 7-O-xylosylation is replaced by 7-O-galactosylation. The possibility that g X encodes an enzym e activity that catalyzes different reactions in the petals and the vegetative parts resulting in the accumulation of the 7 -0 xyloside and the 7-O-galactoside respectively, has been disproved. It is shown that there are two different enzymes catalyzing the biosynthesis o f isovitexin 7-O-galactoside. These 7-O-galactosyltransferase activities differ with respect to heat inactivation, pH optim um , flavone acceptor specificity and Michaelis-Menten enzyme kinetic parameters. The genes controlling these enzyme activities are regulated differentially, with gene 0 7 g (described previously by Steyns et al. [11]), expressed in the cotyledons and the rosette leaves and X gal in the stem leaves and petals.