The Expression of the Isovitexin 7-O-Xylosylating Gene gX in Silene pratensis and S. dioica is Restricted to the Petals

The isovitexin-O-glycosylation patterns of rosette leaves, stem leaves and petals of Silene dioica plants were investigated. The 7-O -xylosylation o f isovitexin, controlled by gene gX, only occurs in the petals. In the leaves isovitexin is 7-O-galactosylated, which is controlled by gene Xgal. Acyl groups may be linked to either the 7 -0 or the 2"-0-substituted sugar; the former only occurs in the leaves, whereas the latter takes place both in leaves and petals. The restriction of the g X controlled enzyme activity and its product to the petals of Silene dioica plants is in complete agreement with previously obtained results (reference [2]) on the expression of g X in the genetic background of the closely related Silene pratensis, into which g X can be introduced by introgressive hybridization. On the basis of serological enzym e inhibition studies, it is argued that the absence of 7-Oxylosylation in the leaves is not due to post-translational inactivation of thegA'controlled enzyme. The regulation of the expression of gene g X throughout ontogeny therefore differs markedly from that of two allelic g locus variants, controlling the 7-O-glucosylation of isovitexin.