07g and D6a: Two Flavone Glycosylating Genes in Silene, which are Only Expressed in Cotyledons and Rosette Leaves

Two further loci can be added to the three already known (g , g l and f g ) in Silene controlling the 7 -0 and 2"-0-glycosylation o f the C-glycosylflavone isovitexin (6-C-glucosylapigenin). These loci, 0 7 g for the 7-O-galactosylation and D6a for the 2"-0-arabinosylation, appear only to be expressed in cotyledons and rosette leaves and control the biosynthesis o f isovitexin 7 -0 galactoside and isovitexin 7-0-galactose 2"-0-arabinoside in these parts o f plants in which the recessive alleles o f the loci g, g l and f g are homozygous (Steyns et al. [9]). The possibility that locus g, whose dominant alleles gG and g X control the 7-0-glucosylation and the 7-0-xylosylation o f isovitexin respectively, controls the synthesis o f isovitexin-7-O galactoside was excluded by demonstrating the presence o f isovitexin-7-O-galactoside and the 7-0-galactosyltransferase catalyzing its biosynthesis in addition to isovitexin-7-O -glucoside and the 7-0-glucosyltransferase in cotyledons o f g G g G seedlings. The synthesis o f the 2"-0-arabinoside is neither controlled by locus gl, whose dom inant alleles gl R and glA control the 2"-0-rham nosylation and 2"-0-arabinosylation o f isovitexin respectively, nor by locus f g , whose dominant allele Fg controls the biosynthesis o f isovitexin 2"-0-glucoside. This was shown by the presence o f isovitexin-7-O-galactose 2"-0-arabinoside and the 2"-0-arabinosyltransferase catalyzing the synthesis o f the 2"-0-arabinoside in addition to isovitexin-7-O-galactose 2"-0-rham noside in cotyledons o f glR glR seedlings and by the presence o f isovitexin-7-O-galactose 2"-0-arabinoside and the 2"-0-arabinosyltransferase in addition to isovitexin-7-O-galactose 2"-0-glucoside and the 2"-0-glucosyltransferase in cotyledons of FgFg seedlings.