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Petals of genetically defined lines of Matthiola incana R.Br. contain a glycosyltransferase which catalyzes the transfer of the xylosyl moiety of uridine 5′-diphosphate-xylose to the glucose of cyanidin 3-glucoside. The enzyme also uses 3-glucosides of pelargonidin and delphinidin, cyanidin 3-( p-coumaroyl)-glucoside and 3-(caffeoyl)-glucoside as substrates. The xylosyltransferase exhibits a pH optimum of 6.5. The enzyme activity depends on the stage of bud and flower development. Accumulation of cyanidin 3-glucoside during flower development is correlated with xylosyltransferase activity. [ABSTRACT FROM AUTHOR]

In flower extracts of defined genotypes of Matthiola incana, an enzyme was demonstrated which catalyzes the transfer of the glucosyl moiety of uridine 5′-diphosphoglucose (UDPGlc) to the 5-hydroxyl group of pelargonidin and cyanidin 3-glycosides and acylated derivatives. The best substrate for 5-glucosylation is the 3-xylosylglucoside acylated with p-coumarate, followed by the 3-xylosylglucoside and by the acylated ( p-coumarate) 3-glucoside. The 3-glucoside itself is a very poor substrate. Besides UDPGlc, thymine 5′-diphosphoglucose is a suitable glucosyl-donor, but with a reduced reaction rate (42%). The anthocyanin 5-O-glucosyltransferase exhibits a pH optimum at 7.5 and is generally inhibited by divalent ions and by ethylenediaminetetraacetic acid and p-chloromercuribenzoate. Investigations on different genotypes showed that the 5-O-glucosyltransferase activity is clearly controlled by the gene l. In confirmation of earlier chemogenetic work, enzyme activity is only present in lines with the wild-type allele l. The anthocyanin 5-O-glucosyltransferase activity is strictly correlated with the formation of 5-glucosylated anthocyanins during bud development. [ABSTRACT FROM AUTHOR]

A cell-free extract from flowers of Matthiola incana catalyzes a NADPH-dependent stereospecific reduction of (+)-dihydrokaempferol to 3,4- cis-leucopelargonidin (5,7,4′-trihydroxyflavan-3,4- cis-diol). The pH-optimum of this reaction is around 6. The rate of reaction with NADH was about 50% of that found with NADPH. (+)-Dihydroquercetin and (+)-dihydromyricetin were also reduced by the enzyme preparation to the corresponding flavan-3,4- cis-diols. Correlation between the genotype of M. incana and the presence of dihydroflavonol 4-reductase is strong evidence that this enzyme is involved in anthocyanin biosynthesis. [ABSTRACT FROM AUTHOR]

In flowers of Matthiola incana, the B-ring hydroxylation pattern of anthocyanins is controlled by the locus b. Recessive genotypes produce pelargonidin and genotypes with wild-type alleles cyanidin as the aglycone. Supplementation experiments on acyanic flowers using extracts of pelargonidin-and cyanidin-producing flowers, respectively, showed not only the presence of compounds with a precursor function for anthocyanin synthesis in the cyanic flowers but also differences in the B-ring hydroxylation pattern of these compounds. Chromatographic investigations proved that flavanones and dihydroflavonols occur in extracts of cyanic flowers. Naringenin, dihydrokaempferol, and their 7-glucosides could be demonstrated in all flower extracts, but in extracts of cyanidin-producing flowers, dihydroquercetin and a further 3′, 4′-hydroxylated dihydroflavonol, tentatively identified as dihydroquercetin 3-glycoside, were additionally found. In no case, however, could eriodictyol be detected. From these results and from the ready hydroxylation of dihydrokaempferol to dihydroquercetin in a white mutant line of Matthiola incana, it can be concluded that introduction of the 3′-hydroxyl group of anthocyanins is not achieved by specific incorporation of caffeic acid during synthesis of the flavonoid skeleton, but by hydroxylation at the dihydroflavonol stage. [ABSTRACT FROM AUTHOR]

After application of dihydroflavonols, naringenin, or suitable substituted chalcones, anthocyanins were synthesized in three genetically defined acyanic lines of Matthiola incana, indicating that the corresponding genetic block concerns the synthesis of the chalcone-flavanone intermediate. Independent of the precursors used, only cyanidin derivatives were produced. This supports the hypothesis that the oxygenation pattern of the B ring in anthocyanin formation is determined at a stage of a C intermediate. In addition to the gene responsible for the oxygenation of the 3′ position, the genes responsible for the glycosylation in the 3 and 5 positions of the anthocyanin molecule, and those responsible for the acylation with various hydroxycinnamic acids can still exert their influence. Two further genetically defined lines containing flavonol glycosides were not able to synthesize anthocyanins with any of the precursors tested. Their genetic blocks are assumed to be localized after dihydroflavonol synthesis but before anthocyanin formation. [ABSTRACT FROM AUTHOR]

8-hydroxyquinoline has been previously used as an inhibitor in studies on porphyrin metabolism, where it is thought to act by chelating iron. It is shown that this compound also rapidly inhibits uridine uptake of seedlings or cotyledons of the crucifer Matthiola incana R.Br. RNA synthesis is also affected but the inhibition is not as severe as reported for fission yeast. [ABSTRACT FROM AUTHOR]