The molecular mechanisms whereby a spectrum of dahlias, from white to yellow to red to purple, get their color are already well known, but the black dahliahas hitherto remained a mystery. Now, a study published November 23, 2012 in BioMed Central's open-access journal BMC Plant Biology reveals for the first time that the distinctive black-red coloring is based on an increased accumulation of anthocyanins as a result of drastically reduced concentrations of flavones. Dahlia variabilis hort. is a popular garden flower. Continuous dahlia breeding worldwide has led to the availability of a huge number of cultivars – 20,000 varieties – many of them showing red hues. However, black hues of dahlia flowers occur rarely, in comparison. Flower color in dahlias is exclusively based on the accumulation of a group of metabolites called flavonoids, for example anthocyanins, flavones, and flavonols. It's known that red tones arise from anthocyanins, whilst white and yellow tones lack anthocyanins but contain large amounts of flavones and chalcones respectively. Flavones and flavonoids are colorless, but they influence flower coloration by acting as co-pigments, interacting with anthocyanins to stabilize their structures. It is assumed that flavones rather than flavonols are the predominant co-pigments present in dahlias because all cultivars show high flavone synthase II (FNS) enzyme activity and low flavonol synthase activity. To examine the biochemical basis for the distinctive dark coloring of the black dahlia, the research team from the Vienna University of Technology in Austria used pigment, enzyme, and gene expression analyses. They determined that the majority of black cultivars have very low concentrations of flavones, as confirmed by low FNS II expression.
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