November 23, 2012
Scientists Finally Understand How Black Dahlia Gets Its Color
Lee Rannals for redOrbit.com — Your Universe Online
The distinctive coloring of a black dahlia is based on an increased accumulation of anthocyanins as a result of drastically reduced concentrations of flavones, according to a study published in the journal BMC Plant Biology.
The dahlia is a popular garden flower, and continuous breed of it has led to 20,000 varieties, many of them showing red hues. The molecular mechanisms for a spectrum of dahlias are already well known, but it wasn't until now scientists understood the black-red coloring of the rarer version of the flower.
Flower color in dahlias is based on the accumulation of a group of metabolites called flavonoids. It is known that red tones come from anthocyanins, while white and yellow tones lack anthocyanins, but contain large amounts of flavones and chalcones.
Flavones and flavonoids are colorless, but they influence flower coloration by acting as co-pigments, interacting with anthocyanins to stabilize their structures. Scientists have assumed that flavones are the predominant co-pigments present in dahlias since all cultivars show high flavone synthase II enzyme activity and low flavonol activity.
In order to examine the biochemical basis for the distinctive dark coloring of the black dahlia, the team used pigment, enzyme and gene expression analyses. They determined that the majority of black cultivars have low concentrations of flavones.
Since flavones compete with anthocyanin biosynthesis for periods, the lack of flavone favors the accumulation of huge amounts of anthocyanins that are found in black dahlias.
The contents of black dahlias increased slightly parallel to the decrease of flavones, the researchers found.
Heidi Halbwirth, lead author of the paper, said the black color of dahlias is not due to increased activity of the anthocyanin pathway, but is the result of the intermediates being converted into anthocynanins.
"The molecular explanation for the specific suppression of flavone formation in the majority of black dahlias will be of interest for further research," Halbwirth said in a statement. "As the dahlia is an octoploid plant and the presence of several alleles is expected, the simultaneous suppression of all FNS II isoenzymes indicates an effective mechanism that could be used for engineering plants with tailor-made flavone contents."