How to Make a Black Dahlia

Credit: Dr. Heidi Halbwirth

New research uncovers the secret of how a flower gets its famous color.

Dahlias (Dahlia variabilis) are very popular garden flowers, with almost 20,000 varieties bred in a wide range of shapes, sizes and colors. As far as color goes, you can find Dahlias  in white, yellow, many shades of red, orange and pink.

There is also a very rare variety: the black Dahlia. About a dozen Black Dahlias exist, known by creative names such as "Arabian Knight", "Chat Noir", and, oddly, "Charles de Gaulle".

For most dahlias plant scientists have long known how they get their colors: metabolites called flavonoids, which accumulate in the plants. For instance, anthocyanins produce red colors, flavones produce white, and chalcones produce yellow colors. But until now, nobody knew how a black dahlia was created. 


A research team led by Dr. Heidi Halbwirth, from Vienna University of Technology, Austria, found that Dahlia's black coloring comes from throwing off balance levels of anthocyanins and flavones. In a study published on November 23 in the journal BMC Plant Biology, researchers found that black Dahlia flowers had much higher concentrations of anthocyanins (as much as 10 fold over bright red varieties), and much lower concentrations of flavones (by about the same ratio as anthocyanins). These concentrations were drastically different even from red varieties, which also are produced by anthocyanins.

Furthermore, the team found that black dahlias acquire their color because of the reduced activity of a key enzyme, called FNS II (short for flavone synthase), that usually makes flavones. With low levels of these enzyme, lower concentrations of flavones can't compete with anthocyanins for the building block molecules they share; hence, more anthocyanins and the black color. 


While anthocyanins and other flavonoids contain powerful antioxidant properties (the same flavonoids are found in berries and other brightly color flowers), these antioxidants can also fend off prey and diseases, both in plants and animals that consume them. Using genetic engineering techniques, breeders could create plants that contain tailored amounts of flavonoids, which could help in nutrition (for edible plants) as well as in gardening and breeding flowers.

For the full article, please go to: http://www.biomedcentral.com/1471-2229/12/225/abstract.


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