Gardeners can choose from more than 20,000 varieties of dahlias, including whites, yellows, deep reds, and magentas. But the rarer black dahlias are especially alluring. Now, a team of researchers in Austria has turned the eye of science on what makes a dahlia black. The team collected 14 varieties of black dahlia—with names such as "Black Barbara," "Arabian Night," "Karma Choc" (left), and "Tisa" (right)—and five varieties with tamer colors, then extensively analyzed their petals. They measured the activity of enzymes that make pigments, investigated gene expression, and measured the pigments themselves. Their conclusion: The black color comes from high levels of anthocyanins , the pigments that—at lower levels—also give orange and red dahlias their colors. The team reports in BMC Plant Biology that they think that most black dahlias raise their anthocyanin levels by blocking an enzyme in the pathway that makes flavones, another molecule that has the same precursor as anthocyanins. If scientists could figure out that trick, they might be able to engineer dahlias to make more black varieties.
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