My love is like a blue, blue rose

About 110 million roses will be sold in the US on February 14 2003, according to Jay Stawarz, Executive Secretary for the International Cut Flower Industry Association. And it's likely that most of those will be red. But would a rose of any other color smell as sweet? Those in the quest for the blue rose — the "holy grail" of horticulture — seem to think so.In the world of blooms, blue is a particularly difficult hue to achieve because of the complex genetic and environmental cues that lead to its expression. The blueness seen in flowers like the petunia depend on the synthesis of a pigment called delphinidin, or 3',5'-hydroxylated anthocyanin. But co-pigments such as flavonol or flavones must also be present to prompt a blue shift in the anthocyanin absorption spectrum. And the vacuolar pH must be high to produce a true blue color.Back in the 1980s, a new breed of horticulturist started to experiment with flower color. Peter Meyer and colleagues at the Max-Planck Institute in Cologne, Germany, were the first to apply genetic modification to flower color.In 1986, the biotechnology company Florigene was founded in Melbourne, Australia, to pursue the development of a blue rose, carnation and chrysanthemums. The three varieties comprise 50% of the world market in cut flowers. The company isolated two genes necessary for delphinidin production and initiated a program to introduce them into the flowers. So far, Florigene has developed four varieties of transgenic "blue" carnation — but even these appear more mauve than truly blue.Tim Holton of the Queensland Biotechnology Center in Brisbane, Australia, led the blue rose project at Florigene for 10 years. He explained "It was easier to transform the carnation, in part, because we began with a white flower. The strategy Florigene is using in the rose requires the blue pigments to compete with the natural red pigments. Suitable white roses did not exist."Holton further clarified, "Three things are needed to produce a blue flower: 100% delphinidin production, flavonol and acyl groups." Insertion of the delphinidin synthesis genes can augment production of the appropriate pigment, but roses lack acyl groups. (Complex acylation pathways are important in producing a blue petunia.) Roses are also acidic. In the alkaline vacuolar environment of the petunia, delphinidin is blue; but in the acidic rose vacuole it is pink. The carnation has a more alkaline vacuolar environment than the rose.A third gene involved in delphinidin synthesis in the petunia was identified in 1999. The gene encodes a cytochrome b5 enzyme that enhances the formation of 3',5' substituted anthocyanins. Petunias in which the gene had been knocked out showed a 60% reduction in delphinidin accumulation compared to wild type.Another possible innovation in the pursuit of the blue bloom has surfaced in the unlikeliest of places — a toxicology laboratory. Elizabeth Gillam of the University of Queensland works on drug metabolism and investigates drug interactions with the cytochrome P450 enzymes — a group of enzymes found in high concentrations in the liver. She collaborates with F. Peter Guengerich (also a toxicologist) at Vanderbilt University School of Medicine in the US.After seeing a flask of bacteria transformed with P450 genes turn blue, Gillam had a "Eureka" moment. "I had previously read about Florigene and immediately thought this presented an alternative" to the existing methods of genetically engineering a blue hue into plant life.Gillam's enzymatic short cut may make the production of a blue bloom a somewhat easier task. Holton explained that the conversion catalyzed by the human P450 enzyme constitutes "a completely different chemical pathway" from that found in blue flowers that is "simpler because it is a single conversion." Gillam admits, "We don't yet have a handle on the challenges it would involve." In the flask of bacteria, indol was the substrate for the P450 enzyme and, although plants contain indol-related compounds, it's not known whether they would react with P450, nor whether the conversion would be toxic to the plant.Gillam said "I would have called you crazy if you'd told me five years ago, I would be pursuing a blue rose." But it's a long shot. Preliminary gene bombardment studies with the aim of introducing P450 enzymes into white petunias have been inconclusive. Hence, anyone desperate to give blue roses this year will have to resort to dipping white roses in ink and letting the phloem to the trick.

My love is like a blue, blue rose

but is there any progress towards a blue rose?

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