Why Are Some Petunia Petals Blue? Genetic Defect Causes Cellular Pump To Fail

By Ajit Jha on January 4, 2014 1:54 PM EST

blue petunia
For about a century, researchers have wondered why some flowers' petals turn blue instead of their normal red or violet. Now, they've discovered that a defective cellular pump could be to blame. (Photo: Diógenes el Filósofo, CC0 1.0)

For a long time, blue colored petunias were an enigma to scientists. Some of those from VU-University in Amsterdam, however, recently solved the enigma and now know the exact mechanism that imparts such a rare shade of blue on some petunias. Their findings are reported in the journal Cell Reports.

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The researchers discovered that there is actually a kind of cellular pump that fails to function properly in some petunias, which turns them blue. The failure of this cellular pump in flowers, including the petunias that the researchers studied, causes special compartments in the petals' cells to fail to acidify, therefore making them unable to take on their normal color - red or violet, NBC reported.

According to Francesca Quattrocchio, of the university, the petals' blue color has caused ongoing speculation among scientists since as early as 1910, when two hypotheses were proposed. The blue colors, according to the first hypothesis, could possibly be due to reduced acidity of the "cell sap." The second hypothesis proposed that the formation of metal-anthocyanin complexes possibly caused flower petals to turn blue. These deleterious defects, the hypothesis said, could have been triggered by drastic changes in the cell sap.

The current study found that both hypotheses were right, the researchers said. Yet, no one really knew how it actually worked. Flowers use several tiny pumps to help regulate acidity (pH) in their membranes; however, researchers had believed since at least the 1980s that all of them helped in transporting hydrogen ion concentrations, which make up pH. The new work finds that this isn't the case. The researchers found that steeper pH gradients are shown in the petals - the newly discovered pump was responsible for accumulating higher concentrations of acid.

Scientists have also known that a handful of pH genes determine the differences in pH between blue petunia petals and red ones. These are the genes that were identified by Quattrocchio and colleagues, which encode a proton-pumping pathway that possibly triggers hyperacidification of particular compartments. There are two distinct proteins that constitute the pump and constantly build acidity, however, when that special pumping system becomes defective, petunias turn blue. In other words, genetic defects are responsible for blue-colored petunias.

"By studying the difference between blue and red flowers of petunias, we have discovered a novel type of transporter able to strongly acidify the inside of the vacuole," Quattrocchio said in a statement.

The study will prove useful, according to the researchers, in imparting "new colors in valuable flowers, or new tastes in fruits, wines, and juices" through genetic intervention. However, it is important that flowers become red instead of blue to attract pollinators. 

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