Blue roses may be on the way.

Can you imagine handing your love a bouquet of blue roses? That scenario is more likely now that researchers have determined what makes blue flowers blue.

"Beautiful flower colors are mostly due to anthocyanins, flower pigments," explains Kumi Yoshida, assistant professor of natural products chemistry, Sugiyama Jogakuen University, Nagoya, Japan. These compounds can vary dramatically in color. Just like litmus paper, anthocyanins change color depending on how acidic or basic their environment is. They are red in acidic media, purple in neutral, and blue in alkaline. That led a scientist early in the century to hypothesize that blue flower petals were caused by alkaline flower cell sap. However, there is a major problem with this theory, Yoshida points out: Plant cell sap usually is weakly acidic or at most neutral. A few years later, another scientist suggested that blue flowers resulted from metal complexes of the flower pigments.

Seeking answers to this puzzle, Yoshida and her colleagues inserted a glass capillary electrode into a single pigment cell of a flower petal from the morning glory, which gradually changes from purplish-red to sky blue as it opens each morning, despite the fact that only one type of pigment molecule--heavenly blue...