November 25, 2009—For bananas, the "angel of death" wears a blue halo.
Seen under ultraviolet light, a ripening banana's brown spots are each ringed by an eerie blue glow that marks where the cells in the peel are dying, according to a recently released study.
The glow comes from substances known as fluorescent chlorophyll catabolites, which are produced by the breakdown of chlorophyll in plants that are undergoing programmed cell death, or senescence.
(See related pictures of animals glowing for science.)
In plants, senescence causes fruit to become ripe and tree leaves to change color in the fall, while in humans, programmed cell death is linked to many of the degenerative diseases associated with aging.
By watching bananas under UV light, researchers can actually watch cell death in action and track its progress at the molecular level—perhaps a first step in better understanding plant life cycles.
"It's a completely new way to look into a critical process in a cell's life," said study co-author Bernhard Kräutler, a professor of organic chemistry at the University of Innsbruck, Austria.
As a bonus, he added, the research can be done without wasting any tasty fruit: "We can measure this phenomenon on the intact banana and study it—and eat the banana later."
Findings published online September 7 in the journal Proceedings of the National Academy of Sciences.