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Untitled Document
Bananas turn from yellow to bright blue under ultra-violet light helping animals decide which ones are ripe enough to eat.
The fluorescent colouring is caused by the breakdown of chlorophyll - the green pigment in plants vital for obtaining energy from light - and provides a tool to identify dying and rotten cells.
Animals that eat bananas can see in the ultraviolet range of the spectrum so they can immediately see which ones to take before they become inedible.
Professor Bernhard Krautler, from Innsbruck University, Austria, said: "In contrast to humans, many of the animals that eat bananas can see light in the UV range.
"The blue luminescence of the banana fruit could give them a distinct signal that the fruit is ripe."
As bananas go rotten the bright yellow peel develops brown and black spots which mark dead tissue and spread quickly to eventually envelop the whole fruit.
Prof Krautler and colleagues, whose findings are published in Proceedings of the National Academy of Sciences, discovered bright blue halos appear around the dead spots under UV light.
As the banana ripens the chlorophyll begins to break down a process called catabolism and the resulting products are concentrated in the banana peel.
He said the appearance of the autumn colours is a hallmark of chlorophyll breakdown in deciduous trees and shrubs.
In bananas unique fluorescent chlorophyll catabolites (FCCs) were discovered, pointing to a "previously unknown path of chlorophyll breakdown."
He said breakdown of chlorophyll is a major contributor to the ripening of apples and pears.
In contrast, in ripening bananas chlorophylls fade to give FCCs, causing yellow bananas to glow blue, when observed under UV light.
"Fruit eating animals might have learned, through survival pressure, to notice the blue luminescence of FCCs in ripening bananas, and the characteristic rings that develop as halos on the spotted peels of very ripe bananas," Prof Krautler said.
"For humans, blue luminescence of yellow bananas has been a recently discovered feature, which has become entertaining and stunning, at first.
"As suggested here, natural fluorescent FCCs may prove to be helpful as a non-invasive, molecular tool for studying cellular processes in plants."
Source: www.telegraph.co.uk
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