Newswise — Scientists have long agreed that the decomposition of chlorophyll is largely responsible for the vibrant hues of most foliage in the fall. But the anthocyanin molecules that give some leaves their red tint could serve a more Darwinian purpose, according to Colgate University biology professor Frank Frey and former student Maggie Eldridge: They could be the trees' own form of chemical warfare.
Foliage changes color in autumn when chlorophyll in leaf cells (which gives them their green color) breaks down and exposes the pigments that remain. For many trees, the leftover pigments are carotenoid pigments, which appear yellow or orange.
But the story is different for maples and a handful of others, whose leaves turn scarlet, said Frey. The anthocyanin pigments in maple foliage are actually manufactured by the trees — rather than simply revealed — at a time of year when the organisms can't afford to use up a lot of metabolic energy for such a complex process.
To investigate the reason for this biological phenomenon, Frey and Eldridge conducted a series of experiments using several separate extracts from green maple leaves, red maple leaves, green beech leaves, and yellow beech leaves. They poured each mixture over lettuce seeds and measured their effect on germination and subsequent growth.
The pair found that seeds treated with the red maple extract had dramatically reduced germination and growth compared to all other treatments. "When scarlet-tinted autumn leaves are dropped in the fall, it appears that anthocyanins leach from the leaves into the soil and protect seedlings and saplings from interspecific competition the following spring," said Frey. "This seems a viable possibility, since the molecular structure of anthocyanin is nearly identical to catechin, a well-described toxin that causes root cells to self-destruct."
The development, said Frey, could one day have implications for humans. "Recent work also suggests that anthocyanins may inhibit the growth of some vertebrate cancer cells," he said.
Founded in 1819, Colgate University is a highly selective, residential, liberal arts college enrolling nearly 2,750 undergraduates. Situated on a rolling 515-acre campus in central New York State, Colgate University attracts motivated students with diverse backgrounds, interests, and talents.
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