New light is thrown on photosynthesis and the role of plant pigments

Researchers from the University of Toronto and University of Glasgow have found that pigments found in plants and purple bacteria employed to provide protection from sun damage do more than just that. They also help to harvest light energy during photosynthesis.

The findings are being reported on various websites including ScienceDaily (here).

Carotenoids, the same pigments which give orange color to carrots and red to tomatoes, are often found together in plants with chlorophyll pigments that harvest solar energy. Their main function is photoprotection when rays of light from the sun are the most intense.

However, a new study published in Science this week shows how they capture blue/green light and pass the energy on to chlorophylls, which absorb red light.

“This is an example of how nature exploits subtleties that we would likely overlook if we were designing a solar energy harvester,” says Greg Scholes, the D.J. LeRoy Distinguished Professor in the Department of Chemistry at the University of Toronto and lead author of the study.

A series of experiments showed that a special “dark state” of the carotenoid — a hidden level not used for light absorption at all — acts as a mediator to help pass the energy it absorbs very efficiently to a chlorophyll pigment.

The researchers performed broadband two-dimensional electronic spectroscopy (a technique used to measure the electronic structure and its dynamics in atoms and molecules) on light-harvesting proteins from purple bacteria.

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