Why are plants green?

Model identifies how organism protects itself against solar energy.

06/25/2020 | 2:51 PM

Until now, scientists have failed to identify how photosynthetic organisms protect themselves from the effects of the massive variations in solar energy. An international team of researchers has now formulated a model that reproduces a common trait of light harvesting, as seen for many photosynthetic organisms. The study was published June 25 in Science.

Sunlight falling on a leaf changes color and intensity quickly and plants must protect themselves from the effects of the enormous variations in solar energy. Photosynthetic organisms, ranging from plants to algae and bacteria, have developed a variety of tactics to deal with this. Light harvesting is the collection of solar energy by protein-bound chlorophyll molecules. During photosynthesis, the process that green plants and other photosynthetic organisms use to produce nutrients from carbon dioxide and water using solar energy, harvesting the necessary solar energy begins with the absorption of sunlight.

Two colours
Involved VU Amsterdam biophysicist Rienk van Grondelle, who studies photosynthetic complexes using ultrafast laser spectroscopy, about the model: "The model shows that if two fairly specific colors can be absorbed, photosynthetic organisms automatically protect themselves against large fluctuations," noise 'in the offered solar energy, resulting in a very stable conversion of solar energy into products. Green plants are green, red bacteria are red because only specific parts of the light spectrum from the sun they absorb are able to protect them from the large fluctuations in the offered sunlight. ”

The model identified a general and fundamental property of photosynthetic light harvesting. The researchers can quite accurately pinpoint the energy difference between the two colors that give the optimal output. A property that can also be used to optimize the functioning of man-made solar cells. Photosynthetic organisms have many mechanisms to prevent damage to the photosynthetic device. Preventing overexposure is an essential step in the successful production of energy and this principle has been used for the development of the model.

Cooperation
The research team was led by physicist Nathaniel Gabor of the University of California, Riverside (UCR) and supported by the biophysicist Rienk van Grondelle, Vrije Universiteit Amsterdam (VU Amsterdam) and the biochemist Richard Cogdell, University of Glasgow, UK (UGUK). You can find the article “Quieting a noisy antenna reproduces photosynthetic light harvesting spectra” here.