An international team, led by the University of California (Riverside) in collaboration with scientists from the Universities of Glasgow and Amsterdam, has constructed a model that reproduces a currently unrecognized general feature of photosynthesis, that can be observed across many types of photosynthetic organisms.

The study –published in Science – uses the model to lay out a remarkable feature of how green plants transform light energy into chemical energy.

Photosynthetic organisms, such as plants and bacteria, protect themselves from surges of sunlight (or solar energy) through various ways – but the underlying mechanisms by which they do this have remained elusive to scientists.  

Photosynthesis — the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water — begins with harvesting light energy by the absorption of sunlight.

In this study, the researchers’ model borrows ideas from the science and operations behind complex systems like mobile phone networks, the human brain, and the power grid.

Nathaniel Gabor, Associate Professor and physicist from the University of California, said: “Our model shows that by absorbing only very specific colors of light, photosynthetic organisms may automatically protect themselves against sudden changes — or ‘noise’ — in solar energy, resulting in remarkably efficient power conversion.

Prof Richard Cogdell, Hooker Chair of Botany at the University of Glasgow’s Institute of Molecular, Cell and Systems Biology, said: “Excitingly, we were able to show that the model worked in other photosynthetic organisms besides green plants, and that the model identified a general and fundamental property of photosynthetic light harvesting.

“Our study shows how, by choosing where you absorb solar energy in relation to the incident solar spectrum, you can minimize the noise on the output — information that can be used to enhance the performance of solar cells.”

Plants and other photosynthetic organisms have a wide variety of tactics to prevent damage due to overexposure to the sun, ranging from molecular mechanisms of energy release to physical movement of the leaf to track the sun. Plants have even developed effective protection against UV light, just as in sunscreen.

Gabor added: “In the complex process of photosynthesis, it is clear that protecting the organism from overexposure is the driving factor in successful energy production, and this is the inspiration we used to develop our model.

“Our model incorporates relatively simple physics, yet it is consistent with a vast set of observations in biology. This is remarkably rare. If our model holds up to continued experiments, we may find even more agreement between theory and observations, giving rich insight into the inner workings of nature.

“Our model is the first hypothesis-driven explanation for why plants are green, and we give a roadmap to test the model through more detailed experiments.”

To construct the model, the researchers applied straightforward physics of networks to the complex details of biology, and were able to make clear, quantitative, and generic statements about highly diverse photosynthetic organisms.

Gabor added: “In photosynthesis, if the flow of solar power into the light harvesting network is significantly larger than the flow out, the photosynthetic network must adapt to reduce the sudden over-flow of energy. When the network fails to manage these fluctuations, the organism attempts to expel the extra energy. In doing so, the organism undergoes oxidative stress, which damages cells.

“Nature will always surprise you. Something that seems so complicated and complex might operate based on a few basic rules. We applied the model to organisms in different photosynthetic niches and continue to reproduce accurate absorption spectra. In biology, there are exceptions to every rule, so much so that finding a rule is usually very difficult. Surprisingly, we seem to have found one of the rules of photosynthetic life.

“Biologists know well that biological systems are not generally finely tuned given the fact that organisms have little control over their external conditions,” he said. “This contradiction has so far been unaddressed because no model exists that connects microscopic processes with macroscopic properties. Our work represents the first quantitative physical model that tackles this contradiction.”

The paper, ‘Quieting a noisy antenna reproduces photosynthetic light harvesting spectra’ is published in Science. The work was funded by the Air Force Office of Scientific Research Young Investigator Program, the National Science Foundation, and through a United States Department of the Navy Historically Black Colleges, Universities and Minority Serving Institutions award. Gabor was also supported through a Cottrell Scholar Award and a Canadian Institute for Advanced Research Azrieli Global Scholar Award. Cogdell was also supported by the Canadian Institute foir Advanced Research and by the BBSRC.

First published: 25 June 2020

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