Why the plants are green? The research team’s model reproduces photosynthesis.

When the sunlight shining on a leaf changes rapidly, plants must protect themselves from the sudden sudden surges of solar energy. To cope with these changes, photosynthetic organisms, from plants to bacteria, have developed numerous tactics. However, scientists have been unable to identify the underlying design principle.

An international team of scientists, led by physicist Nathaniel M. Gabor of the University of California, Riverside, has built a model that replicates a general feature of photosynthetic light harvesting, observed in many photosynthetic organisms.

Light harvesting is the collection of solar energy by protein-bound chlorophyll molecules. In photosynthesis, the process by which green plants and some other organisms use sunlight to synthesize food from carbon dioxide and water, harvesting light energy begins with the absorption of sunlight.

The researchers’ model borrows insights from complex network science, a field of study that explores efficient operation in cell phone networks, brains, and the electrical grid. The model describes a simple grid that is capable of entering light of two different colors and yet generating a constant rate of solar energy. This unusual choice of only two inputs has notable consequences.

“Our model shows that by absorbing only very specific light colors, photosynthetic organisms can automatically protect themselves against sudden changes (or ‘noise’) in solar energy, resulting in remarkably efficient energy conversion,” said Gabor, professor. associate of physics and astronomy, who led the study that appears today in the journal Science. “Green plants appear green, and purple bacteria appear purple because only the specific regions of the spectrum they absorb from are suitable for protection against rapidly changing solar energy.”

Gabor started thinking about photosynthesis research more than a decade ago, when he was a doctoral student at Cornell University. He wondered why plants rejected green light, the most intense sunlight. Over the years, he worked with physicists and biologists around the world to learn more about statistical methods and quantum biology of photosynthesis.

Richard Cogdell, a renowned botanist from the University of Glasgow in the United Kingdom and co-author of the research work, encouraged Gabor to expand the model to include a wider range of photosynthetic organisms that grow in environments where the incident solar spectrum is very different. .

“Excitingly, we were able to demonstrate that the model worked on photosynthetic organisms other than green plants, and that the model identified a general and fundamental property of photosynthetic light harvesting,” he said. “Our study shows how, by choosing where you absorb solar energy relative to the incident solar spectrum, you can minimize noise at the output, information that can be used to improve the performance of solar cells.”

Co-author Rienk van Grondelle, an influential experimental physicist at Vrije Universiteit Amsterdam in the Netherlands working on the primary physical processes of photosynthesis, said the team found that the absorption spectra of certain photosynthetic systems select certain regions of spectral excitation they cancel noise and maximize energy. stored

“This very simple design principle could also be applied in the design of artificial solar cells,” said van Grondelle, who has vast experience in collecting photosynthetic light.

Gabor explained that plants and other photosynthetic organisms have a wide variety of tactics to avoid damage from overexposure to the sun, ranging from molecular energy release mechanisms to physical movement of the leaf to follow the sun. Plants have even developed effective protection against UV light, just like in sunscreen.

“In the complex process of photosynthesis, it is clear that protecting the organism from overexposure is the factor that drives successful energy production, and this is the inspiration we use to develop our model,” he said. “Our model incorporates relatively simple physics, but it is consistent with a vast set of observations in biology. This is remarkably rare. If our model supports continuous experiments, we can find even more agreement between theory and observations, which gives us a deeper insight into the inner workings of nature. “

To build the model, Gabor and his colleagues applied direct network physics to the complex details of biology, and were able to make clear, quantitative, and generic statements about very diverse photosynthetic organisms.

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

Gabor added that photosynthesis can be thought of as a kitchen sink, where a faucet enters water and a drain allows water to drain out. If the flow to the sink is much greater than the flow to the outside, the sink overflows and water spills all over the floor.

“In photosynthesis, if the flow of solar energy in the light-gathering network is significantly greater than the outflow, the photosynthetic network must adapt to reduce sudden excess energy,” he said. “When the grid fails to handle these fluctuations, the body tries to expel the extra energy. In doing so, the body suffers from oxidative stress, which damages cells.”

The researchers were surprised by how simple and general their model is.

“Nature will always amaze you,” said Gabor. “Something that seems so complicated and complex could work based on a few basic rules. We apply the model to organisms in different photosynthetic niches and continue to reproduce accurate absorption spectra. In biology, there are exceptions to each rule, so much so that the finding was a rule. It is usually very difficult. Surprisingly, it seems that we have found one of the rules of photosynthetic life. “

Gabor noted that in recent decades, photosynthesis research has focused primarily on the structure and function of the microscopic components of the photosynthetic process.

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

Next, supported by several recent grants, the researchers will design a new microscopy technique to test their ideas and advance the technology of photobiology experiments using quantum optics tools.

“There is a lot to understand about nature, and it only looks more beautiful as we unravel its mysteries,” said Gabor.