What gives sunlight chlorophyll

Why plants are green

Plants absorb sunlight to turn water and carbon dioxide into high-energy carbohydrates. In order to allow the necessary biochemical processes to run as evenly as possible, the leaves do not convert all the radiated wavelengths of the electromagnetic spectrum into energy. How the plants succeed in doing this has now been analyzed by both physicists and botanists working with Nathaniel Gabor from the University of California at Riverside. In the journal “Science”, the team presents an amazingly simple model for photosynthesis that applies to both green plants and sunlight-absorbing algae and bacteria.

“Our model explains why plants are green,” explains Gabor. At first glance, it is surprising that plants reflect green sunlight and do not use it for photosynthesis, even though this part of the solar spectrum provides a particularly large amount of energy. One reason lies in the self-protection of the plants: the intensity of the sunlight fluctuates between a cloud-free and overcast sky, and with it the amount of energy available. These fluctuations can damage the plant cells on a leaf. The scientists around Gabor tried to reproduce this ability with the help of a simplified model system.

The leaves of green plants contain the pigment chlorophyll, which absorbs sunlight. In order to convert as much light energy as possible, the chlorophyll molecules are arranged in so-called light-collecting complexes. Almost every light particle arriving from the sun releases an electron in these combinations, which drives the subsequent biochemical processes. In this way, natural photosynthesis achieves an efficiency of almost one hundred percent - even under constantly changing lighting conditions. With their models, Gabor and his colleagues simulated different networks of pigments and simulated the conditions under full sun, partial shade and under water. They discovered that the light-harvesting complexes only have to contain two different pigments - each of which absorbs different wavelengths of sunlight - in order to successfully compensate for fluctuating light intensities. This basic principle can also be applied to photoactive bacteria.

The current study not only helps to better understand the details of natural photosynthesis. The researchers can also envision technical applications. “If you only use a certain part of the entire solar spectrum, this minimizes fluctuations in the energy provided. This knowledge can also be used to increase the performance of solar cells, ”says Gabor.