filamentous cyanobacteria also called blue-green algae
Shutterstock/Ecky Ilham
Two research teams have explored microscopically how oxygen is formed during photosynthesis, the process by which plants, algae and some bacteria use sunlight to generate the energy they need to grow. details have been revealed. Understanding photosynthesis at this level can advance the development of clean fuels.
Researchers previously knew that four consecutive light particles, or photons, needed to hit a molecular structure within a plant to initiate photosynthesis. These photons are absorbed by clusters of manganese, calcium, and oxygen atoms, breaking down plant water molecules and releasing the oxygen bound in the water. But the details of exactly what happens after the fourth photon hits this cluster have eluded researchers for decades. Two experiments filled some of them.
Jan Kahn and his colleagues at the Lawrence Berkeley National Laboratory in California used pulses of high-energy X-rays to capture microscopic details of photosynthesis. They placed clusters of molecules extracted from cyanobacteria on a conveyor belt and first irradiated them with a pulse of visible light that gave them the photons needed to initiate the decomposition of water. X-rays then captured the arrangement of atoms during the process.
After the fourth photon hits, a protein complex known as photosystem II (PSII) splits the water molecule within a few millionths of a second. The X-rays were fast enough to show the time delay between the decomposition of water and the formation of molecular oxygen of the type that could eventually be released into the atmosphere. No. However, the X-ray images taken during these two steps were not sharp enough to show the exact arrangement of the oxygen atoms.
However, the arrangement of other parts of the PSII molecule around these oxygen atoms indicated that the oxygen had formed some new structure. At this stage, the oxygen atoms were not bound to hydrogen as they are in water or clustered into larger oxygen molecules, but were probably temporarily bound to another part of PSII. This stage of the process has so far only been theorized, Khan says.
Holger Dow and his colleagues at the Free University of Berlin also looked at the tail end of the water splitting process, but instead of taking X-ray images of atoms, they determined how electrons and protons move between atoms. Infrared was used to They extracted his PSII from 40 kilograms of fresh spinach, exposed it to visible light photons, and then irradiated it with infrared light.
When PSII absorbed infrared light, each wavelength correlated with the vibration of a specific bond. The researchers combined these measurements with his computer simulation of how electrons and protons move during photosynthesis carried out by his Leonardo Guidoni and team at the University of L’Aquila in Italy. . This reveals an important new step in the process in which three He protons are exchanged for one He electron between the oxygen atom and the rest of PSII.
Philip Simon, also at Lawrence Berkeley National Laboratory, even says that some X-ray snapshots suggest that this proton motion may occur twice at the end of the water-splitting process. . Both teams hope to use faster X-rays, cleaner PSII samples, and more infrared to reveal even more detail in the future. Guidoni says these approaches for studying photosynthesis are complementary. “The more data we can get from every experiment, the closer we can get to filling in every little step in the process,” he says.
Understanding water splitting during photosynthesis is also important for developing devices that turn water into hydrogen fuel, says Dimitrios Pantazis of the Max Planck Institute for Coal Research in Germany. “While we cannot directly replicate any biological system, it is the only system known to break down water so efficiently. We need to uncover the tricks of ,” he says.
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