In a recent study, researchers from India and the US have found an answer to the mystery centered around electron flow during photosynthesis, a process that plants use natural sunlight to produce oxygen.
The study by the researchers from the Indian Institute of Science (IISc) and the California Institute of Technology (Cal Tech) is said to help design efficient fuel cells, efficient artificial leaves, address future energy requirements, and other systems that mimic photosynthesis.
Plants, some bacteria, and algae species perform photosynthesis with the help of protein complexes called photosystems – Photosystem I and II. The researchers demonstrated how one of the two identical branches of photosystems, named D1 and D2, goes dominant over the other during the initial phases of photosynthesis.
According to the researchers, there is a series of chain reactions underway in photosynthesis during which electrons get transferred across multiple pigment molecules.
They have underscored the importance of electron movements for the energy transfer across one of the D branches during the initial stages of photosynthesis.
Previous studies had shown electrons flowing only along D1, but the reasons for that behaviour remained a mystery. It is the photosystem II (PSII), which kickstarts photosynthesis, first by trapping energy from sunlight and splitting water, later providing oxygen molecules and supplying electrons that get transported to the subsequent proteins and molecules.
But as the energy transfer happens at ultrafast speeds and the inter-plant or organism variations, researchers had not fully deciphered the early processes of photosynthesis.
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The scientific team at IISc used a combination of molecular dynamics simulations, quantum mechanical calculations, and the Marcus theory to first map the energy landscape for electron movement in both D1 and D2 branches.
“We assessed the electron transfer efficiency step-by-step through both D1 and D2 branches,” said Shubham Basera, a PhD student in the Department of Physics and one of the authors of the paper published in the journal Proceedings of National Academy of Science.
The findings suggested that the energy barrier posed by D2 was higher, which in turn prevented the electron movement. Another possibility for this behaviour by electrons, they said, could be due to the minor differences in the protein environment around the PSII in addition to the nature in which the pigments are embedded in it.
The researchers also suggested that tweaking some of these components can boost or rewire electron flow across PSII; for instance, by swapping chlorophyll and pheophytin in D2, the electron blockade could be addressed, as this chlorophyll needed lower activation energy than pheophytin.
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“The findings may help design efficient artificial photosynthetic systems capable of converting solar energy into chemical fuels, contributing to innovative and sustainable renewable energy solutions,” said Prabal K Maiti, Professor, Department of Physics, IISc.