By | March 31, 2023
Sunlight shining through the top of a ring of trees.

One of the most well-studied chemical processes in nature, photosynthesis, may not work quite as we thought it did, scientists have accidentally discovered.

Photosynthesis is the process by which plants, algae and some bacteria convert carbon dioxide and water into oxygen and sugars to use as energy. To do this, the organisms use sunlight to oxidize, or take electrons from, water; and reduce, or donate electrons to, carbon dioxide molecules. These chemical reactions require photosystems – protein complexes that contain chlorophyll, a pigment that absorbs light and gives plant leaves and algae their green color – to transfer electrons between different molecules.

In the new study, published March 22 in the journal Nature (opens in new tab), researchers used a new technique known as ultrafast transient absorption spectroscopy to study how photosynthesis works on a time scale of one quadrillionth of a second (0.00000000000000001 second). The team first tried to find out how quinones – ring-shaped molecules that can steal electrons during chemical processes – affect photosynthesis. But instead, the researchers found that electrons could be released from photosystems much earlier during photosynthesis than scientists had previously thought possible.

“We thought we were just using a new technique to confirm what we already knew,” the study’s co-author Jenny Zhang (opens in new tab)a biochemist specializing in photosynthesis at the University of Cambridge in England, said in a statement (opens in new tab). “Instead, we found a completely new path and opened the black box of photosynthesis a little further.”

Related: New ‘artificial’ photosynthesis is 10 times more efficient than previous attempts

Two photosystems are used during photosynthesis: photosystem I (PSI) and photosystem II (PSII). PSII primarily provides electrons to PSI by taking them from water molecules: PSI then further excites the electrons before releasing them to eventually be given to carbon dioxide to create sugars, via a series of complex steps.

Previous research had suggested that the protein scaffolds in PSI and PSII were very thick, helping to contain electrons within them before passing them on to where they were needed. But the new ultrafast spectroscopy technique revealed that the protein scaffolds were more “leaky” than expected and that some electrons could escape from the photosystems almost immediately after light was absorbed by the chlorophyll in the photosystems. These electrons were therefore able to reach their destinations faster than expected.

“The new electron transfer pathway we found here is completely surprising,” Zhang said. “We didn’t know as much about photosynthesis as we thought we did.”

The electron leakage was observed in both isolated photosystems and in “living” photosystems inside cyanobacteria.

In addition to rewriting what we know about photosynthesis, the discovery opens new avenues for future research and biotechnological applications. The team believes that by “hacking” photosynthesis to release more of these electrons at earlier stages, the process could become much more efficient, which could help produce plants that are more resistant to sunlight or artificially replicated to create renewable energy sources to help to combat climate change, according to the statement. However, much more research is needed before this can happen.

“Many scientists have tried to extract electrons from an earlier point in photosynthesis, but said it was not possible because the energy is so buried in the protein scaffold,” Zhang said. “The fact that we can [potentially] to steal them in an earlier process is astonishing.”


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