Plants and algae, as well as cyanobacteria, use photosynthesis to produce oxygen and "fuels," the latter being oxidizable substances like carbohydrates and hydrogen. There are two pigment-protein complexes that orchestrate the primary reactions of light in oxygenic photosynthesis: photosystem I (PSI) and photosystem II (PSII). Researchers writing in PNAS say they have taken a significant step closer to understanding how these photosystems work their magic, which may boost the effort to develope new sources of energy.

The team created mutations in a single-celled green alga (Chlamydomonas reinhardtii or 'Chlamy' for short). Using these mutants,they have shown that the primary light-triggered electron transfer event in the PSI reaction center can be initiated independently in each of its parallel branches. At the same time, they showed that PSI has two charge separation devices that effectively work in parallel to increase the overall efficiency of electron transfer.

"Although we knew that both branches were being used in PSI, and that our mutations had an effect upon the relative use of each pathway, what we did not know was how these mutations were having their effect," Kevin Redding, an associate professor in the department of chemistry and biochemistry at Arizona State University, explained. "Unraveling that has led to the discovery of how charge separation – the moment when electromagnetic energy is converted to chemical energy – actually occurs."

Other researchers working on the project at the Max Planck Institute (MPI) used lasers that sent out pulses of light lasting only 60 millionths of one billionth of a second to investigate the electron transfer processes in the two branches of PSI. This allowed them to look at extremely early events in the photosynthetic mechanism, events occurring in just a few picoseconds (a millionth of a millionth of a second), which is a time so short that a typical lattice atom could only execute a dozen oscillations on its lattice site.

The current research will help scientists understand how these complex processes work in Nature. And the use of two charge separation devices working cooperatively to maximize efficiency is a design theme that may well be applied in future efforts to create artificial photosynthetic devices.

The use of solar energy to produce a clean fuel such as hydrogen is essentially the only process, the researchers say, that can satisfy these criteria on a scale large enough to meet the world's energy demands.