Scientists at the Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL) have made a discovery that shows photosynthesis - the production of sugars in plant cells from carbon dioxide in our atmosphere - can occur with just one light reaction. This contradicts the classic theory of photosynthesis, published in dozens of textbooks, which requires two light reactions.
With this discovery, Elias Greenbaum, biotechnology group leader in ORNL's Chemical Technology Division, believes it may be possible to genetically alter plants that produce food and perhaps to significantly improve crop productivity. Economic incentives alone should interest many agriculture and forest products companies in this work, said Greenbaum, who conceived the idea for the research project. The experimental demonstration was performed by ORNL staff scientist James Lee, supported by technicians Ginger Tevault and Steve Blankinship. Laurie Mets of the University of Chicago also collaborated on the research.
The finding, however, also represents "an experimental and conceptual breakthrough in our understanding of the molecular mechanism of how green plants convert light energy into chemical energy," said Greenbaum, who credits several scientists, including the late Daniel Arnon and V.V. Klimov, for laying the groundwork for the discovery. Arnon, who made significant findings related to photosynthesis, was a professor at the University of California at Berkeley. Klimov is a leading photosynthesis researcher in Russia.
"From a basic science standpoint, the finding that photosynthesis can occur with just one light reaction suggests a logical candidate for the 'missing link' of photosynthesis that has evaded scientists for decades," Greenbaum said. "This discovery provides experimental evidence for how natural green plant photosynthesis developed during the transition from the Earth's primitive oxygen-free atmosphere to today's atmosphere, which contains 21 percent oxygen."
The discovery was made with a mutant algal strain that performed photosynthesis more stably under anaerobic conditions (lacking oxygen) than in an environment containing oxygen. It implies that the current method of photosynthesis, utilizing two light reactions, evolved as the atmosphere became oxygen-rich. It also implies that the maximum thermodynamic conversion efficiency of light energy into chemical energy can potentially be doubled from about 10 percent to 20 percent, Greenbaum said. This gain in efficiency is what could lead to more productive food-producing and biomass plants.
"Just think of the possibilities," Greenbaum said. "With hybrids, we get excited about productivity gains of 5 percent. What we're talking about here, at least in theory, involves far more significant improvements in food crops." A technical paper by Greenbaum and his colleagues was published in the Aug. 3 issue of Nature.
The research was supported by DOE, the Pittsburgh Energy Technology Center and the National Science Foundation.
ORNL, one of DOE's multiprogram national research and development facilities, is managed by Lockheed Martin Energy Systems, which also manages the Oak Ridge Y-12 Plant and the Oak Ridge K-25 Site.
You can learn more about this research and many other exciting projects by visiting ORNL Oct. 21, during its Community Day event. Many of the lab's facilities will be open to the public that day. For additional information, call ORNL Public Affairs, (865) 574-4160.