BLOOMINGTON, Ind. -- All life on Earth depends on photosynthesis for food and oxygen. The origin of this crucial process in green plants is a longstanding problem in biology, and a number of different theories have been proposed to explain it. But there has been no clear evidence to support any of these theories.
In a paper in the Sept. 8 issue of the journal Science, a team of biologists lead by Carl E. Bauer, Clyde Culbertson Professor of Biology at Indiana University, reports the results of their study of the evolution of photosynthesis.
In photosynthesis, green plants use the energy of sunlight to convert carbon dioxide into hydrocarbons that promote plant growth while generating oxygen from water and releasing the oxygen to the atmosphere. All animals including humans depend either directly or indirectly on this source of food and oxygen. Consequently, photosynthesis is considered the most important chemical process on Earth.
Scientists agree that photosynthesis originated in bacteria, with some bacteria containing photosystems that release oxygen in a way very similar to that found in green plants today, and some other bacteria containing simplified photosystems that do not release oxygen. What was not clear is which species of bacteria contains the most ancient photosystem and how photosynthesis in green plants evolved from photosynthesis in bacteria.
By generating a large new molecular data set, Bauer's group, which includes IU postdoctoral fellow Jin Xiong and IU doctoral student William Fischer, has determined that non-oxygen-producing bacterial species such as the purple and green bacteria are the most ancient photosynthetic bacteria. Another group of non-oxygen-producing bacteria known as heliobacteria evolved later.
The scientists also found that heliobacteria are the most closely related to the common ancestor of the oxygen-producing photosynthetic cyanobacteria. Cyanobacteria eventually gave rise to chloroplasts in algae and
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Contact: Hal Kibbey
hkibbey@indiana.edu
812-855-0074
Indiana University
6-Sep-2000