The cheatgrass labeling experiment was then compared to a labeling experiment performed on soybeans in 2006.
A video of the scientists running the soybean labeling experiment can be found on Schaefer's lab page (http://www.chemistry.wustl.edu/~schaefer/Soybean_Labelingwmv.htm)
The surprising results
Neither plant behaved as it was supposed to in the low carbon dioxide atmosphere.
Both plants made glycine, an amino acid that is an intermediate product in the photorespiration cascade, but the glycine, instead of being fed back into the carbon fixation process, was combined with other amino acids to form glycine-rich proteins.
Glycine-rich proteins are structural proteins that the plants use to strengthen cell walls, particularly those in xylem, the specialized water-transporting tissue, and to counter the effects of dehydration.
So instead of spinning their wheels, the plants were responding adaptively to the low carbon dioxide condition, strengthening tissues that would help them survive the water stress for which low carbon dioxide is usually a proxy.
Their response to the high carbon dioxide atmosphere was another matter entirely.
The soybeans stopped making the glycine-rich protein and instead starting routing most of the glycine back to carbon fixation in classic photorespiration wheel-spinning fashion. In other words, they stopped responding adaptively and started wasting energy.
The cheatgrass, on the other hand, kept right on trucking, churning out more glycine-rich protein.
What it all means
Soybeans probably have a switch, or control system, Schaefer says, that responds to carbon dioxide concentrations inside the leaf. If the carbon dioxide level falls, this switch turns on protein synthesis. If the carbon dioxide level rises, the switch turns off pr
|Contact: Diana Lutz|
Washington University in St. Louis