The standard explanation, says Schaefer, is that the enzyme in question evolved when there was no oxygen in Earth's atmosphere. So it didn't matter that it could bind either carbon dioxide or molecular oxygen.
Now that oxygen levels are higher, however, the oxygen-based reactions get in the way of the carbon-based reactions.
Schaefer was aware of the photorespiration problem because he had worked in the 1960s and 1970s at Monsanto, the St. Louis-based agricultural business.
"The consensus at the time was that photorespiration was wasteful, and if you could inhibit it, the plant would be more productive," Schaefer says.
"Monsanto had a big research effort to find a chemical that would do that. They had hundreds of guys working on it. I started using nuclear magnetic resonance to characterize photorespiration, but I didn't have the right techniques to resolve the chemical interactions I wanted to study."
The rooftop experiment
By the time he read about cheatgrass in the L.A. Times, however, Schaefer had the technique he needed (see sidebar "The Right Tool for the Job.") So when he returned to St. Louis, he started growing pots of cheatgrass on the roof of WUSTL's McMillan Hall.
In a special labeling experiment, one pot was exposed to an atmosphere with a carbon dioxide concentration of 200 parts per million, substantially below the current atmospheric level. The other pot was exposed to 600 parts per million, a concentration likely to be reached by 2050.
Both the nitrogen in the fertilized soil and the carbon in the carbon dioxide were unusual isotopes. The isotopes acted as tracers, allowing the scientists to see how the plant used the nitrogen and carbon. (They also explain the small scale of the experiment, because one bottle of artificial air with labeled carbon di
|Contact: Diana Lutz|
Washington University in St. Louis