Thursday, July 29, 2004

Nitrate Assimilation in Plant Shoots Depends on Photorespiration

That's the title of this paper, which appears in the current issue of the PNAS. The paper is based on the work of three scientists at the University of California at Davis, led by Dr. Arnold Bloom.

Papers in the PNAS tend to be rather technical, and this one is no exception. Happily, the UC Davis website has provided this readable summary of the paper's results. Here's an excerpt:


Though elegantly simple in concept, this process, known as photosynthesis, is remarkably complex in detail. And for years, researchers have been puzzled by another process, photorespiration, which seems to have annoyingly associated with photosynthesis down the evolutionary pathway.

Photorespiration has appeared to be downright wasteful because it virtually undoes much of the work of photosynthesis by converting sugars in the plant back into carbon dioxide, water and energy.

Believing that photorespiration is a consequence of the higher levels of atmospheric carbon dioxide in long past ages, many scientists concluded that photorespiration is no longer necessary. Some have even set about to genetically engineer crop plants so that the activity of the enzyme that initiates both the light-independent reactions of photosynthesis and photorespiration would favor photosynthesis to a greater extent and minimize photorespiration.

The result, they have thought, would be more productive crop plants that make more efficient use of available resources.

But the new UC Davis study suggests that there is more to photorespiration than meets the eye and any attempts to minimize its activity in crop plants would be ill advised.

“Photorespiration is a mysterious process that under present conditions dissipates about 25 percent of the energy that a plant captures during photosynthesis,” said Arnold Bloom, a professor in UC Davis' vegetable crops department and lead researcher on the study. “But our research has shown that photorespiration enables the plant to take inorganic nitrogen in the form of nitrate and convert it into a form that is useful for plant growth.”


Fascinating stuff. Also fascinating is how I became aware of this paper: Our friends over at Access Research Network seem to think this result comes as a blow to evolutionists. Here, in its entirety, is the summary of the article provided by ARN, written by Tom Magnusun:


Photorespiration, “a biological process in plants, thought to be useless and even wasteful” and “just an evolutionary leftover” from an age when carbon dioxide was more prevalent, has been found to be “necessary for healthy plant growth and if impaired could inhibit plant growth,” according to a UC Davis study. It functions as a way to inhibit nitrate assimilation. Some agricultural scientists assumed it was an unnecessary process to be genetically engineered out of plants because it was wasteful, “But the new UC Davis study suggests that there is more to photorespiration than meets the eye and any attempts to minimize its activity in crop plants would be ill advised.”

Evolutionary presuppositions stood in the way of scientific progress. A design model would have simply tried to determine the reason for the phenomenon.


Of course, the assertion that “evolutionary presuppositions” stood in the way of this particular discovery is not even based on sound logic, much less any evidence.

What, exactly, is Magnusun alleging? Is he saying that other scientists were keen on studying the photorespiration system in plants but were discouraged from doing so by that dogmatic, Darwinian thought police the ID's are always warning us about? Is he saying that in some way the uselessness of the photorespiration system is a prediction of evolutionary theory? Is he implying that evolutionists should be disappointed that the photorespiration system performs an important function in plants?

In reality, the expectation is just the opposite. The photorespiration system is complex and consumes a considerable amount of the plant's resources. Prior to the present research, it seemed that the primary function of this system was harmful to the plant (in that it seemed to undo much of the work that photosynthesis did). If the photorespiration system did not also perform some useful function for the plant then it is hard to believe that natural selection would have kept it around and functional for so long. Far from being a blow to evolutionists, this work provides a plausible explanation for why this system persists in plants.

I e-mailed Dr. Bloom and showed him the description of his paper that appeared at ARN. He was kind enough to send me the following reply:


I do not have extensive experience with the “intelligent-design theory,” but our results are not at all in conflict with evolutionary theory. What we found is that the process of photorespiration is associated with nitrate assimilation, so that conditions that inhibit photorespiration interfere with the ability of a plant to convert nitrate into organic forms of nitrogen. The statement on the arn.org web site that states “It (sic. Photorespiration) functions as a way to inhibit nitrate assimilation.” is incorrect. Our studies reveal a previously unrecognized function for photorespiration, and may provide an evolutionary explanation for why the process of photorespiration has persisted in most plants despite dramatic changes in the composition of the Earth's atmosphere.


There is one other curious thing about Magnusun's summary. He is explicitly committing the ID folks to the proposition that every part of every organism serves some useful function for the organism. I suspect every working biologist has his own catalog of favorite examples of poor engineering in nature. Perhaps Magnusun would like to get started on an explanation for, say, the useulss eyes of certain cave-dwelling rodents or the pelvic bones in snakes.

This paper is not an example of evolutionary presuppositions standing in the way of scientific progress. But it is yet another example of ID folks misrepresenting the scientific literature for the purpose of folling nonscientists.