Competitive Photosynthesis

Announcement: See the earlier blog post about the Second Annual Oklahoma Evolution Road Trip! Full information, and registration, are available at the website of the Oklahoma Science Teachers Association. Bob Melton will soon post one revision: the Saturday afternoon trip will not visit the fossil site out on Highway 51. It takes too long to get there and the parking along a busy highway seems inadequate to me. My wife and I went out to check on Redbud Valley yesterday, and she helped me find even more fossils there than I had known about.

Warning: If you go to a Chinese buffet and have one of those steamed mussels, do not open up the body. Just pretend the whole thing looks like that nice grayish muscle tissue. If you open the body up, you will see a bunch of organs, most of which are digestive and some, I assume, reproductive. A knowledge of biology only makes the experience worse. Tastes good, though. Now for the essay.

Like many botany instructors, I use variegated coleus as a way of demonstrating that photosynthesis occurs only in green tissue. The leaves of variegated coleus have sections that are green, or red, or white, or both red and green. The procedure is simple. You use a double boiler and ethanol to remove chlorophyll and anthocyanin from a leaf, then use iodine solution to stain the starch. Starch is present only in the green parts of the leaf. (The ethanol boiling process is itself a source of pleasure, I might add.) A variegated coleus leaf is sort of like a field trial with two experimental conditions (chlorophyll vs. anthocyanin), a control (the white part), and an interaction (red overlaps green).

Variegated coleus grows well in gardens and greenhouses and homes, even though approximately half the leaf area is non-photosynthetic. It only recently occurred to me that this ought to seem strange. Why would a plant produce non-photosynthetic leaf area, unless it is modified for some other function? The answer is obvious: variegated coleus is an example of a mutant form that would not survive in the wild.

But why would it not survive in the wild? The plant grows perfectly well. But a plant that produces twice as much leaf area as it “needs” would be unable to survive in the wild because of competition with other plants. That is, if plants produced only as much leaf area as they needed to keep themselves alive, the world would have only about half as much leaf area as it does. Forests and grasslands would look very shabby, and noticeably less green. Even from outer space, our planet would look a lot less green if it were not for the extra leaf area that plants produce in order to compete with other plants. This is what I mean by “competitive photosynthesis,” which might otherwise sound like a new Olympic sport. (The sportscaster would say, Look, there goes a carbon dioxide molecule now…it made it into a glucose molecule! There goes a water molecule, and here comes the oxygen!)

This is not a new idea, but it is a good one to stop and think about. A long time ago Garrett Hardin pointed out that if it were not for competition, all plants would be crusty green goo. Why do any plants grow up into the air? The sun is 93 million miles away, so a 300-foot-tall tree is not significantly closer to the sun than is a one-foot-tall shrub. But the tree’s leaves are closer to the sun than the shrub’s leaves. It is like the old saying, if you and another person are running from a bear, you don’t have to outrun the bear, just outrun the other person. This is competition, the basis of natural selection and evolution. Hardin called it “in praise of waste.”

A natural world without competition would be much less interesting, at least much less green. Competition is a good thing. In our economic system, however, it has gotten out of hand. Big money crushes small business, and anyone who chooses to serve humankind rather is doomed to a life of near-poverty. I say this as a college professor, husband of a librarian, and father of a school teacher. We public servants work hard and well, harder and better than many people richer than we are. Competition is good, but so is altruism. In our species, we need to lay a greater claim on altruism.