We all know about inhibition and stimulation—or at least in human terms. These are important in the natural world as well, and much of what organisms do is in response to one, the other, or both. Now we generally don't think of plants in terms such as these, which perhaps imply either mobility or consciousness, but the concepts are quite applicable.
With many kinds of plants, clipping off the ends of branches results in
thicker growth as formally dormant buds awaken and form new twigs. This is a pretty
good example of an inhibition that works through stimulation. In plants showing apical
dominance, a chemical called auxin is produced at the tip of the branch, and this
inhibits active growth of buds that are lower down on the branch. The way it appears to
do so is by stimulating the production of a plant hormone, ethylene. The ethylene, in
turn, inhibits the bud tissues from growing. So what we have is a chemical that
inhibits by stimulating another chemical that inhibits. And you thought botany was
simple!
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.