If plants did not defend themselves in some way, they would certainly be gobbled up by a whole suite of voracious predators ranging from little insects to large mammalian herbivores. Indeed, not only do plants defend themselves, they typically have more than one kind of defense. When a plant has several options, how does it choose? Does it allocate multiple defenses to the same tissues or defend different tissues in different ways?
Diane Wagner and colleagues from the University of Alaska, Fairbanks, examined how two defensesphenolic glycosides (a direct chemical defense) and extrafloral nectaries (an indirect defense)were distributed among leaves of a plant in the trembling aspen (Populus tremuloides) in Alaska. They found unique findings contradicting all expectations and published them in the April issue of the American Journal of Botany (http://www.amjbot.org/cgi/content/full/97/4/601).
Diane Wagner has had a long-standing interest in extrafloral nectaries, or EFNs, which in general serve as an indirect plant defense. EFNs are found on the petiole at the base of a leaf and serve to attract insect predators who consume both the nectar produced by the plant and herbivorous insects that attack the plant.
"After noticing EFNs on aspen leaves about 7 years ago, I was surprised to find that very few biologists had studied their function in aspen," Wagner noted. Trembling aspen is common and widespread in North America and is a species of considerable aesthetic and ecological importance. So Wagner joined forces with Pat Doak, an insect population ecologist, to look at the functional significance of EFNs in trembling aspen. The study was funded by the National Science Foundation.
"The expression of EFNs in aspen is unusually variable," Wagner notes. "Some leaves within a plant express nectaries but others do not, and the frequency with which EFNs are ex
|Contact: Richard Hund|
American Journal of Botany