Rooted in place, plants can't run from herbivoresbut they can fight back. Sensing attack, plants frequently generate toxins, emit volatile chemicals to attract the pest's natural enemies, or launch other defensive tactics.
Now, for the first time, researchers reporting in the June 2007 issue of Plant Physiology have identified a specific class of small peptide elicitors, or plant defense signals, that help plants react to insect attack.
In this colorful self-defense strategy, proteins already present in the plant are ingested by insect attackers. Digesting the proteins, the insects unwittingly convert this food into a peptide elicitor, which gets secreted back onto plants during later feedings. Recognizing the secreted elicitor as a kind of "SOS," plants launch defensive chemistry. This defense discovery opens the door for the development and genetic manipulation of plants with improved protection against pests.
Although researchers have long known that some plants distinguish different insect attackers, this defensive behavior has proven difficult to describe at the molecular level. Exceedingly few model systems have been utilized to characterize the potential interactions between what researchers estimate to be at least four million insects and 230,000 flowering plant species. Moreover, highly active plant defense signals can occur at trace levels, too small to easily detect or isolate.
Still, scientists have determined that insect herbivory, mechanical damage, and pathogens such as bacteria and fungi can all set off a variety of peptide warning signals in plants, which respond by increasing phytohormones, particularly ethylene, jasmonic acid, or salicylic acid, that regulate defensive responses. But which peptide signals act as alarmsand how"
To address those questions, Dr. Eric Schmelz at the United States Department of Agriculture's Center for Medical, Agricultural and Veterinary Entomology operated by th
Contact: Dr. Eric Schmelz
American Society of Plant Biologists