Plant signalling and induced defence in insect attack.

Abstract Plants can produce compounds which act as semiochemicals, that is, signals modifying the development or behaviour of other organisms without having direct physiological activity. Among such semiochemicals are plant stress signals associated with the induction of defence systems, and these may include phytopheromones that naturally influence plant development. It is well known that plant-derived semiochemicals can be exploited by colonizing organisms, particularly pathogens and insect pests. Recently proposed external signals not yet proven as natural phytopheromones are nitric oxide and the volatile methyl esters of jasmonic and salicylic acids. Since it is now possible to use sophisticated electrophysiological techniques to investigate insect interactions with prospective phytopheromones, the detection and characterization of signalling systems has been made much easier and can provide a molecular characterization of signals that are active beyond the insects themselves. In addition to the advances these studies have brought to the understanding of plant/insect and plant/plant interactions, plant signals are potentially valuable in the regulation of gene expression for improved or alternative approaches to crop protection or for other developmental processes in plants.