Max-Planck-Institute for Chemical Ecology, Tatzendpromenade 1a, 07745 Jena, Germany.
Plants under attack by a herbivore or pathogens may emit characteristic volatiles that are implicated in the attraction of the natural enemies of the herbivore. The signal cascade between the leaf damage and the volatile production is stimulated by high- or by low molecular elicitors from the secretions of the herbivore/pathogen. The signal transduction generally involves the activation of the octadecanoid pathway, as exemplified by the transient increase of endogenous jasmonate (JA), in leaves of Phaseolus lunatus, after treatment with the macromolecular elicitor cellulysin. Within this pathway the lima bean (P. lunatus, as model system) possesses at least two different biologically active signals triggering different biosynthetic activities. Early intermediates of the pathway, especially 12-oxo-phytodienoic acid (PDA), are only able to induce the biosynthesis of the diterpenoid-derived 4,8,12-trimethyltrideca -1,3,7,11-tetraene and minor amounts of 4,8-dimethylnona -1,3,7-triene. High concentrations of PDA result in more complex patterns of additional volatiles. JA, the last compound in the sequence, lacks the ability to induce diterpenoid-derived compounds, but is highly effective at triggering the biosynthesis of other volatiles. The phytotoxin coronatine mimics the action of PDA and JA, but does not increase the endogenous level of endogenous JA. Novel peptide elicitors for volatile biosynthesis and their mode of action will be presented. T. Koch, V. Jung, T. Krumm, J. Engelberth & W. Boland. (1999) Plant Physiol., in press.