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The phytotoxic principle, coronatine, which is present in several pathovars of the plant pathogen, Pseudomonas syringae was shown to be highly active in completely different, jasmonate-selective bioassays. At nanomolar to micromolar concentrations, coronatine induced the accumulation of defense-related secondary metabolites in several plant cell cultures, induced transcript accumulation of the elicitor-responsive gene encoding the berberine bridge enzyme of Eschscholtzia califomica, as well as the coiling response of Bryonia dioica tendrils. Biological activity critically depended upon the structure of coronatine, and slight moditications, such as methylation of the carboxyl moiety or reduction of the carbonyl group, rendered the molecules almost inactive. Coronafacic acid, obtained by hydrolysis of coronatine, was also nearly inactive. Coronatine did not elicit the accumulation of endogenous jasmonic acid in the systems analyzed. While coronafacic acid is similar in structure to jasmonic acid, we found coronatine to be a close structural analogue of the cyclic Cl&precursor of jasmonic acid, lZoxo-phytodienoic acid. The phytotoxic symptoms produced by coronatine can now be understood on the basis of the toxin's action as a mimic of the octadecanoid signalling molecules of higher plants.

Fungal cell wails and fragments thereof (elicitors) induce the formation of low and high molecular weight defense compounds in plant cell suspension cultures. This induced synthesis requires a signal molecule transmitting the message between the elicitor plant cell wail receptor and gene activation. We demonstrate in this study that cis-jasmonic acid is rapidly synthesized in plant cell cultures ofdiverse taxonomic origin (gymnosperms and mono-and dicotyledonous plants) after challenge with a fungal elicitor preparation. The rapid decline ofcis-jasmonic acid in some ofthese issues is attributed to rapid metabolism of this pentacyclic acid. The induction of alkaloids by several different molecules provoking the elicitation process is strictly correlated with the synthesis of jasmonates. Elicitation leads to a rapid release of a-linolenic acid from the lipid pool of the plant cell. a-Linolenic acid and 12-oxophytodienoic acid, the formation of which is also induced, are known to be distant precursors ofjasmonic acid. We assume cis-jasmonic acid and its precursors to be the signaling molecules in the elicitation process.

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