Similarities of the biological activities of coronatine and coronafacic acid to those of jasmonic acid

Coronatine, a phytotoxin produced by Pseudomonas syringae pv. atropurpurea and an amide of coronafacic acid and coronamic acid, is known to induce the expansion of cells in potato tubers just as jasmonic acid (JA) does. Furthermore, the chemical structure of coronafacic acid resembles that of JA to some extent. These observations led us to postulate that coronatine and related compounds might have biological activities similar to those of JA. We compared the biological activities of coronatine and coronafacic acid to those of JA in four jasmonate-responsive assay systems, namely, in assays for tuber-inducing activity (with single-node segments of potato stems), for cell expansion-inducing activity (with cells of potato tubers), for cell division-inhibiting activity (with soybean callus) and for senescence-promoting activity (with oat leaves). Coronatine had a positive effect in all these assays and its activity was 100 to 10 000 times higher than that of JA in terms of the threshold concentration for activity. Coronafacic acid also gave a positive result in all the assays, but its activity was slightly weaker than that of JA in two assay systems. These results suggest that the special configuration of side chains with respect to the plane of the cyclopentanone ring, namely, the 1R, 2S configuration in JA and the 3aS, 7aR configuration in coronatine and coronafacic acid, is necessary for these various biological activities.