Structure-activity analyses reveal the existence of two separate groups ofactive octadecanoids in elicitation of the tendril-coiling response of Bryonia dioica Jacq.

The Bryonia dioica tendril-coiling assay provides a rapid, sensitive and se lective bioassay for jasmonates. Using this assay, a large number of jasmon ate and coronatine analogs were analyzed for their biological activities. I n a systematic study, C-3 analogs, C-2 analogs, C-1 homologs and -analogs, C-1(1') analogs of jasmonic acid, as well as analogs of coronatine altered in both the amino acid and the coronafacic acid moiety, were compared. The results demonstrated at least two structurally non-overlapping centers of b iological activity, one centered around the structure of jasmonic acid allo wing only minor C-1(1') modifications and a second center around the struct ure of 12-oxophytodienoic acid and having different structural requirements for activity, thus allowing quite different structural modifications. The C18-group of the jasmonates [12-oxophytodienoic acid and 3-oxo-2(2'(Z)-pent enyl)-cyclopentane-1-octanoic acid], for which coronatine is a structural m imic, was the much more potent inducer of tendril coiling, when applied ext ernally. The levels of jasmonic acid and 3-oxo-2(2'(Z)pentenyl)-cyclopentan e-1-octanoic acid in mechanically stimulated tendrils remained very low and did not change detectably, while the level of 12-oxophytodienoic acid had earlier been shown to change drastically and transiently during the onset a nd progression of the coiling reaction. Thus, 12-oxophytodienoic acid, rath er than jasmonic acid or 3-ore-2(2'(Z)-pentenyl)-cyclopentane-1-octanoic ac id, has to be considered as an endogenous signal transducer in B, dioica me chanotransduction.