The Bryonia dioica tendril-coiling assay provides a rapid, sensitive and selective bioassay for jasmonates. Using this assay, a large number of jasmonate and coronatine analogs were analyzed for their biological activities. In 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 biological activity, one centered around the structure of jasmonic acid allowing only minor C-1(1') modifications and a second center around the structure 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)-pentenyl)-cyclopentane-1-octanoic acid], for which coronatine is a structural mimic, was the much more potent inducer of tendril coiling, when applied externally. The levels of jasmonic acid and 3-oxo-2(2'(Z)pentenyl)-cyclopentane-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 and progression of the coiling reaction. Thus, 12-oxophytodienoic acid, rather than jasmonic acid or 3-ore-2(2'(Z)-pentenyl)-cyclopentane-1-octanoic acid, has to be considered as an endogenous signal transducer in B, dioica mechanotransduction.
