Isolation and structural characterization of a water-soluble germination inhibitor from Scotch thistle (Onopordum acanthium) cypselas.

Cypsela dormancy in Scotch thistle (Onopordum acanthium) may be affected by the presence of chemical inhibitors. To investigate this phenomenon, a leachate from O. acanthium cypselas was tested for its ability to inhibit germination of the cypselas from which it was derived (i.e., autoinhibition). Leachates varied in their degree of autoinhibition, depending on the cypsela population from which they were prepared. Overall, removal of leachate from a group of O. acanthium cypselas increased their germinability. Using lettuce (Lactuca sativa) cypselas as an indicator species, bioactivity-guided fractionation was used to isolate a water-soluble, para-substituted benzamide from O. acanthium cypselas, which caused germination inhibition. Various chromatographic, spectroscopic, and spectrometric techniques were applied to the characterization of the bioactive compound.