Abstract
The following tannins, Chinese gallotannin, 1,2,3,4,6-pentagalloyl glucose, chebulinic acid, procyanidin dimers, and procyanidin trimers were tested and found to be antagonists of seven gibberellins (GAs). Each tannin inhibited the growth induced by any of the gibberellins GA(1), GA(3), GA(4), GA(7), GA(9), GA(13), and GA(14) in the dwarf pea assay. Endogenous growth was not affected. The highest ratio of tannin to gibberellin tested (1000:1 by weight) inhibited from 60 to 95% of the induced growth for all tannins and all gibberellins tested. The tannins were particularly inhibitory against GA(4) and GA(14) where a ratio of 10:1 (tannins: GA by weight) resulted in up to 85% growth reduction. Inhibition could be completely reversed by increasing the amount of gibberellin in all combinations studied. The procyanidin dimers and trimers were the first purified components of condensed tannins to be tested in this system and were potent inhibitors particularly against growth induced by GA(4) and GA(14). Inhibition by these compounds along with similar inhibition by previously tested hydrolyzable tannins demonstrates that the effect is general to tannins of all classes.