Comparative Studies on the Growth Inhibition by Caffeic and trans-Cinnamic Acids

1) Both caffeic and trans-cinnamic acids inhibited the IAA-induced growth of Avena coleoptile sections. The inhibition by caffeic acid, at 5×10-4M, was observed only in the presence of high concentrations of IAA, while that by trans-cinnamic acid, at 10-4M, was more conspicuous in the absence of IAA than in its presence.2) At the concentration of 10-3M, caffeic acid as well as chlorogenic acid inhibited the hypocotyl growth of Brassica seedling, but trans-cinnamic acid, at the same concentration, did not.3) In the root growth of Brassica seedling, caffeic acid, at a concentration of 10-3M, acted as a promoter, while trans-cinnamic acid acted only as an inhibitor.4) The gibberellin induced growth of Avena leaf segment was suppressed remarkably by 2×10-4M of trans-cinnamic acid, but was not affected by caffeic acid even at 10-3M.