Phytogrowth-Inhibitory Activities of Tropolone and Hinokitiol

Tropolone (I) and hinokitiol (II) at concentrations of 50 ppm showed strong inhibitory activity on the growth of all plants examined. Compounds I and II completely inhibited the germination of the seeds of some plants at the same concentration. The phytogrowth-inhibitory activities of both compounds were higher than that of sodium 2, 4-dichlorophenoxyacetate (2, 4-D), which was used as a standard. Both compounds inhibited the growth of some plants even at a concentration as low as 10 ppm. On the other hand, unlike 2.4-D, I and II stimulated the growth of all plants at the low concentration of 1 ppm. At 7d after treatment with I and II, the amount of chlorophyll in leaves of Brassica camperstris L. subsp. rapa. HOOK. f. et ANDERS treated with both compounds was greatly decreased as compared with the control group.