Phytogrowth-Inhibitory Activities of [beta]-Dolabrin and [gamma]-Thujaplicin, Hinokitiol-Related Compounds and Constituents of Thujopsis dolabrata Sieb. et Zucc. var hondai MAKINO

β-Dolabrin and γ-thujaplicin isolated from Thujopsis dolabrata Sieb. et Zucc. var hondai MAKINO, like hinokitiol, showed strong phytogrowth-inhibitory activities, and their growth-inhibitory activities were as high as that of sodium 2, 4-dichlorophenoxyacetate used as a positive control. In particular, the phytogrowth-inhibitory activity of γ-thujaplicin was strong and it completely inhibited the germination of this seed ob Brassica campestris L. subsp. rapa HOOK f. et ANDERS at the concentration of 30 ppm. Both compounds exhibited inhibitory activities on B. campestris L. subsp. rapa HOOK f. et ANDERS and Sesamum inducum LINNE, even at the low concentraiton of 10 ppm. At 7 d after treatment with β-dolabrin and γ-thujaplicin, the amount of chlorophyll in the cotyledons of B. campestris L. subsp. rapa HOOK f. et ANDERS treated with both compounds was greatly decreased as compared with the control. The findings in dicate that the phytogrowth-inhibitory action might be a common biological activity of hinokitiol-related compounds, suggesting that at least a part of their phytogrowth-inhibitory actions seems to be related to a decrease in chlorophyll content.