Natural Inhibitors of Germination and Growth, V Possible Allelopathic Effects of Compounds from Thuja occidentalis

Volatile com pounds which are released from fresh leaves o f Thuja occidentalis inhibited ger­ m ination o f seeds o f Amaranthus caudatus and Lepidium sativum. The volatile com pounds were obtained by a vacuum m ethod applied to the leaves, by direct analysis o f the content o f secretory organs and by solvent extraction o f leaves. The bioactive com pounds proved to be m onoterpenes. The highest bioactivity were found for alcoholic com pounds followed by ketones, esters and finally hydrocarbons. N on-volatile germ ination inhibitors which were ex­ tracted w ith ho t w ater were abscisic acid ( 3 4 |ig/g fresh weight o f leaves), and two oxidation products o f thujone, 2-[2 '-acetyl-l'-isopropyl]cyclopropylacetic acid (“T hu jaketosäure”) and 3-isopropyl-5-oxohex-2-enoic acid. These com pounds could also be prepared from thujone. The relationship o f these com pounds with possible allelopathic effects o f Thuja occidentalis is discussed.