Comparative Effects of Alicyclic Compounds and Quinones on Inhibition of Lettuce Fruit Germination

Germination of lettuce (Lactuca sativa L. cv. Great Lakes) fruits was inhibited by many alicyclic compounds including monoterpenes. Quinones were particularly active. The hydrocarbons showed little activity correlated with their insolubility in water while compounds containing a keto group conjugated with a double bond showed highest activity. As in previous studies the lipophilicity of the molecule was one of the main contributing factors to inhibition, provided that the value was not extreme, as for the hydrocarbons. In natural compounds noted for high inhibitory activity, several different substituents were present in the molecule and it seems likely that each contributes different factors to the overall effect. Some of these compounds are well known plant constituents implicated in allelopathy.