Toxicity of allelopathic monoterpene suspensions on yeast dependence on droplet size

The toxic effects of the allelopathic nonsubstituted monoterpenes β-pinene and limonene on yeast,Saccharomyces cerevisiae, were proportional to the size of the monoterpene droplets in suspension. Both the toxic effects and the size of the droplets in suspension were decreased by adding different solvents with the monoterpene as follows: dimethylsulfoxide - dimethylformamide ≫ ethanol > dioxane. Oxygen consumption was inhibited about 80% by 1 mM β-pinene added in dimethylsulfoxide but less than 10% when β-pinene was added in dioxane. Parallel decreases in droplet size and toxic effects of either monoterpene were also induced by hydrating the monoterpene-dimethylformamide or monoterpene-dimethylsulfoxide before addition to yeast. Molecular aggregation may be a mechanism to potentiate the allelopathic properties of monoterpenes when these associate with diverse soil components.