Arabidopsis thaliana for testing the phytotoxicity of volatile organic compounds

Geosmin and C-8 hydrocarbons are among the major volatile organic compounds (VOC) responsible for the distinctive, musty odor of filamentous fungi. In this study, we developed a plant bioassay for testing the possible toxicity of these compounds, as well as four air freshener products sometimes used to mask their odor. Seeds and vegetative plants of Arabidopsis thaliana were exposed to 1 ppm of 14 different volatile treatments (both single compounds and mixtures) for 72 h and monitored for germination rate, seedling formation, vegetative plant vigor and chlorophyll concentration. All VOCs tested had some inhibitory effect on seed germination or seedling formation; 1-octen-3-one was the most active, giving almost complete inhibition of germination. Geosmin did not prevent germination (radicle protrusion) but seedling formation was arrested 90 %. Of solvents and fragrance products tested, only the scented oil product was as active as the C-8 biogenic compounds in inhibiting seed germination and seedling formation. Two-week-old plants exposed to 1 ppm of individual fungal VOCs for 72 h all exhibited some degree of stress symptoms including smaller leaf size and weight, discoloration, leaf curling, small necrotic lesions, and reduced chlorophyll concentration. Two-week-old vegetative plants exposed to solvents and air freshener products were generally smaller in size. The single most phytotoxic compound tested was 1-octen-3-one which almost completely inhibited seed germination and was lethal to vegetative phase plants. Formaldehyde at 1 ppm killed 2-week-old seedlings but had little effect on seed germination. In conclusion, the A. thaliana bioassay provides an inexpensive approach for testing the toxicity of gas phase molecules.