Behavioral Responses of the Ciliated Protozoan Paramecium caudatum to 2,4-Dichlorophenoxyacetic Acid and Its Analogues

摘要

We found that the ciliated protozoan Paramecium caudatum ON-1 was repelled by 2,4-dichlorophenoxyacetic acid (2,4-D). P. caudatum was also repelled by phenoxyacetic acid, while it was attracted o benzoic acid. No significant behavioral response was detected with 2,4-dichlorophenol (2,4-DP) and phenol. These results suggested that the substitution of -OH of phenol with -OCH_2COOH, but not the chlorination of phenol, was important for eliciting the avoiding resp9nse to 2,4-D in P. caudatum. Electrophysiological analysis revealed that 2,4-D and phenoxyacetic acid were able to trigger the action potential in P. caudatum, whereas 2,4-DP and phenol failed to elicit electrical responses in this organism. Well test assays suggested that the avoiding reactions allowed P. caudatum to escape from the harm caused by this herbicide.