Abstract
A drop method using fluorinated hydrocarbon (FC-72) was successfully applied as a quantitative assay to determine the threshold concentration of cochliophilin A, a potent Aphanomyces cochlioides zoospore attractant originally isolated from spinach roots. This method revealed that the number of zoospores attracted to droplets containing cochliophilin A increased with time, until approximately 60 to 90sec after injection of the droplet into a zoospore suspension. The threshold concentration, above which cochliophilin A was able to function as a zoospore attractant, was determined to be ca. 3.0×10-9M. Interestingly, zoospores attracted to droplets containing cochliophilin A at a concentration greater than 1.1×10-7M massed on the surface of the droplets, a behavior that was quite similar to that observed on the root surface of host plants. This result suggested that the drop method would be useful not only as a quantitative assay of chemotaxis, but also as a technique to investigate the mechanism of zoospore massing.
