Negative Chemotaxis of Zoospores of the Fungus Phytophthora palmivora

Phytophthora palmivora zoospores are repelled by many low molecular weight cations. This negative chemotactic response occurs at a different threshold concentration for each cation, that for the most effective ion, H+, being 150 μ m. The effectiveness of different cations parallels their ionic conductivities, the most active cations having the highest conductivities. It is suggested that the close approach of cations to the cell surface reduces the negative charge at the surface and hence changes the transmembrane potential, altering flagellum activity in such a way as to cause turning and negative chemotaxis.