VIEW ARTICLE

Physiology and Biochemistry

Mechanism of Electrotaxis of Zoospores of Phytopathogenic Fungi. B. M. Morris, Department of Molecular and Cell Biology, Marischal College, University of Aberdeen, Aberdeen AB9 1AS, Scotland, UK; N. A. R. Gow, Department of Molecular and Cell Biology, Marischal College, University of Aberdeen, Aberdeen AB9 1AS, Scotland, UK. Phytopathology 83:877-882. Accepted for publication 6 May 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-877.

Plant roots generate weak electrical fields in the rhizosphere that may stimulate electrotactic swimming of zoospores of plant pathogenic fungi. Here we show that in vitro electrotaxis of zoospores of Pythium aphanidermatum was cathodic, whereas those of two other Pythium species and Phytophthora palmivora were anodic. Electrotaxis occurred in electrical fields comparable in magnitude to those generated by plant roots. Electrical fields of a physiological magnitude had little effect on the velocity of swimming but increased the turning frequency of the zoospores of P. palmivora over threefold. Reagents that affected calcium-ion transport or calmodulin function had an apparent effect on electrotaxis, but most also induced premature encystment or cell lysis. The surface charge of the posterior flagellum of an anodotactic zoospore of P. palmivora was positive, whereas the anterior flagellum was relatively electronegative. In contrast, the posterior flagellum of a cathodotactic zoospore of Pythium aphanidermatum was negatively charged, and the anterior flagellum was relatively electropositive. Results suggest that electrotactic swimming of zoospores is mediated by the combined effects of modulation of the turning frequency and electrophoretic orientation of the zoospore in the electrical field. Electrotaxis may be used, in conjunction with chemotaxis, to identify and locate the plant root regions most susceptible to infection.