Thrust reversal by tubular mastigonemes: Immunological evidence for a role of mastigonemes in forward motion of zoospores of Phytophthora cinnamomi

The role of tubular mastigonemes in the reversal of thrust of the anterior flagellum of Phytophthora cinnamomi was analysed using mastigoneme-specific monoclonal antibodies and immunofluorescence and video microscopy. Exposure of live zoospores of P. cinnamomi to the mastigoneme-specific Zg antibodies caused alterations in the arrangement of mastigonemes on the flagellar surface and at Zg concentrations above 0.3 mu g/ml, mastigonemes became detached from the flagellum. As a consequence of antibody binding to the mastigonemes there were concentration-dependent perturbations in zoospore swimming behaviour and anterior flagellum beat pattern. With increasing antibody concentration zoospores swam more slowly and other parameters of their swimming pattern, such as the wavelength of the swimming helix and the frequency of rotation, were also reduced. The effects of Zg antibodies were specific at two levels: control immunoglobulins or antibodies that bound to other flagellar surface components did not have an effect on motility, and Zg antibodies did not interfere with the motility of zoospores of oomycete species to which they did not bind. The effects of antibody-induced disruption of mastigoneme arrangement strongly support previous hypotheses that tubular mastigonemes are responsible for thrust reversal by the anterior flagellum, enabling it to pull the cell through the surrounding medium.