FLUNARIZINE AFFECTS F-ACTIN PATTERN IN MUCOR-ROUXII GERMLINGS

The effect of the Ca2+ antagonist flunarizine on Mucor rouxii germling s was analyzed. In sporangiospores cultivated in aerobiosis, the drug blocked germ tube emergence, but enlarged spheres continued to grow is odiametrically. The formation of broad protuberances and irregular bud s was observed. Calcofluor staining indicated aberrations on the surfa ce of the flunarizine-treated cells. This was not a simple switch to t he yeast form, since labelling with rhodamine-tagged phalloidin reveal ed various ring-shaped structures of F-actin, indicating furrowing of the plasma membrane. Flunarizine apparently did not interfere with nuc lear divisions or with the integrity of microtubules. In young germlin gs, flunarizine treatment induced cessation of tip growth and promoted septation associated with the rearrangement of F-actin. Apical growth was reestablished after either the drug was removed or an excess of C a2+ ions was added to the medium. The results suggest that tip-related arrangement of F-actin requires flunarizine-sensitive Ca2+ entry.