EFFECTS OF METHYL BENZIMIDAZOLE-2-YL CARBAMATE ON MICROTUBULE AND ACTIN CYTOSKELETON IN ASPERGILLUS-NIDULANS

The effects of methyl benzimidazole-2-yl carbamate (MBC) on microtubul e and actin cytoskeleton were analyzed by indirect immunofluorescence and transmission electron microscopy in a wild-type strain and a benom yl-resistant mutant (benA(t0)) of Aspergillus nidulans. The treatment of the wild-type strain with sublethal doses of MBC not only caused de polymerization of cytoplasmic microtubules (MTs), but also changed the pattern of actin at the hyphal tips. In the MBC-treated hyphae, the a ctin fluorescence was concentrated at the very tip region of the hypha , whereas in the control hyphae, the actin fluorescence was weak at th e very tip and strong below the tip. The dose of MBC used for the wild -type strain did not depolymerize the MTs or modify the actin organiza tion at the apex in the mutant strain, which confirmed that the change in actin distribution in the wild-type strain was due to the disrupti on of MTs. In the mutant strain, a seven times higher concentration of MBC than in the wild-type strain was required to depolymerize MTs and to alter the actin organization at the apex. The ultrastructural stud y of the MBC-treated hyphae revealed that the area containing apical v esicles was larger and the number of microvesicles was higher than ill control hyphae. These changes probably resulted from the disassembly of MTs and the reorientation of actin cytoskeleton in MBC-treated apex es and suggested that MTs would organize the actin at the apex, which in turn would restrict the vesicle fusion to a narrow area at the hyph al tip. In treated hyphae of both strains without cytoplasmic MTs, mit otic spindles were detected although in lower number and with slightly modified morphology.