Effects of methyl benzimidazoIe-2-yl carbamate on microtubule and actin cytoskeleton inAspergillus nidulans

Abstract

The effects of methyl benzimidazole-2-yl carbamate (MBC) on microtubule and actin cytoskeleton were analyzed by indirect immunofluorescence and transmission electron microscopy in a wild-type strain and a benomyl-resistant mutant (benA 10) ofAspergillus nidulans. The treatment of the wild-type strain with sublethal doses of MBC not only caused depolymerization of cytoplasmic microtubules (MTs), but also changed the pattern of actin at the hyphal tips. In the MBC-treated hyphae, the actin fluorescence was concentrated at the very tip region of the hypha, whereas in the control hyphae, the actin fluorescence was weak at the 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 organization at the apex in the mutant strain, which confirmed that the change in actin distribution in the wild-type strain was due to the disruption 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 study of the MBC-treated hyphae revealed that the area containing apical vesicles was larger and the number of microvesicles was higher than in control hyphae. These changes probably resulted from the disassembly of MTs and the reorientation of actin cytoskeleton in MBC-treated apexes 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 hyphal tip. In treated hyphae of both strains without cytoplasmic MTs, mitotic spindles were detected although in lower number and with slightly modified morphology.