Effects of the demethylase inhibitor, cyproconazole, on hyphal tip cells ofSclerotium rolfsii. II. An electron microscope study

Hyphal tip cells ofSclerotium rolfsii, prepared by freeze substitution, were examined by transmission electron microscopy after continued growth on cyproconazole-amended potato dextrose agar at fungistatic concentrations of 0.1, 0.75, and 1.0 μg/ml which respectively produced 50, 80, and 95% growth inhibition. Alternatively, observations were made of control tip cells that were transferred onto potato dextrose agar amended with 0.75 μg/ml cyproconazole for 30, 60, and 240 min. Ultrastructural abnormalities observed in hyphal tip cells as a result of cyproconazole treatment included (1) Spitzenkörper disorganization, (2) proliferation of smooth endoplasmic reticulum with inflated cisternae, (3) increased vacuolar contents, (4) presence of monovesicular bodies, and (5) irregular cell wall characteristics. Alterations of the Spitzenkörper, endoplasmic reticulum, and vacuoles were noted 30 min after exposing control hyphae to cyproconazole (0.75 μg/ml). Abnormal wall depositions were observed 60 min after fungicide exposure. After a 140-min exposure to fungicide, tip cell morphology was similar to that of cells grown in the continual presence of 0.75 μg/ml cyproconazole. The changes in hyphal morphology are discussed relative to the mode of action of cyproconazole.