Hyphae of Sclerotium rolfsii were grown on cyproconazole-amended agar at fungistatic concentrations of 0.1, 0.75, and 1.0 μg/ml, which respectively produced approximately 50, 80, and 95% inhibition of hyphal extension. Hyphal tip cells were prepared for transmission electron microscopy by cryofixation and freeze substitution methods. Cell walls of control and fungicide-treated hyphal tip cells were compared cytochemically using periodic acid-thiocarbohydrazide-silver protein, gold-conjugated lectins, and immunocytochemical staining. Cell walls of both control and fungicide-treated cells reacted positively to periodic acid-thiocarbohydrazide-silver protein staining although the patterns of staining were different. Apical walls of control cells were generally thinner than those in fungicide-treated hyphae. Two distinct cell wall layers were identified in the subapical walls of control hyphae while distinct wall layers were typically not observed in fungicide-treated hyphae. Staining characteristics of abnormal cell wall deposits were variable after periodic acid-thiocarbohydrazide-silver protein stain. In regions of mature cell wall of control hyphal tip cells, wheat germ agglutinin-binding sites were localized along the inner layer of the cell wall. In fungicide-treated hyphae, binding sites for wheat germ agglutinin occurred throughout the cell wall except in electron opaque wall inclusions. Concanavalin A-binding sites were localized along the plasma membranes of both control and cyproconazole-treated hyphae in subapical cell regions. Electron opaque inclusions in abnormal cell wall deposits had affinities for concanavalin A. Immunocytochemical localization of β-1,3 glucans occurred in mature cell walls of control and fungicide-treated cells. No β-1,3 glucans were detected in electron opaque wall inclusions of hyphae exposed to cyproconazole. Alterations in the cell wall are discussed in light of the mode of action of the fungicide and aspects of cell wall deposition. © 1990.
