Ultrastructure of the ungerminated conidium of Blumeria graminis f.sp. hordei

Abstract

Ungerminated conidia of Blumeria graminis f.sp. hordei were prepared for transmission electron microscopy using cryofixation and freeze-substitution. Conidia were uninucleate, with the nucleus located in the central portion of the conidium, typically off to one side. The nucleus was spherical and contained a distinct nucleolus with an associated satellite. Conidia contained numerous large, spherical vacuoles that occupied much of the spore volume. Vacuolar contents were mostly homogeneous with occasional electron-opaque inclusions. Much of the cytoplasm consisted of lightly staining aggregations of glycoprotein that could be labelled with Concanavalin A – gold and that stained darkly using a modified Thiéry's reaction specific for carbohydrates containing vicinal hydroxyl groups. Mitochondria, strands of endoplasmic reticulum, Golgi body equivalents, multivesicular bodies, microbodies, Woronin bodies, and microtubules were present in the conidium. Cuboidal, stacked, electron-translucent structures also were present in the cytoplasm. The conidium was surrounded by a two-layered wall that labelled with gold-conjugated wheat germ agglutinin-ovomucoid, indicating the presence of chitin. The wall between attached conidia contained areas that did not label with gold-conjugated wheat germ agglutinin-ovomucoid. Keywords: Erysiphe, ultrastructure, electron microscopy, freeze substitution.