Hyphal tip cell ultrastructure of the fungus Fusarium: Improved preservation by freeze-substitution

Abstract

Ultrastructure of freeze-substituted hyphal tip cells of Fusarium acuminatum was compared to that after conventional chemical fixation. As a result of improved preservation by a modified freeze-substitution procedure, we document here: (i) an extensive system of smooth membrane cisternae with electron-dense contents, including tubules and single, fenestrated cisternae; (ii) two types of apical vesicles with a homogeneously electron-dense interior; (iii) an extensive system of microtubules which extend well into the apical dome; (iv) four distinct layers in the apical “primary” cell wall, with basipetal thickening due almost exclusively to enlargement of the outer cell wall layer; (v) hexagonal microvesicles; and (vi) a smooth profile of all cellular membranes and most organelles.