THE CYTOPLASMIC ORGANIZATION OF HYPHAL TIP CELLS IN THE FUNGUS ALLOMYCES-MACROGYNUS

Light and transmission electron microscopy were used to examine hyphal tip cells of the fungus Allomyces macrogynus (Chytridiomycetes). A well defined apical body, i.e., Spitzenkorper, was observed at the extreme apex of hyphal cells. This distinctive, spherical cytoplasmic region consisted of a granular matrix devoid of ribosomes and most organelles. To our knowledge this is the first report describing such a structure in hyphae of an aseptate fungus. Vesicles (45-65 nm diameter) were concentrated in the peripheral cytoplasm of the apex, while relatively few were observed within the Spitzenkorper. Filasomes, spherical patches of dense fibrillar material containing a microvesicle core, were abundant in the apical regions near the plasma membrane. Microtubules traversed the Spitzenkorper at various angles and were in close association with the plasma membrane. Microfilaments were observed as individual elements in the cytoplasm or were organized into bundles. Individual microfilaments were frequently in close association with the plasma membrane, vesicles and microtubules. In the immediate subapical region mitochondria, multivesicular bodies, microbodies, Golgi equivalents and nuclei were abundant.