The fine structure of hyphae in Aspergillus niger has been investigated by means of ultrathin sectioning and electron microscopy with special reference to the developmental stages of colonial growth starting from germinated conidia.
Cell components such as cell wall, cell membrane, nuclei encircled by nuclear envelope, mitochondria with cristae, endoplasmic reticulum and several kinds of cytoplasmic granules have been observed in common to all hyphae obtained from any region of a colony. Structural differentiation in hyphal cells taken from different loci in a colony has been distinguished in particular by characteristic changes in membraneous systems in cytoplasm; hyphae in the extending zone showed rather typical structures of nuclei and mitochondria and remarkable inf oldings of cell membrane, while cells found in the productive zone are characterized by the presence of irregularly extended mitochondria, the appearance of which is confused with that of endoplasmic reticulum. Continuities among such membraneous structures have been clearly demonstrated. Large vacuoles were shown to contain a number of polyphosphate granules as revealed by the OsO4-fixation followed by Pb-acetate treatment. Granules appearing in association with septum formation were also described. Mycelia of the fruiting and aged zones were characterized by the deposition of electron dense granules in the KMnO4- fixation. These granules may probably be the aggregates of denatured cytoplasmic protein.