The fine structure of Phycomyces: I. Autophagic vesicles

Abstract

The fungus Phycomyces blakesleeanus was examined at several developmental stages. The sporangiophores contain vesicles with either a single membrane or a pair of concentric membranes. Such vesicles contain either intact cytoplasm with organelles or a complex form of debris. These findings suggest that certain endoplasmic cisternae of the sporangiophore are engaged in the isolation and lysis of cytoplasm. Longitudinal sections of the sporangiophore reveal axial groupings of vesicles suggesting formation of vesicles near the cell tip, maturation in lower regions, and final discharge of the lytic debris into the large sporangiophore vacuole. The presence of large (above 1 μ) granules in vesicles, cytoplasm, and nuclei; the frequent proximity of endoplasmic cisternae to nuclei; the occurrence of nuclei with widely separated inner and outer membranes; and the extension of nuclear membranes into the cytoplasm suggest that the vesicle membranes originate from nuclear membranes. These phenomena were found in all stages of sporangiophore development but not in the vegetative hyphae.