title: A freeze-fracture study of microsporidia (Protozoa: Microspora): II. The extrusion apparatus: Polar filament, polaroplast, posterior vacuole.
abstract: Developmental stages (sporoblasts and spores) of five species of microsporidia (Amblyospora bracteata, A. varians, A. weiseri, Nosema apis, Tuzetia sp.), fixed by conventional EM fixatives or by glutaraldehyde supplemented with potassium chloride, were studied by freeze-fracture using ultrathin sections as controls. It was found that the polar filament is formed by coalescence of cytoplasmic vesicles of the Golgi zone. The filament is enveloped by a single cytoplasmic membrane ("filament ensheathing membrane" = FEM) showing more intramembrane particles (IP) on the EF face (in the order of 1000 IP/μm(2)) and less IP (in the order of 500 IP/μm(2)) on the PF face. During maturation of the spore the IP on the FEM progressively disappear. The polaroplast is a stack of cytoplasmic membranes revealing more IP (in the order of 1500 IP/μm(2)) on the PF face and less particles (in the order of 400 IP/μm(2)) on the EF face. When KCl is added to the fixative the polaroplast remains unswollen and its membranes are smooth. In swollen polaroplasts the membranes are modified, probably by mechanical stretching. The polaroplast membranes are not direct outgrowths of the FEM. The posterior vacuole is limited by a single cytoplasmic membrane. No evidence was found supporting the idea that the filament ends in the posterior vacuole.
authors.affiliation: Service de Protistologie, Laboratoire de Biologie Animale, Université des Sciences et Technologies de Lille, Villeneuve D'Ascq, France.
authors.forename: D
authors.initials: D
authors.lastname: Vinckier
authors.forename: E
authors.initials: E
authors.lastname: Porchet
authors.forename: E
authors.initials: E
authors.lastname: Vivier
authors.forename: J
authors.initials: J
authors.lastname: Vávra
authors.forename: G
authors.initials: G
authors.lastname: Torpier