The Fine Structure of Cortical Components of Paramecium multimicronucleatum

• Published in: Journal of biophysical and biochemical cytology 1955-11, Vol.1 (6), p.583-604
• Main Authors: Sedar, Albert W., Porter, Keith R.
• Format: Article
• Language: English
• Subjects: Animals; Basal Bodies; Cell Membrane; Cell membranes; Cilia; Ciliophora; Cytoplasm; Cytoskeleton; Electron microscopes; Electrons; Endoplasmic Reticulum; Fine structure; Materials; Membranes; Microscopy; Microscopy, Electron; Microtubule-Organizing Center; Microvilli; Mitochondria; Mitochondrial Membranes; Old Medline; P branes; Paramecium; Solar fibrils
• ISSN: 0095-9901; 0021-9525; 1540-8140
• DOI: 10.1083/jcb.1.6.583

The electron microscope was used to study the structure and three dimensional relationships of the components of the body cortex in thin sections of Paramecium multimicronucleatum. Micrographs of sections show that the cortex is covered externally by two closely apposed membranes (together approximately 250 A thick) constituting the pellicle. Beneath the pellicle the surface of the animal is molded into ridges that form a polygonal ridgework with depressed centers. It is these ridges that give the surface of the organism its characteristic configuration and correspond to the outer fibrillar system of the light microscope image. The outer ends of the trichocysts with their hood-shaped caps are located in the centers of the anterior and posterior ridges of each polygon. The cilia extend singly from the depressed centers of the surface polygons. Each cilium shows two axial filaments with 9 peripheral and parallel filaments embedded in a matrix and the whole surrouned by a thin ciliary membrane. The 9 peripheral filaments are double and these are evenly spaced in a circle around the central pair. The ciliary membrane is continuous with the outer member of the pellicular membrane, whereas the plasma membrane is continuous with the inner member of the pellicular membrane. At the level of the plasma membrane the proximal end of the cilium is continuous with its tube-shaped basal body or kinetosome. The peripheral filaments of the cilium, together with the material of cortical matrix which tends to condense around them, form the sheath of the basal body. The kinetodesma connecting the ciliary kinetosomes (inner fibrillar system of the light microscopist) is composed of a number of discrete fibrils which overlap in a shingle-like fashion. Each striated kinetosomal fibril originates from a ciliary kinetosome and runs parallel to other kinetosomal fibrils arising from posterior kinetosomes of a particular meridional array. Sections at the level of the ciliary kinetosomes reveal an additional fiber system, the infraciliary lattice system, which is separate and distinct from the kinetodesmal system. This system consists of a fibrous network of irregular polygons and runs roughly parallel to the surface of the animal. Mitochondria have a fine structure similar in general features to that described for a number of mammalian cell types, but different in certain details. The structures corresponding to cristae mitochondriales appear as finger-like projections or microvilli