THE NUCLEUS OF NOCTILUCA SCINTILLANS

Abstract

A B S T R A C TThc unicellular organism, Noctiluca, has becn cxamincd with thc electron microscope. The nuclcus is small compared to the very large size of the cell, but the nuclear border has an organization which indicates an active nucleocytoplasmic exchange. Whereas annuli arc missing over most parts of the nuclear membranc propcr, there arc "annulated vesiclcs" in a layer inside the nuclcar membranc. Thc hypothesis is put forth that nuclear substanccs move through the annuli into these vesicles, and that the annulated vesicles themsclves are transported through the nuclear membrane. The various forms ot the annulated vesicles are consistent with this hypothesis. An implication of this postulate is the synthesis of annulatcd mcmbrancs inside a closed nucleus which arc physically separate from the endoplasmic reticulum. The chromosomes arc in a state resembling prophase chromosomes and arc surrounded by granular masscs. Only a small portion of thc entire nuclear volume is occupicd by the chromosomes. There are many nucleolus-likc bodies.Following the description of the morphology of the nuclear membrane (1, 8, 42) a number of theories have been proposed which attempt to explain the exchange of substances through the nuclear membrane at a fine structural level. The notion that the annuli of the nuclear membrane contain ribosomelike granules (1) has been taken as evidence for transport of particles through the annuli (e.g. reference 41). It has also been proposed that substances may diffuse from the nucleus to the perinuclear space (i.e., the cleft between the two electron-opaque layers of the nuclear membrane) and reach the cavities of the endoplasmic reticulum by means of several open communications between the two structures (17,42). A third concept is the "membrane flow hypothesis" of Bennett (5), implying a transport of particles from nucleus to cytoplasm by means of a "flowing" of the membranes with attached particles through the pore and in some way around the annulus. In a fourth hypothesis it is assumed that relatively large "emission bodies" may pass the nuclear membrane by tearing a hole in it and thus leaving an open nucleo-cytoplasmic connection (26). Finally, it has been suggested that there might be a passage of large emission bodies, but that the nuclear membrane is closed by a regenerating membrane under the body before its actual emission (reference 2, and, similarly, reference 12). This mechanism presupposes formation of nuclear membrane inside a closed nucleus. The only mechanism of nucleocytoplasmic transport which has received experimental support is the route through the annuli, as demonstrated in amebas by injection of colloidal gold (I 1).In a study of the cytology of the luminescent

Structures and Functions of the Nuclear Envelope

“…A unique pattern of nuclear envelope organizations is seen in the dinoflagellate genus Noctiluca, where pore complexes occur only in the invaginated parts, the ampullae (Afzelius, 1963;Soyer, 1969a, b).…”

THE FINE STRUCTURE OF GYMNODINIUM FUSCUM (DINOPHYCEAE)

“…A somewhat similar envelope with what were termed 'annulated vesicles' has been described from the large holozoic dinoflagellate Noctiluca scintillans (Afzelius, 1962). However, here, the vesicles are discrete structures, bounded by a double membrane.…”

Experimental Studies of Cytoplasmic Organization in Zonaria Apical Cells

“…Although this may be realized through nuclear pores (Feldherr, 1965), the cellular membrane systems seem to represent a more important pathway in these zonately polar apical cells. Communication across the nuclear envelope through nuclear membrane evaginations and fusions has been suggested (Clark, 1960;Hadek and Swift, 1962;Afzelius, 1963;Szollosi, 1965;Bell, Frey-Wyssling, and Muhlethaler, 1966), and the perinuclear globular bodies observed may represent that in Zonaria. However, the most attractive system is that of a membrane flow originating at the nuclear envelope and resulting in a direct or indirect relationship between it and cytoplasmic membranes of the GERL (golgi, endoplasmic reticulum, lysosomal) system (Flickinger, 1968;Morre, Mollenhauer, and Bracker, 1971).…”