Ref ID : 7542
Jean-Pierre Mignot; [Etude Ultrastructurale de la Pedogamie chez Actinophrys sol (Heliozoaire) I. - La Division Progamique]. Protistologica XV(3):387-406, 1979
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The different phases of this special autogamy analyzed by Belar (1923) were reexamined with the electron microscope. The results described in this report are limited to the first phases, that is to say the progamic division. We confirm most of Belar's observations: disappearance of axopodia, elaboration of a cyste membrane, storage of granular inclusions, caryokinesis characterized by the persistence of the nuclear membrane, no diversified spindle pole body, fusorial fibers invading the nuclear lumen. One ultrastructural study also shows, that the cell synthetizes in the cortical cytoplasm scales, which will be used to build the protective cyst-wall, and that new membranes are growing at different moments on both sides of the nuclear envelope. The old nuclear membrane, characterized by the accumulation of dense bodies in the perinuclear space of the vegetative cells and by nucleating centers of the axopodial axonemes, becomes locally disrupted by polar fenestrae during the formation of the metaphase spindle. During metakinesis and telophase, intranuclear vesicles are formed by a blibbing activity of the inner layer of the nuclear envelope. They will be incorporated in the elongating nuclear membrane during anaphase, and then, in telophase they will fuse, giving rise to a new nuclear envelope. Parts of the old nuclear envelope associated with vesicles and disrupted microtubules constitute the polar caps described by Belar. The meaning of these cell transformations toward the mitotic mechanism and intracellular differentiation is discussed.