Ref ID : 7564
Marina A. Frenkel; Fine Structure of the Macronucleus of the Active and Encysted (dividing) forms of Ciliate Colpoda steini. Protistologica XVI(2):339-351, 1980
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The macronucleus of Colpoda steini is surrounded by a conventional two-membraned envelope pierced with pores which have central granules. The single nucleolus is composite and contains dozens of fibrillar cores embedded in a common granular mass. The fibrillar cores contain nucleolus-organizing centres. The macronuclear chromatin elements appear as rather typical "small bodies", measuring at average 0.1 µm. Their DNA nature is confirmed ultracytochemically by the Bernhard's regressive staining. The "small bodies" seem to be thickenings of the general loose chromatin net. During preparation to division, the macronuclear material becomes redistributed: the common chromatin zone pulls into several aggregates, and the nucleolar fibrillar cores scatter between the chromatin aggregates. No conspicuous changes occur in the ultrastructure of chromatin bodies; they are only somewhat drawn together. Each macronuclear division within a reproduction cyst of Colpoda steini is accompanied by extrusion of a rather large nuclear fragment containing loose fibrillar material. The contrast of the macronuclear fragments undergoing no changes after treatment with EDTA, they appear to contain no or very little chromatin (especially, no condensed chromatin). The significance of this extrusion process, previously unknown in Colpoda steini, remains obscure.