[Dynamics of structural changes of Paramecium caudatum and Bursaria truncatella macronuclear chromatin and nucleoli under hypotonic conditions]. / Dinamika ul'trastrukturnykh izmenenii khromatina i iadryshek makronukleusa infuzorii Paramecium caudatum i Bursaria truncatella pri gipotonicheskoi obrabotke.

Dynamics of structural changes of nucleoli, complex nucleolar aggregates and chromatin bodies in macronuclei (Ma) of ciliates Paramecium candatum and Bursaria truncatella under hypotonic conditions was studied. It was shown that after a 3 min hypotonic treatment nuclei swelled and became highly vacuolated. 3D-reconstruction showed that such nucleoli were formed by nucleolonema-like threads about 100-200 nm in thickness. Intranucleolar chromatin bodies decompacted, but remained bound with fibrillar component of the nucleolus by thin fibres about 10 nm thick. After 6 min hypotonic treatment the nucleolar material loosened and had a "gauze", or network-like appearence. After 10 min hypotonic treatment nucleoli dissociated completely. It was shown that a transition of chromatin bodies from completely compact to partially and fully decompacted state occurred cooperatively in different regions of Ma. In particular, chromatin bodies in the central part of complex nucleolar aggregates decompacted much faster than those in the Ma karyoplasm. It evidences for a specific, well-ordered chromatin organization in Ma. Prolonged hypotonic treatment led to a complete dissociation of Ma components; fibres 6-10 nm thick were solely observed in such preparations. Such fibres may represent remnant structures of the nuclear matrix. Dynamics of Ma chromatin bodies decompaction correlates well with that of chromomeres in the nuclei of higher eukaryotes. Our data confirm that chromatin 100-200 nm bodies in the ciliate Ma are analogues of chromomeres--looped discrete chromatin domains, observed in the nuclei of higher eukaryotes.

Nuclear fine structure at interphase and during encystment in two forms of the testacean Arcella vulgaris.

Arcella vulgaris and A. vulgaris var. multinucleata have two and seven vesicular nuclei, respectively. In early interphase, the nuclei are spherical, with a main central nucleolus and several small peripheral nucleoli. The main nucleolus has mixed fibrillar and granular components and no apparent chromatin bodies in the nucleolus-organizing regions (NORs). The nuclear chromatin is dispersed except for small heterochromatin lumps. Nuclear bodies of fibrous structure occur outside the main nucleolus. The nuclear envelope shows an internal lamina and an external layer of tangential fibres. In middle interphase, the nuclei become irregular in shape and adjacent to the plasma membrane at the dorsolateral cell surface. The condensation of the chromatin increases. The nucleolus is often eccentric and its NORs show conspicuous bodies of condensed chromatin surrounded by a halo and a fibrous transcription zone. By the end of interphase, the main nucleolus becomes polymorphic and segregated into a fibrillar basal part which contains a vacuolar area with dense inclusions, and a fibro-granular cap which contains many fibrous electron dense bodies. These are likely to be the nuclear chromatin elements. In early resting cysts, the nuclei detach from the cell membrane and approach one another. The main nucleolus segregates into large, mainly peripheral fibrillar blocks inside a granular mass. The NORs consist of condensed chromatin bodies without a transcription zone around them. The nuclear chromatin is condensed. Conspicuous intranuclear annulate lamellae bearing pore complexes occur only in cysts.