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The macro nuclear chromatin structure of the infusorian bursaria truncatella


Tsitologiya 19(10): 1146-1154
The macro nuclear chromatin structure of the infusorian bursaria truncatella
Macronuclei (Ma) of B. truncatella, shown on ultrathrin sections through vegetative and mating ciliates, contain numerous chromatin bodies (Chb) in the nucleoplasm, and a lot of nucleoli composed of fibrillar component only. The nucleoli are commonly associated with chromatin. The Chb vary in size from 0.05-0.2 .mu.m. The similar distribution of macronuclear organelles is observed in cells fixed with a mixture of glutaraldehyde, paraformaldehyde and picric acid, or with osmium tetroxide. The Chb are composed of bundles of DNP [dinucleoprotein] fibers whose thickness is 10-20 nm in vegetative cells, and from 3-10 nm in mating ones. The continuity of DNP fibers can be observed throughout several bodies connected to each other bundles of loosely packed fibrils. The fibrillar packing inside the Chb is better revealed in swollen Ma, during the conjugation. In mating cells the cable packing of DNP fibers can be seen occasionally in Chb. The Chb seen with the EM in the definitive Ma of B. truncatella are short fragments of long chromatin threads, earlier revealed by Ruthmann and Heckmann (1961) with the light microscope. These chromatin threads may be polytenic. It remains obscure whether or not they are polytenic along their whole extention, or are composed of the polytenic segments alernating with non-polytenic ones, both arranged along the same axial DNP chromosome fiber. The availability of DNP fiber segments with thickness 10 or 20 and 3-6 nm suggests that Ma chromatin of B. truncatell may contain histones. In mating ciliates, Chb and chains of these bodies can be seen whose size much exceeds that of bodies seen in vegetative animals. Such atypical Chb may be a structural reflection of intensification of the transcription process in some Ma fragments occurring during the conjugation of B. truncatella. Such an intensification may be due in part to amplification of some genes that function actively in the Bursaria Ma during sexual process.

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Accession: 006712731



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