MORPHO-FUNCTIONAL PARAMETERS OF NUCLEOLI IN POLYPLOID MUCOUS AND ALBUMEN CELLS OF SALIVARY GLAND IN THE SNAIL
SUCCINEA LAUTA
A. A. Anisimova, A. P. Anisimov
Chair of Cell Biology, the Far East State University, Vladivostok, Russia;
e-mail: anis@bio.dvgu.ru
Variation of some characteristics of nucleoli of polyploid mucous and albumen cells was examined in salivary glands
of the snail Succinea lauta. The number, total area and Ag-protein content of nucleoli, and DNA content in each nucleus were
estimated on squashed preparations incubated with AgNO3, decolorized and then Feulgen stained. The ultrastructure of nucleoli
was studied by electron microscopy. Differentiated mucous cells had 4c-8c-16c-32c nuclei; albumen cells had 8c-16c-32c-64c-128c nuclei.
The ultrastructure of nucleoli of the two cell types was essentially the same. Normally, a large fibrous to granular zone was observed
in the nucleoli, without a clear distinction between fibrous and granular components. At the same time, aggregations of granular
matter could be discerned at the periphery of nucleoli. No fibrous centers were observed. Occassionally, nucleolonema-like structures
occurred. Normally each nucleolus contacted several chromosomes. On squashed preparations, the least size of nucleoli was 2-3 μm,
and the largest size amounted to 14 μm in mucous cells, and to 50-80 μm in albumen cells. The number of nucleoli rose
from 1-2 in tetraploid nuclei to 2-3 in 32c-nuclei, and to 5-7 in 128c-nuclei. The disparity between the ploidy levels of nuclei
and the numbers of nucleoli may be due, presumably, to aggregation of chromosome NORs. The Ag-protein content in the nucleoli,
and the total nucleolar area displayed a strong mutual correlation. Both parameters differed significantly by 1.5-2.2 times in
mucous and albumen cells of the same ploidy level. Thus, in albumen and mucous cells the total Ag-protein content in octaploid
nuclei was 3.3 and 2.2 relative units (r. u.), respectively. In 16c- and 32c-nuclei of albumen cells, it was 7.6 and 15.1 r. u.;
and in the same nuclei of mucous cells - 3.8 and 6.8 r. u., respectively. On the whole, in albumen cells, in the course of 4
endocycles (4c-128c), the total Ag-protein content increased by 17 times. Therefore, the mean multiplication factor for this
parameter was found to be 2.05 per endocycle. In mucous cells, in the course of 3 endocycles (4c-32c), the total Ag-protein content
increased by 5.2 times against 8 times expected, with the mean multiplication factor equal to 1.75 per endocycle. Thus, in the
course of polyploidization of albumen and mucous cell nuclei, the gene dosage effect was fully pronounced in the former, and only
partly in the latter. This differtence is due obviously to peculiarities of differentiation of the two cell types, in particular,
to differences in the number of activated ribosomal genes.
Key words: AgNOR, AgNO3, endopolyploidy, Gastropoda, nucleolus, polyploidy, ribosomal genes, ultrastructure
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