Summary
The uptake of Ca45 into cells of the dinoflagellateGlenodinium foliaceum was investigated using insoluble compound light microscope autoradiography. The distribution of silver grains showed marked localisation to the dinocaryotic nucleus, with a random scatter of grains over the surrounding protoplasm (cytoplasm and supernumerary nucleus). Correction of grain counts for lateral sensitisation from the dinocaryotic nucleus indicated an isotope concentration 16–32 times greater in this organelle compared to the rest of the cell.
Cells labelled for varying periods of time showed differences in the pattern of Ca45 uptake throughout the sample populations, but no increase in the mean level of uptake per cell. This would suggest a rapid incorporation of isotope within 1–2 hours, with little subsequent uptake. The presence of high levels of label after processing with both additive (glutaraldehyde, paraformaldehyde) and coagulative (acetic alcohol) fixatives indicated that the retention of Ca45 in these preparations was not simply a fixation artefact.
Although the isotope did not appear to be suitable for (high resolution) electron microscope autoradiography, the intranuclear site of incorporation was demonstrated indirectly using a buffer extraction technique. Prolonged treatment with phosphate buffer resulted in a large scale loss of label from both cytoplasm and dinocaryotic nucleus. The latter appeared to show specific correlation with the loss of (protein) matrix from the chromosomes — as observed under both light and electron microscopy, with no apparent change in either nucleolus or nucleoplasm. This would suggest that incorporated Ca45 in the nucleus was largely confined to the condensed chromatin, where it was combined with the acidic proteins which make up the bulk of the chromatin matrix.
The results obtained in this investigation are related to previous studies involving X-ray microanalysis and uptake of Ni63.
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Sigee, D.C. Localised uptake and extraction of Calcium45 in dinoflagellate nuclei: an autoradiographic study. Protoplasma 117, 185–195 (1983). https://doi.org/10.1007/BF01281822
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DOI: https://doi.org/10.1007/BF01281822