Phosphorus distribution in perichromatin granules and surrounding nucleoplasm as visualized by electron spectroscopic imaging.

The in situ distribution of phosphorus in perichromatin granules (PCGs), and in the surrounding nucleoplasm was investigated in rat liver cells by means of electron spectroscopic imaging of unstained preparations. A 2-3 nm fibril containing high concentration of phosphorus was found to be the main substructural feature of the PCGs revealed in the maps of phosphorus. This fibril is folded within the PCG with no apparent order. Fibrils of similar diameter and phosphorus content were also found in both the halo surrounding the PCG and dispersed in the nucleoplasm. Some of such fibrils are in continuity with those occurring within PCGs. Sometimes these fibrils are grouped forming a stalk connecting the PCG to chromatin. Some stalked PCGs are U-shaped or kidney-shaped, resembling Balbiani ring granules in the process of formation as observed in Chironomus salivary gland cell nuclei. The external fibrils are interpreted as perichromatin fibrils considered to be precursors of PCGs.