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 ce lls by means of electron spectroscopic imaging of unstained preparatio ns. A 2-3 nm fibril containing high concentration of phosphorus was fo und to be the main substructural feature of the PCGs revealed in the m aps of phosphorus. This fibril is folded within the PCG with no appare nt order. Fibrils of similar diameter and phosphorus content were also found in both the halo surrounding the PCG and dispersed in the nucle oplasm. Some of such fibrils are in continuity with those occurring wi thin PCGs. Sometimes these fibrils are grouped forming a stalk connect ing the PCG to chromatin. Some stalked PCGs are U-shaped or kidney-sha ped, resembling Balbiani ring granules in the process of formation as observed in Chironomus salivary gland cell nuclei. The external fibril s are interpreted as perichromatin fibrils considered to be precursors of PCGs.