ELECTRON SPECTROSCOPIC IMAGING ANALYSES OF THE DISTRIBUTION OF PHOSPHORUS IN BALBIANI RING GRANULES AND IN THE SURROUNDING NUCLEOPLASM

The in situ distribution of phosphorus was studied in unstained ultrat hin sections of salivary glands of Chironomus tentans and Ch. thummi l arvae using elemental mapping by means of an energy-filtering transmis sion electron microscope. This distribution was related to the structu res observed using contrast enhancement with inelastically scattered e lectrons at 250 eV. This procedure demonstrated that a phosphorus-cont aining fibril about 2 nm thick is the common substructure of the follo wing nuclear ribonucleoprotein structural constituents: the Balbiani r ing granules, their precursor fibrils seen at the sites of transcripti on, especially at the Balbiani rings, and the fibres traversing the po re of the nuclear envelope. These phosphorus-containing thin fibrils a re sensitive to RNase. Thicker substructural features of the Balbiani ring granules, occurring as a curved ribbon on a dense particle, appea r to be formed by the dense packing of the fine fibrils. The Balbiani ring granules located near the nuclear envelope are often linked to it by fine filaments.