Light- and electron- microscope studies on the spleen of the newt Triturus cristatus: the fine structure of erythropoietic cells.

The stages of erythrocyte maturation were identified in spleen smears stained with MayGriinwald-Giemsa. The fine structure of sectioned cells from about the basophilic erythroblast stage onwards was investigated in the electron microscope and serial i-/t sections were examined by microspectrophotometry to ascertain haemoglobin content. The nuclei of basophilic erythroblasts contain large and small blocks of chromatin as well as light-staining zones of unknown composition and ill-defined structure: the nuclear sap contains numerous interchromatin granules, about 400 A in diameter. During maturation the small blocks of chromatin aggregate and the nuclear light-staining zones tend to disappear, as do the interchromatin granules. Storage lysosomes occur in the basophilic and early polychromatic erythroblasts and during subsequent maturation these lysosomes are probably involved in the degradation of mitochondria. The changes in distribution of ribosomes in cells at the later stages of maturation have been investigated by counting the numbers of single ribosomes and polysomes seen in electron micrographs. During erythropoiesis the ratio of the amount of fibrillar material to the amount of granular material in the nucleolus increases; in the mature erythrocyte the nucleolus consists almost exclusively of fine fibrillar material.