[Genome multiplication in the development of albumen gland polyploid cells of Succinea lauta (Gastropoda:Pulmonata).VII. Transcriptive activity of the nuclei in the endomitotic cycle].

Using 3H-uridine autoradiography and electron microscopy a study was made of the activity of RNA synthesis in the interphasic nuclei, mitoses and endomitoses of different ploidy classes (4c-32c) in the albumen gland cells of Succinea lauta. The incorporation of 3H-uridine into mitotic and endomitotic condensed chromosomes was temporarily stopped or kept at the lowest level: 0.7% in normal and abnormal mitoses and about 3-4% in endomitoses, as calculated from the highest possible level in the resting nuclei of the respective ploidy classes. In the interphasic nuclei, chromatid and chromonemal structures are revealed at the ultrastructural level, in addition to thin euchromatinous fibres with perichromatia granules, which makes the brushy appearance of chromonemes and chromocentres. During endomitosis the chromosomes become compacted and free from granules, which well compares with autoradiographical data on transcription stopping. The results obtained corroborate once again that endomitosis is a real endoreproductive mechanism, and allow to make distinctions between real endomitosis and pseudoendomitotic nuclei.