Main Content

The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 7546

B.P. Karadzhan and I.B. Raikov; Ultrastructural and Autoradiographic Investigation of the Resorption of the Old Macronucleus and of the Development of the New Macronucleus following Conjugation in Didinium nasutum. Protistologica XV(4):507-519, 1979

Reprint

In File

Notes

The old macronucleus of Didinium nasutum fragments into pieces 2 or 3 hr after the start of conjugation; at the same time, its nucleoli segregate into granular and fibrillar parts, and nucleolar organizers disappear. Later, the chromatin bodies fuse into a spongy mass, and the macronuclear envelope falls into flattened cisternae which peel off from the surface of the macronuclear fragments. The fragments undergo autolysis inside autophagic vacuoles at the time of the 3rd synkaryon division. Fine structural autoradiography shows that macronuclear fragments continue to synthesize RNA until their isolation in autophagic vacuoles. The label is at first mainly over the nucleoli, whereas it becomes preferentially localized over the chromatin during the 2nd meiotic division (mRNA synthesis ?). The development of the macronuclear anlagen includes progressive accumulation of both chromatin bodies and nucleoli. Extrusion of some lamellar material has been observed at late stages of their development. No polytene chromosomes have been observed in the anlagen. As shown by fine structural autoradiography, DNA synthesis starts in the anlagen just after their differentiation (a little before separation of the conjugants) and continues without interruption until the end of their development. The first nucleoli appear in the anlagen 3-4 hr after separation, and this coincides with the start of [3H]-uridine incorporation.