Protistology 3 (2) 99–106 (2003) Fine structure of nucleoli in the ciliate Didinium nasutum
Bella P. Karajan 1, Vladimir I. Popenko 2 and Olga G. Leonova 2
1 Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russia
Summary
The macronuclear nucleoli of vegetative non-dividing cells of Didinium nasutum display inverted position of the
main parts: the granular component is inside and the dense fibrillar one, in form of discrete bands, is mainly at the periphery. Before binary fission,
the nucleoli are degranulated and their fibrillar bands scatter throughout the macronucleus, to be segregated during division between
the daughter cells, where they begin to re-form the granular parts. In young resting cysts small nucleoli consist of granular material
only, larger nucleoli show a clear segregation of its fibrillar and granular elements. During conjugation, nucleoli of the old
macronucleus or of its fragments become segregated into granular and fibrillar parts and the latter are largely eliminated. The
nucleoli lose contact with the chromatin bodies. In the developing anlagen of the new macronuclei the first nucleoli appear as fibrous
bodies and only later develop granular parts; simultaneously the number of nucleoli increases.
Key words: macronucleus, nucleoli, cell cycle, cysts, Didinium nasutum
|