Morphometric analysis of macronuclei and macronuclear fragments in autogamous cultures of Paramecium aurelia

Abstract

The general pattern of ultrastructural organization of macronuclear fragments which appear during autogamous changes of the nuclear apparatus of Paramecium aurelia is similar to that observed in undisturbed macronuclei. Morphometric analysis of electron-micrographs reveals, however, that only the nucleolar relative surface area remains unchanged in macronuclear fragments as compared with macronuclei, this suggesting the same intensivity of rRNA synthesis in them. Moreover, there exists, between the relative surface area covered by heterochromatin and the nucleoli in macronuclear fragments, an inversely proportional, statistically significant correlation, different than that calculated for macronuclei. The relative surface area of heterochromatin in macronuclear fragments is smaller than in macronuclei, what may be a sign either of enhancement of chromatin activity or of proceeding nuclear lysis.