Comparison of Singlet and Doublet Paramecium tetraurelia: DNA Content, Protein Content and the Cell Cycle*

Abstract

SYNOPSIS. Doublet Paramecium tetraurelia contain either a single macronucleus which is substantially larger than that in a singlet cell, or 2 smaller macronuclei. Doublets have approximately twice the DNA content and twice the total protein content of singlets. The cell cycle of doublets is 164% as long as that of singlets, but the relative position of the macronuclear DNA synthesis period within the cell cycle is the same as in singlets. The DNA content of doublets is regulated so that differences in the number of macronuclei do not produce corresponding changes in DNA content; bimacronucleate doublets have only 27% more DNA than unimacronucleate doublets.

Studies on the Macronuclei of Doublet Paramecium tetraurelia: Distribution of Macronuclei and DNA at Fission*

“…The macronuclei are segregated, undivided, one to each of the daughter cells (Figs. 3, 4), resulting in the production of unimacronucleate progeny, each containing a macronucleus with substantially higher DNA content than that typical of the individual macronuclei in a dimacronucleate doublet ( 12).…”

“…Routine staining of nuclei with Azure A was done as described previously (3); it is based on DeLamater's Azure A procedure (9). Photometric measurements of Feulgen-stained macronuclei were made from photographs in a scanning microdensitometer ( 12).…”

“…This occurred even when the macronucleus was improperly positioned for normal macronuclear division and proper segregation of the daughter macronuclei to different daughter cells (Figs. 4, 7, 11, 12,13). If division of these macronuclei subsequently occurred, the resulting distributions of macronuclei to daughter cells could be interpreted as having arisen through abnormal segregation of both products of division to the same daughter cell (Fig.…”

“…Each of these doublets would be expected to contain 2 macronuclei and 2 sets of 2 micronuclei if the development of the nuclear apparatus of doublets were exactly analogous to that of singlet cells. This is not so, for most doublets contain a single macronucleus (1 1) which is substantially larger than that in singlets (21) and which contains about twice the DNA content of a singlet macronucleus (12). Sonnebom (21) has shown that macronuclei of singlets and doublets are genitally identical and that the increased size of the macronucleus of unimacronucleate doublets is a consequence of the development of the macronucleus in a doublet cytoplasmic milieu.…”

Multiconjugant Complexes of Euplotes Crassus: an Instance of Coordination of Nuclear Events*,†

“…Doublets thus seem to take more time to complete a cell cycle than singlets of stock H,, which had a cell cycle of 10 h and a G , of 5.7 h at a 2 C higher temperature (1). This lengthening of the doublet cell cycle with respect to singlets occurs also in the Paramecium tetruurelia doublets (14).…”