The DNA content of isolated micronuclei, differentiating macronuclei (macronuclear Anlagen), and adult macronuclei of Loxodes magnus was measured cytofluorimetrically in preparations stained with a Schiff-type reagent, auramine-SO2, following hydrochloric acid hydrolysis. The DNA content of the youngest macronuclear Anlagen proved to be the same as that of telophasic micronuclei (2 c). The Anlagen thus differentiate from micronuclei which are still in G1. The quantity of DNA in the macronuclear Anlagen thereafter rises to the 4-c level, simultaneously with DNA replication in the micronuclei which immediately follows mitosis. In non-dividing animals most micronuclei are already in G2. Adult macronuclei here contain on average 1.5 times more DNA than the micronuclei; their DNA content is about 5–6 c (in some individual nuclei, up to 10 c). These data are consistent with autoradiographic evidence indicating a weak DNA synthesis in the macronuclei of Loxodes and make likely the existence of partial DNA replication (e.g. gene amplification) in the macronuclei. The DNA content of adult macronuclei isolated from dividing animals proved to be significantly smaller than that of macronuclei isolated from non-dividing specimens of the same clone. In 3 clones studied, the former value amounted on average to 71–79, 78 and 95% of the latter, respectively. This drop of DNA content cannot be explained by ‘dilution’ of the old macronuclei with newly formed ones. The quantity of DNA in adult macronuclei thus seems to undergo cyclical changes correlated with cytokinesis, despite the fact that, in Loxodes magnus, the macronuclei themselves never divide and are simply segregated at every cell division. The macronuclei of Loxodes can be termed paradiploid or hyperdiploid.

Cells of algae-containing ("green") and alga-free ("white") strains of the ciliate Climacostomum virens were compared for their responses towards a 1 h pulse of temperature stress. Although the upper heat shock temperature limits for the two strains were different (40-41 °C for "green", and 37-38 °C for "white" cells), the responses to high temperature were similar. The delay in the completion of cell cycle depended on the cell cycle stage at which heat shock was given. Cells exposed to heat shocks at G 1 stage or at the late dividing stage and returned back to 22 °C did not show any noticeable cell cycle lengthening. The most prominent effect was observed when the cells were heat-shock treated at the early dividing stage. In this case, heat shock resulted in up to 4 h delay of the cell cycle completion. It was found that in all experiments, when heat shock was given at different stages of division, the cell cycle duration of the progeny cells was significantly longer (42-50 h) than that of the control cells (21-25 h).