Variation of Cell and Nuclear Volume ofTetrahymena pyriformiswith Three Parameters of Growth: Age of Culture, Age of Cell, and Generation Time*

Analysis of growth of tetraploid nuclei in roots of Vicia faba

Growth of nuclei of a marked population of cells was determined from G1 to prophase in roots of Vicia faba. The cells were marked by inducing them to become tetraploid by treatment with 0.002% colchicine for 1 hr. Variation in nuclear volume is large; it is established in early G1 and maintained through interphase and into prophase. One consequence of this variation is that there is considerable overlap between volumes of nuclei of different ages in the cell cycle; nuclear volume, we suggest, cannot be used as an accurate indicator of the age of the cell in its growth cycle. Nuclei exhibit considerable variation in their growth rate through the cell cycle. Of the marked population of cells, about 65% had completed a cell cycle 14--15 hr after they were formed. These tetraploid nuclei have a cell cycle duration similar to that of fast cycling diploid cells of the same roots. Since they do complete a cell cycle, at least 65% of the nuclei studied must come from rapidly proliferating cells, showing that variability in nuclear volumes must be present in growing cells and cannot be attributed solely to the presence, in our samples, of non-cycling cells.

Cell size, macromolecular composition, and O2 consumption during agitated cultivation of Naegleria gruberi

Cell size, macromolecular composition, carbohydrate utilization patterns, and O2 concentrations were measured throughout the growth stages of Naegleria gruberi in agitated culture in a complex medium. Biphasic logarithmic growth occurred during the intial 83 hr of growth and the mean generation time was 7.0 hr and 19 hr during initial and secondary log growth stages, respectively. The maximum yield was 5 X 10(6) amebae/ml. The pH rose rapidly (1 pH unit) during the secondary log growth phase (52-83 hr) and continued into the stationary growth phase (83-120 hr). Dry weight, total protein, carbohydrate, and RNA per ameba increased just before the secondary log growth phase. RNA increase 31% to 35% per ameba at the end of each phase of log growth. DNA increased approximately 2-fold throughout the different growth phases. Average cell size increased 90% during biphasic log growth then decreased during stationary phase. O2 tension decreased from 100% to 18% of saturation during the biphasic growth phase, then increased during stationary growth to near 100% saturation. Glucose and total carbohydrate assays showed little utilization of those substrates throughout the growth stages. Naegleria gruberi presumably has a predominantly aerobic metabolism, also its metabolism may change during the different growth phases.

The size distribution of Tetrahymena in relation to its position in the cell cycle

Tetrahymena size distribution during the cell cycle was analyzed by means of radioautography with the aid of a sonic-digitizer, and a computer. The study demonstrates that as the organism ages and passes through the various cell cycle phases the volume distribution of the organisms in each phase remains lognormal.

Nucleocytoplasmic ratio requirements for the initiation of DNA replication and fission in Tetrahymena

Hydroxyurea (10 mM) arrests the exponential growth of Tetrahymena by blocking DNA replication during S-phase. After removal of the hydroxyurea (HU), they have a long recovery period during which they are active in DNA synthesis. 3H-TdR uptake showed that on completion of the recovery period, the cells divide (recovery division) and enter a cell cycle which lacks G1. The frequency, size and DNA content of the extranuclear chromatin bodies (ECB) formed at this division are all markedly increased (2-4) over the corresponding values obtained from exponential growth phase controls. Microspectrophotometric analysis of macronuclear DNA content (N) coupled with the cytoplasmic dry mass (C) values suggest that specific N to C ratios (N/C) are required for the initiation of DNA replication and fission: during a normal (exponential growth) cell cycle, both N and C double, but asynchronously, so that the N/C of both post-fission-daughter cells and pre-fission cells is identical (standardized to N/C = 1) but late G1 cells have a low N/C. During a 10 hr exposure to HU, the N remains essentially the same whereas the C increases. When the HU is removed, the N increases by 4X and the C continues to increase until just prior to recovery division when it also reaches a value 4X that of the original daughter cells. Thus, the N/C = 1 is re-established. The enlarged ECB formed during recovery division may function to lower the N/C in the daughter cells, which in turn may in some way stimulate immediate DNA replication, thus eliminating G1. The elimination of G1 (and shortening in a few subsequent cell cycles) allows less time for cytoplasmic growth and results in the return of the cells to the generation time and the N and C values observed prior to the HU treatment.

EFFECTS OF PHENOTHIAZINES ON GROWTH, GLUCOSE UPTAKE, AND CELL COMPOSITION IN TETRAHYMENA PYRIFORMIS W

The effect of phenothiazine derivatives on growth, glucose uptake, and cell composition was studied in the ciliate protozoan Tetrahymena pyriformis W. The most effective inhibitor of growth in a chemically defined medium was promazine (PRZ), followed by chlorpromazine (CPZ), promethazine (PMZ), prochlorperazine (PCP), acetophenazine (ACP), and trifluoperazine (TFP). The uptake of glucose was highest in resting suspensions of cells in the logarithmic phase (40 hours), but decreased with increasing age of the culture. Little or no uptake of glucose occurred in cells pre-inhibited by PRZ or CPZ. The most effective inhibitor of glucose uptake was TFP, followed by ACP, PCP, PRZ, CPZ, and PMZ. The concentration of protein in cells grown with Tween 80 was unaffected by PRZ, although total cell populations were reduced. Under these conditions, PRZ or CPZ delayed the accumulation of lipid in the cells. Similarly, PRZ reduced the amount of RNA and DNA during the logarithmic phase.These results demonstrated that phenothiazine derivatives can influence lipid and nucleic acid levels in Tetrahymena, and further suggest that the drugs may interfere directly with the mechanism of glucose transport into the cell. These observations support the hypothesis that metabolic effects are related to the ability of phenothiazine derivatives to alter permeability of cell membranes.