Correlation of betacyanin synthesis with cell division in cell suspension cultures of Phytolacca americana

In suspension cultures of Phytolacca americana , betacyanin accumulation was reduced when cell division was inhibited by treatment with various inhibitors of DNA synthesis or anti-microtubule drugs. Aphidicolin (APC), an inhibitor of DNA synthesis, reduced the incorporation of radioactivity from labeled tyrosine into betacyanin, but the incorporation of radioactivity from labeled 3,4-dihydroxyphenylalanine (DOPA) into betacyanin was not affected by similar treatments. Propyzamide, another anti-microtubule drug, reduced incorporation of radioactivity from tyrosine and DOPA into betacyanin. However, the rate of incorporation from DOPA was higher than that from tyrosine. The results suggest that inhibition of betacyanin accumulation in Phytolacca americana cells by APC and propyzamide is due to suppression of the reaction converting tyrosine to DOPA, which may be closely related to cell division.     

Correlation between size and age at different events in the cell division cycle of Escherichia coli.

The variability of (i) the B period between birth and initiation of chromosome replication, (ii) the U period between initiation of chromosome replication and initiation of cell constriction, and (iii) the interdivision period (tau) have been estimated for slowly growing Escherichia coli B/r F. Cultures synchronized by the membrane elution technique were pulse-labeled with [3H]thymidine or continuously labeled with [3H]thymine. After fixation, the pattern of deoxyribonucleic acid replication was analyzed by electron microscopic radioautography. Cell length was found to increase exponentially with age at two different slow growth rates. The coefficient of variation of the B period was estimated to be 60%, that of the U period was 29%, and that of the interdivision period was 12%. From these values and the coefficient of variation of length at different cell cycle events were calculated a negative correlation between the B and U period (r = -0.9) and a positive correlation between length at birth and cell separation (r = 0.6). Initiation of chromosome replication and cell constriction were strictly correlated both with respect to age (r = 0.7) and length (r = 0.8). On the other hand, length at initiation of chromosome replication was distantly correlated with age (r = 0.1) or length at birth (r = 0.3). This low correlation excludes a model in which chromosome initiation is controlled by a random event in the B period. It favors a model in which chromosome initiation occurs at a particular distributed size independent of cell division.     

Correlation between biomass and medium conductivity in suspension cultures of rice cells

Summary An intercept in the linear relationship between the biomass increase and decrease in medium conductivity was found in suspension cultures of rice cells. It was due to the. consumption of medium salts by the cells during the lag phase. An equation was established for accurate monitoring of the cell growth which aids understanding of the cell physiology especially during the initial stage of cell growth.     

Sloppy size control of the cell division cycle

In an asynchronous, exponentially proliferating cell culture there is a great deal of variability among individual cells in size at birth, size at division and generation time (= age at division). To account for this variability we assume that individual cells grow according to some given growth law and that, after reaching a minimum size, they divide with a certain probability (per unit time) which increases with increasing cell size. This model is called sloppy size control because cell division is assumed to be a random process with size-dependent probability. We derive general equations for the distribution of cell size at division, the distribution of generation time, and the correlations between generation times of closely related cells. Our theoretical results are compared in detail with experimental results (obtained by Miyata and coworkers) for cell division in fission yeast, Schizosaccharomyces pombe. The agreement between theory and experiment is superior to that found for any other simple models of the coordination of cell growth and division.     

Imprinting with oxytocin and vasopressin in Chang liver cell cultures: hormonal overlap, binding and influence on cell division

In Chang liver cells the administration of oxytocin and vasopressin as well as the combined application of the two hormones will result in a positive binding imprinting for oxytocin and a negative binding imprinting for vasopressin. The hormones are able to increase the mitotic capacity of the liver cells even without previous imprinting, both in the case of treatment for 4 hours and for 24 hours; the change, however, is more marked in the case of treatment for 4 hours. Treatment for 24 hours results also in some functional imprinting.     

Correlation between cell nutrition, cell size and division control. Part I.

The conventional concept of division control assumes that a certain sequence of biochemical events throughout the cell cycle results in the generation of some specific mitotic trigger. An alternative approach has been examined by us on Tetrahymena pyriformis, namely, that division is started without any specific starter but by deficiency in the cell pool of nutrients. This deficiency, in its turn, is caused by various space disproportions accompanying cell growth.In accordance with the hypothesis under examination, a prompt shift-down in cell nutrition has induced a wave of division in an asynchronous culture of Tetrahymena; a shift-up in nutrition has resulted in delay of division and in a stepwise increase of mean volume of dividing cells.     

Correlation between cell nutrition, cell size and division control. Part II.

The correlation between cell size and the rate of cell growth and endocytosis was investigated. The increase in cell volume was found to proceed at a slowing rate throughout interphase. It virtually stops some time before cytokinesis and is rather rapid at the time of cytokinesis, although the divider volume decreases markedly for a short period of cell cleavage.Endocytosis was monitored with the aid of carmine. The oral apparatus is inactive during cytokinesis and some time after it. Then endocytosis increases, reaching a stable level at the middle of interphase. It accelerates significantly again just before cytokinesis. There is a positive correlation between the activity of the oral apparatus throughout interphase and the cell size at the inception of growth.The correlation between the rate of growth and the rate of endocytosis was found to be negative. Calculations which take into account the time of food digestion in Tetrahymena show that the cell pool of nutrients must be maximal at the inception of the generation cycle and minimal at the end of interphase. The rate of cell growth correlates positively with these oscillations, whereas the rate of endocytosis correlates with them negatively.     

Cell division and plant development from protoplasts of carrot cell suspension cultures

Summary Cell regeneration and sustained division have been observed in protoplasts from carrot cell suspension cultures. Carrot plants were produced from the protoplasts by embryogenesis.NRCC No. 12268.     

Cell cycle parameters and accumulation of metaphase cells in maize suspension cultures

Cell cycle parameters of maize (Zea maysL cv Black Mexican Sweet) suspension cultures and root meristem cells were determined by pulse labelling with [³H]thymidine ([³H]TdR). Total cell cycle time for the suspension cultures was 27 h; 3 h in G1, 14 h in S, 6 h in G2, 2.2 h in prophase, 1 h in metaphase, 0.1 h in anaphase, and 0.7 h in telophase. Cell cycle durations in root meristem cells of Black Mexican Sweet (BMS) corn with and without B chromosomes in vivo were 20.0 h and 18.3h, respectively. Chemical and physical methods were used successfully to accumulate mitoses in the suspension cultures; compared to the untreated control, the mitotic index of the treated cultures was increased from 4 to 23% and the frequency of metaphase cells increased dramatically from 3 to 19%.     

Regulation of DNA synthesis and cell division by polyamines in Catharanthus roseus suspension cultures

Summary Various inhibitors of polyamine biosynthesis were used to study the role of polyamines in DNA synthesis and cell division in suspension cultures of Catharanthus roseus (L.) G. Don. Arginine decarboxylase (ADC; EC 4.1.1.19) was the major enzyme responsible for putrescine production. DL -difluoromethylarginine inhibited ADC activity, cellular putrescine content, DNA synthesis, and cell division. The effect was reversible by exogenous putrescine. Ornithine decarboxylase (ODC; EC 4.1.1.17) activity was always less than 10% of the ADC activity. Addition of DL -difluoromethylornithine had no effect on ODC activity, cellular polyamine levels, DNA synthesis, and cell division within the first 24 h but by 48 to 72 h it did inhibit these activities. Methylglyoxal bis(guanyl-hydrazone) inhibited S-adenosylmethionine decarboxylase (EC 4.1.1.50) activity without affecting DNA synthesis and cell division.Abbreviations ADC arginine decarboxylase - ODC ornithine decarboxylase - SAMDC S-adenosylmethionine decarboxylase - DFMA DL -difluoro-methylarginine - DFMO DL -difluoromethylornithine - MGBG methylglyoxal bis(guanylhydrazone)     

Mitochondrial growth and division during the cell cycle in HeLa cells

The growth and division of mitochondria during the cell cycle was investigated by a morphometric analysis of electron micrographs of synchronized HeLa cells. The ratio of total outer membrane contour length to cytoplasmic area did not vary significantly during the cell cycle, implying a continuous growth of the mitochondrial outer membrane. The mean fraction of cytoplasmic area occupied by mitochondrial profiles was likewise found to remain constant, indicating that the increase in total mitochondrial volume per cell occurs continuously during interphase, in such a way that the mitochondrial complement occupies a constant fraction( approximately 10-11(percent)) of the volume of the cytoplasm. The mean area, outer membrane contour length, and axis ratio of the mitochondrial profiles also did not vary appreciably during the cell cycle; furthermore, the close similarity of the frequency distributions of these parameters for the six experimental time-points suggested a stable mitochondrial shape distribution. The constancy of both the mean mitochondrial profile area and the number of mitochondrial profiles per unit of cytoplasmic area was interpreted to indicate the continuous division of mitochondria at the level of the cell population. Furthermore, no evidence was found for the occurrence of synchronous mitochondrial growth and division within individual cells. Thus, it appears that, in HeLa cells, there is no fixed temporal relationship between the growth and division of mitochondria and the events of the cell cycle. A number of statistical methods were developed for the purpose of making numerical estimates of certain three-dimensional cellular and mitochondrial parameters. Mean cellular and cytoplasmic volumes were calculated for the six time-points; both exhibited a nonlinear, approx. twofold increase. A comparison of the axis ratio distributions of the mitochondrial profiles with theoretical distributions expected from random sectioning of bodies of various three-dimensional shapes allowed the derivation of an "average" mitochondrial shape. This, in turn, permitted calculations to be made which expressed the two-dimensional results in three-dimensional terms. Thus, the estimated values for the number of mitochondria per unit of cytoplasmic volume and for the mean mitochondrial volume were found to remain constant during the cell cycle, while the estimated number of mitochondria per cell increase approx. twofold in an essentially continuous manner.     

Variation of cell cycle duration within suspension cultures ofDaucus carota and its consequence for the induction of ploidy changes with colchicine

Summary Continuous exposure to colchicine was used to estimate the variation in cell cycle time between cells within suspension cultures ofDaucus carota. Observations were made of the pattern of disappearance of cells of the initially predominant ploidy levels in diploid and tetraploid cultures having markedly different aggregation patterns. Both cultures showed a similar range of cycle times, normally distributed about the culture mean. Shorter colchicine treatments, followed by regrowth in colchicine-free medium, showed that spread of cycle times in the diploid culture prevented uniform induction of tetraploidy, and that the resulting mixoploid suspensions showed a gradual reversion to diploidy during subsequent subculture.     

Physiological and biochemical effects of the mycotoxin patulin on Chang liver cell cultures.

Patulin exhibits both cytotoxic and cytopathic effects on cultured Chang liver cells. The LD50 found was 1.85 mug per ml of patulin. Effects on growth were observed with as little as 0.1 mug per ml of patulin; a 50% reduction in growth was observed at 0.38 mug per ml of patulin. Using a challenge dose of 2.5 mug per ml of patulin, the cytotoxic effect was reversible after an exposure of 10 min, but was not reversible after 20 min. Protein synthesis was depressed after 60 min and RNA synthesis after 20 min of contact with patulin. Neither protein nor RNA synthesis was completely inhibited after 260 min.     

The relationship between yeast cell size and cell division in Candida albicans

The mean size and percentage of budded and unbudded cells of Candida albicans grown in batch culture over a wide range of doubling times have been measured. Cell volume decreased with increased doubling time and a nonlinear approach to an asymptotic minimum was observed. When cells were separated by age according to bud scars, each age showed a similar decrease. During each cell division cycle, size increased slowly during both budded and unbudded periods so that each generation was significantly larger than the preceding. There was no difference in size between the parent portion of budded cells and unbudded cells of the same age. Time-lapse photomicroscopy of cells growing on solid medium showed that cells divide asymmetrically with larger parents having a shorter subsequent cycle time than the smaller daughter, although the time utilized for bud formation was similar. When cells were shifted from a medium supporting a low growth rate and small size to a medium supporting a faster growth rate and larger size, both budded and unbudded cells increased significantly in size. As the doubling time increased, both the budded and unbudded portions of parental and daughter cycles increased.     

Sterol and sesquiterpenoid biosynthesis during a growth cycle of tobacco cell suspension cultures

The accumulation and biosynthesis of sterols and fungal elicitor-inducible sesquiterpenoids by tobacco (Nicotiana tabacum) cell suspension cultures were examined as a function of a 10 day culture cycle. Sterols accumulated concomitantly with fresh weight gain. The rate of sterol biosynthesis, measured as the incorporation rate of [¹⁴C]acetate and [³H]mevalonate, was maximal when the cultures entered into their rapid phase of growth. Changes in squalene synthetase enzyme activity correlated more closely with thein vivo synthesis rate and accumulation of sterols than 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) enzyme activity. Cell cultures entering into the rapid phase of growth also responded maximally to fungal elicitor as measured by the production of capsidiol, an extracellular sesquiterpenoid. However, the rate of sesquiterpenoid biosynthesis, measured as the incorporation rate of [¹⁴C]acetate and [³H]mevalonate, could not be correlated with elicitor-inducible HMGR or sesquiterpene cyclase enzyme activities, nor elicitor-suppressible squalene synthetase enzyme activity.Abbreviations FPP farnesyl diphosphate - HMGR 3-hydroxy-3-methylglutaryl coenzyme A reductase