scholarly journals RADIATION EFFECTS ON THE GROWTH RATE AND CELL POPULATION KINETICS OF ACTIVELY GROWING AND DORMANT ROOTS OF TRADESCANTIA PALUDOSA

1965 ◽  
Vol 26 (1) ◽  
pp. 187-199 ◽  
Author(s):  
Jack Van't Hof ◽  
A. H. Sparrow
Keyword(s):  
Growth Rate ◽  
Root Growth ◽  
Cell Population ◽  
Mitotic Cycle ◽  
Tritiated Thymidine ◽  
Cycle Duration ◽  
X Rays ◽  
Proliferating Cells ◽  
Population Kinetics ◽  
Tradescantia Paludosa

Actively growing and dormant roots of Tradescantia paludosa were exposed to x-rays to compare the radiosensitivity of an actively proliferating tissue with that of one which is not active but is potentially proliferative. The level of effect was ascertained by the degree of change in the rate of root growth 4 days after exposure. Cell population kinetics were measured in control and in irradiated roots to determine whether or not a change was produced either in the number of proliferating cells or in the mitotic cycle duration which was sufficient to explain the altered rate of root growth. Nuclear volumes were also measured to provide an estimate of the relative total target size in actively growing vs. dormant roots. Tritiated thymidine was used to measure the cycle duration and the proportion of cells synthesizing DNA. The results showed that 184 and 305 r respectively were required to reduce the linear root growth rate to 37 per cent of that of the control for actively growing and dormant roots. Mitotic cycle duration, measured 4 days after x-ray exposure, was the same as in the control. The number of proliferating cells, however, was reduced. The rate of cell production in the irradiated roots was reduced to approximately one-half that of the controls. The average nuclear volumes of active and dormant roots were 733 and 491 µ3 respectively; thus the difference in the number of roentgens required to reduce growth to 37 per cent of that of the control can be attributed to the different average nuclear volumes. Therefore, the experiments suggest that part if not most of the differences in sensitivity between an actively dividing and an essentially non-dividing meristematic cell population resides in their different average nuclear volumes. Thus the law of Bergonie and Tribondeau needs to be reinterpreted, since the basic reason for the differences is secondary to whether or not the meristematic cells are proliferating.

scholarly journals CELL POPULATION KINETICS OF EXCISED ROOTS OF PISUM SATIVUM

1965 ◽  
Vol 27 (1) ◽  
pp. 179-189 ◽  
Author(s):  
Jack Van't Hof
Keyword(s):  
Cell Population ◽  
Mitotic Cycle ◽  
Sucrose Concentration ◽  
Tritiated Thymidine ◽  
Cycle Duration ◽  
Population Kinetics ◽  
Pea Roots ◽  
Mitotic Figures ◽  
Kinetics Of ◽  
Subsequent Rise

The cell population kinetics of excised, cultured pea roots was studied with the use of tritiated thymidine and colchicine to determine (1) the influence of excision, (2) the influence of sucrose concentration, (3) the average mitotic cycle duration, and (4) the duration of mitosis and the G1, S, and G2 periods of interphase.1 The results indicate that the process of excision causes a drop in the frequency of mitotic figures when performed either at the beginning of the culture period or after 100 hours in culture. This initial decrease in frequency of cell division is independent of sucrose concentration, but the subsequent rise in frequency of division, after 12 hours in culture, is dependent upon sucrose concentration. Two per cent sucrose maintains the shortest mitotic cycle duration. The use of colchicine indicated an average cycle duration of 20 hours, whereas the use of tritiated thymidine produced an average cycle duration of 17 hours.

Cell Population Kinetics of the Rhabdomyosarcoma R1H of the Rat after Single Doses of X-rays

1990 ◽  
Vol 57 (3) ◽  
pp. 567-589 ◽  
Author(s):  
H. Jung ◽  
H.-J. Krüger ◽  
I. Brammer ◽  
F. Zywietz ◽  
H.-P. Beck-Bornholdt
Keyword(s):  
Cell Population ◽  
X Rays ◽  
Population Kinetics ◽  
Kinetics Of

Cytokinins regulate root growth through its action on meristematic cell proliferation but not on the transition to differentiation

2018 ◽  
Vol 45 (2) ◽  
pp. 215 ◽  
Author(s):  
Victor B. Ivanov ◽  
Alexey N. Filin
Keyword(s):  
Cell Proliferation ◽  
Root Growth ◽  
Life Span ◽  
Mitotic Cycle ◽  
Meristematic Cell ◽  
Cycle Duration ◽  
Triple Mutant ◽  
Cytokinin Synthesis ◽  
Transition To Elongation ◽  
Cell Transition

Contrary to the wide-spread view that cytokinins change the rate of root growth and meristem size by regulating the cell transition to elongation (differentiation), our data showed that cytokinins affected the cell cycle duration in the meristem. The rate of meristematic cell transition to elongation itself is regulated by two groups of independent processes, through influence on (i) the life-span of cells in the meristem, and (ii) the cell proliferation rate in the meristem. Trans-zeatin slows down the root growth rate and the cell transition to elongation as a result of prolongation of mitotic cycles. The life-span of cells in the meristem does not change. The number of meristematic cells in one file decreases due to inhibition of cell proliferation but not to an acceleration of cell transition to elongation. Roots of triple mutant ipt3ipt5ipt7, in which cytokinin synthesis is slowed down, behave in an opposite way such that the rate of cell transition to elongation and cell proliferation is speeded up. Their peculiarity is that the life-span of cells in meristem becomes shorter than in control roots. In both cases, a change in concentration of endogenous cytokinin or in its signalling are associated with a change in mitotic cycle duration.

LONG-RANGE PREDICTABILITY IN MODELS OF CELL POPULATIONS SUBJECTED TO PHASE-SPECIFIC DRUGS: GROWTH-RATE APPROXIMATION USING PROPERTIES OF POSITIVE COMPACT OPERATORS

2006 ◽  
Vol 16 (supp01) ◽  
pp. 1155-1172 ◽  
Author(s):  
Y. KHEIFETZ ◽  
Y. KOGAN ◽  
Z. AGUR
Keyword(s):  
Growth Rate ◽  
Drug Treatment ◽  
Cell Population ◽  
Initial Conditions ◽  
A Priori ◽  
Age Distribution ◽  
Specific Treatment ◽  
Cycle Duration ◽  
Cell Age

The aim of the present work is twofold: to develop numerical procedures for a priori determining whether a given cell population, having a distributed cell-cycle duration, will grow or decay when subjected to prescribed chemotherapy; to evaluate the cumulative error in the long-term predictions for such populations. We show that cell population dynamics under drug treatment can be modelled by iterative application of a compact operator on the initial cell age-distribution. We further show that this model can be approximated by iterative application of matrices on some finite-dimensional vector, containing initial conditions. Moreover, we develop a method for estimating the growth rate of cell population and show that in fully periodic treatments the estimated error does not grow as time tends to infinity. From the biomedical viewpoint this means that only fully periodic (strictly periodic) schedules can be considered for successfully predicting the long-term effect of chemotherapy. Thus, cyclic drug treatment is shown to be advantageous, not only in increasing selectivity of chemotherapy, as has been previously demonstrated, but also in increasing long-term predictability of specific treatment schedules.

Regulation of cell reproduction in bud meristems of Tradescantia paludosa

1973 ◽  
Vol 51 (6) ◽  
pp. 1137-1145 ◽  
Author(s):  
Kyu-Byung Yun ◽  
J. M. Naylor
Keyword(s):  
Apical Dominance ◽  
Mitotic Cycle ◽  
Plant Cells ◽  
Central Zone ◽  
Apparent Absence ◽  
Cell Reproduction ◽  
Terminal Bud ◽  
Terminal Buds ◽  
Regulation Of Growth ◽  
Tradescantia Paludosa

The mitotic cycle can be arrested in the apical summit of vegetative terminal buds of Tradescantia paludosa by restricting the level of nitrogen or light available to the plant. Cells in this portion of the bud are much more sensitive to these stress conditions than those in the subjacent portion of the meristem. This differential response induced the establishment of a quiescent "central zone" which is distinguished from the rest of the meristem by the apparent absence of mitosis and DNA synthesis, larger nuclear volume, and a lower histone content of chromatin. These features are identical with those imposed by apical dominance in apices of inhibited lateral buds.The results support the view that competition for nutrients is an important causal factor in apical dominance. They suggest also that competition for nutrients within the terminal bud meristem is important in the regulation of growth in vegetative shoots in respones to conditions of the environment.

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