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Division Rate (division + rate)
Kinds of Division Rate Selected AbstractsVariation in toxin compositions of two harmful raphidophytes, Chattonella antiqua and Chattonella marina, at different salinitiesENVIRONMENTAL TOXICOLOGY, Issue 2 2002Shahroz Mahean Haque Abstract Toxin compositions of the two species of raphidophytes, Chattonella antiqua (Hada) Ono and Chattonella marina (Subrahmanyan) Hara et Chihara, were investigated at different salinities under laboratory conditions. C. antiqua contained toxin components CaTx-I, CaTx-II, CaTx-III, and CaTx-IV, which corresponded to brevetoxin components PbTx-1, PbTx-2, PbTx-3, and oxidized PbTx-2. Similarly, C. marina included CmTx-I, CmTx-II, CmTx-III, and CmTx-IV corresponding to PbTx-2, PbTx-9, PbTx-3, and oxidized PbTx-2. Toxin yields in both species varied markedly with a change in salinity concentration. In C. antiqua CaTx-I, CaTx-II, and CaTx-III peaked at 25 P.P.t. with yields of 0.99, 0.42, and 2.90 pg/cell, but the highest yield (2.35 pg/cell) of CaTx-IV was attained at 30 P.P.t. The yields of all CaTx components decreased sharply at salinities exceeding 30 P.P.t. On the other hand, C. marina yielded higher proportions of CmTx-I (0.55 pg/cell) and CmTx-III (2.50 pg/cell) at 25 P.P.t. However, CmTx-IV was present in its highest amount (1.65 pg/cell) at 30 P.P.t., as seen in C. antiqua. A small amount of CmTx-II was also detected at 20 P.P.t.,35 P.P.t. Both species showed the highest ichthyotoxicities at 25 P.P.t., at which the maximum cell division rate was obtained. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 113,118, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10039 [source] Phenotypical variation in a toxic strain of the phytoplankter, Cylindrospermopsis raciborskii (nostocales, cyanophyceae) during batch cultureENVIRONMENTAL TOXICOLOGY, Issue 6 2001Peter R. Hawkins Abstract A nonaxenic strain of Cylindrospermopsis raciborskii Woloszynska (AWT 205) was grown in batch culture, with and without nitrate as the primary N source. Rapid log-phase growth with nitrate was 1.0 doubling/day versus 0.3 doubling/day without nitrate. Cylindrospermopsin (CYN) production was measured by HPLC. The rate of intracellular CYN production matched cell division rate for both the diazotrophies at cell densities less than 107 cell/ml. At cell density >107 cell/ml, additional resource limitation in batch culture slowed log-phase growth to 0.04 division/day and cell division and CYN production decoupled. Intracellular CYN concentration increased at a rate of 0.08 doubling/day, twice the cell division rate. Extracellular CYN as a proportion of the total CYN increased from 20% during the rapid growth phase, to 50% during the slow growth phase. The total CYN yield from cultures grown out to stationary phase (55 days) exceeded 2 mg CYN/l. C. raciborskii cells in log-phase growth, exposed to 1 ppm copper (as copper sulphate), lysed within 24 hours. After copper treatment, all CYN was in the filterable fraction. These findings imply that in naturally occurring blooms of C. raciborskii, the movement of intracellular CYN into solution will be the greatest during stationary phase, when intracellular concentrations are highest and cell lysis is more frequent. The application of algicides that promote cell lysis will exacerbate this effect. © 2001 John Wiley & Sons, Inc. Environ Toxicol 16: 460,467, 2001 [source] Spatial and Temporal Quantitative Analysis of Cell Division and Elongation Rate in Growing Wheat Leaves under Saline ConditionsJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 1 2008Yuncai Hu Abstract Leaf growth in grasses is determined by the cell division and elongation rates, with the duration of cell elongation being one of the processes that is the most sensitive to salinity. Our objective was to investigate the distribution profiles of cell production, cell length and the duration of cell elongation in the growing zone of the wheat leaf during the steady growth phase. Plants were grown in loamy soil with or without 120 mmol/L NaCl in a growth chamber, and harvested at day 3 after leaf 4 emerged. Results show that the elongation rate of leaf 4 was reduced by 120 mmol/L NaCl during the steady growth phase. The distribution profile of the lengths of abaxial epidermal cells of leaf 4 during the steady growth stage shows a sigmoidal pattern along the leaf axis for both treatments. Although salinity did not affect or even increased the length of the epidermal cells in some locations in the growth zone compared to the control treatment, the final length of the epidermal cells was reduced by 14% at 120 mmol/L NaCl. Thus, we concluded that the observed reduction in the leaf elongation rate derived in part from the reduced cell division rate and either the shortened cell elongation zone or shortened duration of cell elongation. This suggests that more attention should be paid to the effects of salinity on those properties of cell production and the period of cell maturation that are related to the properties of cell wall. [source] IMPACT OF IRON LIMITATION ON THE PHOTOSYNTHETIC APPARATUS OF THE DIATOM CHAETOCEROS MUELLERI (BACILLARIOPHYCEAE)JOURNAL OF PHYCOLOGY, Issue 6 2001Margaret Davey Iron starvation induced marked increases in flavodoxin abundance and decreases in light-saturated and light-limited photosynthesis rates in the diatom Chaetoceros muelleri. Consistent with the substitution of flavodoxin for ferredoxin as an early response to iron starvation, increases of flavodoxin abundance were observed before declines of cell division rate or chl a specific photosynthesis rates. Changes in the abundance of flavodoxin after the addition of iron to iron-starved cells indicated that flavodoxin was not actively degraded under iron-replete conditions. Greater declines in light-saturated oxygen evolution rates than dark oxygen consumption rates indicated that the mitochondrial electron transfer chain was not affected as greatly by iron starvation as the photosynthetic electron transfer chain. The carbon:nitrogen ratio was unaffected by iron starvation, suggesting that photosynthetic electron transfer was a primary target of iron starvation and that reductions in nitrate assimilation were due to energy limitation (the C:N ratio would be expected to rise under nitrogen-limited but energy-replete conditions). Parallel changes were observed in the maximum light-saturated photosynthesis rate and the light-limited initial slope of the photosynthesis-light curve during iron starvation and recovery. The lowest photosynthesis rates were observed in iron-starved cells and the highest values in iron-replete cells. The light saturation parameter, Ik, was not affected by iron starvation, nor was the chl-to-C ratio markedly reduced. These observations were consistent with iron starvation having a similar or greater effect on photochemical charge separation in PSII than on downstream electron transfer steps. Declines of the ratio of variable to maximum fluorescence in iron-starved cells were consistent with PSII being a primary target of iron starvation. The functional cross-section of PSII was affected only marginally (<20%) by iron starvation, with the largest values observed in iron-starved cells. The rate constant for electron transfer calculated from fast repetition rate fluorescence was found to covary with the light-saturated photosynthesis rate; it was lowest in the most severely starved cells. [source] Nitrogen deficiency inhibits leaf blade growth in Lolium perenne by increasing cell cycle duration and decreasing mitotic and post-mitotic growth ratesPLANT CELL & ENVIRONMENT, Issue 6 2008MONIKA KAVANOVÁ ABSTRACT Nitrogen deficiency severely inhibits leaf growth. This response was analysed at the cellular level by growing Lolium perenne L. under 7.5 mm (high) or 1 mm (low) nitrate supply, and performing a kinematic analysis to assess the effect of nitrogen status on cell proliferation and cell growth in the leaf blade epidermis. Low nitrogen supply reduced leaf elongation rate (LER) by 43% through a similar decrease in the cell production rate and final cell length. The former was entirely because of a decreased average cell division rate (0.023 versus 0.032 h,1) and thus longer cell cycle duration (30 versus 22 h). Nitrogen status did not affect the number of division cycles of the initial cell's progeny (5.7), and accordingly the meristematic cell number (53). Meristematic cell length was unaffected by nitrogen deficiency, implying that the division and mitotic growth rates were equally impaired. The shorter mature cell length arose from a considerably reduced post-mitotic growth rate (0.033 versus 0.049 h,1). But, nitrogen stress did not affect the position where elongation stopped, and increased cell elongation duration. In conclusion, nitrogen deficiency limited leaf growth by increasing the cell cycle duration and decreasing mitotic and post-mitotic elongation rates, delaying cell maturation. [source] Promotion of callus propagation by 5-aminolevulinic acid in a Laminaria japonica sporophyteAQUACULTURE RESEARCH, Issue 1 2009Katsuhiro Tabuchi Abstract The effects of 5-aminolevulinic acid (ALA) on the induction and growth of callus-like cells in Laminaria japonica were investigated in explants obtained from basal, middle and apical portions along the sporophyte. 5-Aminolevulinic acid treatment promoted the induction of callus-like cells in explants obtained from all portions, and the induction rate was higher when a concentration of 50,500 mg L,1 of ALA was used. The promotion was especially remarkable in apical explants, and the induction was 10,14 times higher in the 100,500 mg L,1 range than that in the 0 mg L,1. The cell division rate of callus-like cells showed the highest value in the explants cultured with 500 mg L,1 of ALA for 14 days. The promotion of the cell division rate by culturing with 500 mg L,1 ALA was also observed under white, blue and red lights. The callus-like cells, which were cultured in 500 mg L,1 of ALA for 2 months, had many clear chloroplasts. After 3 months, young thalli occurred. These results suggest that the ALA treatment is effective for stable propagation of callus-like cells in L. japonica. [source] THE ECOLOGY AND GENETICS OF FITNESS IN CHLAMYDOMONAS.EVOLUTION, Issue 1 2002VIII. Abstract According to classical evolutionary theory, sexual recombination can generate the variation necessary to adapt to changing environments and thereby confer an evolutionary advantage of sexual over asexual reproduction. Using the green alga, Chlamydomonas reinhardtii, we investigated the effect of a single sexual episode on adaptation of heterotrophic growth on different carbon sources. In an initial mixture of isolates, sex was induced and the resulting offspring constituted the sexual populations, along with any unmated vegetative cells; the unmated mixture of isolates represented the asexual populations. Mean and variance in division rates (i.e., fitness) were measured four times during approximately 50 generations of vegetative growth in the dark on all possible combinations of four carbon sources. Consistent with effects of recombination of epistatic genes in linkage disequilibrium, sexual populations initially had a higher variance in fitness, but their mean fitness was lower than that of asexual populations, possibly due to recombinational load. Subsequently, fitness of sexual populations exceeded that of asexual ones, but finally they regained parity in both mean and variance of fitness. Although recombination was not more effective on more complex substrates, these results generally support the idea that sex can accelerate adaptation to novel environments. [source] Biosynthesis profile and endogenous titers of polyamines differ in totipotent and recalcitrant plant protoplastsPHYSIOLOGIA PLANTARUM, Issue 1 2005Anastasia K. Papadakis The expression of totipotency in plant protoplasts is a complex developmental phenomenon and is affected by genetic and physiological factors. Polyamines (PAs) are known to be involved in a variety of growth and developmental processes in higher plants, as well as in adaptation to stresses. In this study, we present the homeostatic characteristics of the endogenous PA putrescine (Put), spermidine (Spd), and spermine (Spm) in totipotent (T) and non-totipotent (NT) tobacco protoplasts and in recalcitrant (R) grapevine protoplasts. T-tobacco protoplasts, with high division rates, have the highest level of endogenous PAs. In these protoplasts, the soluble-hydrolyzed fraction predominates and increases, and the insoluble-hydrolyzed fraction also increases, whereas soluble (S) PAs decrease rapidly during culture. The isolation process contributes to the increased Put levels, which are higher in freshly isolated NT-tobacco protoplasts than in T-protoplasts. During culture, total Put predominates over Spd and Spm, and the highest accumulation is found in T-protoplasts. Ornithine decarboxylase and arginase activities both increase in T-protoplasts, whereas arginine decarboxylase activity causes Put accumulation in NT-tobacco protoplasts. R-grapevine protoplasts show a different PA profile, mostly due to the lower PA content, the higher S-fraction, and the higher ratio of Spm to total PAs. The data suggest that the levels and metabolism of the intracellular PAs could be related to the expression of totipotency of plant protoplasts. [source] Axenic Culture of the Heterotrophic Dinoflagellate Pfiesteria shumwayae in a Semi-Defined MediumTHE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 1 2009HAYLEY M. SKELTON ABSTRACT. A semi-defined, biphasic culture medium was developed that supported the axenic growth of three strains of the heterotrophic dinoflagellate Pfiesteria shumwayae. Maximum cell yields and division rates in the semi-defined medium ranged from 0.1 × 105 to 4.0 × 105 cells/ml and 0.5 to 1.7 divisions/day, respectively, and depended on the concentration of the major components in the medium as well as the P. shumwayae strain. The medium contained high concentrations of certain dissolved and particulate organic compounds, including amino acids and lipids. Pfiesteria shumwayae flagellated cells were attracted to insoluble lipids present in the medium and appeared to feed on the lipid particles, suggesting that phagocytosis may be required for growth in axenic culture. Development of a semi-defined medium represents significant progress toward a completely defined axenic culture medium and subsequent determination of the biochemical requirements of P. shumwayae, needed to advance understanding of the nutritional ecology of this species. Further, this medium provides an economical, simplified method for generating high cell densities of P. shumwayae in axenic culture that will facilitate controlled investigations on the physiology and biochemistry of this heterotrophic dinoflagellate. [source] Microzooplankton grazing on harmful dinoflagellate blooms: Are ciliates or heterotrophic dinoflagellates important?THE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 2 2005DIANE K. STOECKER Microzooplankton grazing can be important in regulating growth of dinoflagellate populations, including species responsible for harmful algal blooms. In the Chesapeake Bay region, microzooplankton community grazing coefficients on small cell-size dinoflagellates are often greater than potential gross growth coefficients of dinoflagellates, and thus grazing may prevent bloom formation. Who are the major microzooplankton grazers on small dinoflagellates? Ciliates or other dinoflagellates? Data from Chesapeake Bay and its tributaries indicate both; sometimes ciliates and sometimes dinoflagellates are the major grazers. The importance of ciliates and heterotrophic dinoflagellates varies with season and location, but often one group dominates the microzooplankton assemblage. Specific clearance and division rates of ciliates are higher than that of heterotrophic dinoflagellates, thus it could be expected that ciliates would be the dominant microzooplankton grazers. However, during summer, small heterotrophic dinoflagellates are often the dominant grazers on small dinoflagelllates in the mesohaline Bay. Differential predation by copepods on ciliates may be responsible for this pattern. When microzooplankton community grazing is less than dinoflagellate cell division, red tides may result. Thus, it is important to understand the factors controlling both ciliate and heterotrophic dinoflagellate populations and their grazing impacts. [source] A novel assay based on fluorescence microscopy and image processing for determining phenotypic distributions of rod-shaped bacteriaBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2009Konstantinos Spetsieris Abstract Cell population balance (CPB) models can account for the phenotypic heterogeneity that characterizes isogenic cell populations. To utilize the predictive power of these models, however, we must determine the single-cell reaction and division rates as well as the partition probability density function of the cell population. These functions can be obtained through the Collins,Richmond inverse CPB modeling methodology, if we know the phenotypic distributions of (a) the overall cell population, (b) the dividing cell subpopulation, and (c) the newborn cell subpopulation. This study presents the development of a novel assay that combines fluorescence microscopy and image processing to determine these distributions. The method is generally applicable to rod-shaped cells dividing through the formation of a characteristic constriction. Morphological criteria were developed for the automatic identification of dividing cells and validated through direct comparison with manually obtained measurements. The newborn cell subpopulation was obtained from the corresponding dividing cell subpopulation by collecting information from the two compartments separated by the constriction. The method was applied to E. coli cells carrying the genetic toggle network with a green fluorescent marker. Our measurements for the overall cell population were in excellent agreement with the distributions obtained via flow cytometry. The new assay constitutes a powerful tool that can be used in conjunction with inverse CPB modeling to rigorously quantify single-cell behavior from data collected from highly heterogeneous cell populations. Biotechnol. Bioeng. 2009;102: 598,615. © 2008 Wiley Periodicals, Inc. [source] Epidermal kinetic alterations required to generate the psoriatic phenotype: a reappraisalCELL PROLIFERATION, Issue 3 2010T. Simonart Objectives:, Although there have been major advances in understanding immunopathogenesis of psoriasis, the basic processes causing psoriatic morphology remain to be identified. Materials and methods:, Our group has designed a systematic review of studies (1962,2009) on keratinocyte kinetics in psoriasis. We obtained data from MEDLINE, PubMed, Current Contents, reference lists and specialist textbooks. A general equation for evolution of the differentiated epidermis has been analysed. Necessary conditions for observed qualitative change in homeostasis between normal skin and established psoriatic lesions were determined. Results and discussion:, Increase in the number of cell divisions (or imbalance in symmetric division rates of committed progenitor cells) and/or decrease in physiological apoptosis in the germinative compartment, together with feedback loops that limit thickening of the skin, are required to generate psoriatic morphology, that is, to increase the absolute size but decrease relative size of the differentiated cell compartment with respect to the germinative compartment. [source] | |||||||||||||