Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    The cell size distribution of tomato fruit can be changed by overexpression of CDKA1
    Czerednik, A. ; Busscher, M. ; Angenent, G.C. ; Maagd, R.A. de - \ 2015
    Plant Biotechnology Journal 13 (2015)2. - ISSN 1467-7644 - p. 259 - 268.
    cyclin-dependent kinase - lycopersicon-esculentum mill - plant development - arabidopsis - endoreduplication - growth - gene - expression - division - dna
    Tomato is one of the most cultivated vegetables in the world and an important ingredient of the human diet. Tomato breeders and growers face a continuous challenge of combining high quantity (production volume) with high quality (appearance, taste and perception for the consumers, processing quality for the processing industry). To improve the quality of tomato, it is important to understand the regulation of fruit development and of fruit cellular structure, which is in part determined by the sizes and numbers of cells within a tissue. The role of the cell cycle therein is poorly understood. Plant cyclin-dependent kinases (CDKs) are homologues of yeast cdc2, an important cell cycle regulator conserved throughout all eukaryotes. CDKA1 is constitutively expressed during the cell cycle and has dual functions in S- and M-phase progression. We have produced transgenic tomato plants with increased expression of CDKA1 under the control of the fruit-specific TPRP promoter, which despite a reduced number of seeds and diminished amount of jelly, developed fruits with weight and shape comparable to that of wild-type fruits. However, the phenotypic changes with regard to the pericarp thickness and placenta area were remarkable. Fruits of tomato plants with the highest expression of CDKA1 had larger septa and columella (placenta), compared with wild-type fruits. Our data demonstrate the possibility of manipulating the ratio between cell division and expansion by changing the expression of a key cell cycle regulator and probably its activity with substantial effects on structural traits of the harvested fruit.
    Sharp bends associated with deep scours in a tropical river: The river Mahakam (East Kalimantan, Indonesia)
    Vermeulen, B. ; Hoitink, A.J.F. ; Berkum, S.W. van; Hidayat, H. - \ 2014
    Journal of Geophysical Research: Earth Surface 119 (2014)7. - ISSN 2169-9003 - p. 1441 - 1454.
    circular meander pools - flow separation - mackenzie delta - channel bends - concave-bank - evolution - discharge - division - width - hole
    Autogenic scouring in sharp river bends has received ample attention in laboratory and modeling studies. These studies have significantly advanced our understanding of how flow processes are influenced by strong curvature and how they affect the bathymetry. Here we present a 300 km reach of the Mahakam River in Indonesia, which features several sharp bends (W/R > 0.5), providing a unique field data set to validate existing knowledge on sharp bends. Scour depths were found to strongly exceed what can be expected based on existing understanding of sharp bends and are highly correlated with curvature. A comprehensive stream reconnaissance was carried out to compare the occurrence of sharp bends and deep scours with lateral bank migration. Histograms of the occurrence of erosive, stable, advancing, and bar-type banks as a function of curvature quantify the switch from a mildly curved bend regime to a sharp bend regime. In mild bends, outer banks erode and inner banks advance. In sharp bends the erosion pattern inverts. Outer banks stabilize or advance, while inner banks erode. In sharply curved river bends, bars occur near the outer banks that become less erosive for higher curvatures. Inner banks become more erosive for higher curvatures but nevertheless accommodate the larger portion of exposed bars. No relation was found between the land cover adjacent to the river and the occurrence of sharp bends. Soil processes may play a crucial role in the formation of sharp bends, which is inferred from iron and manganese concretions observed in the riverbanks, indicating ferric horizons and early stages of the formation of plinthic horizons. Historical topographic maps show the planform activity of the river is low, which may relate to the scour holes slowing down planimetric development.
    Improved flow velocity estmates from oving-boat ADCO measurements
    Vermeulen, B. ; Sassi, M.G. ; Hoitink, A.J.F. - \ 2014
    Water Resources Research 50 (2014)5. - ISSN 0043-1397 - p. 4186 - 4196.
    doppler current profiler - suspended sediment - turbulence measurements - acoustic measurement - river - discharge - transport - division - channel - vessel
    Acoustic Doppler current profilers (ADCPs) are the current standard for flow measurements in large-scale open water systems. Existing techniques to process vessel-mounted ADCP data assume homogeneous or linearly changing flow between the acoustic beams. This assumption is likely to fail but is nevertheless widely applied. We introduce a new methodology that abandons the standard assumption of uniform flow in the area between the beams and evaluate the drawbacks of the standard approach. The proposed method strongly reduces the extent over which homogeneity is assumed. The method is applied to two field sites: a mildly curved bend near a junction featuring a typical bend flow and a sharply curved bend that features a more complex sheared flow. In both cases, differences are found between the proposed method and the conventional method. The proposed technique yields different results for secondary flow patterns compared with the conventional method. The velocity components estimated with the conventional method can differ over 0.2 m/s in regions of strong shear. We investigate the number of repeat transects necessary to isolate the mean flow velocity vector from the raw ADCP signal, discarding the influences of noise, positioning and projection errors, and turbulence. Results show that several repeat transects are necessary. The minimum number of repeat measurements needed for robust mean velocity estimates is reduced when applying the proposed method
    WOX5 Suppresses CYCLIN D Activity to Establish Quiescence at the Center of the Root Stem Cell Niche
    Forzani, C. ; Aichinger, E. ; Willemsen, V. ; Murray, J.A. - \ 2014
    Current Biology 24 (2014)16. - ISSN 0960-9822 - p. 1939 - 1944.
    arabidopsis-thaliana root - division - meristem - differentiation - organization - transition - expression - complex - protein
    In Arabidopsis, stem cells maintain the provision of new cells for root growth. They surround a group of slowly dividing cells named the quiescent center (QC), and, together, they form the stem cell niche (SCN). The QC acts as the signaling center of the SCN, repressing differentiation of the surrounding stem cells [1] and providing a pool of cells able to replace damaged stem cells [2, 3]. Maintenance of the stem cells depends on the transcription factor WUSCHEL-RELATED HOMEOBOX 5 (WOX5), which is specifically expressed in the QC [4]. However, the molecular mechanisms by which WOX5 promotes stem cell fate and whether WOX5 regulates proliferation of the QC are unknown. Here, we reveal a new role for WOX5 in restraining cell division in the cells of the QC, thereby establishing quiescence. In contrast, WOX5 and CYCD3;3/CYCD1;1 both promote cell proliferation in the nascent columella. The additional QC divisions occurring in wox5 mutants are suppressed in mutant combinations with the D type cyclins CYCD3;3 and CYCD1;1. Moreover, ectopic expression of CYCD3;3 in the QC is sufficient to induce cell division in the QC. WOX5 thus suppresses QC divisions that are otherwise promoted by CYCD3;3 and CYCD1;1, in part by interacting with the CYCD3;3 promoter to repress CYCD3;3 expression in the QC. Therefore, we propose a specific role for WOX5 in initiating and maintaining quiescence of the QC by excluding CYCD activity from the QC.
    Circadian rhythms in the cell cycle and biomass composition of Neochloris oleoabundans under nitrogen limitation
    Winter, L. de; Schepers, L.W. ; Cuaresma Franco, M. ; Barbosa, M.J. ; Martens, D.E. ; Wijffels, R.H. - \ 2014
    Journal of Biotechnology 187 (2014). - ISSN 0168-1656 - p. 25 - 33.
    chlamydomonas-reinhardtii - nutrient starvation - microalgae - division - growth - accumulation - quadricauda - clock - death
    The circadian clock schedules processes in microalgae cells at suitable times in the day/night cycle. To gain knowledge about these biological time schedules, Neochloris oleoabundans was grown under constant light conditions and nitrogen limitation. Under these constant conditions, the only variable was the circadian clock. The results were compared to previous work done under nitrogen-replete conditions, in order to determine the effect of N-limitation on circadian rhythms in the cell cycle and biomass composition of N. oleoabundans. The circadian clock was not affected by nitrogen-limitation, and cell division was timed in the natural night, despite of constant light conditions. However, because of nitrogen-limitation, not the entire population was able to divide every day. Two subpopulations were observed, which divided alternately every other day. This caused oscillations in biomass yield and composition. Starch and total fatty acids (TFA) were accumulated during the day. Also, fatty acid composition changed during the cell cycle. Neutral lipids were built up during the day, especially in cells that were arrested in their cell cycle (G2 and G3). These findings give insight in the influence of circadian rhythms on the cell cycle and biomass composition.
    Human impacts on tides overwhelm the effect of sea level rise on extreme water levels in the Rhine–Meuse delta
    Vellinga, N.E. ; Hoitink, A.J.F. ; Vegt, M. van der; Zhang, W. ; Hoekstra, P. - \ 2014
    Coastal Engineering 90 (2014). - ISSN 0378-3839 - p. 40 - 50.
    rivieren - waterstand - getijden - zeespiegelschommelingen - delta's - menselijke activiteit - inventarisaties - rivers - water level - tides - sea level fluctuations - deltas - human activity - inventories - river flow - netherlands - variability - subsidence - division - china
    With the aim to link tidal and subtidal water level changes to human interventions, 70 years of water level data for the Rhine–Meuse tidal river network is analysed using a variety of statistical methods. Using a novel parameterization of probability density functions, mean high and low water levels are examined, and extreme water levels are investigated by applying the combined Mann–Kendall and Pettitt tests to find trends and trend changes. Tidal water levels are studied based on harmonic analysis. Results show that the mean water levels throughout the system rise with the same pace as the mean sea level. However, high- and low water levels do not show the same increase, and the spatial variability in decadal trends in high- and low water levels is high. High water and low water extremes generally decrease. Both the extreme water level analysis and the harmonic analysis display significant trend breaks in 1970, 1981 and 1997. These breaks can be attributed to the closure of the Haringvliet estuary, the removal of sluices and the removal of a dam, respectively, which radically alter the tidal motion. These results demonstrate that the direct human influence on the tidal motion can overwhelm the effect of mean sea level rise on water level extremes.
    A SCARECROW-RETINOBLASTOMA Protein Network Controls Protective Quiescence in the Arabidopsis Root Stem Cell Organizer
    Cruz-Ramirez, A. ; Diaz Trivino, S. ; Wachsman, G. ; Du, Y. ; Arteága-Vázquez, M. ; Zhang Hongtao, ; Benjamins, R. ; Blilou, I. ; Neef, A.B. ; Chandler, V. ; Scheres, B. - \ 2013
    PloS Biology 11 (2013)11. - ISSN 1545-7885 - 12 p.
    thaliana root - replication stress - cycle progression - clonal analysis - self-renewal - dna-damage - in-vivo - division - meristem - gene
    Quiescent long-term somatic stem cells reside in plant and animal stem cell niches. Within the Arabidopsis root stem cell population, the Quiescent Centre (QC), which contains slowly dividing cells, maintains surrounding short-term stem cells and may act as a long-term reservoir for stem cells. The RETINOBLASTOMA-RELATED (RBR) protein cell-autonomously reinforces mitotic quiescence in the QC. RBR interacts with the stem cell transcription factor SCARECROW (SCR) through an LxCxE motif. Disruption of this interaction by point mutation in SCR or RBR promotes asymmetric divisions in the QC that renew short-term stem cells. Analysis of the in vivo role of quiescence in the root stem cell niche reveals that slow cycling within the QC is not needed for structural integrity of the niche but allows the growing root to cope with DNA damage
    Rooting plant development
    Scheres, B. - \ 2013
    Development 140 (2013)5. - ISSN 0950-1991 - p. 939 - 941.
    arabidopsis root - cell fate - meristem - differentiation - mechanism - shoot - framework - epidermis - division - pattern
    In 1993, we published a paper in Development detailing the anatomical structure of the Arabidopsis root. The paper described how root growth was maintained by the precisely tuned activity of a small set of 'initials', which acted as the source of dividing and differentiating cells, and how these stem cell-like cells surrounded a few infrequently dividing cells. This work underpinned subsequent research on root developmental biology and sparked a detailed molecular analysis of how stem cell groups are positioned and maintained in plants.
    Spatial coordination between stem cell activity and cell differentiation in the root meristem
    Moubayidin, L. ; Mambro, R. Di; Sozzani, R. ; Pacifici, E. ; Salvi, E. ; Terpstra, I. ; Bao, D. ; Dijken, A. van; Dello loio, R. ; Perilli, S. ; Ljung, K. ; Benfey, P.N. ; Heidstra, R. ; Costantino, P. ; Sabatini, S. - \ 2013
    Developmental Cell 26 (2013)4. - ISSN 1534-5807 - p. 405 - 415.
    gras gene family - arabidopsis root - auxin biosynthesis - scarecrow - expression - thaliana - transport - division - growth - niche
    A critical issue in development is the coordination of the activity of stem cell niches with differentiation of their progeny to ensure coherent organ growth. In the plant root, these processes take place at opposite ends of the meristem and must be coordinated with each other at a distance. Here, we show that in Arabidopsis, the gene SCR presides over this spatial coordination. In the organizing center of the root stem cell niche, SCR directly represses the expression of the cytokinin-response transcription factor ARR1, which promotes cell differentiation, controlling auxin production via the ASB1 gene and sustaining stem cell activity. This allows SCR to regulate, via auxin, the level of ARR1 expression in the transition zone where the stem cell progeny leaves the meristem, thus controlling the rate of differentiation. In this way, SCR simultaneously controls stem cell division and differentiation, ensuring coherent root growth.
    Regulation of tomato fruit pericarp development by an interplay between CDKB and CDKA1 cell cycle genes
    Czerednik, A. ; Busscher, M. ; Bielen, A.A.M. ; Wolters-Arts, M. ; Maagd, R.A. de; Angenent, G.C. - \ 2012
    Journal of Experimental Botany 63 (2012)7. - ISSN 0022-0957 - p. 2605 - 2617.
    lycopersicon-esculentum mill - dependent kinase - endoreduplicating cells - arabidopsis - protein - plants - expression - division - growth - rich
    Growth of tomato fruits is determined by cell division and cell expansion, which are tightly controlled by factors that drive the core cell cycle. The cyclin-dependent kinases (CDKs) and their interacting partners, the cyclins, play a key role in the progression of the cell cycle. In this study the role of CDKA1, CDKB1, and CDKB2 in fruit development was characterized by fruit-specific overexpression and down-regulation. CDKA1 is expressed in the pericarp throughout development, but is strongly up-regulated in the outer pericarp cell layers at the end of the growth period, when CDKB gene expression has ceased. Overexpression of the CDKB genes at later stages of development and the down-regulation of CDKA1 result in a very similar fruit phenotype, showing a reduction in the number of cell layers in the pericarp and alterations in the desiccation of the fruits. Expression studies revealed that CDKA1 is down-regulated by the expression of CDKB1/2 in CDKB1 and CDKB2 overexpression mutants, suggesting opposite roles for these types of CDK proteins in tomato pericarp development.
    Verrucomicrobia subdivision 1 strains display a difference in colonization in the colonization of the leek (Allium porrum) rhizosphere
    Nunes da Rocha, U. ; Elsas, J.D. van; Overbeek, L.S. van - \ 2011
    FEMS microbiology ecology 78 (2011)2. - ISSN 0168-6496 - p. 297 - 305.
    bacterial diversity - pseudomonas-fluorescens - microbial communities - root colonization - soil - determinants - survival - division - impact - maize
    Strains CHC12 and CHC8, belonging to, respectively, Luteolibacter and Candidatus genus Rhizospheria (Verrucomicrobia subdivision 1), were recently isolated from the leek rhizosphere. The key question addressed in this study was: does attraction to and colonization of the rhizosphere occur in the same way for both strains? Therefore, the fate of the two strains was studied near in vitro-grown leek roots and in soil zones proximate to and at a further distance from roots in a model plant–soil microcosm set-up. Quantitative PCR detection with specific primers was used, as the cultivation of these bacteria from soil is extremely fastidious. The data indicated that natural populations of Luteolibacter (akin to strain CHC12) had lower numbers in the rhizosphere than in the corresponding bulk soil. On the other hand, the populations of Candidatus genus Rhizospheria, i.e. strain CHC8, showed higher numbers in the rhizosphere than in the bulk soil. Increased strain CHC8 cell-equivalent numbers in the rhizosphere were not only the result of in situ cell multiplication, but also of the migration of cells towards the roots. Luteolibacter and Candidatus genus Rhizospheria cells displayed differences in attraction to the rhizosphere and colonization thereof, irrespective of the fact that both belonged to Verrucomicrobia subdivision 1
    Microtubule configurations and nuclear DNA synthesis during initiation of suspensor-bearing embryos from Brassica napus cv. Topas microspores
    Dubas, E. ; Custers, J.B.M. ; Kieft, H. ; Wedzony, M. ; Lammeren, A.A.M. van - \ 2011
    Plant Cell Reports 30 (2011)11. - ISSN 0721-7714 - p. 2105 - 2116.
    heat-shock - sporophytic development - cultured microspores - rape embryogenesis - in-vitro - induction - pollen - organization - division - visualization
    In the new Brassica napus microspore culture system, wherein embryos with suspensors are formed, ab initio mimics zygotic embryogenesis. The system provides a powerful in vitro tool for studying the diverse developmental processes that take place during early stages of plant embryogenesis. Here, we studied in this new culture system both the temporal and spatial distribution of nuclear DNA synthesis places and the organization of the microtubular (MT) cytoskeleton, which were visualized with a refined whole mount immunolocalization technology and 3D confocal laser scanning microscopy. A 'mild' heat stress induced microspores to elongate, to rearrange their MT cytoskeleton and to re-enter the cell cycle and perform a predictable sequence of divisions. These events led to the formation of a filamentous suspensor-like structure, of which the distal tip cell gave rise to the embryo proper. Cells of the developing pro-embryo characterized endoplasmic (EMTs) and cortical microtubules (CMTs) in various configurations in the successive stages of the cell cycle. However, the most prominent changes in MT configurations and nuclear DNA replication concerned the first sporophytic division occurring within microspores and the apical cell of the pro-embryo. Microspore embryogenesis was preceded by pre-prophase band formation and DNA synthesis. The apical cell of the proembryo exhibited a random organization of CMTs and, in relation to this, isotropic expansion occurred, mimicking the development of the apical cell of the zygotic situation. Moreover, the apical cell entered the S phase shortly before it divided transversally at the stage that the suspensor was 3-8 celled.
    Combined Genetic and Modeling Approaches Reveal That Epidermal Cell Area and Number in Leaves Are Controlled by Leaf and Plant Developmental Processes in Arabidopsis
    Tisne, S. ; Reymond, M. ; Vile, D. ; Fabre, J. ; Dauzat, M. ; Koornneef, M. ; Granier, C. - \ 2008
    Plant Physiology 148 (2008). - ISSN 0032-0889 - p. 1117 - 1127.
    quantitative trait loci - soil-water deficit - organ shape - thaliana - growth - expansion - erecta - kinase - division - cycle
    Both leaf production and leaf expansion are tightly linked to cell expansion and cell division, but the functional relationships between all these variables are not clearly established. To get insight into these relationships, a quantitative genetic analysis was performed in 118 recombinant inbred lines derived from a cross between the Landsberg erecta and Antwerp accessions and was combined with a structural equation modeling approach. Main effects and epistatic interactions at the quantitative trait locus (QTL) level were detected for rosette area, rosette leaf number, leaf 6 area, epidermal cell area and number. A QTL at ERECTA marker (ER) controlled cell expansion and cell division, in interaction with two other QTLs at SNP295 and SNP21 markers. Moreover, both the screening for marker association involved in the variation of the relationships between leaf growth variables and the test of alternative functional models by structural equation modeling revealed that the allelic value at ER controlled epidermal cell area and epidermal cell number in a leaf. These effects are driven both by a whole plant mechanism associated with leaf production and by a single leaf mechanism associated with leaf expansion. The complex effects of the QTL at ER were validated in selected heterogeneous inbred families. The ERECTA gene, which is mutated in the Landsberg erecta parental line, was found to be a putative candidate responsible for these mapped effects by phenotyping mutants of this gene at the cellular level. Together, these results give insight into the complex determination of leaf epidermal cell number and area
    A new whole-mount DNA quantification method and the analysis of nuclear DNA content in the stem-cell niche of Arabidopsis roots
    Willemse, J. ; Kulikova, O. ; Jong, H. de; Bisseling, T. - \ 2008
    The Plant Journal 55 (2008)5. - ISSN 0960-7412 - p. 886 - 894.
    flow-cytometry - thaliana root - fluorescence - division - meristem - growth
    A semi-automated method to quantify fluorescence intensity of objects in intact organs and tissues, composed of several cell layers, has been designed. The method has been developed on whole-mount propidium-iodide stained Arabidopsis thaliana (Arabidopsis) root tips, in which the DNA content of individual nuclei could be quantified. A diameter of less than 150 microm makes this organ most appropriate for whole-mount imaging. Further advantages are the lack of chlorophyll and transparent cell walls, with only a little background fluorescence. The method has a great advantage over flow cytometry, as the information regarding the positions of nuclei is maintained, and nuclei with aberrant DNA content can be re-assessed individually, which facilitates the efficient distinction between technical artefact and aberrant DNA content. Our averaging 3D method calculates the average of the summed fluorescence intensities of all sections of a nucleus and interpolates the missing sections, thereby allowing for the correction of detection problems. Furthermore, this method has the advantage of detecting objects in tissues covering multiple cell layers. The results of our method in Arabidopsis root tips showed that the quiescent centre cells, which rarely divide, are diploid, and are arrested in G1 or G0. Most stem cells, with the exception of those of the vascular tissue, are diploid cells, and their rather low division rate is caused by an elongated G1 phase. In contrast, the majority of the vascular stem cells are tetraploid.
    ENOD40 affects elongation growth in tobacco Bright Yellow-2 cells by alteration of ethylene biosynthesis kinetics
    Ruttink, T. ; Boot, K. ; Kijne, J. ; Bisseling, T. ; Franssen, H. - \ 2006
    Journal of Experimental Botany 57 (2006)12. - ISSN 0022-0957 - p. 3271 - 3282.
    rhizobium-legume interaction - soybean nodule development - white clover - expression - protoplasts - division - gene - arabidopsis - nodulation - patterns
    Plant developmental processes are controlled by co-ordinated action of phytohormones and plant genes encoding components of developmental response pathways. ENOD40 was identified as a candidate for such a plant factor with a regulatory role during nodulation. Although its mode of action is poorly understood, several lines of evidence suggest interaction with phytohormone response pathways. This hypothesis was investigated by analysing cytokinin-, auxin-, and ethylene-induced responses on cell growth and cell division in transgenic 35S:NtENOD40 Bright Yellow-2 (BY-2) tobacco cell suspensions. It was found that cell division frequency is controlled by the balance between cytokinin and auxin in wild-type cells and that this regulation is not affected in 35S:NtENOD40 lines. Elongation growth, on the other hand, is reduced upon overexpression of NtENOD40. Analysis of ethylene homeostasis shows that ethylene accumulation is accelerated in 35S:NtENOD40 lines. ENOD40 action can be counteracted by an ethylene perception blocker, indicating that ethylene is a negative regulator of elongation growth in 35S:NtENOD40 cells, and that the NtENOD40-induced response is mediated by alteration of ethylene biosynthesis kinetics.
    EBP1 regulates organ size through cell growth and proliferation in plants
    Horvath, B.M. ; Magyar, Z. ; Zhang, Y. ; Hamburger, A.W. ; Bako, L. ; Visser, R.G.F. ; Bachem, C.W.B. ; Bogre, L. - \ 2006
    The EMBO Journal 25 (2006)20. - ISSN 0261-4189 - p. 4909 - 4920.
    differential gene-expression - potato-tuber development - erbb-3 binding-protein - transcription factor - cycle regulation - arabidopsis - expansion - division - leaf - organogenesis
    Plant organ size shows remarkable uniformity within species indicating strong endogenous control. We have identified a plant growth regulatory gene, functionally and structurally homologous to human EBP1. Plant EBP1 levels are tightly regulated; gene expression is highest in developing organs and correlates with genes involved in ribosome biogenesis and function. EBP1 protein is stabilised by auxin. Elevating or decreasing EBP1 levels in transgenic plants results in a dose-dependent increase or reduction in organ growth, respectively. During early stages of organ development, EBP1 promotes cell proliferation, influences cell-size threshold for division and shortens the period of meristematic activity. In postmitotic cells, it enhances cell expansion. EBP1 is required for expression of cell cycle genes; CyclinD3;1, ribonucleotide reductase 2 and the cyclin-dependent kinase B1;1. The regulation of these genes by EBP1 is dose and auxin dependent and might rely on the effect of EBP1 to reduce RBR1 protein level. We argue that EBP1 is a conserved, dose-dependent regulator of cell growth that is connected to meristematic competence and cell proliferation via regulation of RBR1 level.
    Reduction of cell size induced by enod40 in Arabidopsis thaliana
    Guzzo, F. ; Portaluppi, P. ; Grisi, R. ; Barone, S. ; Zampieri, S. ; Franssen, H. ; Levi, M. - \ 2005
    Journal of Experimental Botany 56 (2005)412. - ISSN 0022-0957 - p. 507 - 513.
    soybean nodule development - plant development - sucrose synthase - gene-expression - flow-cytometry - growth - division - cultures - rna - organogenesis
    An extensive analysis of organ and cell size was performed in three different Arabidopsis lines transformed with the early nodulin gene enod40 under control of the CaMV35S promoter. All three transgenic lines presented a significant decrease in the mean size of both epidermal internode and leaf mesophyll cells. Flow cytometric and image analysis of enod40-transfected protoplasts prepared from wild-type Arabidopsis cell suspensions showed that transient expression of the gene resulted in reduced forward light scattering (a factor correlated with particle size) and cell size. The direct administration of ENOD40 peptide to fresh protoplasts also resulted in reduced forward scattering with respect to the control and to the administration of unrelated peptides. As far as is known this is the first report documenting a biological effect of enod40 at the cellular level in non-legume plants
    The role of the cell cycle machinery in resumption of postembryonic development
    Barroco, R.M. ; Poucke, K. van; Bergervoet, J.H.W. ; Veylder, L. de; Groot, S.P.C. ; Inze, D. ; Engler, G. - \ 2005
    Plant Physiology 137 (2005)1. - ISSN 0032-0889 - p. 127 - 140.
    beta-tubulin accumulation - in-situ hybridization - arabidopsis-thaliana - tomato seeds - maize germination - dependent kinases - dna-replication - expression - division - plants
    Cell cycle activity is required for plant growth and development, but its involvement in the early events that initiate seedling development remains to be clarified. We performed experiments aimed at understanding when cell cycle progression is activated during seed germination, and what its contribution is for proper seedling establishment. To this end, the spatial and temporal expression profiles of a large set of cell cycle control genes in germinating seeds of Arabidopsis (Arabidopsis thaliana) and white cabbage (Brassica oleracea) were analyzed. The in vivo behavior of the microtubular cytoskeleton was monitored during Arabidopsis seed germination. Flow cytometry of Arabidopsis germinating seeds indicated that DNA replication was mainly initiated at the onset of root protrusion, when germination reached its end. Expression analysis of cell cycle genes with mRNA in situ localization, -glucuronidase assays, and semiquantitative reverse transcription-polymerase chain reaction showed that transcription of most cell cycle genes was detected only after completion of germination. In vivo green fluorescent protein analysis of the microtubule cytoskeleton demonstrated that mitosis-specific microtubule arrays occurred only when the radicle had started to protrude, although the assembly of the microtubular cytoskeleton was promptly activated once germination was initiated. Thus, seed germination involves the synthesis and/or activation of a reduced number of core cell cycle proteins, which only trigger DNA replication, but is not sufficient to drive cells into mitosis. Mitotic divisions are observed only after the radicle has protruded and presumably rely on the de novo production of other cell cycle regulators
    Victivallis vadensis gen. nov., sp. nov., a sugar-fermenting anaerobe from human faeces
    Zoetendal, E.G. ; Plugge, C.M. ; Akkermans, A.D.L. ; Vos, W.M. de - \ 2003
    International Journal of Systematic and Evolutionary Microbiology 53 (2003). - ISSN 1466-5026 - p. 211 - 215.
    16s ribosomal-rna - rice paddy soil - sequence-analysis - fecal samples - bacteria - division - prosthecobacter - communities - commensal - culture
    A novel strictly anaerobic, cellobiose-degrading bacterium, strain Cello, was isolated from a human faecal sample by combining enrichments in liquid and soft-agar basal media. A noteworthy characteristic was its inability to grow on normal agar plates and in roll tubes. The cells were coccus shaped and non-motile, with an extracellular slime layer. Growth of strain Cello T occurred between 20 and 40 degreesC, with optimal growth at 37 degreesC. The pH range for growth was 5-7-5 with an optimum at 6-5. In pure culture, strain Cello T could only grow on a variety of sugars. Glucose was converted to acetate, ethanol and H-2. The doubling time on glucose was 0.5 h. In a syntrophic co-culture with Methanospirillum hungatei strain JF-1(T), strain Cello(T) converted glucose to acetate and H-2. The G+C content was 59.2 mol%. 16S rDNA analysis revealed that the closest relatives of strain Cello(T) were two uncultured bacteria from anaerobic digesters, both with 94% 16S rDNA sequence similarity. The closest cultured representatives belong to genera of the bacterial division 'Verrucomicrobia'. The name Victivallis vadensis gen. nov., sp. nov. is proposed for strain Cello(T) (=DSM 14823(T) =ATCC BAA-548(T)).
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