Timing in Chenopodium rubrum of export of the floral stimulus from the cotyledons and its action at the shoot apex

1972 ◽  
Vol 50 (4) ◽  
pp. 697-702 ◽  
Author(s):  
R. W. King
Keyword(s):  
Cell Division ◽  
Mitotic Index ◽  
Shoot Apex ◽  
Essential Role ◽  
Floral Development ◽  
Dark Period ◽  
Chenopodium Rubrum ◽  
Floral Stimulus ◽  
Dividing Cells ◽  
Short Days

When the cotyledons of 6-day-old seedlings of Chenopodium rubrum were removed at various intervals after exposure to a single 13.5-h dark period, defoliation during the first 6 h after darkness prevented flowering. If the cotyledons remained on the plant for a further 5 or more hours flowering gradually increased. Within 20 h after the end of the dark period, the cotyledons had completed their essential role and subsequent defoliation had no influence on flowering. A cotyledon area of about 30 mm2 was required for maximal floral induction.It can be concluded that a transmissible factor—often termed floral stimulus—was produced in the cotyledons following a short-day exposure. It is also apparent that flowering in Chenopodium rubrum depends on the generation of a floral stimulus in short days, rather than on control by a transmissible inhibitor of flowering produced under long days.After arrival of the floral stimulus at the apex there was a doubling from 2% to 4% in the percentage of cells undergoing mitosis. This increased value of the mitotic index was maintained during floral development and probably reflected an increased rate of cell division. There were rapid and sometimes rhythmic fluctuations in the percentage of dividing cells.

Multiple circadian rhythms regulate photoperiodic flowering responses in Chenopodium rubrum

1975 ◽  
Vol 53 (22) ◽  
pp. 2631-2638 ◽  
Author(s):  
R. W. King
Keyword(s):  
Cell Division ◽  
Shoot Apex ◽  
Dark Period ◽  
Chenopodium Rubrum ◽  
Adult Plant ◽  
Photoperiodic Flowering ◽  
Contrast Exposure ◽  
Varied Duration ◽  
Fluctuating Temperatures ◽  
Adult Plants

In constant conditions that follow daily temperature cycles, a circadian rhythm of cell division (20-h period) was apparent at the shoot apex of seedlings of Chenopodium rubrum. There was also rhythmicity in capacity to flower (21- to 24-h period) when the seedlings were exposed at various ages to a 12-h dark period. Neither oscillation was evident in seedlings raised under constant conditions. Rhythmical changes in flowering (20- to 24-h period) were also found upon treatment of seedlings for 6 h at different times with solutions of glucose (0.4 M), gibberellic acid (10−6 M), or ethanol (0.1%). This latter rhythm was apparent in constant conditions in the light long after export of floral stimulus from the cotyledons. It is argued that rhythmicity at the shoot apex, possibly in cell division, confers a 20- to 24-h periodicity on the flowering responses of C. rubrum.By contrast, exposure of seedlings or adult plants to a dark period of varied duration revealed a rhythm in capacity to flower but with a considerably longer period (about 30 h). This rhythm was present whether or not seedlings had been raised in fluctuating temperatures. The oscillation was also distinctive in that it originated in the leaf. Exposure of only one leaf on an adult plant to different durations of darkness induced the 30-h rhythm of flowering. Therefore, more than one rhythm, a leaf and an apex rhythm, may control flowering in C. rubrum.

scholarly journals A polo-like kinase modulates cytokinesis and flagella biogenesis in Giardia lamblia

2020 ◽  
Author(s):  
Eun-Ah Park ◽  
Juri Kim ◽  
Mee Young Shin ◽  
Soon-Jung Park
Keyword(s):  
Cell Division ◽  
Mitotic Index ◽  
Giardia Lamblia ◽  
Specific Inhibitor ◽  
Subcellular Fractionation ◽  
Immunofluorescence Assay ◽  
Kinase Assay ◽  
Nuclear Fraction ◽  
Dividing Cells

Abstract Background Polo-like kinases (PLKs) are conserved serine/threonine kinase, regulating cell cycle. Giardia lamblia PLK (GlPLK) role in its cell has not been yet studied. Here, the function of GlPLK was investigated to provide the insight of roles in Giardia cell division, especially during cytokinesis and in flagella formation. Methods To access the function of GlPLK, Giardia trophozoites were treated with PLK-specific inhibitor, GW843286X (GW) or anti-glplk morpholino, then growth of the cells was monitored and phenotypic characteristics of GlPLK-inhibited cells were observed by using mitotic index and flow cytometry assay. Transgenic G. lamblia expressing GlPLK as a hemagglutinin (HA)-tagging was constructed and used for immunofluorescence assay to detect the localization of GlPLK, followed by the subcellular fractionation. Furthermore, kinase assay was performed to assess the phosphorylation activities of GlPLK by purified proteins or in vitro synthesized proteins. To elucidate the role of phosphorylated GlPLK, the phosphorylation residues were mutated and expressed in Giardia trophozoites. Results After incubating trophozoites with 5 µM GW, the percentages of cells with four nuclei and/or longer flagella were increased. Immunofluorescence assays indicated that GlPLK was mainly localized at basal bodies and transiently localized at mitotic spindles in the dividing cells. Fractionation experiments demonstrated that GlPLK is present in the nuclear fraction, as did the centromeric histone H3. Morpholino-mediated GlPLK knockdown resulted in the same phenotypes as those observed in GW-treated cells, i.e., increased mitotic index and flagella length. Kinase assays using mutant recombinant GlPLKs indicated that mutation at Lys51 or at both Thr179 and Thr183 resulted in loss of kinase activity. Giardia expressing these mutant GlPLKs also demonstrated defects in cell growth, cytokinesis, and flagella. Conclusions These data indicated that GlPLK plays roles in Giardia cell division, especially during cytokinesis, and in flagella formation.

scholarly journals Anatomical Changes in Rudbeckia hirta L. during Transition to Flowering

1993 ◽  
Vol 118 (6) ◽  
pp. 835-839 ◽  
Author(s):  
Richard L. Harkess ◽  
Robert E. Lyons
Keyword(s):  
Leaf Primordium ◽  
Floral Initiation ◽  
Anatomical Changes ◽  
Rudbeckia Hirta ◽  
Floral Stimulus ◽  
Long Day ◽  
Dividing Cells ◽  
Histochemical Examination ◽  
Short Days ◽  
Transition To Flowering

Histological and histochemical examination of floral initiation was conducted to determine the pattern of flowering in Rudbeckia hirta, a long-day (LD) plant. Plants were grown under 8-hour short days (SDs) until they had 14 to 16 expanded leaves. Half of the group of plants was moved to LD conditions consisting of natural daylength plus a 4-hour night interruption. Rudbeckia hirta had a pattern of differentiation in flowering similar to that reported in species requiring one inductive day for initiation. Rudbeckia hirta required 8 LDs for evocation and 18 LDs for completion of initiation. Involucral bracts initiated after 18 LDs, after which the receptacle enlarged and was capped by a meristematic mantle of cells signaling the start of development. Floret primordia did not initiate, even after 20 LDs. Increases in pyronin staining were observed in actively dividing cells of the procambium, leaf primordium, and corpus of the vegetative meristems. After 8 LDs, the pith rib meristem stained darkly, a result indicating the arrival of the floral stimulus. An increase in pyronin staining was also observed in the meristematic mantle covering the receptacle after 18 LDs, a result indicating increased RNA levels.

Haemopoiesis in Lepidoptera. III. A note on the multiplication of spherule cells and granular haemocytes

1983 ◽  
Vol 61 (1) ◽  
pp. 275-277 ◽  
Author(s):  
J. W. Arnold ◽  
C. F. Hinks
Keyword(s):  
Mitotic Index ◽  
Alcian Blue ◽  
Maximum Production ◽  
Spherule Cell ◽  
Dividing Cells ◽  
Lepidoptera Noctuidae ◽  
Potential Maximum ◽  
Hematoxylin Eosin ◽  
Cell Mitosis

Blood films from early sixth instar larvae of Euxoa declarata (Lepidoptera: Noctuidae) stained in hematoxylin – eosin – alcian blue showed unequivocal examples of mitosis in spherule cells. The improved visibility of mitosis and the estimation of the mitotic index from counts of dividing cells per 1000 cells of each type indicated a far greater potential maximum production of spherule cells and granular haemocytes by mitosis than reported previously. Certain other methods of staining showed similar clear examples of spherule cell mitosis.

scholarly journals Cytokinesis and Midzone Microtubule Organization inCaenorhabditis elegans Require the Kinesin-like Protein ZEN-4

1998 ◽  
Vol 9 (8) ◽  
pp. 2037-2049 ◽  
Author(s):  
William B. Raich ◽  
Adrienne N. Moran ◽  
Joel H. Rothman ◽  
Jeff Hardin
Keyword(s):  
Cell Division ◽  
Null Allele ◽  
Time Lapse ◽  
Equatorial Region ◽  
Microtubule Organization ◽  
Dividing Cells ◽  
Spindle Midzone ◽  
Cross Links ◽  
Complete Cell

Members of the MKLP1 subfamily of kinesin motor proteins localize to the equatorial region of the spindle midzone and are capable of bundling antiparallel microtubules in vitro. Despite these intriguing characteristics, it is unclear what role these kinesins play in dividing cells, particularly within the context of a developing embryo. Here, we report the identification of a null allele ofzen-4, an MKLP1 homologue in the nematodeCaenorhabditis elegans, and demonstrate that ZEN-4 is essential for cytokinesis. Embryos deprived of ZEN-4 form multinucleate single-celled embryos as they continue to cycle through mitosis but fail to complete cell division. Initiation of the cytokinetic furrow occurs at the normal time and place, but furrow propagation halts prematurely. Time-lapse recordings and microtubule staining reveal that the cytokinesis defect is preceded by the dissociation of the midzone microtubules. We show that ZEN-4 protein localizes to the spindle midzone during anaphase and persists at the midbody region throughout cytokinesis. We propose that ZEN-4 directly cross-links the midzone microtubules and suggest that these microtubules are required for the completion of cytokinesis.

fumble Encodes a Pantothenate Kinase Homolog Required for Proper Mitosis and Meiosis in Drosophila melanogaster

Genetics ◽  
2001 ◽  
Vol 157 (3) ◽  
pp. 1267-1276
Author(s):  
Katayoun Afshar ◽  
Pierre Gönczy ◽  
Stephen DiNardo ◽  
Steven A Wasserman
Keyword(s):  
Cell Division ◽  
Chromosome Segregation ◽  
Cell Division Cycle ◽  
Protein Isoforms ◽  
Pantothenate Kinase ◽  
Male Germline ◽  
Dividing Cells ◽  
Mutant Cells ◽  
Mitosis And Meiosis

Abstract A number of fundamental processes comprise the cell division cycle, including spindle formation, chromosome segregation, and cytokinesis. Our current understanding of these processes has benefited from the isolation and analysis of mutants, with the meiotic divisions in the male germline of Drosophila being particularly well suited to the identification of the required genes. We show here that the fumble (fbl) gene is required for cell division in Drosophila. We find that dividing cells in fbl-deficient testes exhibit abnormalities in bipolar spindle organization, chromosome segregation, and contractile ring formation. Cytological analysis of larval neuroblasts from null mutants reveals a reduced mitotic index and the presence of polyploid cells. Molecular analysis demonstrates that fbl encodes three protein isoforms, all of which contain a domain with high similarity to the pantothenate kinases of A. nidulans and mouse. The largest Fumble isoform is dispersed in the cytoplasm during interphase, concentrates around the spindle at metaphase, and localizes to the spindle midbody at telophase. During early embryonic development, the protein localizes to areas of membrane deposition and/or rearrangement, such as the metaphase and cellularization furrows. Given the role of pantothenate kinase in production of Coenzyme A and in phospholipid biosynthesis, this pattern of localization is suggestive of a role for fbl in membrane synthesis. We propose that abnormalities in synthesis and redistribution of membranous structures during the cell division cycle underlie the cell division defects in fbl mutant cells.

Freeze-fracture analysis of membrane events during early neogenesis of cilia in Tetrahymena: changes in fairy-ring morphology and membrane topography

1983 ◽  
Vol 60 (1) ◽  
pp. 137-156
Author(s):  
L.A. Hufnagel
Keyword(s):  
Cell Division ◽  
Membrane Structure ◽  
Freeze Fracture ◽  
Fracture Analysis ◽  
Basal Bodies ◽  
Membrane Topography ◽  
Fairy Rings ◽  
Dividing Cells ◽  
Cortical System ◽  
Membrane Particle

A freeze-fracture analysis of early neogenesis of somatic and oral cilia of Tetrahymena was conducted using exponentially grown cultures and also cells induced to undergo oral reorganization. In this report, presumptive ciliary domains (PCDs), sites of future outgrowth of somatic cilia, are identified and their membrane structure is described in detail. The fairy ring, an array of membrane particles that occurs within the PCD and appears to be a precursor of the ciliary necklace, is described. A sequence of early stages in the formation of the ciliary necklace of somatic cilia is deduced from topographical information and membrane particle arrangements and numbers. Evidence is presented that basal bodies are seated at the cell surface prior to initiation of necklace assembly and a possible role for the basal body in necklace assembly is suggested. In dividing cells, new oral cilia grow out prior to orientation of cilia-parasomal sac complexes relative to cell axes. In dividing cells and during oral reorganization, new cilia also develop prior to their alignment into membranelles. Thus, growth of cilia is independent of their spatial orientation. Fairy rings were not observed during oral reorganization. During cell division, proliferation of new cilia is accompanied by the formation of a network of junctions between a cortical system of membranous cisternae, the cortical ‘alveoli’. These interalveolar junctions may serve as tracks for early positioning and orientation of new oral basal bodies.

discordia mutations specifically misorient asymmetric cell divisions during development of the maize leaf epidermis

Development ◽  
1999 ◽  
Vol 126 (20) ◽  
pp. 4623-4633 ◽  
Author(s):  
K. Gallagher ◽  
L.G. Smith
Keyword(s):  
Cell Division ◽  
Preprophase Band ◽  
Cytochalasin D ◽  
Leaf Epidermis ◽  
Asymmetric Cell Divisions ◽  
Maize Leaf ◽  
Cell Divisions ◽  
Cytoskeletal Structure ◽  
Dividing Cells ◽  
Preprophase Bands

In plant cells, cytokinesis depends on a cytoskeletal structure called a phragmoplast, which directs the formation of a new cell wall between daughter nuclei after mitosis. The orientation of cell division depends on guidance of the phragmoplast during cytokinesis to a cortical site marked throughout prophase by another cytoskeletal structure called a preprophase band. Asymmetrically dividing cells become polarized and form asymmetric preprophase bands prior to mitosis; phragmoplasts are subsequently guided to these asymmetric cortical sites to form daughter cells of different shapes and/or sizes. Here we describe two new recessive mutations, discordia1 (dcd1) and discordia2 (dcd2), which disrupt the spatial regulation of cytokinesis during asymmetric cell divisions. Both mutations disrupt four classes of asymmetric cell divisions during the development of the maize leaf epidermis, without affecting the symmetric divisions through which most epidermal cells arise. The effects of dcd mutations on asymmetric cell division can be mimicked by cytochalasin D treatment, and divisions affected by dcd1 are hypersensitive to the effects of cytochalasin D. Analysis of actin and microtubule organization in these mutants showed no effect of either mutation on cell polarity, or on formation and localization of preprophase bands and spindles. In mutant cells, phragmoplasts in asymmetrically dividing cells are structurally normal and are initiated in the correct location, but often fail to move to the position formerly occupied by the preprophase band. We propose that dcd mutations disrupt an actin-dependent process necessary for the guidance of phragmoplasts during cytokinesis in asymmetrically dividing cells.

scholarly journals 5-AMINOURACIL TREATMENT

1971 ◽  
Vol 48 (2) ◽  
pp. 248-252 ◽  
Author(s):  
S. H. Socher ◽  
D. Davidson
Keyword(s):  
Mitotic Index ◽  
Vicia Faba ◽  
Cell Population ◽  
Lateral Roots ◽  
Proliferating Cells ◽  
Dividing Cells ◽  
Proliferating Cell ◽  
Two Populations

Treatment of Vicia faba lateral roots with a range of concentrations of 5-aminouracil (5-AU) indicate that cells are stopped at a particular point in interphase. The timing of the fall in mitotic index suggests that cells are held at the S - G2 transition. When cells are held at this point, treatments with 5-AU can be used to estimate the duration of G2 + mitosis/2 of proliferating cells. Treatment with 5-AU can also be used to demonstrate the presence of subpopulations of dividing cells that differ in their G2 duration. Using this method, 5-AU-induced inhibition, we have confirmed that in V. faba lateral roots there are two populations of dividing cells: (a) a fast-dividing population, which makes up ∼85% of the proliferating cell population and has a G2 + mitosis/2 duration of 3.3 hr, and (b) a slow-dividing population, which makes up ∼15% of dividing cells and has a G2 duration in excess of 12 hr. These estimates are similar to those obtained from percentage labeled mitosis (PLM) curves after incorporation of thymidine-3H.

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