scholarly journals Rape embryogenesis. IV. Appearance and disappearance of starch during embryo development

2014 ◽  
Vol 51 (3-4) ◽  
pp. 381-387 ◽  
Author(s):  
Teresa Tykarska
Keyword(s):  
Apical Part ◽  
Embryo Axis ◽  
Starch Grains ◽  
Cell Divisions ◽  
Embryo Cells ◽  
Dividing Cells ◽  
Gradual Accumulation ◽  
Black Seeds ◽  
Mother Cells ◽  
Storage Starch

Starch appears first in the suspensor of the proembryo with two-cell apical part. It is observed in the embryo proper from the octant stage. At first it is visible in all the embryo cells in the form of minute transient grains which disappear during cell divisions. But the columella mother cells and their derivatives have persistent large grains. When the embryo turns green in the heart stage a gradual accumulation of storage starch begins and lasts to the end of embryogenesis. Storage starch grains appear first in the auter cortex layers of the hypocotyl where the largest grains are to be found later, and afterwards in all the other tissues. Starch is usually absent in the frequently dividing cells, but even there it appears in the form of minute grains after the end of cell divisions. Disappearance of starch starts when the intensive green colour of the seed coat begins to fade. The first to disappear are the smallest granules in the regions where they were noted latest. In the embryo axis the starch grains remain deposited longest in dermatogen and cortex cells in the lower hypocotyl part. They are visible there, still when the seed turns brown. In black seeds starch may be only found in the columella the cells of which throughout embryogenesis contain amyloplasts filled with starch. These grains disappear completely at the time when the seeds become dry.

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 Emerging mechanisms of asymmetric stem cell division

2018 ◽  
Vol 217 (11) ◽  
pp. 3785-3795 ◽  
Author(s):  
Zsolt G. Venkei ◽  
Yukiko M. Yamashita
Keyword(s):  
Stem Cells ◽  
Stem Cell ◽  
Cell Division ◽  
Asymmetric Cell Division ◽  
Binary Outcomes ◽  
Cellular Mechanisms ◽  
Asymmetric Cell Divisions ◽  
Cell Divisions ◽  
Dividing Cells ◽  
Stem Cell Division

The asymmetric cell division of stem cells, which produces one stem cell and one differentiating cell, has emerged as a mechanism to balance stem cell self-renewal and differentiation. Elaborate cellular mechanisms that orchestrate the processes required for asymmetric cell divisions are often shared between stem cells and other asymmetrically dividing cells. During asymmetric cell division, cells must establish asymmetry/polarity, which is guided by varying degrees of intrinsic versus extrinsic cues, and use intracellular machineries to divide in a desired orientation in the context of the asymmetry/polarity. Recent studies have expanded our knowledge on the mechanisms of asymmetric cell divisions, revealing the previously unappreciated complexity in setting up the cellular and/or environmental asymmetry, ensuring binary outcomes of the fate determination. In this review, we summarize recent progress in understanding the mechanisms and regulations of asymmetric stem cell division.

Lateral bud growth on excised stem segments: effect of the stem

1975 ◽  
Vol 53 (3) ◽  
pp. 243-248 ◽  
Author(s):  
Carol A. Peterson ◽  
R. A. Fletcher
Keyword(s):  
Sucrose Solution ◽  
Apical Part ◽  
Endogenous Auxin ◽  
Cell Divisions ◽  
Cotyledonary Nodes ◽  
Lateral Buds ◽  
Lateral Bud ◽  
Bud Growth ◽  
Soybean Plants ◽  
Stem Segments

Lateral buds at the cotyledonary nodes of soybean plants grown under the conditions used in this study usually remain inhibited. These buds grow when the apical part of the plant is removed. They will grow, but less strongly, when the roots as well as the apex of the plant are removed and the basal end of the cut stem is placed in a mineral salt solution. Bud growth is further diminished by decreasing the length of stem left attached to the bud. The cotyledon is essential for bud growth on plant segments maintained in nutrient solution, but it can be replaced by a 1% sucrose solution during the early days of bud growth. Buds which are completely detached from the stem and placed in 1% sucrose do not elongate, but a small number of cell divisions are detectable, indicating that the early events of the release from inhibition have occurred. Buds elongate when they are apically or centrally located on stem segments. Increasing the length of the attached stem segments increases the growth of the buds. Additions of the cytokinin benzyladenine to plants causes a dramatic increase in bud growth when buds are attached to stem segments but does not stimulate growth of buds without stem segments. It is concluded that benzyladenine alone will not substitute for a factor(s) present in the stem which is necessary for bud growth. Increasing stem lengths above buds located at the basal ends of segments inhibits bud growth. It is suggested that this may be due to an accumulation of endogenous auxin at the site of the buds.

scholarly journals Autoradiographic study of 3H colchicine binding in synchronously dividing cells of antheridial filaments of Chara vulgaris L. during successive stages of development

2015 ◽  
Vol 44 (1) ◽  
pp. 29-39 ◽  
Author(s):  
Maria J. Olszewska
Keyword(s):  
Protein Synthesis ◽  
Daughter Cell ◽  
Mitotic Cycle ◽  
Autoradiographic Study ◽  
Chara Vulgaris ◽  
Cytoplasmic Surface ◽  
Dividing Cells ◽  
Successive Generations ◽  
Mother Cells

The intensity of <sup>3</sup>H colchicine binding was investigated autoradiographically as a marker of an amount of the microtubule subunits during interphase and mitosis in synchronously dividing 4-, 8-, 16- and 32-celled antheridial filaments of <i>Chora vulgaris</i>. These cells were incubated with 3H colchicine in vivo or after fixation. The radioactivity of cells in the successive generations of antheridial filaments diminishes, similarly as the surface of cytoplasm and intensity of protein synthesis. During interphase the intensity of <sup>3</sup>H colchicine binding is proportional to the increase of cytoplasmic surface; the highest increase of radioactivity occurs in G<sub>2</sub>. During mitosis the increase of radioactivity continues in prophase; the highest radioactivity was found in prophase and telophase cells, the lowest in anaphase cells; a comparatively pronounced radioactivity is visible in metaphase. Radioactivity in posttelophase, as estimated per one daughter cell, is approximately one half of that of the mother cells in telophase of the previous generation suggesting the reutilization of microtubule proteins in the next mitotic cycle.

scholarly journals An illustrated step-by-step protocol for investigating liverwort chromosomes

2021 ◽  
Vol 43 (1) ◽  
Author(s):  
ARETUZA SOUSA ◽  
SUSANNE S. RENNER
Keyword(s):  
Acetic Acid ◽  
Developmental Stage ◽  
Vascular Plants ◽  
Glacial Acetic Acid ◽  
Mitotic Chromosome ◽  
Cell Divisions ◽  
Cytogenetic Studies ◽  
The Right ◽  
Mother Cells ◽  
Young Sporophytes

Cytogenetic studies in bryophytes have been limited by the difficulty of obtaining sufficient dividing nuclei and by the absence of modern protocols. The technical difficulties stem from the plants’ small size and lack of roots and pollen mother cells, the main sources of cells in division in vascular plants. In bryophytes instead, tiny sporophytes, antheridia, or phyllid meristems must be used to obtain meiotic or mitotic chromosome spreads. We here describe the preparation of such spreads from phyllids, antheridia, and sporophytes in several species of liverworts and compare available protocols with or without prefixation treatments. We also provide illustrated step-by-step instructions. The three prefixation agents (including colchicine) that we tested failed to improve synchronization of cell divisions. Young sporophytes were the best source of diploid synchronized cells, while antheridia were the best source of haploid cells. For meiotic nuclei, a short fixation of capsule tissue at the right developmental stage with 45% acetic acid sufficed to conserve the DNA for cytological investigations, while for mitotic nuclei, fixation in 3:1 ethanol/glacial acetic acid for a longer period (4–24 h) worked well.

scholarly journals The sequence of cell divisions in the I tunic layer of Actinidia arguta Planch in light of the development of twin cell complexes

2014 ◽  
Vol 55 (2) ◽  
pp. 171-179 ◽  
Author(s):  
Zofia Puławska
Keyword(s):  
Leaf Primordia ◽  
Cell Complexes ◽  
Actinidia Arguta ◽  
Cell Divisions ◽  
Meristematic Activity ◽  
Mother Cells

In <em>Actinidia arguta</em>, the I tunc layer is formed by four cell complexes which descend from single initials. These initials are positioned in a corner of their complex, around the meristem axis. The meristematic activity of the I tunic layer depends on the formative divisions of the initials; the entire I tunic layer above the youngest leaf primordia is formed during the time the initials undergo only 4-8 divisions. In light of the development of the twin cell complexes. it is impossible for cells to be displaced from the I tunic layer into the meristem. The supposition is set forth that the impermanent. mericlinal sectors on variegated perinclinal chimeras develop due to periclinal cleavages within the subcomplexes which derive from tissue mother cells. Whereas. the cell initials do not undergo periclinal divisions and are not displaced.

scholarly journals The dynamic equilibrium of nascent and parental MCMs safeguards replicating genomes

2019 ◽  
Author(s):  
Hana Sedlackova ◽  
Maj-Britt Rask ◽  
Rajat Gupta ◽  
Chunaram Choudhary ◽  
Kumar Somyajit ◽  
...  
Keyword(s):  
Nuclear Translocation ◽  
Dynamic Equilibrium ◽  
Genome Instability ◽  
Replication Stress ◽  
Minichromosome Maintenance ◽  
Daughter Cells ◽  
Mild Reduction ◽  
Dividing Cells ◽  
High Level ◽  
Mother Cells

The MCM2-7 (minichromosome maintenance) protein complex is a DNA unwinding motor required for the eukaryotic genome duplication1. Although a huge excess of MCM2-7 is loaded onto chromatin in G1 phase to form pre-replication complexes (pre-RCs), only 5-10 percent are converted into a productive CDC45-MCM-GINS (CMG) helicase in S phase – a perplexing phenomenon often referred to as the ‘MCM paradox’2. Remaining pre-RCs stay dormant but can be activated under replication stress (RS)3. Remarkably, even a mild reduction in MCM pool results in genome instability4, 5, underscoring the critical requirement for high-level MCM maintenance to safeguard genome integrity across generations of dividing cells. How this is achieved remains unknown. Here, we show that for daughter cells to sustain error-free DNA replication, their mothers build up a stable nuclear pool of MCMs both by recycling of chromatin-bound MCMs (referred to as parental pool) and synthesizing new MCMs (referred to as nascent pool). We find that MCMBP, a distant MCM paralog6, ensures the influx of nascent MCMs to the declining recycled pool, and thereby sustains critical levels of MCMs. MCMBP promotes nuclear translocation of nascent MCM3-7 (but not MCM2), which averts accelerated MCM proteolysis in the cytoplasm, and thereby fosters assembly of licensing-competent nascent MCM2-7 units. Consequently, lack of MCMBP leads to reduction of nascent MCM3-7 subunits in mother cells, which translates to poor MCM inheritance and grossly reduced pre-RCs formation in daughter cells. Unexpectedly, whereas the pre-RC paucity caused by MCMBP deficiency does not alter the overall bulk DNA synthesis, it escalates the speed and asymmetry of individual replisomes. This in turn increases endogenous replication stress and renders cells hypersensitive to replication perturbations. Thus, we propose that surplus of MCMs is required to safeguard replicating genomes by modulating physiological dynamics of fork progression through chromatin marked by licensed but inactive MCM2-7 complexes.

The Effect of Trifluralin on the Ultrastructure of Dividing Cells of the Root Meristem of Cotton (Gossypium Hirsutum L. ‘ACALA 4-42’)

1974 ◽  
Vol 15 (2) ◽  
pp. 429-441
Author(s):  
D. HESS ◽  
D. BAYER
Keyword(s):  
Cell Division ◽  
Gossypium Hirsutum ◽  
Lateral Root ◽  
Root Meristem ◽  
Metaphase Plate ◽  
Threshold Concentration ◽  
Gossypium Hirsutum L ◽  
Ultrastructural Studies ◽  
Cell Divisions ◽  
Dividing Cells

Ultrastructural studies of trifluralin-treated cells in lateral root meristems of cotton (Gossypium hirsutum L.) revealed that mitotic disruptions were due to the absence of microtubules. The extent of disruption varied between individual roots and correlated with the presence or absence of microtubules. Where microtubules were absent, cells began division with a normal prophase chromosome cycle. The chromosomes did not line up along a metaphase plate, but coalesced in the cell. If cell division had begun prior to microtubule disappearance the mitotic process was arrested at the stage that had been reached when the disappearance occurred. In some cell divisions randomly oriented microtubules were noted, with mitosis apparently arrested at those stages. Nuclear envelope reformation yielded cells that were polyploid, polymorphonucleate, binucleate, or occasionally multinucleate. If microtubules were present and if their orientation were normal, all stages of mitosis occurred. The range of mitotic disruption observed can be explained by the threshold concentration for microtubule disappearance being very near aqueous saturation of trifluralin.

scholarly journals The mechanism of the action of the growth substance of plants

1933 ◽  
Vol 113 (781) ◽  
pp. 126-149 ◽  
Keyword(s):  
Cell Division ◽  
Cell Growth ◽  
Plant Growth ◽  
Experimental Evidence ◽  
Recent Literature ◽  
Growth Substance ◽  
Extensive Literature ◽  
Growth Substances ◽  
Cell Divisions ◽  
Gradual Accumulation

It was first suggested by Sachs that stimulating substances of the type which would now be called hormones play an important part in cell growth. Experimental evidence followed much later along two lines, ( a ) the discovery by Haberlandt (1921) of a substance produced in wounded tissue, stimulating cell division, and ( b ) the gradual accumulation of evidence from many workers of the existence of a substance present in growing plants which stimulates growth by increase in cell size. It is with certain aspects of this latter phenomenon with which we are concerned. Since the earlier extensive literature has been reviewed by Stark (1926) and the more recent literature by Went (1928) and Nielsen (1930), it will be sufficient here to summarize briefly the properties of this growth substances in relation to plant growth, so far as they have been determined. Although the growth substances has been shown to be non-specific, we have limited ourselves in this work to consideration of the phenomena occuring in Avena coleoptiles. In these coleoptiles, at the age used for experiment, cell divisions do not occur, and growth takes place by extension only. On this account they have been the principal objects studied.

scholarly journals Ultrastructural analysis of initial stages of dedifferentiation of root explants of Gentiana cruciata seedlings

2014 ◽  
Vol 71 (4) ◽  
pp. 287-297 ◽  
Author(s):  
Anna Mikuła ◽  
Teresa Tykarska ◽  
Jan Rybczyński ◽  
Mieczysław Kuraś
Keyword(s):  
Callus Formation ◽  
Induction Medium ◽  
Elongation Zone ◽  
Root Explants ◽  
Regular Type ◽  
Cell Divisions ◽  
Zone Cell ◽  
Dividing Cells ◽  
Gentiana Cruciata ◽  
Axial Cylinder

The studies were carried out on isolated roots of 10-day old seedlings of <em>Gentiana cruciata</em>, which were placed and cultured on induction medium of Murashige and Skoog (1962) supplemented with 1.0 mg/dm<sup>3</sup> dicamba + 0.l mg/dm<sup>3</sup> NAA + 2.00 mg/dm<sup>3</sup> BAP + 80.0 mg/dm<sup>3</sup> adenine sulphate. Changes in explants from the 3rd to the l lth day of culture with the help of light and electron microscope were observed. Observations showed gradual dedifferentiation of root tissues, which was seen earliest in cortex at the proximal end of the explant and shifted gradually inwards the root and towards distal parts of its elongation zone. The most intensive callus formation appeared at cut surface of explant, where proliferation of cells in both cortex and axial cylinder was recognised. In the distal part of the elongation zone, cell divisions occurred only in endoderm and in axial cylinder. The meristematic part of the root was inactive. Finally, the following areas were distinguished in the explant: (I) an area of intensive cell divisions, i.e., the elongation zone; (II) an area of cell dispersion; and (III) the inactive meristem. The ultrastructure brought evidences of cell reorganisation as the meaning of cell readiness to the division. Observations showed an increased activity of mitochondria and Golgi structures, thickening of walls and disappearance of plasmodesmal connections. Amyloplasts and lipid bodies in tissues in which they had been scarce or had not appeared before founding. Intensively dividing cells showed features of meristematic cells. They had dense cytoplasm with numerous organelles, large centrally located nuclei, and "nucleolar vacuoles" inside nucleoli. Cortex-derived callus formed aggregates. Both pericycle and endoderm produced callus of characteristic dense structure and regular type of divisions.

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