Microtubules and root protophloem ontogeny in wheat

1985 ◽  
Vol 75 (1) ◽  
pp. 165-179
Author(s):  
E.P. Eleftheriou
Keyword(s):  
Cell Plate ◽  
Sieve Element ◽  
Companion Cell ◽  
Cortical Zone ◽  
Companion Cells ◽  
Asymmetrical Division ◽  
Single Precursor ◽  
Position And Orientation ◽  
Asymmetrical Divisions

Protophloem ontogeny in roots of Triticum aestivum has been investigated ultrastructurally. Each protophloem pole consists of three cells, a protophloem sieve element and two companion cells, all originating from a single precursor cell usually having a pentahedral shape. This protophloem mother cell (PMC) undergoes two successive asymmetrical divisions: the first one gives rise to a smaller cell that will differentiate into a companion cell, and a larger one that divides again asymmetrically yielding another companion cell and a protophloem sieve element. The latter divides once more, but now symmetrically, increasing the number of cells. Both asymmetrical and symmetrical divisions are preceded by preprophase microtubule bands (PMBs), well demarcated by a great number (more than 100 profiles in a single band section) of microtubules (MTs). The plane of a PMB coincides with that of the succeeding cell plate, which fuses with parent walls at sites previously occupied by the PMB. The strict correspondence between PMB and cell plate suggests that a cytokinesis the latter bisects the PMB cortical zone. The possible role of PMB cortical zone in positioning the cell plate and guiding its expanding edges towards predetermined sites is discussed in relation to recent discoveries in other anatomical situations. The plane of PMBs (and hence of divisions) changes from one division to the next, so that the three successive divisions occur in three spatial planes transversely to each other. This change is probably influenced by cell polarity. Prior to each asymmetrical division peri-nuclear MTs were observed besides the MTs of the PMB. They appear before the PMB organization and persist throughout preprophase, but they change their position and orientation in response to the transition from PMB to the spindle organization.

scholarly journals Differential Distribution of Proteins Expressed in Companion Cells in the Sieve Element-Companion Cell Complex of Rice Plants

2005 ◽  
Vol 46 (11) ◽  
pp. 1779-1786 ◽  
Author(s):  
Akari Fukuda ◽  
Syu Fujimaki ◽  
Tomoko Mori ◽  
Nobuo Suzui ◽  
Keiki Ishiyama ◽  
...  
Keyword(s):  
Sieve Element ◽  
Cell Complex ◽  
Companion Cell ◽  
Differential Distribution ◽  
Rice Plants ◽  
Companion Cells

Fine structure of the phloem of Pisum sativum. II. The companion cell and phloem parenchyma

1965 ◽  
Vol 13 (2) ◽  
pp. 185
Author(s):  
MC Wark
Keyword(s):  
Fine Structure ◽  
Sieve Element ◽  
Companion Cell ◽  
Secondary Phloem ◽  
Sieve Elements ◽  
Phloem Parenchyma ◽  
Wall Structures ◽  
Companion Cells ◽  
Parenchyma Cells ◽  
Vacuolated Cells

The companion cells of the secondary phloem of Pisum contain all the organelles characteristic of cells possessing an active metabolism. The cytoplasm of the companion cells shows little change during ontogeny. Complex plasmodesmata connect the sieve elements and companion cells. These are the only connections observed between the sieve elements and other phloem cells. New wall structures of the companion cells are described. These structures are here tentatively called trabeculae; they intrude into the cytoplasm, but never completely cross the cell. The trabeculae alter in appearance at the time when the sieve element nucleus and tonoplast disappear. The phloem parenchyma cells are large vacuolated cells wider in diameter but shorter in length than the sieve elements. They contain all the organelles found in normal photosynthetic tissue. The cytoplasm of the phloem parenchyma shows little change during ontogeny. Plasmodesmata of well-developed pit fields connect the phloem parenchyma with the companion cells. The phloem parenchyma does not communicate with the sieve elements.

An Ultrastructural Study of the Phloem of Drimys (Winteraceae)

IAWA Journal ◽  
1985 ◽  
Vol 6 (3) ◽  
pp. 255-268 ◽  
Author(s):  
Jennifer Thorsch ◽  
Katherine Esau
Keyword(s):  
Endoplasmic Reticulum ◽  
Ultrastructural Study ◽  
Protein Body ◽  
Sieve Element ◽  
Companion Cell ◽  
Young Cell ◽  
P Protein ◽  
Companion Cells ◽  
Protein Granules ◽  
Sieve Plates

The ultrastructural features of mainly primary phloem of three species of Drimys (Winteraceae), D. winteri J. R. ' G. Forst., D. lanceolata (Poiret) Baill. and D. granadensis L. f. var. mexicana (DC.) A. C. Smith are similar to those usually observed in dicotyledons. The sieve element is early discernible by its association with a companion cell, the deposition of callose in nascent sieve areas, and the appearance in the cytoplasm of the nondispersing paracrystalline protein body. Plastids with starch (and in D. lanceolata also with paracrystalline protein granules), mitochondria, sparse endoplasmic reticulum cisternae (ER), dictyosomes, and ribosomes are present in the young cell. Stacking of ER was not conspicuous. The nucleus is moderately chromatic before its breakdown. P-protein occurs in more or less dense aggregates that usually become dispersed after the tonoplast disappears. The subunits of the P-pro tein have tubular structure before the dispersal. The plasmalemma is retained. The sieve areas are combined into sieve plates on long radial walls and on some transverse walls originating during secondary partitioning of sieve element precursors. The numerous lateral sieve areas intergrade with those of the sieve plates. The pores develop from plasmodesmatal connections and may involve the formation of median cavities. The connections between sieve elements alld companion cells consist of the usual combination of a pore embedded in callose and one plasmodesma or several branches of one on the companion cell side.

Sieve element and companion cell: the story of the comatose patient and the hyperactive nurse

2000 ◽  
Vol 27 (6) ◽  
pp. 477 ◽  
Author(s):  
Aart J. E. van Bel ◽  
Michael Knoblauch
Keyword(s):  
Phloem Transport ◽  
Division Of Labour ◽  
Sieve Element ◽  
Companion Cell ◽  
Concerted Action ◽  
Sieve Elements ◽  
Cell Complexes ◽  
Photoassimilate Translocation ◽  
Companion Cells ◽  
Evolutionary Descent

Sieve elements and companion cells constitute the modules of the conducting elements in the phloem ofAngiosperms. Consequently, phloem transport basically relies on the concerted action of the sieve element/companion cell complexes. Sieve elements and companion cells are highly interactive units and show an extreme division of labour as exemplified by their state of life. Whereas the sieve element is almost ‘clinically’ dead, the companion cell is a paragon of bubbling activity. In the course of evolution, the sieve element has sacrificed all of its genetic and most of its metabolic equipment to serve photoassimilate translocation. A small part of the structural and metabolic outfit has been retained for a proper accomplishment of its function. In contrast, the cells bordering the sieve element have gained metabolic weight during evolution. With reference to their evolutionary descent, the peculiarities of sieve elements and companion cells are discussed in the light of recent cell-biological and molecular-biological findings. Emphasis is focused on their interaction, which is the secret of the success of the sieve element/companion cell complex.

Sieve element biology provides leads for research on phytoplasma lifestyle in plant hosts

2019 ◽  
Vol 70 (15) ◽  
pp. 3737-3755 ◽  
Author(s):  
Aart J E van Bel ◽  
Rita Musetti
Keyword(s):  
Cell Biology ◽  
Sieve Element ◽  
Companion Cell ◽  
Electron Microscopic ◽  
Sieve Elements ◽  
Cell Complexes ◽  
Companion Cells ◽  
Phytoplasma Infection ◽  
Sieve Tubes ◽  
Physical And Chemical

Abstract Phytoplasmas reside exclusively in sieve tubes, tubular arrays of sieve element–companion cell complexes. Hence, the cell biology of sieve elements may reveal (ultra)structural and functional conditions that are of significance for survival, propagation, colonization, and effector spread of phytoplasmas. Electron microscopic images suggest that sieve elements offer facilities for mobile and stationary stages in phytoplasma movement. Stationary stages may enable phytoplasmas to interact closely with diverse sieve element compartments. The unique, reduced sieve element outfit requires permanent support by companion cells. This notion implies a future focus on the molecular biology of companion cells to understand the sieve element–phytoplasma inter-relationship. Supply of macromolecules by companion cells is channelled via specialized symplasmic connections. Ca2+-mediated gating of symplasmic corridors is decisive for the communication within and beyond the sieve element–companion cell complex and for the dissemination of phytoplasma effectors. Thus, Ca2+ homeostasis, which affects sieve element Ca2+ signatures and induces a range of modifications, is a key issue during phytoplasma infection. The exceptional physical and chemical environment in sieve elements seems an essential, though not the only factor for phytoplasma survival.

Proteins in the sieve element-companion cell complexes: their detection, localization and possible functions

2000 ◽  
Vol 27 (6) ◽  
pp. 489 ◽  
Author(s):  
Hiroaki Hayashi ◽  
Akari Fukuda ◽  
Nobuo Suzui ◽  
Shu Fujimaki
Keyword(s):  
Sieve Tube ◽  
Soluble Proteins ◽  
Sieve Element ◽  
Tissue Extract ◽  
Companion Cell ◽  
Phloem Sap ◽  
Sieve Elements ◽  
Cell Complexes ◽  
Companion Cells ◽  
Sieve Tubes

Many kinds of proteins have been found in the sieve element–companion cell complexes by the analyses of phloem sap and microscopic observations. The cDNAs, which encode some of these sieve-tube proteins, have already been cloned. As mature sieve elements lack nuclei and most ribosomes, sieve-tube proteins have been hypothesized to be synthesized in the companion cells and then transported to the lumina of the functional sieve tubes through the plasmodesmata connecting the companion cells and sieve elements. Soluble proteins present in the sieve tubes can be collected by several techniques, such as incision or the aphid technique. The composition of the proteins in the phloem sap is unique compared with that of tissue extract, suggesting these proteins have important roles for the development and functions of sieve tubes.

The Immunomodulatory Role of G2013 (α-L-Guluronic Acid) on the Expression of TLR2 and TLR4 in HT29 cell line

2019 ◽  
Vol 16 (1) ◽  
pp. 91-95 ◽  
Author(s):  
Hamid Farhang ◽  
Laleh Sharifi ◽  
Mohammad Mehdi Soltan Dallal ◽  
Mona Moshiri ◽  
Zahra Norouzbabaie ◽  
...  
Keyword(s):  
Inflammatory Responses ◽  
Inflammatory Diseases ◽  
Rna Extraction ◽  
Cell Plate ◽  
Inhibitory Effect ◽  
Control Group ◽  
Ht29 Cells ◽  
Guluronic Acid ◽  
Tlr4 Mrna

Background: The non-steroidal anti-inflammatory drugs (NSAIDs) play crucial role in the controlling of inflammatory diseases. Due to the vast side effects of NSAIDs, its use is limited. G2013 or &amp;#945;-L-Guluronic Acid is a new NSAID with immunomodulatory features. Objectives: Considering the leading role of TLRs in inflammatory responses, in this study, we aimed to evaluate G2013 cytotoxicity and its effect on the expression of TLR2 and TLR4 molecules. Methods: HEK293-TLR2 and HEK293-TLR4 cells were cultured and seeded on 96-well cell plate, and MTT assay was performed for detecting the viability of the cells after treatment with different concentrations of G2013. HT29 cells were grown and treated with low and high doses of G2013. After total RNA extraction and cDNA synthesis, quantitative real-time PCR were performed to assess the TLR2 and TLR4 mRNA synthesis. Results: We found that concentrations of ≤125 &amp;#181;g/ml of G2013 had no apparent cytotoxicity effect on the HEK293-TLR2 and -TLR4 cells. Our results indicated that after G2013 treatment (5 &amp;#181;g/ml) in HT29 cells, TLR2 and TLR4 mRNA expression decreased significantly compared with the untreated control group (p=0.02 and p=0.001 respectively). Conclusion: The results of this study revealed that G2013 can down regulate the TLR2 and TLR4 gene expression and exerts its inhibitory effect. Our findings are parallel to our previous finding which showed G2013 ability to down regulate the signaling pathway of TLRs. However, further studies are needed to identify the molecular mechanism of G2013.<p&gt;

scholarly journals Sheep Digestive Physiology and Constituents of Feeds

2021 ◽  
Author(s):  
Samir Medjekal ◽  
Mouloud Ghadbane
Keyword(s):  
Cell Wall ◽  
Plant Cell ◽  
Plant Cell Wall ◽  
Early Stage ◽  
Growth Period ◽  
Cell Plate ◽  
Soluble Carbohydrates ◽  
Winter Period ◽  
The Common

Sheep have a gastrointestinal tract similar to that of other ruminants. Their stomach is made up of four digestive organs: the rumen, the reticulum, the omasum and the abomasum. The rumen plays a role in storing ingested foods, which are fermented by a complex anaerobic rumen microbiota population with different types of interactions, positive or negative, that can occur between their microbial populations. Sheep feeding is largely based on the use of natural or cultivated fodder, which is exploited in green by grazing during the growth period of the grass and in the form of fodder preserved during the winter period. Ruminant foods are essentially of plant origin, and their constituents belong to two types of structures: intracellular constituents and cell wall components. Cellular carbohydrates play a role of metabolites or energy reserves; soluble carbohydrates account for less than 10% dry matter (DM) of foods. The plant cell wall is multi-layered and consists of primary wall and secondary wall. Fundamentally, the walls are deposited at an early stage of growth. A central blade forms the common boundary layer between two adjacent cells and occupies the location of the cell plate. Most of the plant cell walls consist of polysaccharides (cellulose, hemicellulose and pectic substances) and lignin, these constituents being highly polymerized, as well as proteins and tannins.

The Role of Constant Curvature in 2-D Contour Shape Representations

Perception ◽  
10.1068/p6970 ◽  
2011 ◽  
Vol 40 (11) ◽  
pp. 1290-1308 ◽  
Author(s):  
Patrick Garrigan ◽  
Philip J Kellman
Keyword(s):  
Retention Interval ◽  
Constant Curvature ◽  
Visual Information ◽  
Recognition Performance ◽  
Shape Representations ◽  
Contour Shape ◽  
Position And Orientation ◽  
Retention Intervals ◽  
Invariant Shape

In early cortex, visual information is encoded by retinotopic orientation-selective units. Higher-level representations of abstract properties, such as shape, require encodings that are invariant to changes in size, position, and orientation. Within the domain of open, 2-D contours, we consider how an economical representation that supports viewpoint-invariant shape comparisons can be derived from early encodings. We explore the idea that 2-D contour shapes are encoded as joined segments of constant curvature. We report three experiments in which participants compared sequentially presented 2-D contour shapes comprised of constant curvature (CC) or non-constant curvature (NCC) segments. We show that, when shapes are compared across viewpoint or for a retention interval of 1000 ms, performance is better for CC shapes. Similar recognition performance is observed for both shape types, however, if they are compared at the same viewpoint and the retention interval is reduced to 500 ms. These findings are consistent with a symbolic encoding of 2-D contour shapes into CC parts when the retention intervals over which shapes must be stored exceed the duration of initial, transient, visual representations.

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