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.

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.

Plasma membrane localization of the type I H+-PPase AVP1 in sieve element–companion cell complexes from Arabidopsis thaliana

Plant Science ◽  
2011 ◽  
Vol 181 (1) ◽  
pp. 23-30 ◽  
Author(s):  
Julio Paez-Valencia ◽  
Araceli Patron-Soberano ◽  
Alejandra Rodriguez-Leviz ◽  
Jonathan Sanchez-Lares ◽  
Concepcion Sanchez-Gomez ◽  
...  
Keyword(s):  
Arabidopsis Thaliana ◽  
Plasma Membrane ◽  
Sieve Element ◽  
Membrane Localization ◽  
Type I ◽  
Companion Cell ◽  
Cell Complexes ◽  
Plasma Membrane Localization

Fine structure of the primary root phloem of Pisum

1968 ◽  
Vol 16 (1) ◽  
pp. 37 ◽  
Author(s):  
SY Zee ◽  
TC Chambers
Keyword(s):  
Primary Root ◽  
Root Apex ◽  
Sieve Element ◽  
Cross Wall ◽  
Secondary Phloem ◽  
Sieve Elements ◽  
Phloem Parenchyma ◽  
Pisum Sativum L ◽  
Companion Cells ◽  
Stem Internode

The morphogenesis of the sieve elements, companion cells, and phloem parenchyma in the region between 0.5 and 2.0 mm from the actively growing root apex of seedlings of Pisum sativum L. cv. Telephone is described. The overall developmental pattern is essentially similar to that already described for the secondary phloem of the young stem internode of the same species, although differences in the development of some organelles do exist between the two types of phloem. The development of the sieve element is traced from the earliest stages of cross wall formation up to the morphologically mature stages. Very few sieve elements reach morphological maturity in this region. The possibility that the functional translocatory sieve elements are those at earlier stages of development is discussed.

scholarly journals Evidence for functional heterogeneity of sieve element–companion cell complexes in minor vein phloem of Alonsoa meridionalis

2009 ◽  
Vol 60 (6) ◽  
pp. 1873-1883 ◽  
Author(s):  
Olga V. Voitsekhovskaja ◽  
Elena L. Rudashevskaya ◽  
Kirill N. Demchenko ◽  
Marina V. Pakhomova ◽  
Denis R. Batashev ◽  
...  
Keyword(s):  
Sieve Element ◽  
Functional Heterogeneity ◽  
Companion Cell ◽  
Cell Complexes ◽  
Minor Vein

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

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.

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