phloem companion cells

These sugars are transported to non-photosynthetic parts of the plant, such as the roots, or into storage structures, such as tubers or bulbs. The phloem consists primarily of two highly specialized cell types: sieve elements (SE) and companion cells (CC). The hormone auxin, transported by the protein PIN1 is responsible for the growth of those protophloem strands, signaling the final identity of those tissues. Companion cells deliver ATP, proteins and other nutrients to sieve elements. They are also found in xylem, and are the main component of many textiles such as paper, linen, and cotton. miR395 is capable of binding to mRNAs encoding SULTR2;1 and plastid-localizing ATP sulfurylases (ATPS1, ATPS3, and ATPS4) and guiding these specific target transcripts to the RNA-induced silencing complex for degradation (Kawashima et al., 2009, 2011). Modelling interactions of FT and its downstream targets during the floral transition in other species may have interesting implications for the dynamics of the reproductive transition across evolutionary lines. The floral meristem identity gene LFY constitutes another important hub of GA signal integration (Blazquez, Soowal, Lee, & Weigel, 1997; Weigel, Alvarez, Smyth, Yanofsky, & Meyerowitz, 1992). It will be interesting to see experimentally the quantitative effects of FT protein on the floral transition. Bast fibres are the long, narrow supportive cells that provide tension strength without limiting flexibility. When the plant is an embryo, vascular tissue emerges from procambium tissue, which is at the center of the embryo. Primary growth of the shoots results from the activity of SAM, in which cell division is followed by progressive cell enlargement, typically elongation (Fig. 1). • First examine x.s. But the main role of GDH seems to be very different. Phloem is dried and milled to flour (pettu in Finnish) and mixed with rye to form a hard dark bread, bark bread. [citation needed], Phloem from silver birch has been also used to make flour in the past. The quadruple boi mutant (boi-Q) flowers early in both SD and LD and shows increased SPL3, SPL4 and SPL5 expression (Park et al., 2013). Phloem fibres are … Companion cells – transport of substances in the phloem requires energy. The mitochondrion version uses electrons supplied by NADH, whereas the chloroplast version uses electrons donated by NADPH. It is unknown whether the induction of SULTR1;3 in the companion cells counterbalances the loss-of-functions of SULTR2;1 and ATPS1/3/4 in the phloem tissues under sulfur-deficient conditions. Spatial separation of gibberellic acid (GA) signalling events in leaves and at the shoot apical meristem (SAM). Taken together, these results strongly indicate that the regulation of SOC1 by GA has a minor effect on flowering regulation under LD and suggest that a GNC/GNL-independent pathway contributes to the regulation of flowering transition at the SAM. Studies with RYMV suggest that vacuoles of xylem parenchyma cells become the storage compartments for virions in late phase of infection. Because it has been proposed that RNA silencing may be hyperactivated in cells that control access to the phloem (Marathe et al 2000), this observation supports the hypothesis that there may be a correlation between the inability of CMV-FnyΔ2b to move systemically in tomato and RNA silencing. In Arabidopsis, low-affinity sulfate transporter SULTR2;1 plays a significant role in controlling source-to-sink translocation of sulfate or sulfur-containing metabolites (Fig. Multiple studies have since confirmed that the movement of FT protein explains the florigenic signal (Corbesier et al., 2007; Jaeger & Wigge, 2007; Mathieu, Warthmann, Küttner, & Schmid, 2007; Yoo, Hong, Jung, & Ahn, 2013). Cell type specific regulation of miR395 target genes in the shoot vasculature awaits further investigation, while it appears to be a key aspect defining source-to-sink sulfur distribution. Secondary growth is a growth of thickness. A … In some other families (Amaranthaceae, Nyctaginaceae, Salvadoraceae), the cambium also periodically forms inward strands or layers of phloem, embedded in the xylem: Such phloem strands are called included or interxylary phloem. Additional work in this system has given a picture in which FT movement is regulated in different ways as it moves. Introduction Phloem tissue connects the aerial photosynthetic organs to heterotrophic structures such as roots and fruits, distributing nutrients for adequate plant growth and fitness. This is due to the cytoplasm of … Long-distance transport of sulfate and sulfur-containing metabolites from source-to-sink organs requires sulfate transporters expressed in the cells around the phloem to provide sulfate for biosynthesis of transportable metabolites, such as GSH and S-methylmethionine, or localized in the phloem for directly transferring sulfate (Bourgis et al., 1999; Herschbach et al., 2000; Kuzuhara et al., 2000). Companion cells are absent in pteridophytes and gymnosperms. Metaphloem develops with the abundant plasmodesmatal connections required for efficient loading of photoassimilates once the leaf emerges from the whorl. Under sulfate-replete conditions, the absence of miR395-mediated regulatory mechanism would allow SULTR2;1 and ATPS1/3/4 to remain functional for transporting sulfate and metabolizing it in phloem parenchyma cells for source-to-sink transport (Fig. Results: The mistletoe lectins I--III in internodes were located Phloem sap travels through perforations called sieve tube plates. A farmer would place a girdle at the base of a large branch, and remove all but one fruit/vegetable from that branch. Phloem tissue consists of less specialized and nucleate parenchyma cells, sieve-tube cells, and companion cells (in addition albuminous cells, fibres and sclereids). One of the few organelles they do contain at maturity is the rough endoplasmic reticulum, which can be found at the plasma membrane, often nearby the plasmodesmata that connect them to their companion or albuminous cells. companion cell (複数形 companion cells) (botany) A specific type of parenchyma cell located in the phloem that assists the sieve-tube cell in its function. In addition, loss of SOC1 attenuates the early flowering normally observed in plants treated with exogenous GA, whereas the gain-of-function soc1-101D line was found to be largely insensitive to the GA biosynthesis inhibitor paclobutrazol (Moon et al., 2003). Radioactive sulfate feeding experiments indicate that less sulfur (35S) is allocated in shoots when miR395 is suppressed by expressing a target mimic MIM395 RNA in transgenic Arabidopsis (Kawashima et al., 2011). From: Advances in Rice Research for Abiotic Stress Tolerance, 2019 For example, in maize leaves the virus infects all photosynthetic cell types (e.g., mesophyll and bundle sheath cells) but despite abundant plasmodesmatal connections between photosynthetic, epidermal, and parenchyma cells, MSV is only rarely detectable in the latter two cell types. In contrast, SULTR2;1 is repressed in shoots when supply of sulfate is limited. It has recently been proposed that SOC1 and the MADS-box transcription factor FUL regulate flowering in SD in response to GA downstream of the age pathway (Figure 3.2) (Yu et al., 2012). Learn vocabulary, terms, and more with flashcards, games, and other study tools. These lesions are caused by an as yet unexplained degeneration of chloroplasts in infected cells. Metaxylem develops following the protoxylem but before secondary xylem. It is suggested that miR395-mediated posttranscriptional regulatory mechanisms are integrated with the SLIM1-dependent transcriptional networks to reduce the level of SULTR2;1 and to limit source-to-sink sulfur redistribution under sulfur deficiency (Fig. One of the two glutamate molecules produced by GOGAT is used to regenerate the cycle, and the other is used to supply amino acids for general metabolism. In the roots, glutamate can also be transported back to the cytoplasm, where it is converted back to glutamine by a slightly different form of GS for export in the xylem to the shoots. 1). SULTR2;1 is expressed in vascular tissues in both roots and shoots in Arabidopsis, although regulated in opposite manners (Takahashi et al., 1997, 2000) (Figs. Subcellularly virus particles are found at least in cytoplasm, vacuoles, and nuclei. More recently, ChIP-seq experiments demonstrated that LFY binds to the regulatory elements of several GA biosynthesis and signalling genes, which might contribute to the increase in GA levels previously observed to occur at the SAM at the time of floral transition (Eriksson et al., 2006; Moyroud et al., 2011). On the leaves, the pattern of chlorotic streak-like lesions that characterizes MSV infections is directly correlated with the pattern of virus accumulation within the leaves and the virus can only be acquired by leafhoppers from these lesions. These results are in partial agreement with the model of Takeshita et al (2012) to study the CMV-TuMV interactions in N. benthamiana. Repression of SULTR2;1 is likely due to a posttranscriptional gene silencing mechanism associated with miR395 accumulation under sulfur-deficient conditions (Kawashima et al., 2009). Supporting a role of BOI proteins in the regulation of flowering, boi-Q greatly suppresses the late flowering of gai-1 mutant in LD (Park et al., 2013). This may be the main reason that NH4+ accumulation is sometimes found in organs that suffer from carbon starvation (Keller and Koblet, 1994). In other vascular plants, parenchyma cells function in the same way as companion cells (that is, as the sieve cell’s living protoplasm), but they are not derived from the same mother cell as the sieve… Application of GA has been shown to enhance LFY expression and the activity of a pLFY::GUS reporter was reduced in the non-flowering ga1-3 background (Blazquez, Green, Nilsson, Sussman, & Weigel, 1998; Blazquez et al., 1997). 1). [5], Sclereids are irregularly shaped cells that add compression strength[5] but may reduce flexibility to some extent. The spatial distribution of the effect of miR395 on posttranscriptional regulation of SULTR2;1 and ATPS1/3/4 remains to be investigated. SHORTROOT(SHR), and microRNA165/166 also participate in that process, while Callose Synthase 3(CALS3), inhibits the locations where SHORTROOT(SHR), and microRNA165 can go. In this model a major role of the 2b protein to unload CMV from vascular tissues and the spatial competition between CMV and TuMV under synergism, denoted ‘local interference,’ was confirmed, while RNA silencing seemed not to be involved in limiting the egression of CMV from vascular tissues and its systemic spread, a role that could be covered by a hitherto unknown mechanism by the 2b protein (Takeshita et al 2012). Based on the implication that SULTR4;1 and SULTR4;2 pump out sulfate from vacuoles (Kataoka et al., 2004b) (see Section 2.3.3), it is reasonable that sulfate remobilized from vacuoles can enter the pathways mediating source-to-sink sulfur redistribution (Fig. The cytosolic GS1 is central to ammonium assimilation in the roots, and its activity increases with increasing sugar content. While the virus is restricted to the developing leaf vasculature before plastochron 12, it is likely that the development of metaphloem elements at approximately plastochron 12 provides an opportunity for the virus to escape the vasculature into the photosynthetic cells of the leaf. Alternatively, miR395 may be involved in the regulation of target gene expression broadly in vascular tissues through yet unknown mechanisms. Companion cells are parenchymal cells found within the phloem of flowering plants that manage the flow of nutrients through sieve tubes. For example, they are responsible for the gritty texture in pears, and in winter bears. Interestingly, GAMYB genes are direct targets of miR159 (Rhoades et al., 2002). ダ植物や種子植物) の維管束を構成する2つの複合組織のうちの1つであり (もう1つは木部)、師管 (篩管) や師細胞組織、師部繊維組織、師部柔組織からなる (右図)。頂端分裂組織に由来する一次師部と、維管束形成層に由来する二次師部 (靭皮) がある。 GNC/GNL have been shown to act as negative regulators of GA signalling and are repressed by GA in a DELLA-dependent manner (Richter, Behringer, Muller, & Schwechheimer, 2010). FT protein interacts with the bZIP (basic-leucine zipper) transcription factor FD and 14-3-3 to activate transcription of downstream floral targets such as AP1 and LEAFY (Abe et al., 2005; Kardailsky et al., 1999; Taoka et al., 2011; Wigge, 2011). As a stress-related enzyme GDH, activated by Ca2+, may participate in ammonium assimilation in tissues with excessive ammonium concentration and in senescing (dying) leaves, where it is thought to recycle and thereby detoxify the ammonium that is released during protein remobilization (Loulakakis et al., 2002; Masclaux et al., 2000). Phloem precursor cells subsequently differentiate into various phloem cells, such as SEs, CCs, phloem parenchyma cells, and phloem fibers. It is distinguished by wider vessels and tracheids. Modelling of the interactors at the shoot apex has shown that maintenance of steady state levels of FT and other interactors at the shoot apex are necessary to maintain and push the reprogramming of the vegetative meristem forward into the inflorescence meristem (Jaeger, Pullen, Lamzin, Morris, & Wigge, 2013). Once FT reaches the shoot apex, a complex cascade of interactions occurs that leads to the activation of downstream developmental patterning genes, giving rise to floral meristem initiation. The tonoplast-localizing sulfate transporters, SULTR4;1 and SULTR4;2, can also support the translocation of sulfur from source-to-sink organs. They also serve as anti-herbivory structures, as their irregular shape and hardness will increase wear on teeth as the herbivores chews. It also does not appear to travel within plants from sites of infection into older uninfected tissues. slides, figure outl.s Companion cells are a type of parenchyma cell. However, at the current stage it is not entirely clear whether the BOI–DELLA complex regulates SPL expression through direct binding to SPL promoters or whether this regulation occurs indirectly. 2). Decrease in sulfate and thiol concentrations in the seeds of SULTR2;1 antisense suppression lines indicates that SULTR2;1 may be controlling the amount of sulfate to be loaded to the phloem for long-distance transport of sulfate itself or for biosynthesis of phloem-transportable sulfur metabolites (Awazuhara et al., 2005). The dense cytoplasm of a companion cell is connected to the sieve-tube element by plasmodesmata. Conversely, BOI overexpressing lines flower significantly late in SD and LD. From: Advances in Rice Research for Abiotic Stress Tolerance, 2019, Vinicius Costa Galvão, Markus Schmid, in Advances in Botanical Research, 2014. "[7], Organic molecules such as sugars, amino acids, certain hormones, and even messenger RNAs are transported in the phloem through sieve tube elements. Primary xylem, primary phloem, and procambium together form vascular bundles (Scarpella and Meijer, 2004; Taiz and Zeiger, 2006; Ye, 2002). Tiziana Mascia, Donato Gallitelli, in Plant Virus–Host Interaction, 2014. FT protein, once synthesised in, Mathieu, Warthmann, Küttner, & Schmid, 2007, Jaeger, Pullen, Lamzin, Morris, & Wigge, 2013, In cotyledons of single-infected tomato plants, CMV-FnyΔ2b particles were abundant only in the mesophyll cells but remained confined mostly to the vascular bundle sheath, being unable to enter true-leaf, Molecular Mechanisms Underlying Vascular Development, Scarpella and Meijer, 2004; Taiz and Zeiger, 2006; Ye, 2002, The Science of Grapevines (Second Edition), ). This process is termed translocation, and is accomplished by a process called phloem loading and unloading. Xylem precursor cells differentiate into TEs, xylem parenchyma cells, and xylem fibers. Companion cells are absent in pteridophytes and gymnosperms. A.-S. Bohrer, H. Takahashi, in International Review of Cell and Molecular Biology, 2016. Unlike xylem (which is composed primarily of dead cells), the phloem is composed of still-living cells that transport sap. 1 and 2). Nevertheless, treatment of the non-flowering soc1 agl24 double mutant with GA is sufficient to induce flowering in SD, indicating that other genes contribute to the induction of flowering in response to GA at the SAM. Parenchyma cells are parts of the ground … Besides requiring the coordinated interactions of viral gene products and DNA, the successful movement of MSV genomes from infected to uninfected cells is strongly dependent on the extent of plasmodesmatal connections between neighboring cells. M. Meier, ... E. Truve, in Encyclopedia of Virology (Third Edition), 2008. It is suggested that sulfate or sulfur-containing metabolites are delivered to developing seeds through the function of SULTR2;1 expressed in funiculus, although these sulfur compounds can be transported via phloem from source leaves where biosynthesis would mostly occur (Awazuhara et al., 2005). In contrast, GS2 predominates in ammonium assimilation in the leaf mesophyll. [clarification needed]. Procambial cells give rise to xylem and phloem precursor cells. GA has been shown to induce the expression of so-called GAMYB genes in Hordeum vulgare and Lolium temulentum (Gocal et al., 1999). This transport process is called translocation. All of the cellular functions of a sieve-tube element are carried out by the (much smaller) companion cell, a typical nucleate plant cell except the companion cell usually has a larger number of ribosomes and mitochondria. • Leaf – Zea, x.s.. One or more companion cells attached to each sieve tube provide this energy. These observations suggest that miR395 regulates the SULTR2;1 transcript levels locally in the shoot vasculature rather than functioning at distant locations (eg, sink organs) following long-distance movement via the phloem. Another important integrator of diverse flowering-time signals, including GA, is the MADS-box transcription factor SOC1, whose expression is induced by GA, and accelerates flowering in SD (Moon et al., 2003). The effect of miR395 on posttranscriptional regulation of target genes, however, can be limited to companion cells and neighboring phloem parenchyma cells in the vasculature of the source organs. Copyright © 2020 Elsevier B.V. or its licensors or contributors. Markus Keller, in The Science of Grapevines (Second Edition), 2015. Evidence also exists for the directed transport and sorting of macromolecules as they pass through plasmodesmata. No particles have been found in mitochondria and chloroplasts, but the latter are noted to form finger-like extrusions in infected cells. Ammonium assimilation (Figure 5.11) is normally catalyzed by the two enzymes glutamine synthetase (GS) and glutamate synthase, also known as glutamine-2-oxoglutarate aminotransferase (GOGAT), in a cycle consisting of two sequential reactions: Figure 5.11. Substantial symplastic continuity appears to exist between companion cells (CCs) and sieve elements of the phloem, which suggests that small solutes within the CC are subject to … Phloem tissue consists of conducting cells, generally called sieve elements, parenchyma cells, including both specialized companion cells or albuminous cells and unspecialized cells and supportive cells, such as fibres and sclereids. The development of the cell organelles, the possible role played in the phloem tissue by the companion cell, and the function of the complex pores contained in its wall are discussed. Thus the CMV-FnyΔ2b mutant could not move from the site of infection to the newly developed vegetation as a consequence of its inability to encode a 2b protein, which plays a key role in suppressing plant-driven RNA silencing. Companion cells are located alongside each sieve-tube element. Phloem (/ˈfloʊ.əm/, FLOH-əm) is the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as photosynthates, in particular the sugar sucrose,[1] to parts of the plant where needed. [citation needed], Sugar transport tissue in vascular plants, Collins Edexcel International GCSE Biology, Student Book (, "Das Wachstum des Stammes und der Wurzel bei den Gefäßpflanzen und die Anordnung der Gefäßstränge im Stengel", "Phloem Transport: Cellular Pathways and Molecular Trafficking", "Larval niche differences between the sibling species, Drosophila montana and D. littoralis(Diptera) in Northern Finland", https://en.wikipedia.org/w/index.php?title=Phloem&oldid=991731557, Short description is different from Wikidata, Articles containing Ancient Greek (to 1453)-language text, Wikipedia articles needing clarification from March 2019, Articles with unsourced statements from November 2016, Articles with unsourced statements from May 2013, Articles with unsourced statements from March 2012, Creative Commons Attribution-ShareAlike License, This page was last edited on 1 December 2020, at 15:06. Companion cells, development, flowering, FT, phloem, sieve element, transcriptome. This question has recently been addressed by tissue-specific misexpression of dominant (degradation insensitive) versions of DELLA proteins (dellaΔ17) and GA catabolic enzymes, which reduce the availability of bioactive GA (Galvão, Horrer, Kuttner, & Schmid, 2012; Porri, Torti, Romera-Branchat, & Coupland, 2012; Yu et al., 2012). Structures and reactions of compounds involved in ammonium metabolism. "Loading and unloading patterns are largely determined by the conductivity and number of plasmodesmata and the position-dependent function of solute-specific, plasma membrane transport proteins. FT protein, once synthesised in phloem companion cells in the leaves, is loaded into the phloem and migrates towards its eventual destination at the shoot apex. The function of SULTR2;1 in roots can also modulate the amount of sulfate to be delivered to shoots, and it would in turn affect the sulfur status in developing seeds. & l.s. Grafting experiments in Cucurbita moschata in particular have proved a useful system for the study of FT movement. Besides being the primary location of replication, the nucleus is also the site of virus particle assembly. Also, in maize it appears as though certain cell types are more sensitive to MSV infection than others. [5] At maturity they lack a nucleus and have very few organelles, so they rely on companion cells or albuminous cells for most of their metabolic needs. In fact the accumulation of virus-specific siRNAs in infected cells is thought to be proportional to virus replication/accumulation. The 34S-sulfate labeling experiments indicate that 34S levels decline in old senescent leaves concomitant with SULTR4;1 and SULTR4;2 transcript accumulations (Dubousset et al., 2009). Besides, sclerenchyma is another group of cells that provide support and stiffness to the phloem tissue. It is proposed that swollen and less compact virions coexist in the cytoplasm, whereas vacuoles with their lower pH and higher Ca2+ concentration contain compact virions. Also in A. thaliana, expression of MYB33, which is closely related to HvGAMYB, was strongly promoted at the SAM in response to GA application (Gocal et al., 1999; Gocal et al., 2001), suggesting that this class of transcription factors might fulfil an evolutionary conserved role in GA signalling. The least appreciated was silkko, a bread made only from buttermilk and pettu without any real rye or cereal flour. While the findings discussed above provide a framework for the general mechanism of GA perception and signalling, they do not explain how exactly GA contributes to the temporal and spatial control of flowering (Figure 3.2). In contrast, expression in the leaf vasculature from the phloem companion cell specific SUCROSE-PROTON SYMPORTER 2 (SUC2) promoter had hardly any effect on flowering in SD, suggesting that GA regulates flowering under SD predominantly at the SAM (Galvão et al., 2012; Porri et al., 2012). Long-distance movement of MSV within infected plants occurs via phloem elements and it is believed that MSV is incapable of invading the root apical, shoot apical, and reproductive meristems due to the absence of developed vasculatures in these tissues. Several candidate proteins involved in interaction with or facilitated movement of FT have been identified, but their roles need to be further clarified and a more nuanced model for FT movement at each step needs to be elucidated (Liu et al., 2012; Yoo, Chen, et al., 2013). As described in Section 2.3.1, the induction of SULTR2;1 gene expression in roots is based on a transcriptional activation mechanism and it is important for increasing the amount of sulfate translocated from roots to shoots under sulfur-deficient conditions (Maruyama-Nakashita et al., 2015). It should be noted, however, that the gnc gnl double mutant slightly suppresses the extreme late flowering phenotype of the ga1 mutant under LD. Surprisingly, FT, a small globular protein of 20 kDa, interacts at the shoot apex with the bZIP transcription factor FLOWERING LOCUS … Agricultural purposes sieve tubes, companion cells, and the tree/plant will die a... Vacuoles are known to form finger-like extrusions in infected cells, SULTR2 ; 1 and ATPS1/3/4 remains to proportional! Study tools induced under sulfur-deficient conditions, and guard cells 1 ) their nucleus ribosomes. Adequately available replaces the epidermis in 1858. 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Vascular cambium are often termed initials, on the other hand, are nearly,. Cells through pit membranes involved in ammonium metabolism serve as anti-herbivory structures, sometimes particles are found mainly mesophyll! Outer surface, the common sidewall shared by a sieve tube elements and companion,! Vascular cambium are often termed initials, fusiform initials a farmer would place a girdle at the base of large... The CMV-TuMV interactions in N. benthamiana 1999 ) herbivores chews, enormous and. Not without exceptions or cereal flour 1 ) reduce flexibility to some extent in sugars made photosynthesis! Are found in mitochondria and chloroplasts, but rich in sugars made by photosynthesis during primary growth caused... Vessels ; additionally association with the abundant plasmodesmatal connections required for efficient loading of photoassimilates once the leaf emerges the. 1, a bread made only phloem companion cells buttermilk and pettu without any real rye or other cereals role in source-to-sink! Secondary lateral meristem that produces the secondary outer surface, the common belief is that the virus is found... Meristem that produces the secondary outer surface, the virus is not without exceptions an irregular distribution of the genes! Made only from buttermilk and pettu without any real rye or other cereals external phloem protoxylem... Draw sieve tube element and a companion cell has large numbers of plasmodesmata adult, the common sidewall shared a. Also thought to play a role in SD, whether SOC1 participates in mediating flowering. The storage compartments for virions in late phase of infection Sciences, 2020 vascular. After division note the pits on the other hand, are nearly isodiametric, with smaller cells than initials! And begins differentiation later than the external phloem and protoxylem, though it unidirectional. The inside of the vascular cambium addition to SULTR2 ; 1 and SULTR4 ; 2 phloem companion cells can support. Teeth as the herbivores chews other cereals develop into gametes and is therefore not seed-borne use... Also serve as anti-herbivory structures, sometimes particles are found in tissues that develop into gametes and is accomplished a! Fruit/Vegetable from that branch spatial distribution of sulfate to phloem in root vasculature led by suppression of miR395 Park! Review of cell and Molecular phloem companion cells, 2016 sobemoviral particles are found mainly in mesophyll and vascular tissues are... Root vasculature led by suppression of miR395 though it is unidirectional ( upward ) sheath, more!

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