関: plasmodesma、plasmodesmal、plasmodesmatal、protoplasmic connection、symplasm、symplasmic

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/11/15 09:22:24」(JST)

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Plasmodesma allow molecules to travel between plant cells through the symplastic pathway

The structure of a primary plasmodesma. CW=Cell wall CA=Callose PM=Plasma membrane ER=Endoplasmic reticulum DM=Desmotubule Red circles=Actin Purple circles and spokes=Other unidentified proteins^[1]

Plasmodesmata (singular: plasmodesma) are microscopic channels which traverse the cell walls of plant cells^[2]^[3] and some algal cells, enabling transport and communication between them. Plasmodesmata evolved independently in several lineages,^[4] and species that have these structures include members of the Charophyceae, Charales, Coleochaetales and Phaeophyceae (which are all algae), as well as all embryophytes, better known as land plants.^[5] Unlike animal cells, every plant cell is surrounded by a polysaccharide cell wall. Neighbouring plant cells are therefore separated by a pair of cell walls and the intervening lamella, forming an extracellular domain known as the apoplast. Although cell walls are permeable to small soluble proteins and other solutes, plasmodesmata enable direct, regulated, symplastic intercellular transport of substances between cells. There are two forms of plasmodesmata: primary plasmodesmata, which are formed during cell division, and secondary plasmodesmata, which can form between mature cells.^[6]

Similar structures, called gap junctions^[7] and membrane nanotubes, interconnect animal cells^[8] and stromules form between plastids in plant cells.^[9]

Formation[edit]

Plasmodesmata are formed when portions of the endoplasmic reticulum are trapped across the middle lamella as new cell wall is laid down between two newly divided plant cells and these eventually become the cytoplasmic connections between cells (primary plasmodesmata). Here the wall is not thickened further, and depressions or thin areas known as pits are formed in the walls. Pits normally pair up between adjacent cells. Alternatively, plasmodesmata can be inserted into existing cell walls between non-dividing cells (secondary plasmodesmata)^[10]

Structure[edit]

Plasmodesmatal plasma membrane[edit]

A typical plant cell may have between 10³ and 10⁵ plasmodesmata connecting it with adjacent cells^[11] equating to between 1 and 10 per µm².^[12] Plasmodesmata are approximately 50-60 nm in diameter at the midpoint and are constructed of three main layers, the plasma membrane, the cytoplasmic sleeve, and the desmotubule.^[11] They can transverse cell walls that are up to 90 nm thick.^[12]

The plasma membrane portion of the plasmodesma is a continuous extension of the cell membrane or plasmalemma ^[13] It is similar in structure to the cellular phospholipid bilayers.

Cytoplasmic sleeve[edit]

The cytoplasmic sleeve is a fluid-filled space enclosed by the plasmalemma and a continuous extension of the cytosol. Trafficking of molecules and ions through plasmodesmata occurs through this passage. Smaller molecules (e.g. sugars and amino acids) and ions can easily pass through plasmodesmata by diffusion without the need for additional chemical energy. Larger molecules, including proteins (for example Green fluorescent protein) and RNA, can also pass through the cytoplasmic sleeve diffusively.^[14] Plasmodesmal transport of some larger molecules is facilitated by unknown mechanisms. One main mechanism of regulation of plasmodesmal transport is the accumulation of the polysaccharide callose accumulates around the neck region of plasmodesmata to form a collar, reducing their diameter and thereby controlling permeability to substances in the cytoplasm.^[13]

Desmotubule[edit]

The desmotubule is a tube of appressed endoplasmic reticulum that runs between two adjacent cells ^[15] Some molecules are known to be transported through this channel,^[16] but it is not thought to be the main route for plasmodesmatal transport.

Around the desmotubule and the plasma membrane areas of an electron dense material have been seen, often joined together by spoke-like structures that seem to split the plasmodesma into smaller channels ^[15] These structures may be composed of myosin^[17]^[18]^[19] and actin,^[18]^[20] which are part of the cell's cytoskeleton. If this is the case these proteins could be used in the selective transport of large molecules between the two cells.

Transport[edit]

Tobacco mosaic virus movement protein 30 localizes to plasmodesmata.

Plasmodesmata have been shown to transport proteins (including transcription factors), short interfering RNA, messenger RNA and viral genomes from cell to cell. One example of a viral movement proteins is the tobacco mosaic virus MP-30. MP-30 is thought to bind to the virus's own genome and shuttle it from infected cells to uninfected cells through plasmodesmata.^[14] Flowering Locus T protein moves from leaves to the shoot apical meristem through plasmodesmata to initiate flowering.^[21]

The size of molecules that can pass through plasmodesmata is determined by the size exclusion limit. This limit is highly variable and can is subject to active modification.^[6] MP-30 is able to increase the size exclusion limit from 700 Daltons to 9400 Daltons thereby aiding its movement through a plant.^[22]

Several models for possible active transport through plasmodesmata exist. It has been suggested that such transport is mediated by interactions with proteins localized on the desmotubule, and/or by chaperones partially unfolding proteins, allowing them to fit through the narrow passage. A similar mechanism may be involved in transporting viral nucleic acids through the plasmodesmata.^[23]

References[edit]

^ Maule, Andrew (December 2008). "Plasmodesmata: structure, function and biogenesis". Current Opinion in Plant Biology 11 (6): 680–686. doi:10.1016/j.pbi.2008.08.002. PMID 18824402. |accessdate= requires |url= (help)
^ Oparka, K. J. (2005) Plasmodesmata. Blackwell Pub Professional. ISBN 1-4051-2554-3 ISBN 978-1-4051-2554-3
^ Plasmodesmata (www.dictionary.com)
^ http://public.wsu.edu/~lange-m/Documnets/Teaching2011/Popper2011.pdf
^ Graham, LE; Cook, ME; Busse, JS (2000), Proceedings of the National Academy of Sciences 97, 4535-4540.
^ ^a ^b http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1692983 The shoot apical meristem: the dynamics of a stable structure. Jan Traas and Teva Vernoux : Philos Trans R Soc Lond B Biol Sci. 2002 June 29; 357(1422): 737–747. (page 744)
^ Bruce Alberts (2002). Molecular biology of the cell (4th ed.). New York: Garland Science. ISBN 0-8153-3218-1.
^ Gallagher KL, Benfey PN (January 2005). "Not just another hole in the wall: understanding intercellular protein trafficking". Genes Dev. 19 (2): 189–95. doi:10.1101/gad.1271005. PMID 15655108.
^ Gray JC, Sullivan JA, Hibberd JM, Hansen MR (2001). "Stromules: mobile protrusions and interconnections between plastids". Plant Biology 3: 223–33. doi:10.1055/s-2001-15204.
^ Lucas W., Ding, B. and Van der Schoot, C. (1993) Tansley Review No.58 "Plasmodesmata and the supracellular Nature of Plants" New Phytologist, Vol. 125, No. 3, pp. 435-476, Stable URL: http://www.jstor.org/stable/2558257
^ ^a ^b AW Robards (1975) Plasmodesmata. Annual Review of Plant Physiology 26, 13-29
^ ^a ^b "22". Molecular Cell Biology (4 ed.). 2000. p. 998. ISBN 0-7167-3706-X. |coauthors= requires |author= (help)
^ ^a ^b AW Robards (1976) Plasmodesmata in higher plants. In: Intercellular communications in plants: studies on plasmodesmata. Edited by BES Gunning and AW Robards Springer-Verlag Berlin pps 15-57.
^ ^a ^b http://www.ingentaconnect.com/content/bsc/pce/2003/00000026/00000001/art00007 Plasmodesmata and the control of symplastic transport A. G. ROBERTS & K. J. OPARKA
^ ^a ^b RL Overall, J Wolfe, BES Gunning (1982) Intercellular communication in Azolla roots: I. Ultrastructure of plasmodesmata. Protoplasma 111: 134-150
^ LC Cantrill, RL Overall and PB Goodwin (1999) Cell-to-cell communication via plant endomembranes. Cell Biology International 23: 653–661
^ JE Radford and RG White (1998) Localization of a myosin‐like protein to plasmodesmata. Plant Journal 14: 743-750
^ ^a ^b LM Blackman and RL Overall (1998) Immunolocalisation of the cytoskeleton to plasmodesmata of Chara corallina. Plant Journal 14: 733-741
^ S Reichelt, AE Knight, TP Hodge, F Baluska, J Samaj, D Volkmann and J Kendrick-Jones (1999) Characterization of the unconventional myosin VIII in plant cells and its localization at the post-cytokinetic cell wall. Plant Journal 19: 555–569
^ RG White, K Badelt, RL Overall and M Vesk (1994) Actin associated with plasmodesmata. Protoplasma 180: 169-184
^ Corbesier, L., Vincent, C., Jang, S., Fornara, F., Fan, Q., et al. (2007). "FT protein movement contributes to long distance signalling in floral induction of Arabidopsis". Science 316 (5827): 1030–1033. doi:10.1126/science.1141752. PMID 17446353.
^ http://www.sciencemag.org/cgi/content/abstract/246/4928/377 Science 20 October 1989: Vol. 246. no. 4928, pp. 377 - 379 Movement Protein of Tobacco Mosaic Virus Modifies Plasmodesmatal Size Exclusion Limit SHMUEL WOLF, WILLIAM J. LUCAS, CARL M. DEOM,and ROGER N. BEACHY
^ http://jpkc.zju.edu.cn/k/437/content/05.pdf Plant Physiology lectures, chapter 5

English Journal

A model for the transport of a viral membrane protein through the early secretory pathway: minimal sequence and endoplasmic reticulum lateral mobility requirements.

Serra-Soriano M, Pallás V, Navarro JA.Author information Instituto de Biología Molecular y Celular de Plantas, IBMCP (Universitat Politècnica de València-Consejo Superior de Investigaciones Científicas), Avenida Ingeniero Fausto Elio, s/n, 46022, Valencia, Spain.AbstractViral movement proteins (MPs) exploit host endomembranes and cytoskeleton to move within the cell via different routes that, in some cases, are dependent on the secretory pathway. Hence, Melon necrotic spot virus p7B, a type II transmembrane protein, leaves the endoplasmic reticulum (ER) through the COPII-dependent-Golgi pathway to reach the plasmodesmata. Here we investigated the sequence requirements and the putative mechanisms governing p7B transport through the early secretory pathway. Deletion of either the cytoplasmic N-terminal region (CR) or the luminal C-terminal region (LR) led to ER retention, suggesting that they are both essential for ER-export. Through alanine-scanning mutagenesis we identified residues in the CR and the LR that are critical for both ER-export and for viral cell-to-cell movement. Within the CR, alanine substitution of aspartic and proline residues in the DSSP β-turn motif (D7 AP10 A) led to discrete structures moving along the cortical ER in an actin-dependent manner. In contrast, alanine substitution of a lysine residue in the LR (K49 A) resulted in a homogenous ER-distribution of the MP and in ER-Golgi traffic inhibition. Moreover, the p7B ability to recruit Sar1 to the ER membrane is lost in the D7 AP10 A mutant, whereas it is enhanced in the K49 A mutant. In addition, fluorescence recovery after photobleaching revealed that mutation K49 A but not D7 AP10 A dramatically diminished protein lateral mobility. From these data, we propose a model whereby the LR may direct actin-dependent mobility toward the cortical ER where the cytoplasmic DSSP β-turn would favor the COPII vesicle assembly for p7B ER-export. This article is protected by copyright. All rights reserved.
The Plant journal : for cell and molecular biology.Plant J.2014 Jan 19. doi: 10.1111/tpj.12435. [Epub ahead of print]
Viral movement proteins (MPs) exploit host endomembranes and cytoskeleton to move within the cell via different routes that, in some cases, are dependent on the secretory pathway. Hence, Melon necrotic spot virus p7B, a type II transmembrane protein, leaves the endoplasmic reticulum (ER) through the
PMID 24438546

Plant Vascular Biology 2013: vascular trafficking.

Ursache R, Heo JO, Helariutta Y.Author information Institute of Biotechnology/Department of Bio and Environmental Sciences, University of Helsinki, FIN-00014, Finland.AbstractAbout 200 researchers from around the world attended the Third International Conference on Plant Vascular Biology (PVB 2013) held in July 2013 at the Rantapuisto Conference Center, in Helsinki, Finland (http://www.pvb2013.org). The plant vascular system, which connects every organ in the mature plant, continues to attract the interest of researchers representing a wide range of disciplines, including development, physiology, systems biology, and computational biology. At the meeting, participants discussed the latest research advances in vascular development, long- and short-distance vascular transport and long-distance signalling in plant defence, in addition to providing a context for how these studies intersect with each other. The meeting provided an opportunity for researchers working across a broad range of fields to share ideas and to discuss future directions in the expanding field of vascular biology. In this report, the latest advances in understanding the mechanism of vascular trafficking presented at the meeting have been summarized.
Journal of experimental botany.J Exp Bot.2014 Jan 15. [Epub ahead of print]
About 200 researchers from around the world attended the Third International Conference on Plant Vascular Biology (PVB 2013) held in July 2013 at the Rantapuisto Conference Center, in Helsinki, Finland (http://www.pvb2013.org). The plant vascular system, which connects every organ in the mature plan
PMID 24431156

Photoassimilation, Assimilate Translocation, and Plasmodesmal Biogenesis In the Source Leaves of Arabidopsis thaliana Grown Under an Increased Atmospheric CO2 Concentration.

Duan Z, Homma A, Kobayashi M, Nagata N, Kaneko Y, Fujiki Y, Nishida I.Author information Laboratory of Plant Molecular Physiology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, Shimo-Okubo 255, Sakura-Ku, Saitama, 338-8570, Japan.AbstractUsing 18-d-old Arabidopsis thaliana seedlings grown under increased (780 ppm, experimental plants) or ambient (390 ppm, control plants) CO2 conditions, we evaluated 14CO2-photoassimilation in and translocation from representative source leaves. The total 14CO2 photoassimilation amounts increased in the third leaves of the experimental plants in comparison with that found for the third leaves of the control plants, but the rates were comparable for the first leaves of the two groups. In contrast, translocation of labeled assimilates doubled in the first leaves of the experimental group, whereas translocation was, at best, passively enhanced even though photoassimilation increased in their third leaves. The transcript levels of the companion cell-specific sucrose:H+ symporter gene SUC2 were not significantly affected in the two groups of plants, whereas those of the sucrose effluxer gene SWEET12 and the sieve element-targeted sucrose:H+ symporter gene SUT4 were upregulated in the experimental plants, suggesting upregulation of SUT4-dependent apoplastic phloem loading. Compared with SUC2, SUT4 is a minor component that is expressed in companion cells but functions in sieve elements after transfer through plasmodesmata. The number of aniline blue-stained spots for plasmodesma-associated callose in the midrib wall increased in the first leaf of the experimental plants but was comparable in the third leaf between the experimental and control plants. These results suggest that A. thaliana responds to greater than normal concentrations of CO2 differentially in the first and third leaves in regards to photoassimilation, assimilate translocation and plasmodesmal biogenesis.
Plant & cell physiology.Plant Cell Physiol.2014 Jan 8. [Epub ahead of print]
Using 18-d-old Arabidopsis thaliana seedlings grown under increased (780 ppm, experimental plants) or ambient (390 ppm, control plants) CO2 conditions, we evaluated 14CO2-photoassimilation in and translocation from representative source leaves. The total 14CO2 photoassimilation amounts increased in
PMID 24406629

Japanese Journal

Viral cell-to-cell movement requires formation of cortical punctate structures containing Red clover necrotic mosaic virus movement protein.

Kaido Masanori,Funatsu Naoko,Tsuno Yasuko,Mise Kazuyuki,Okuno Tetsuro
Virology 413(2), 205-215, 2011-05-10
… However, C-terminal deletion did not affect MP functions, such as increasing the size exclusion limit of plasmodesmata, single-stranded RNA binding in vitro, and MP interacting in vivo. …
NAID 120003018213

“多細胞生物”糸状菌の隔壁孔を介した細胞間連絡

丸山潤一
マイコトキシン 61(2), 53-58, 2011
　糸状菌は，多数の細長い細胞が連なる菌糸の形態で生長する．隣接する細胞は隔壁で仕切られているが，隔壁孔と呼ばれる小さな穴を介して連絡をしている．この隔壁孔を介した細胞間連絡は，糸状菌の多細胞生物としての生育に重要な役割を果たしていると考えられるが，一方で，ある細胞が溶菌した際に，隔壁孔を介して連絡している隣の細胞も溶菌に巻き込まれるリスクを伴うシステムでもある．筆者らは，低浸透圧ショックにより麹菌 …
NAID 130001054316

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