Behaviour of plasma membrane, cortical ER and plasmodesmata during plasmolysis of onion epidermal cells

During plasmolysis of onion epidermal cells, the contracting protoplast remains connected to the cell wall by an intricate, branched system of plasma membrane (PM) ‘Hechtian strands’ which stain strongly with the fluorescent probe DiOC₆. In addition, extensive regions of the cortical endoplasmic reticulum (ER) network remain anchored to the cell wall during plasmolysis and do not become incorporated into the contracting protoplast with the other cell organelles. These ER profiles become tightly encased by the PM as the latter contracts towards the centre of the cell. Thus, although the cortical ER is left outside the main protoplast body, it is nonetheless still bound by the PM of the cell. As well as being anchored to the wall, the cortical ER remains intimately linked with plasmodesmata and retains continuity between cells via the central desmotubules which become distended during plasmolysis. The PM also remains in close contact with the plasmodesmatal pore following plasmolysis. It is suggested that plasmodesmata, although sealed, may not be broken during plasmolysis, their substructure being preserved by continuity of both ER and PM through the plasmodesmatal pore. A structural model is presented which links the behaviour of PM, ER and plasmodesmata during plasmolysis.     

Distribution and structure of the plasmodesmata in mesophyll and bundle-sheath cells of Zea mays L.

In leaf blades of Zea mays L. plasmodesmata between mesophyll cells are aggregated in numerous thickened portions of the walls. The plasmodesmata are unbranched and all are characterized by the presence of electron-dense structures, called sphincters by us, near both ends of the plasmodesmatal canal. The sphincters surround the desmotubule and occlude the cytoplasmic annulus where they occur. Plasmodesmata between mesophyll and bundle-sheath cells are aggregated in primary pit-fields and are constricted by a wide suberin lamella on the sheath-cell side of the wall. Each plasmodesma contains a sphincter on the mesophyll-cell side of the wall. The outer tangential and radial walls of the sheath cells exhibit a continuous suberin lamella. However, on the inner tangential wall only the sites of plasmodesmatal aggregates are consistently suberized. Apparently the movement of photosynthetic intermediates between mesophyll and sheath cells is restricted largely or entirely to the plasmodesmata (symplastic pathway) and transpirational water movement to the cell walls (apoplastic pathway).Abbreviation ER endoplasmic reticulum     

Plasmodesmal Dynamics in Both Woody Poplar and Herbaceous Winter Wheat Under Controlled Short Day and in Field Winter Period

Electron microscopic observation revealed that poplar (Populus deltoides Marsh.) and winter wheat (Triticum aestivum L. cv. Seward 80004) plasmodesmatal structures significantly changed under short day (SD, 8 h light) and in winter period, and such changes differed also noticeably between these two woody and herbaceous plants. Under long day (LD, 16 h light), many plasmodesmata with strong stain appeared in the cell wall of both poplar apical buds and winter wheat young leaf tissues, and connections of cytoplasmic endoplasmic reticulum (ER) with the ER in some plasmodesmata were observed. In addition, the typical “neck type” plasmodesmata were observed in winter wheat young leaf tissues, and their central desmotubules (appressed-ER) could be clearly identified. Under SD, many poplar plasmodesmata showed only a partial structure in the cell wall and appeared to be discontinued; some plasmodesmata swelled in the mid-wall, forming the cavity, and no appressed-ER appeared. In winter wheat, however, no noticeable alterations of plasmodesmata occurred, and the plasmodesmatal structure essentially remained same as it was under LD. In winter period, poplar plasmodesmata had a similar morphology as those observed under SD, however, winter wheat manifested at least two types of significant plasmodesmatal alterations: one plugged by electron-dense materials and the other of reduced neck region compared to those under LD. The above dynamic difference of the two species plasmodesmata under SD and winter period revealed the difference of their dormancy development under those environmental conditions.     

The ultrastructure of plasmodesmata in the filamentous green alga,Bulbochaete hiloensis (Nordst.) tiffany

Summary The ultrastructure of the plasmodesmata found in the green alga Bulbochaete hiloensis has been examined by electron microscopy of ultra-thin sections. Unlike most other plasmodesmata that have been described recently, there are no internal components such as a desmotubule or a derivative of the endoplasmic reticulum. Each plasmodesma consists of a cylindrical connection between the plasma membranes of adjacent cells. The cylinder is constricted at each end to orifices which may be less than 100 Å in diameter. Within the cylinder the cytoplasmic face of the plasma membrane is lined with material probably consisting of helically arranged particles. The lumen here is 400–450 Å in diameter.The observations are discussed in relation to possible functions in intercellular transport.     

Substructure of freeze-substituted plasmodesmata

Summary The substructure of plasmodesmata in freeze-substituted tissues of developing leaves of the tobacco plant (Nicotiana tabacum L. var. Maryland Mammoth) was studied by high resolution electron microscopy and computer image enhancement techniques. Both the desmotubule wall and the inner leaflet of the plasmodesmatal plasma membrane are composed of regularly spaced electron-dense particles approximately 3 nm in diameter, presumably proteinaceous and embedded in lipid. The central rod of the desmotubule is also particulate. In plasmodesmata with central cavities, spoke-like extensions are present between the desmotubule and the plasma membrane in the central cavity region. The space between the desmotubule and the plasma membrane appears to be the major pathway for intercellular transport through plasmodesmata. This pathway may be tortuous and its dimensions could be regulated by interactions between desmotubule and plasma membrane particles.Abbreviations ER endoplasmic reticulum - PJF propane jet freezing - HPF high pressure freezing - CRT cathode ray tube - IP₃ inositoltrisphosphate     

Filament Disruption in Funaria Protonemata: Occlusion of Plasmodesmata

Plasmodesmata are occluded when Funaria chloronemata are fragmented by the development of tmema cells (TCs). The TC deposits a new wall layer along the cross wall toward the neighbouring non-sister cell (NC). This wall layer cuts off the plasmodesmata and its connection with the cross wall is soon lost. The plasmodesmata become isolated when the NC forms a new wall layer along the former cross wall. At the end of TC development, before its disintegration, the sister cell (SC) also deposits a new wall layer along the cross wall toward the TC, cutting off the plasmodesmata. For some time the plasmalemma of the plasmodesmata remains connected to the NC or the TC, whereas the desmotubule soon disappears. Relicts of the plasmalemma remain even after the isolation of the plasmodesmata and the disintegration of the TC. During the decay of the plasmodesmata, a cylinder of electron-dense material is frequently formed along the border of the plasmodesmatal channel. This may extend over the surface of the cell wall. Eventually, the plasmodesmatal channel is filled with wall material. Callose is only observed around functional plasmodesmata and does not seem to play a role in their occlusion.     

Fine structure of plasmodesmata in mature leaves of sugarcane

The fine structure of plasmodesmata in vascular bundles and contiguous tissues of mature leaf blades of sugarcane (Saccharum interspecific hybrid L62–96) was studied with the transmission electron microscope. Tissues were fixed in glutaraldehyde, with and without the addition of tannic acid, and postfixed in OsO₄. The results indicate that the fine structure of plasmodesmata in sugarcane differs among various cell combinations in a cell-specific manner, but that three basic structural variations can be recognized among plasmodesmata in the mature leaf: 1) Plasmodesmata between mesophyll cells. These plasmodesmata possess amorphous, electron-opaque structures, termed sphincters, that extend from plasma membrane to desmotubule near the orifices of the plasmodesmata. The cytoplasmic sleeve is filled by the sphincters where they occur; elsewhere it is open and entirely free of particulate or spokelike components. The desmotubule is tightly constricted and has no lumen within the sphincters, but between the sphincters it is a convoluted tubule with an open lumen. 2) Plasmodesmata that traverse the walls of chlorenchymatous bundle-sheath cells and mestome-sheath cells. In addition to the presence of sphincters, these plasmodesmata are modified by the presence of suberin lamellae in the walls. Although the plasmodesmata are quite narrow and the lumens of the desmotubules are constricted where they traverse the suberin lamellae, the cytoplasmic sleeves are still discernible and appear to contain substructural components there. 3) Plasmodesmata between parenchymatous cells of the vascular bundles. These plasmodesmata strongly resemble those found in the roots of Azolla, in that their desmotubules are closed for their entire length and their cytoplasmic sleeves appear to contain substructural components for their entire length. The structural variations exhibited by the plasmodesmata of the sugarcane leaf are compared with those proposed for a widely-adopted model of plasmodesmatal structure.Abbreviation ER endoplasmic reticulum This study was supported by National Science Foundation grants DCB 87-01116 and DCB 90-01759 to R.F.E. and a University of Wisconsin-Madison Dean's Fellowship to K. R.-B. We also thank Claudia Lipke and Kandis Elliot for photographic and artistic assistance, respectively.     

Plasmodesmata between synchronously and asynchronously developing cells of the antheridial filaments ofChara vulgaris L.

Summary Plasmodesmata connecting synchronously developing cells are filled with electron-transparent, homogenous ground cytoplasm. At the middle lamella, their average diameter is about 67 nm; the relative area occupied by plasmodesmata is calculated to be about 8 to 9% of the wall.Plasmodesmata occurring between cells which develop asynchronously are plugged by an electron-dense homogenous material. The plug fits tightly to the plasmalemma inside the plasmodesmatal canal. Occasionally (in 8% of the walls), the closing plugs are also found between synchronously dividing cells. Generally, the plugging takes place in the walls formed at the first stages of development of the antheridial filaments and is probably an irreversible process.It is supposed that the plugging of plasmodesmata is the cause of the appearance of two or more synchronous cell groups within a single filament.     

Effects of various treatments on microtubules and axial units of lung-fluke spermatozoa

Summary Sperm of the frog lung-fluke, Haematoloechus medioplexus, were treated in various ways and their microtubules and axial units were subsequently studied in sectioned and negatively-stained material. Microtubules and axial units were generally unaffected by exposure to colchicine, cold, and KCl, although with KCl certain lateral projections from doublet tubule A appeared more prominent in negatively-stained preparations. Both mercaptoethanol and urea have a dissociative effect on doublet tubules and microtubules, with doublet tubules being the more sensitive. Pepsin-HCl initially digests the dense region associated with the A tubule of a doublet pair and the core of the axial unit. Microtubules and B tubules of doublet units are later digested; in microtubules, there appears to be a proteinaceous material in the lucent central region which is digested before disappearance of the wall of the microtubule. Further evidence is presented indicating that the characteristically helical wall of the microtubules is made up of spherical subunits about 50 Å in diameter, with about 8 subunits in one turn of the helix. Under certain conditions, the helical structure may be altered to form a wall comprised of longitudinal filaments. It is emphasized that not all microtubules are structurally and chemically equivalent, and it follows that all microtubules do not share a common function.This research was supported by U.S. Public Health Service Grant AI-06448 and an institutional grant from the American Cancer Society.     

Signalling via plasmodesmata—the neglected pathway

This review considers recent studies on the role of plasmodesmata in the conduction of small solutes and signalling molecules between plant cells. The substructure of plasmodesmata is described in relation to the potential pathways available for symplastic signalling between cells. At least two discrete pathways are available for transport through plasmodesmata, the cytoplasmic sleeve between the desmotubule and the plasmalemma, and the endoplasmic reticulum which connects contiguous cells via the central desmotubule. This latter pathway has been shown recently to function as a dynamic continuum for the movement of lipids and lipid-signalling molecules between plant cells. The role of plasmodesmata in the conduction of hormones and electrical signals is also considered, as is the potential for movement of macromolecular signalling molecules via the symplast. The factors which regulate plasmodesmatal conductance and the significance of symplast 'domains' are discussed in relation to the control of movement of signalling molecules in the symplast.     

紫竹梅雄蕊毛细胞发育过程中胞间连丝超微结构的变化

紫竹梅（Ｓｅｔｃｒｅａｓｅａ ｐｕｒｐｕｒｅａ）雄蕊毛细胞间的胞间连丝随着细胞的生长、发育、衰老而呈现动态变化的过程．花蕾和开放花的雄蕊毛细胞间的胞间连丝,具备胞间连丝的一般结构,直径约５０ ｎｍ ．衰老花雄蕊毛细胞间的胞间连丝拓宽,内部结构逐步降解、撤离,呈开放式通道,直径约１００ ｎｍ ． 在胞间连丝的动态开放过程中,细胞内的细胞器也发生相应变化． 对胞间连丝形成开放性通道及其机理进行了讨论     

Ultrastructural Changes of Plasmodesmata in Staminal Hairs of Setcreasea purpurea During Development

Structural changes of plasmodesmata occurred in along with growth, development and senescence of staminal hair cells of Setcreasea purpurea. The plasmodesmata in the staminal hair cells of buds and open flowers were normal having a diameter of 50 mm. Those of senescent flowers became enlarged and underwent modification, such as the appressed endoplasmic reticulum disintegrated and the cell wall around the plasmodesmata degraded, so that it formed a channel with such as a diameter of 100 nm, twice or threefold as that of normal plasmodesmata. In the process of plasmodesma enlargement and modification, a series of changes occurred in the organelles.     

Der Feinbau der Mikrotubuli in Hefe nach Gefrierätzung

Zusammenfassung Im Zellkern der Bäckerhefe wunden beim Übergang von anaeroben zu aeroben Kulturbedingungen drei verschiedene Sorten vom Mikrotubuli beobachtet. Die Durchmesser der Röhrchen betragen 210, 224 und 250 Å, die Lumina 60, 75 und 105 Å. Der Grundbaustein dieser Mikrotubuli ist ein 80 Å großes, in erster Näherung globuläres Teilchen, in dem höchst wahrscheinlich acht Untereinheiten mit einem Durchmesser von 40 Å enthalten sind. Das Bauprinzip der Mikrotubuli ist eine eingängige Schraube, die von einer Perlenkette der Grundbausteine aufgebaut wird. Die drei verschiedenen Tubuli-Sorten unterscheiden sich darin, daß bei der einen 5, bei der anderen 6 und bei der drittem 7 Perlen (80 Å-Einheiten) pro Umgang der Schraube zu finden sind. Wenn man die 40 Å großen Untereinheiten berücksichtigt, so besteht die Tubulus-Wand aus einer doppelten Lage dieser Teilchen mit 10, 12 oder 14 Einheiten pro Schraubenumgang. Die Übereinstimmung vieler Daten aus der Literatur mit diesem Modell läßt den gleichartigen Aufbau aller Mikrotubuli und Spindelfasern als wahrscheinlich erschieinen.

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Summary Three different classes of microtubules have been detected in the nucleus of yeast cells passing from anaerobiosis to aerobiosis. The diameter of theses structures is 210, 224 and 250 Å respectively, the lumen 60, 75 and 105 Å. The structural unit of all these microtubules is a nearly globular particle having a diameter of 80 Å. This unit most probably contains 8 subunits of a diameter of 40 Å. The 80 Å-units are arranged in a beaded chain which is screwd up to form the tubule. This screw may contain 5, 6 or 7 of the units per turn. Taking into account the subunits, the wall of a tubule would then be constructed of two layers of 40 Å-particles; so we may count 10, 12 or 14 beads per turn of a double threaded screw. This model can be compared with many data about microtubules available in the literature.

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Zu besoniderem Dank verpflichtet bin ich Herrn Dr. C. Robinow für viele anregende Diskussionen, Herrn Dr. Matile für die Ausarbeitung der Kulturbedingunigen, Frl. S. Chicherio für die sachkundige Präparation und Frl. Tür ler für die graphische Ausstattung dieses Berichtes. Diese Arbeit wurde durch einen Kredit das Schweizerischen Nationalfonds unterstützt.     

Subcellular localization of ubiquitin in plant protoplasts and the function of ubiquitin in selective degradation of outer-wall plasmodesmata in regenerating protoplasts

Immunocytochemical localizations in Vicia faba L. protoplasts and cultures of regenerating Solanum nigrum L. protoplasts support former observations that in plant cells ubiquitin occurs within the cytoplasm, the nucleus, the chloroplasts and at the plasmalemma, but not within the vacuole or the cell wall. Immunoresponses were also observed within mitochondria and associated with the endoplasmic reticulum, which is in accordance with previous findings on animal cells. Moreover, the tonoplast membrane system was found to be labelled. For regenerating S. nigrum protoplasts, evidence is given that ubiquitin plays a role in selective degradation even of whole subcellular structures. Most of the discontinuous plasmodesmata formed in the newly deposited outer cell walls during the early stages of culture disappear later on, except for those near the periphery of division walls or of non-division walls, which are probably used for the formation of continuous cell connections during further culture. Outer-wall plasmodesmata which are destined to disappear show high immunoreactivity to ubiquitin antibody, but no conspicuous immunolabelling was observed with the remaining plasmodesmata. Thus, the selective disintegration of whole plasmodesmatal structures is obviously regulated by ubiquitination of plasmodesmatal proteins. A model for the mechanism of degradation of outer-wall plasmodesmata during extension growth of the cell wall is presented.Dedicated to Professor Dr. Andreas Sievers on the occasion of his retirementThis work was supported by grants to R. K. (Deutsche Forschungsgemeinschaft) and to M. S. (Bennigsen-Foerder Preis des Landes Nordrhein-Westfalen). We thank Dipl.— Biol. Kirsten Leineweber for help with the V. faba protoplast isolation and Dr. Olaf Parge, Institut für Psychologie und Sozialforschung, Kiel, Germany, for giving assistance with the statistical analysis.     

Observations on tubules derived from the endoplasmic reticulum in leaf glands ofPhaseolus vulgaris

Summary Tubular systems present in bean leaf glands have been studied electron microscopically. Ordered arrays of small tubules (290 Å in diameter) arise from the endoplasmic reticulum in early stages of gland development and remain connected to it. Subsequently larger tubules (560–660 Å in diameter) appear among the smaller tubules and gradually replace many of them. The large tubules are not connected to the endoplasmic reticulum. They contain an electron dense material and their walls exhibit a patterned substructure. In older gland cells the bundles of large tubules run randomly through the cytoplasm. The relationship of the two types of gland tubules to conventional microtubules has been examined morphologically and experimentally. The small tubules have larger diameters and thicker walls than microtubules. Neither type of gland tubule is affected by low temperature or colchicine, or, in thin sections, by pepsin digestion. This suggests that these tubules are not closely related chemically to either cytoplasmic or ciliary microtubules. The two systems of tubules are closely associated with prominent protein vacuoles in the gland cells, but are not directly connected to them.This work was supported in part by grant no. GB-6161 from the National Science Foundation.     

The structure of plasmodesmata as revealed by plasmolysis, detergent extraction, and protease digestion

Plasmodesmata or intercellular bridges that connect plant cells are cylindrical channels approximately 40 nm in diameter. Running through the center of each is a dense rod, the desmotubule, that is connected to the endoplasmic reticulum of adjacent cells. Fern, Onoclea sensibilis, gametophytes were cut in half and the cut surfaces exposed to the detergent, Triton X 100, then fixed. Although the plasma membrane limiting the plasmodesma is solubilized partially or completely, the desmotubule remains intact. Alternatively, if the cut surface is exposed to papain, then fixed, the desmotubule disappears, but the plasma membrane limiting the plasmodesmata remains intact albeit swollen and irregular in profile. Gametophytes were plasmolyzed, and then fixed. As the cells retract from their cell walls they leave behind the plasmodesmata still inserted in the cell wall. They can break cleanly when the cell proper retracts or can pull away portions of the plasma membrane of the cell with them. Where the desmotubule remains intact, the plasmodesma retains its shape. These images and the results with detergents and proteases indicate that the desmotubule provides a cytoskeletal element for each plasmodesma, an element that not only stabilizes the whole structure, but also limits its size and porosity. It is likely to be composed in large part of protein. Suggestions are made as to why this structure has been selected for in evolution.     

Endoplasmic reticulum in the formation of the cell plate and plasmodesmata

Summary The association of endoplasmic reticulum (ER) with the developing cell plate has been analyzed in lettuce roots fixed in glutaraldehyde and post-fixed in a mixture of osmium tetroxide-potassium ferricyanide (OsFeCN). Electron microscopic observations show that elements of ER, which are selectively stained by the OsFeCN reagent, become loosely associated with aggregating dictyosome vesicles at the onset of plate formation. Subsequently the ER, in a tubular reticulate network, surrounds the vesicular aggregates creating a three dimensional membrane matrix. It is suggested that the ER (1) provides a structural framework that holds the vesicles in position and directs their fusion within the plane of the plate and/or (2) regulates the local release of calcium ions required for vesicle fusion.OsFeCN post-fixation also provides new information about the cell plate vesicles themselves. The results demonstrate that vesicles derived from dictyosomes undergo an abrupt increase in staining as they fuse at the plate.Finally the ER associated with developing and mature plasmodesmata has been examined. Electron micrographs reveal that the OsFeCN staining, seen traversing the cell plate in early stages, later becomes restricted from that portion of the ER extending through the plasmodesmatal canal. These structural observations support the idea that during formation of the plasmodesma a tubular element of ER is tightly furled upon itself and that its inner leaflet is compressed into a rod. The ER cisternal space appears occluded and thus it is argued that intercellular transport occurs through the cytoplasmic annulus of the plasmodesmata.     

The Ultrastructure and Computer-enhanced Digital Image Analysis of Plasmodesmata at the Kranz Mesophyll-Bundle Sheath Interface of Themeda triandra var. imberbis (Retz) A. Camus in Conventionally-fixed Blades

The ultrastructure of the plasmodesmata at the Kranz mesophyll-bundlesheath (KMS-BS) interface in Themeda triandra, and the substructureswithin the plasmodesmata were investigated, using conventionallyfixed leaf-blade material, enhanced by the addition of 0·1%tannic acid to the primary fixative. Examination of high-resolution electronmicrographs, and computer-enhanceddigital images suggests that these plasmodesmata are complexstructures, comprised of helically-arranged particulate material.The electron-dense particles are between 2·5 and 3·0nm in diameter. These particles are specifically associatedwith the inner face of the inner plasmalemma membrane leaflet,and the outer region of the desmotubule wall. The electron-denseparticles are presumably proteinaceous and embedded in a lipidmatrix. In the constricted median portion of the KMS-BS plasmodesmata,the space between the desmotubule and the inner plasmalemmamembrane leaflet and areas surrounding the proteinaceous particlesthereof (the cytoplasmic sleeve) is about 3 nm in cross-section,and constitutes what we believe to be the space through whichintercellular transport takes place.Copyright 1993, 1999 AcademicPress Themeda triandra, Poaceae, cytoplasmic sleeve, image analysis, plasmodesmatal structure, desmotubule, Kranz mesophyll     

Electron microscope investigation of sieve-element ontogeny and structure inUlmus americana

Summary During advanced stages of sieve-element differentiation inUlmus americana L., dispersal of the P-protein (slime) bodies results in formation of a peripheral network of strands consisting of aggregates of P-protein components having a striated, fibrillar appearance. The tonoplast is present throughout the period of P-protein body dispersal. Perforation of the sieve plates is initiated during early stages of P-protein body dispersal.Small P-protein bodies consist of tubular components, most of which measure about 180 Å in diameter. With increase in size of the P-protein bodies narrower components appear. At the time of initiation of P-protein body dispersal, most of the components comprising the bodies are of relatively narrow diameters (most 130–140 Å) and have a striated, fibrillar appearance. Both wide and narrow P-protein components are present throughout the period of sieve-element differentiation and in the mature cell as well, and a complete intergradation in size and appearance exists between the two extremes. Both extremes of P-protein component have a similar substructure: an electron-transparent lumen and an electronopaque wall composed of subunits, apparently in helical arrangement. The distribution of P protein in mature sieve elements was quite variable.The parietal layer of cytoplasm in matureUlmus sieve elements consists of plasmalemma, endoplasmic reticulum cisternae in two forms (as a complex network closely applied to the plasmalemma and in stacks along the wall), mitochondria, and plastids.     

Plasmodesmata: composition,structure and trafficking

Plasmodesmata are highly specialized gatable trans-wall channels that interconnect contiguous cells and function in direct cytoplasm-to-cytoplasm intercellular transport. Computer-enhanced digital imaging analysis of electron micrographs of plasmodesmata has provided new information on plasmodesmatal fine structure. It is now becoming clear that plasmodesmata are dynamic quasi-organelles whose conductivity can be regulated by environmental and developmental signals. New findings suggest that signalling mechanisms exist which allow the plasmodesmatal pore to dilate to allow macromolecular transport. Plant viruses spread from cell to cell via plasmodesmata. Two distinct movement mechanisms have been elucidated. One movement mechanism involves the movement of the complete virus particle along virus-induced tubular structures within a modified plasmodesma. Apparently two virus-coded movement proteins are involved. A second movement mechanism involves the movement of a non-virion form through existing plasmodesmata. In this mechanism, the viral movement protein causes a rapid dilation of existing plasmodesmata to facilitate protein and nucleic acid movement. Techniques for the isolation of plasmodesmata have been developed and information on plasmodesma-associated proteins is now becoming available. New evidence is reviewed which suggests that plasmodesmatal composition and regulation may differ in different cells and tissues.