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At least 19 recordsLinked to original sources
PubMed1992

Secondary plasmodesmata are specific sites of localization of the tobacco mosaic virus movement protein in transgenic tobacco plants.

Expression of the tobacco mosaic virus 30-kD movement protein (TMV MP) gene in tobacco plants increases the plasmodesmatal size exclusion limit (SEL) 10-fold between mesophyll cells in mature leaves. In the present study, we examined the structure of plasmodesmata as a function of leaf development. In young leaves of 30-kD TMV MP transgenic (line 274) and vector control (line 306) plants, almost all plasmodesmata were primary in nature. In both plant lines, secondary plasmodesmata were formed, in a basipetal pattern, as the leaves underwent expansion growth. Ultrastructural and immunolabeling studies demonstrated that in line 274 the TMV MP accumulated predominantly in secondary plasmodesmata of nonvascular tissues and was associated with a filamentous material. A developmental progression was detected in terms of the presence of TMV MP; all secondary plasmodesmata in the tip of the fourth leaf contained TMV MP in association with the filamentous material. Dye-coupling experiments demonstrated that the TMV MP-induced increase in plasmodesmatal SEL could be routinely detected in the tip of the fourth leaf, but was restricted to mesophyll and bundle sheath cells. These findings are discussed with respect to the structure and function of plasmodesmata, particularly those aspects related to virus movement.

Cytoplasm↗
PubMed2025

Live-cell RNA imaging with the inactivated endonuclease Csy4 enables new insights into plant virus transport through plasmodesmata.

Plant-infecting viruses spread through their hosts by transporting their infectious genomes through intercellular nano-channels called plasmodesmata. This process is mediated by virus-encoded movement proteins. Whilst the sub-cellular localisations of movement proteins have been intensively studied, live-cell RNA imaging systems have so far not been able to detect viral genomes inside the plasmodesmata. Here, we describe a highly sensitive RNA live-cell reporter based on an enzymatically inactive form of the small bacterial endonuclease Csy4, which binds to its cognate stem-loop with picomolar affinity. This system allows imaging of plant viral RNA genomes inside plasmodesmata and shows that potato virus X RNA remains accessible within the channels and is therefore not fully encapsidated during movement. We also combine Csy4-based RNA-imaging with interspecies movement complementation to show that an unrelated movement protein from tobacco mosaic virus can recruit potato virus X replication complexes adjacent to plasmodesmata. Therefore, recruitment of potato virus X replicase is mediated non-specifically, likely by indirect coupling of movement proteins and viral replicase via the viral RNA or co-compartmentalisation, potentially contributing to transport specificity. Lastly, we show that a 'self-tracking' virus can express the Csy4-based reporter during the progress of infection. However, expression of the RNA-binding protein in cis interferes with viral movement by an unidentified mechanism when cognate stem-loops are present in the viral RNA.

Plasmodesmata↗
PubMed1991

Maize mesocotyl plasmodesmata proteins cross-react with connexin gap junction protein antibodies.

Polypeptide present in various cell fractions obtained from homogenized maize mesocotyls were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblotted, and screened for cross-reactivity with antibodies against three synthetic polypeptides spanning different regions of the rat heart gap junctional protein connexin43 and the whole mouse liver gap junctional protein connexin32. An antibody raised against a cytoplasmic loop region of connexin43 cross-reacted strongly with a cell wall-associated polypeptide (possibly a doublet) of 26 kilodaltons. Indirect immunogold labeling of thin sections of mesocotyl tissue with this antibody labeled the plasmodesmata of cortical cells along the entire length of the plasmodesmata, including the neck region and the cytoplasmic annulus. Sections labeled with control preimmune serum were essentially free of colloidal gold. An antibody against connexin32 cross-reacted with a 27-kilodalton polypeptide that was present in the cell wall and membrane fractions. Indirect immunogold labeling of thin sections with this antibody labeled the plasmodesmata mainly in the neck region. It is suggested that maize mesocotyl plasmodesmata contain at least two different proteins that have homologous domains with connexin proteins.

Animals↗
PubMed1977

The structure of syncytia induced by the phytoparasitic nematode Nacobbus aberrans in tomato roots, and the possible role of plasmodesmata in their nutrition.

The structure of syncytia induced within galls in tomato roots by the false root-knot nematode Nacobbus aberrans has been examined by light and electron microscopy. A syncytium develops by breakdown or individual cell walls, which allows movement of cytoplasmic contents between transformed cells. The wall breakdown takes place at pit fields, where the plasmodesmata may be protected from digestion until the surrounding wall is removed. Numerous sieve elements differentiate in the cells outside the syncytium. These sieve elements, and also plasmodesmata in pit fields, are demonstrated by fluorescence microscopy. The possibility of a symplastic pathway of solute movement from the phloem to the syncytium is suggested. A massive accumulation of starch occurs in the gall cells and syncytial cells, which may be related to the proliferation of phloem. Wall ingrowths typical of transfer cells are absent, and a comparative survey of the structure and mode of solute entry into nematode-transformed cells in which ingrowths are present or absent is presented.

Cell Differentiation↗
PubMed2026

A conserved COBL3-like protein promotes PDLP5-dependent callose accumulation to confer broad-spectrum plasmodesmata-mediated antiviral defense.

Plasmodesmata (PDs) play vital roles in plant growth and defense by controlling the symplastic transport of important molecules. Here we report that a conserved COBRA-like protein, COBL3, positively regulates callose accumulation and is required for PD-mediated antiviral defense (PMAD) against divergent plant RNA viruses in wheat (Triticum aestivum) and tobacco (Nicotiana benthamiana). The wheat COBL3 protein, TaCOBL3, interacts with the 17K movement protein (MP) of barley yellow dwarf virus-GAV (BYDV-GAV). TaCOBL3 is associated with the plasma membrane and co-localizes with 17K MP at PDs. Genetic analysis with overexpression and knockout lines revealed that TaCOBL3 positively regulates wheat defense against BYDV-GAV by modulating callose accumulation at PDs. Interestingly, TaCOBL3 interacts with the wheat homolog of PDLP5, a conserved key regulator of PD permeability in higher plants. Silencing TaPDLP5 attenuates the elevated BYDV-GAV defense conferred by overexpression of TaCOBL3 in wheat. Furthermore, transient expression of TaCOBL3 promotes callose accumulation and lowers PD permeability in tobacco cells, and these effects are largely compromised when tobacco PDLP5 is silenced. Notably, BYDV 17K MP weakens the interaction between TaCOBL3 and TaPDLP5 and inhibits their callose-binding activities. Finally, silencing of tobacco NbCOBL3 reduces callose content and attenuates host defense against two tobraviruses, one potexvirus, and one hordeivirus. Overall, our study reveals a previously unknown role of COBRA-like proteins in PMAD and provides insight into how a plant viral MP sabotages PMAD by perturbing the COBL3-PDLP5 interaction to facilitate virus spread through PDs. The conserved COBL3 gene may be a valuable target for engineering of broad-spectrum antiviral resistance in crop plants.

COBRA-like protein↗
PubMed1975

Ultrastructural pathology of leaf cells of ryegrass (Lolium multiflorum) infected with ryegrass mosaic virus.

Ryegrass mosaic virus particles and virus induced lamellar inclusions were found in mesophyll and epidermal cells of virus infected ryegrass leaves. The lamellar inclusions were occasionally found in phloem cells also. Virus particles occurred in cytoplasm, inside plasmodesmata and often in membrane bound sacs embedded in a matrix between plasmalemma and cell wall at or near plasmodesmata. Electron dense plugs protruding from plasmodesmata, finger-like cell wall outgrowths and cell wall deposits usually at plasmodesmata were also observed. Cytopathological changes in organelles in infected cells included dense deposits in the cisternae of endosplasmic reticulum and Golgi apparatus, mitochondria with electron-dense or opaque matrix, proliferating cristae and deteriorating unit membrane; and disintegrating chloroplasts.

Cell Nucleus↗
PubMed1991

Plasmodesmatal function is probed using transgenic tobacco plants that express a virus movement protein.

A gene encoding a temperature-sensitive mutant (MPP154A) of the 30-kilodalton movement protein (MP) of tobacco mosaic virus (TMV) was transformed into Nicotiana tabacum cv Xanthi. Transgenic plants expressing the MPP154A gene complemented local and systemic movement of an MP-defective mutant of TMV (U3/12MPfs) at the permissive temperature of 24 degrees C but not at 32 degrees C, the nonpermissive temperature. A microinjection procedure was used to investigate the effects of the modified TMV MP on plasmodesmatal size-exclusion limits. Movement of fluorescein isothiocyanate-labeled dextran (F-dextran), with an average molecular mass of 9.4 kilodaltons, was detected between leaf mesophyll cells of the transgenic plants at 24 degrees C; however, no movement of either 3.9-kilodalton or 9.4-kilodalton F-dextrans was detected when the transgenic plants were held for 6 hours (or longer) at 32 degrees C. When these plants were shifted back to 24 degrees C for 6 hours, cell-to-cell movement of the F-dextrans was again observed. Accumulation of MPP154A was not affected by the temperature regime, nor was the subcellular distribution of the MP altered. These results are consistent with a change in the protein conformation of MPP154A at the nonpermissive temperature, which gives rise to a protein that fails to modify the molecular size-exclusion limits of plasmodesmata to the same extent as wild-type MP. Surprisingly, at 32 degrees C, movement of the F-dextrans was inhibited in transgenic plants expressing the wild-type MP gene; however, the inhibition was transient and was no longer detected after 48 hours at this elevated temperature. This transient inhibition of plasmodesmatal function was alleviated with Sirofluor, an inhibitor of callose ([1----3]-beta-D-glucan) synthesis. This result provides experimental evidence that callose deposition is involved in regulating the molecular size-exclusion limit of plasmodesmata in plants. Sirofluor had no effect on the inhibition of F-dextran movement at 32 degrees C in plants expressing the MPP154A gene, indicating that callose formation was not responsible for the failure of the temperature-sensitive mutant protein to alter the size-exclusion limit of plasmodesmata.

Benzenesulfonates↗
PubMed1976

Scanning electron microscopy in nematode-induced giant transfer cells.

A study of giant cells induced by the root-knot nematode, Meloidogyne incognita, in roots of Impatiens balsamina was made by scanning electron microscopy. The cytoplasmic contents of giant cells were removed by a procedure based on KOH digestion, to reveal inner wall structure. Wall ingrowths typical of transfer cells are present in giant cells from six days onwards after induction. They develop on walls adjacent to vascular tissues, and their distribution and development was examined. Pit fields contianing plasmodesmata become elaborated in walls between giant cells, but pit fields are lost between giant cells and cells outside them. The distribution of plasmodesmata in pit fields suggests that de novo formation of plasmodesmata occurs in walls between giant cells. Various aspects of giant cell formation and function are discussed and wall ingrowth development is compared in giant cells and normal transfer cells.

Autoradiography↗
PubMed1992

Reinvestigation of intracellular localization of the 30K protein in tobacco protoplasts infected with tobacco mosaic virus RNA.

It has been shown that the 30K protein of tobacco mosaic virus (TMV) is responsible for the cell-to-cell movement function of the virus. It is still obscure how the protein is involved in this function at the molecular level. We formerly found that the 30K protein is localized to the plasmodesmata of TMV-infected plants. We also reported that the 30K protein was detected in a nuclei-rich fraction of TMV-infected protoplasts after biochemical fractionation. To clarify the inconsistency, the 30K protein was immunocytologically localized in TMV-infected protoplasts using a newly prepared antibody against the 30K protein. On some sections, the 30K protein was found near the nucleus but not in or on the nucleus. At later stages of infection a novel electron-transparent structure was detected in the cytoplasm where the 30K proteins were localized. This structure might reflect an intermediate form between its synthesis in the cytoplasm and its targeting to the plasmodesmata in whole plants.

Amino Acid Sequence↗
PubMed1977

Differentiation of the tapetum in Avena. I. The cell surface.

The development of the tapetal cell surface and associated structures in Avena has been followed from cell formation to senescence. Plasmodesmata initially connect the tapetal cells to each other, the pollen mother cells, and the inner loculus wall cells. These connexions are subsequently severed, those to the sporogenous cells being broken first at the pollen mother cell surface during callose wall formation. Loss of cellulose from the tapetal walls was followed using the decline in the ability of the wall to bind the fluorescent brightener, Calcofluor White M2R New. Subplasma-membrane microtubules persist after loss of the cellulose wall. The tapetal plasma membrane facing the meiocytes then develops a series of depressions, or cups, over its surface, which are later the site of pro-orbicule formation. Sporopollenin is laid down over the pro-orbicules, to form orbicules, and over other tapetal cell surfaces. No morphological evidence was found for the intracytoplasmic formation of pro-orbicules or polymerized sporopollenin precursors. These observations on Avena are compared with those on other plants. The changes in the cell wall and associated structures, plasmodesmata and microtubules, are considered in detail, while the general significance of cell wall loss to the water relations of the tissue are assessed. Proposals that pro-orbicule formation results from non-specific accumulation of lipid at a free cell surface are rejected, instead this formation is considered to be related to the presence of a specially modified plasmamembrane surface.

Cell Differentiation↗
PubMed1978

Electron microscopic studies in cultivated plants. I. Green pods of Phaseolus vulgaris var. nanus L.

Scanning (SEM) and transmission (TEM) electron microscopic studies in the legumen of Phaseolus vulgaris var. nanus L. (kidney beans) were carried out. In this work emphasis was laid on the analysis of the morphological structure of the parenchyma tissue, being the chief component of the pod at edible maturity. The leaf character of the pod becomes especially evident by the occurence of stomata, trichomes, and typical cuticle structures on the outside of the pod (SEM). The cells of the mesophyll-like parenchyma tissue are distinguished by a great range of variation of their plastids (chloroplasts--chloroamyloplasts--amyloplasts) and some special cytological features such as a strongly developed rough ER, big nuclei, and numerous plasmodesmata (TEM).

Cell Nucleus↗
PubMed1992

Properties of a previously undescribed grapevine nepovirus from Tunisia.

A virus with isometric particles c. 30 nm in diameter and angular contour was isolated by inoculation of sap from a Tunisian grapevine with mild mottling and leaf deformation. The virus sedimented in sucrose density gradients as three components: T (empty shells), M (particles containing a molecule of ssRNA with an apparent size of 5,800 nucleotides, constituting 35% of the particle weight) and B (particles containing a molecule of ssRNA with apparent size of 6,800 nucleotides, constituting 41% of the particle weight). Virus particles had buoyant densities of 1.31 (T), 1.45 (M), and 1.49 g/cm3 (B) in cesium chloride equilibrium gradients. The coat protein subunits consisted of a single polypeptide with mol. wt. of c. 59,000 daltons. An antiserum was produced with a titer of 1:256, which did not react with healthy plant antigens. Cells of artificially infected herbaceous hosts showed cytoplasmic vesiculate-vacuolate inclusion bodies, virus-containing tubules, mostly associated with plasmodesmata and/or cell wall protrusions, and crystalline aggregates of virus particles and empty capsids. The physicochemical and ultrastructural properties of this virus resemble very much those of nepoviruses. However, it was serologically unrelated to 19 different members of the group, including all those reported to infect grapevines. Therefore, the virus is possibly a hitherto unreported nepovirus for which the name of grapevine Tunisian ringspot virus (GTRV) is proposed.

Capsid↗
PubMed1975

An ultrastructural study of acid phosphatase localization in cells of Phaseolus vulgaris phloem by the use of the azo dye method.

The localization of acid phosphatase was studied in the sieve elements and companion cells in the phloem tissue of the bean, Phaseolus vulgaris L. The various organelles in the two kinds of cell showed fine granules of the azo dye as the final reaction product. The aggregated smooth endoplasmic reticulum displayed the dye particularly consistently. The dye was also present in the plasmodesmata and in the contents of the sieve plate pores. The reaction product was conspicuous in the cell walls and tended to be concentrated in the middle lamella and in the nacreous wall layer of the differentiating sieve elements.

Acid Phosphatase↗
PubMed1979

Ultrastructural characteristics of Hydrilla leaf tissue.

The general anatomy and leaf ultrastructure of Hydrilla verticillata (L.f.) Royle, a submersed vascular hydrophyte, are reported. The transversely sectioned leaf consists of only two contiguous epidermal layers, and the single midvein is composed of three to four concentric layers of cells. There are numerous intercellular spaces throughout the tissue. Electron microscopy confirmed the presence of sieve elements in the mid-vein area. P-protein, plastid inclusions and branched plasmodesmata leading into the companion cells are all considered indicative of phloem-type cells. Plastid inclusions are cuneate and lack associated starch granules, characteristics typical of monocots. The outer wall of the lower epidermis protrudes into the cell. Plant cells with wall ingrowths are termed 'transfer cells' and, in aquatics, function in the absorption of solutes from the external environment. In addition to the lower epidermis, spiny projections of the leaf margin could be included in this category. There is a thick fibrous layer which appears to be part of the outer wall of the upper epidermis. Secretory vesicles containing polysaccharide empty into this layer and into the wall. Cell nuclei are distinctly polymorphic. The granal arrangement, presence or absence of starch and peripheral reticulum in chloroplasts varies.

Cell Wall↗
PubMed1992

Production of the tobacco mosaic virus (TMV) transport protein in transgenic plants is essential but insufficient for complementing foreign virus transport: a need for the full-length TMV genome or some other TMV-encoded product.

We have reported previously that tobamoviruses enable the transport of red clover mottle comovirus (RCMV) in tobacco plants normally resistant to RCMV. Here we show that RCMV transport does not take place in transgenic tobacco plants (line To-4) producing the 30K transport protein of tobacco mosaic virus (TMV), whereas the transport of the TMV Ls1 mutant, the cell-to-cell movement of which is temperature sensitive, is complemented in these plants. However, RCMV transport is observed when these transgenic plants are infected with both RCMV and TMV Ls1 at the non-permissive temperature (33 degrees C). It is suggested that (i) the hypothetical modification of transgenic plant plasmodesmata by the TMV 30K transport protein can specifically mediate the cell-to-cell movement of the homologous virus (TMV), but is insufficient to mediate RCMV transport; (ii) the presence of the full-length TMV genome or a certain TMV-encoded product(s) besides the 30K protein is essential for complementation of the RCMV transport function. The possibility that line To-4 might provide enough 30K protein to complement TMV Ls1 but not RCMV cannot be ruled out. During double infection the mutant 30K protein may, in concert with the wild-type 30K protein, provide the transport function for RCMV.

Biological Transport↗