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  • 1
    Electronic Resource
    Electronic Resource
    Intercellular communication in Chara: factors affecting transnodal electrical resistance and solute fluxes (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 15 (1992), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The permeability of plasmodesmata in the nodal complex of branch cells of Chara corallina was examined by measuring both the transnodal electrical resistance and transnodal fluxes of 36CI and 14C-buty-rate. Under normal circumstances, the resistance across the node was low, but increased rapidly in response to metabolic inhibition, pressure gradients across the node or excision of one of the cells. For each of these treatments, there was a substantial reduction in solute transport between the cells. Acidification of the cytoplasm by weak acids or alkalinization by amines did not affect either the electrical resistance or the flux of solutes through the node between whorl cells. The transnodal resistance was significantly higher in older cell pairs, but was unaffected by large transnodal voltage differences or by the passage of action potentials. There was no evidence that short-term increases in cytoplasmic calcium have any effect on plasmodesmatal permeability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1992.tb01484.x
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  • 2
    Electronic Resource
    Electronic Resource
    A calcium influx precedes organogenesis in Graptopetalum (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 14 (1991), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. An account is given of an investigation of net ionic currents and specific ion fluxes occuring during the initiation of organogenesis in detached leaves of Graptopetalum paraguayense E. Walther, in which a dramatic change in growth polarity is cytomorphologically evident 3–5 d after leaf detachment from the plant. Using the vibrating probe, it was possible to identify a peak of ionic current which is focused over the area of the leaf base where organogenesis is initiated. This net current is largest during the initial 12h after leaf detachment. With ion-selective microelectrodes capable of measuring H+, K+ and Ca2+ ion fluxes simultaneously in the same region of the leaf base, H+ and K+ fluxes remain relatively steady during the initial 24 h after detachment, while a large lanthanum-sensitive Ca2+ influx decreases by 50% from 2 to 12h. By 24h, Ca2+ transport is dominated by an efflux. We present evidence from a quantitative comparison of the ion current data collected using these two techniques, that Ca2+, H+ and K+ transport accounts for the major electrogenic ion fluxes during 2 and 12 but not 24 h after leaf detachment. The possibility is addressed that these ion currents, which precede organogenesis, and in particular the predominant Ca2+ flux, play a role in the establishment of growth polarity in higher plant tissues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1991.tb01538.x
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  • 3
    Electronic Resource
    Electronic Resource
    Callose deposition at plasmodesmata (1998)
    Springer
    Protoplasma 201 (1998), S. 30-37 
    Details
    ISSN: 1615-6102
    Keywords: Cell-to-cell communication ; Plasmodesmata ; Ultrastructure ; Wounding ; 2-Deoxy-D-glucose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The transport of ions and metabolites through plasmodesmata has been thought to be controlled at the neck region where the cytoplasmic annulus is constricted and where callose has also been localised. In order to determine the possible structural and functional effects of callose, its deposition was inhibited through incubation of the plant tissue with 2-deoxy-D-glucose (DDG) for 1 h prior to fixation in 2.5% glutaraldehyde. The inhibition of callose formation was monitored through aniline blue-induced fluorescence of callose. The neck region of the plasmodesmata fromAllium cepa L. roots treated with DDG exhibited a funnel-shaped configuration. This is in contrast to the plasmodesmata from tissue not incubated with DDG, which exhibited constricted necks similar to those previously reported. Both initial dissection and glutaraldehyde fixation induced neck constriction in plasmodesmata, however, dissection of tissue increased the frequency of constrictions. The inhibition of callose formation by chemical means showed that the neck constrictions and raised collars in this area are artefacts due to physical wounding and glutaraldehyde fixation. The external electron-dense material observed when tannic acid is included in the primary fixative appears to be unrelated to the deposition of callose at the neck region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01280708
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  • 4
    Electronic Resource
    Electronic Resource
    Microtubule arrays in regeneratingMougeotia protoplasts may be oriented by electric fields (1990)
    Springer
    Protoplasma 158 (1990), S. 73-85 
    Details
    ISSN: 1615-6102
    Keywords: Microtubules ; Protoplasts ; Mougeotia ; Polarity ; Electric fields
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Initially non-polar protoplasts of the green algaMougeotia will regenerate to re-establish their original cylindrical cell shape. The orientation of the growth axis of regenerating protoplasts held in agarose was independent of both the direction of incident white light and gravity. Protoplasts elongated parallel to applied DC electric fields of approx. 0.2 Vcm−1 (1 mV/protoplast) and greater, with an increasing percentage oriented with increasing field strength. At the maximum field strength used (10 mV/cell), 53% of protoplasts were oriented within +- 10° of the 0/180° axis of the field. In untreated controls, the orientation of elongation was random. Protoplast survival was unaffected by field treatment. Some protoplasts (up to 37% in 10 mV/cell fields) formed outgrowths towards the cathode and occasionally towards the anode. Regenerating protoplasts in fields displayed the normal sequence of microtubule reorganization. This means that the positioning of the ordered symmetrical array of microtubules centred on two foci that appears within 3 to 4 h, and the subsequent organization of microtubules by 8 to 12 h into a band that intersects both foci and which is transverse to the axis of elongation (Galway and Hardham 1986), may be controlled by externally applied electric fields. In the region of this microtubule band, the applied field causes the plasma membrane to be stretched parallel to the field (Bryant and Wolfe 1987). We suggest that microtubules may become oriented perpendicular to the direction of field-induced membrane stretching, and that membrane stretching may be one of the orienting mechanisms for membrane-linked microtubules in elongating plant cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01323276
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  • 5
    Electronic Resource
    Electronic Resource
    Re-orientation of cortical F-actin is not necessary for wound-induced microtubule re-orientation and cell polarity establishment (1992)
    Springer
    Protoplasma 169 (1992), S. 97-106 
    Details
    ISSN: 1615-6102
    Keywords: Actin ; Microtubules ; Cytoskeleton ; Polarity ; Pea root ; Wound
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary To assess the relative roles of cortical actin and microtubule re-orientation in the establishment of new cell polarity, we have examined the kinetics of cortical actin re-orientation around a wedge-shaped wound in pea roots. Cortical actin re-orients from a transverse alignment to an approximately longitudinal orientation between 5 and 24h after wounding, that is, after the re-alignment of microtubules, which is known to occur before 5h post-wounding. F-actin in root cortical cells does not appear to be necessary for the establishment of new cell polarity around wounds, since normal MT re-alignment, and new planes of cell division are still established around a wound in cytochalasin treated roots. The cytochalasin treatment appeared to totally disrupt cortical and cytoplasmic F-actin in cells of the root cortex. However, in the apparent absence of F-actin in these cells, the rate of wound-induced cell division, but not cell expansion, is slower, and we suggest that an effect on the phragmosomal actin is involved. Finally, we demonstrate that new cell polarity around a wound is not established if microtubules are disrupted by the herbicide oryzalin, but after re-establishment of these arrays following a wash-out of the drug, the typical new planes of cell expansion are observed. We conclude that microtubules play a critical role in establishing and maintaining cell polarity in this system, and that cortical F-actin has a minor and presently unclear function in these processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01323609
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  • 6
    Electronic Resource
    Electronic Resource
    Electric fields affect the orientation of cortical microtubules and cell expansion in pea callus (1995)
    Springer
    Protoplasma 189 (1995), S. 256-266 
    Details
    ISSN: 1615-6102
    Keywords: Co-ordinated cell expansion ; Cortical microtubules ; Electric fields ; Oryzalin ; Pea callus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cortical microtubules in callus derived fromPisum sativum roots form parallel arrays within cells but are randomly oriented across the tissue. These arrays align perpendicular to the direction of an applied electric field of 6 mV per cell. Application of a field of 6 mV per cell for 4 days resulted in the co-ordinated expansion of cells parallel to the field direction. Cortical microtubule arrays were still aligned perpendicular to the applied field 24 h after removal of the field. The imposition of a field to callus after the removal of cortical microtubules by oryzalin and in the presence of the herbicide resulted in the orientation of recovering microtubules perpendicular to the direction of the field, indicating that microtubules are not directly involved in the detection of the field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01280180
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  • 7
    Electronic Resource
    Electronic Resource
    Inhibition of ethylene biosynthesis does not block microtubule re-orientation in wounded pea roots (1997)
    Springer
    Protoplasma 198 (1997), S. 135-142 
    Details
    ISSN: 1615-6102
    Keywords: L-α-(2-aminoethyoxyvinyl)-glycine hydrochloride ; Cell division ; Ethylene ; Microtubules ; Pisum sativum ; Root ; Wounding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Wounds in pea roots can cause the cortical cells surrounding the wound to change their direction of elongation and division planes in order to replace the removed tissue. These changes in growth polarity are preceded by a re-orientation of microtubules in the affected cells. In an approach to understand the control of this process it was investigated whether or not the plant hormone ethylene plays a role in the re-orientation of microtubules and growth polarity. Our results show that treating pea roots with an inhibitor of ethylene synthesis, L-α-(2-aminoethyoxyvinyl)-glycine hydrochloride (AVG), did not affect wound-induced microtubule re-orientation. However, the effect of AVG on ethylene synthesis in pea roots was confirmed by its stimulation of root elongation. Therefore we conclude that increased ethylene production, which has been observed previously in wounded tissues, is unlikely to be a control factor in microtubule re-orientation in this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01287562
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  • 8
    Electronic Resource
    Electronic Resource
    Intercellular communication inAzolla roots: I. Ultrastructure of plasmodesmata (1982)
    Springer
    Protoplasma 111 (1982), S. 134-150 
    Details
    ISSN: 1615-6102
    Keywords: Azolla ; plasmodesmata ; desmotubule ; membrane ; intercellular communication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A model is proposed for the structure of the plasmodesmata ofAzolla root primordia, based on micrographs obtained by a combination of fixation in glutaraldehyde/p-formaldehyde/tannic acid/ferric chloride, digestion of cell walls and the use of stereo pairs. Unlike the model for plasmodesmatal structure proposed byRobards (1971), the desmotubule is depicted as a virtually closed cylindrical bilayer providing little or no open pathway for transport. In this respect it is similar to the model ofLópez-Sáez et al. (1966). An analysis of the molecular packing of types of lipids found in endoplasmic reticulum (of which the desmotubule is an extension) indicates that the model is geometrically feasible. Details cannot be discerned with accuracy, but material, possibly particulate, occupies much of the space between desmotubule and plasma membrane, the cytoplasmic lumen being reduced to inter-particle spaces of cross-sectional area comparable to that of the bore in a gap junction connexon. Implications for intercellular transport are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01282071
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  • 9
    Electronic Resource
    Electronic Resource
    Intercellular communication inAzolla roots: II. Electrical coupling (1982)
    Springer
    Protoplasma 111 (1982), S. 151-160 
    Details
    ISSN: 1615-6102
    Keywords: Azolla ; Plasmodesmata ; Electrical coupling ; Apical cell ; Root
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary There is a predictable and well defined variation in numbers of plasmodesmata in roots ofAzolla. As the apical cell of the root ages, it lays down walls with progressively fewer plasmodesmata, thereby gradually cutting itself off from the rest of the root (Gunning 1978). Electrical coupling was examined between the apical cell and an adjacent merophyte in roots of various lengths. The apical cell becomes increasingly electrically isolated from the rest of the root as it ages. Electrical coupling is strongly correlated with the number of the plasmodesmata between the coupled cells. The resistance of a plasmodesma, as estimated from equivalent electrical circuits, was 150–600 times more resistive than a value based on theoretical considerations. No evidence was found for a change in the physiology of plasmodesmata as the root ages. Coupling experiments, both on root hairs and at the apex, gave some suggestion that plasmodesmata may be less resistive towards the apical cell than away from it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01282072
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  • 10
    Electronic Resource
    Electronic Resource
    Actin associated with plasmodesmata (1994)
    Springer
    Protoplasma 180 (1994), S. 169-184 
    Details
    ISSN: 1615-6102
    Keywords: Actin ; Cell-cell communication ; Plasmodesmata ; Regulation ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have used several methods to localise actin associated with plasmodesmata. In meristematic plant material fixed in 0.1% glutaraldehyde/1% paraformaldehyde and embedded in LR White resin, actin was localised (in TEM using 5 nm gold-labelled secondary antibody to C4 anti-actin primary antibody) in the neck region by the plasma membrane and endoplasmic reticulum, and also down the length of the plasmodesma, deep in the cell wall. When the chemical fixation was replaced by rapid freezing in liquid propane (without cryoprotectants) and substitution in acetone, the plasmodesmata were labelled in similar positions, but with less background label on sections. While only 8–20% of plasmodesmata were labelled, the label was 10 to 100 fold denser over plasmodesmata than over the surrounding wall indicating specific association with plasmodesmata. We presume the apparent extracellular location of some label was due to the size of the antibodies between the site of attachment and the observed position of the gold particle. Gold label was found in similar locations in material fixed in 3% paraformaldehyde, infiltrated with sucrose, frozen, sectioned (10–12 μm thick), then labelled with antibodies before resin embedding. Furthermore, cell walls in epidermal peels stained with rhodamine-phalloidin showed localised patches of fluorescence, presumably at the site of plasmodesmata (or primary pit-fields), which were connected on either side to fluorescent strands of actin in the cytoplasm. Suspension cultured cells ofNicotiana plumbaginifolia similarly stained showed very faint, narrow fluorescent strands crossing the walls of sister cells, which may indicate actin associated with individual plasmodesmata, shown in TEM to be sparsely distributed in these walls. In addition, the neck regions of cytochalasin-treated plasmodesmata were greatly enlarged and lacked the normal extracellular ring of particles. We propose that actin associated with plasmodesmata stabilizes the neck region and possibly also the cytoplasmic sleeve, and may be actively involved in regulating cell-to-cell transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01507853
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