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  • 1
    Electronic Resource
    Electronic Resource
    Ultrastructural changes in aging leaves of a light-grown achlorophyllous mutant of barley (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 94 (1995), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The pattern and sequence of cellular degradation during the course of leaf senescence remains obscure and the nature of the trigger that induces cell senescence is unknown. In order to probe the pre-mortem phase of senescence temporal changes in cell ultrastucture were studied in aging leaves of light-grown achlorophyllous Hordeum vulgare L. cv. Dyan mutant seedlings. Electron microscope examination of the ultrastructure of mesophyll cell plastids revealed the absence of ribosomes and a highly disorganized prolamellar body. Both the number and size of plastoglobuli increased with aging and this change coincided with depletion of starch grains and dilation of lamellar membranes. Aging of mesophyll cells occurred coincident with a decline in ribosome content of the cytoplasm and loss of matrix granularity. Loss of ribosomes associated with the outer nuclear envelope membrane and a reduction in chromatin were also apparent. Only after 10 days was there evidence of loss of internal membrane integrity and swelling of mitochondrial cristae. Compartmentation was thus maintained during the aging process with membrane dissolution occurring late in senescence. These results suggest that an inability to produce chlorophyll and carotenoids and form thylakoid stacks due to the absence of plastid ribosomes, contributes to the rapid onset of senescence in light-grown achlorophyllous seedlings. Furthermore, disruption of chloroplast ribosome synthesis/assembly may constitute part of the plastid signal involved in triggering cell senescence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1995.tb00944.x
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  • 2
    Electronic Resource
    Electronic Resource
    Plasmodesmatal frequency in relation to short-distance transport and phloem loading in leaves of barley (Hordeum vulgare). Phloem is not loaded directly from the symplast (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 99 (1997), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: We investigated the phloem loading pathway in barley, by determining plasmodesmatal frequencies at the electron microscope level for both intermediate and small blade bundles of mature barley leaves. Lucifer yellow was injected intercellularly into bundle sheath, vascular parenchyma, and thin-walled sieve tubes. Passage of this symplastically transported dye was monitored with an epifluorescence microscope under blue light. Low plasmodesmatal frequencies endarch to the bundle sheath cells are relatively low for most interfaces terminating at the thin- and thick-walled sieve tubes within this C3 species. Lack of connections between vascular parenchyma and sieve tubes, and low frequencies (0.5% plasmodesmata per μm cell wall interface) of connections between vascular parenchyma and companion cells, as well as the very low frequency of pore-plasmodesmatal connections between companion cells and sieve tubes in small bundles (0.2% plasmodesmata per μm cell wall interface), suggest that the companion cell-sieve tube complex is symplastically isolated from other vascular parenchyma cells in small bundles.The degree of cellular connectivity and the potential isolation of the companion cell-sieve tube complex was determined electrophysiologically, using an electrometer coupled to microcapillary electrodes. The less negative cell potential (average –52 mV) from mesophyll to the vascular parenchyma cells contrasted sharply with the more negative potential (–122.5 mV) recorded for the companion cell-thin-walled sieve tube complex. Although intercellular injection of lucifer yellow clearly demonstrated rapid (0.75 μm s-1) longitudinal and radial transport in the bundle sheath-vascular parenchyma complex, as well as from the bundle sheath through transverse veins to adjacent longitudinal veins, we were neither able to detect nor present unequivocal evidence in support of the symplastic connectivity of the sieve tubes to the vascular parenchyma. Injection of the companion cell-sieve tube complex, did not demonstrate backward connectivity to the bundle sheath.We conclude that the low plasmodesmatal frequencies, coupled with a two-domain electropotential zonation configuration, and the negative transport experiments using lucifer yellow, precludes symplastic phloem loading in barley leaves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1997.tb00547.x
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  • 3
    Electronic Resource
    Electronic Resource
    An investigation of preferential feeding habit in fourAsclepiadaceae by the Aphid,Aphis nerii B. de F. (1977)
    Springer
    Protoplasma 92 (1977), S. 1-19 
    Details
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Penetration of the stems ofAraujia sericofera, Asclepias curassavica, Cynanchum ellipticum andSarcostemma viminale by stylets of the aphidAphis nerii was studied with light and differential interference contrast microscopes. Of a total of 118 stylets and 446 stylet tracks observed in cross-sections of stems of the fourAsclepiadaceae, 97 stylets and 372 stylet tracks terminated within the internal primary phloem. Of the remainder, 15 stylets and 74 tracks terminated within the external primary phloem. 22 stylets and 179 of the stylet tracks penetrated the external phloem on the way to the internal phloem. Of these, only four stylets and 32 of the stylet tracks showed signs of attempted probes of the external phloem. It is suggested thatAphis nerii may obtain not only its essential food requirements but also cardiac glycosides as a basis for chemical aposematism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01280197
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  • 4
    Electronic Resource
    Electronic Resource
    Quantification of symplastic continuity as visualised by plasmodesmograms: diagnostic value for phloem-loading pathways (1992)
    Springer
    Planta 187 (1992), S. 359-366 
    Details
    ISSN: 1432-2048
    Keywords: C3, C4 plants ; Phloem loading (apoplastic, symplastic) ; Plasmodesmatal frequencies ; Plasmodesmogram
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The use of plasmodesmatal frequency to correlate cell-cell symplastic transport capacity remains a contentious problem, as variation in cell shape, accurate determination of interface contact area between cell types, distribution (i.e. whether random or aggregated) and shape (i.e. whether single or branched), and state of permeability may confuse the issue. Additionally, variation in the methods used to determine the frequencies compounds the problem further. Data presented in this paper show that plasmodesmograms offer a means to visualise the potential transport pathway from mesophyll cells to sieve tubes. Furthermore, the results allow an instant appreciation of symplastic continuity or discontinuity and, accordingly, the potential symplastic and-or apoplastic stages involved in the overall loading process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195659
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  • 5
    Electronic Resource
    Electronic Resource
    Plasmodesmatal distribution, structure and frequency in relation to assimilation in C3 and C4 grasses in southern Africa (1992)
    Springer
    Planta 187 (1992), S. 348-358 
    Details
    ISSN: 1432-2048
    Keywords: Grass (C3 C4 types) ; Phloem loading (apoplastic, symplastic) ; Photosynthetic assimilation ; Plasmodesmatal frequency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This paper addresses plasmodesmatal distribution and frequency in the leaf-blade bundles of four southern African grasses — one C3, and one each of the NAPD-malic-enzyme (ME), NAD-ME and phosphoenolpyruvate carboxykinase (PCK) C4 photosynthetic subtypes and, additionally, relates the calculated plasmodesmatal frequencies to the photosynthetic carbon-fixation rate. Plasmodesmata are, in all instances, constricted where they traverse suberin lamellae at the Kranz mesophyll-bundle sheath (KMS-BS), the bundle-sheath-vascular parenchyma (BS-VP), or the bundle-sheath-mestome-sheath interfaces (BS-MS). Frequency studies clearly show that plasmodesmata are most numerous at the KMS-BS, BS-MS and BS-VP interfaces, (31.9–76.8% of the total) and that their numbers decrease rapidly with increasing proximity to both thin- and thickwalled sieve tubes. In Themeda triandra var. imberbis (Retz.) A. Camus and Bromus unioloides H.B.K. thickwalled sieve tubes have few connections with vascular parenchyma cells and are, to all intents and purposes, almost totally isolated from the rest of the vascular tissue, indicating that the loading pathways for these sieve tubes are predominantly apoplastic. Although decreasing plasmodesmatal frequencies indicate that loading of assimilate may become progressively more apoplastic with increasing proximity to the sieve tubes, a symplastic route to the thin-walled sieve tubes cannot be ruled out. Studies of net assimilation rate indicate a good correlation of photosynthetic rate with the photosynthetic type (C3, C4 NADP-ME, C4 PCK, and C4 NAD-ME); furthermore, the lowest plasmodesmatal frequencies were associated with C3, and the highest with C4 NAD-ME types.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195658
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  • 6
    Electronic Resource
    Electronic Resource
    Distribution and frequency of plasmodesmata in relation to photoassimilate pathways and phloem loading in the barley leaf (1996)
    Springer
    Planta 198 (1996), S. 572-579 
    Details
    ISSN: 1432-2048
    Keywords: Hordeum ; Leaf ; Phloem loading and unloading ; Plasmodesmatal frequency ; Sieve tube
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Large, intermediate, and small bundles and contiguous tissues of the leaf blade of Hordeum tvulgare L. ‘Morex’ were examined with the transmission electron microscope to determine their cellular composition and the distribution and frequency of the plasmodesmata between the various cell combinations. Plasmodesmata are abundant at the mesophyll/parenchymatous bundle sheath, parenchymatous bundle sheath/mestome sheath, and mestome sheath/vascular parenchyma cell interfaces. Within the bundles, plasmodesmata are also abundant between vascular parenchyma cells, which occupy most of the interface between the sieve tube-companion cell complexes and the mestome sheath. Other vascular parenchyma cells commonly separate the thick-walled sieve tubes from the sieve tube-companion cell complexes. Plasmodesmatal frequencies between all remaining cell combinations of the vascular tissues are very low, even between the thin-walled sieve tubes and their associated companion cells. Both the sieve tube-companion cell complexes and the thick-walled sieve tubes, which lack companion cells, are virtually isolated symplastically from the rest of the leaf. Data on plamodesmatal frequency between protophloem sieve tubes and other cell types in intermediate and large bundles indicate that they (and their associated companion cells, when present) are also isolated symplastically from the rest of the leaf. Collectively, these data indicate that both phloem loading and unloading in the barley leaf involve apoplastic mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00262644
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  • 7
    Electronic Resource
    Electronic Resource
    Plasmodesmatal distribution and frequency in vascular bundles and contiguous tissues of the leaf ofThemeda triandra (1988)
    Springer
    Planta 173 (1988), S. 433-441 
    Details
    ISSN: 1432-2048
    Keywords: Bundle sheath ; Leaf (plasmodesmata) ; Mesophyll ; Plasmodesmatal frequency ; Srevetubes ; Themeda ; Vascular bundle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Small and intermediate vascular bundles and contiguous tissues of the leaf blade ofThemeda triandra var.imberbis (Retz.) A. Camus were examined with transmission and scanning electron microscopes to determine the distribution and frequency of plasmodesmata between various cell types. Plasmodesmata are most abundant at the mesophyll/bundle-sheath cell and bundle-sheath/vascular parenchyma cell interfaces, and their numbers decrease with increasing proximity to both thick- and thin-walled sieve tubes. Among cells of the vascular bundles, the greatest frequency of plasmodesmata occurs between vascular parenchyma cells, followed by that of plasmodesmata between vascular parenchyma cells and companion cells, and then by the pore-plasmodesmata connections between companion cells and thin-walled sieve tubes (sieve tube-companion cell complexes). The sieve tube-companion cell complexes of theT. triandra leaf are not isolated symplastically from the rest of the leaf and, in this respect, differ from their counterparts in theZea mays leaf. However, the thick-walled sieve tubes, like their counterparts inZea mays, lack companion cells and are symplastically connected with vascular parenchyma cells that about the xylem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00958954
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  • 8
    Electronic Resource
    Electronic Resource
    Studies onArtemisia afra Jacq.: The phloem in stem and leaf (1981)
    Springer
    Protoplasma 109 (1981), S. 217-231 
    Details
    ISSN: 1615-6102
    Keywords: Anatomy ; Artemisia ; Cell wall composition ; Compositae ; Phloem ; Sieve element
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The structure of the phloem was studied in stem and leaf ofArtemisia afra Jacq., with particular attention being given to the sieve element walls. Both primary and secondary sieve elements of stem and midvein have nacreous walls, which persist in mature cells. Histochemical tests indicated that the sieve element wall layers contained some pectin. Sieve element wall layers lack lignin. Sieve elements of the minor veins (secondary and tertiary veins) lack nacreous thickening, although their walls may be relatively thick. These walls and those of contiguous transfer cells are rich in pectic substances. Transfer cell wall ingrowths are more highly developed in tertiary than in secondary veins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01287443
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  • 9
    Electronic Resource
    Electronic Resource
    The suberin lamella, a possible barrier to water movement from the veins to the mesophyll ofThemeda triandra forsk (1982)
    Springer
    Protoplasma 112 (1982), S. 1-8 
    Details
    ISSN: 1615-6102
    Keywords: Apoplastic Barrier ; Bundle sheath ; Grass leaf anatomy ; Prussian blue ; Suberin lamella ; Themeda
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Precipitation of ferrous ions by ferricyanide in transpiring leaves ofThemeda triandra Forsk. produced crystalline deposits, which were visible with the light and electron microscope. Prussian blue crystals were formed within the lumina of the tracheary elements and the apoplast, or cell wall continuum of the vascular tissues and bundle-sheath cells. Little if any deposition was noted within the lignified secondary thickenings of the tracheary elements. The localization pattern suggests that the ferrous ions moved from the lumina of the tracheary elements via the exposed primary walls. Prussian blue crystals were abundant in the outer tangential and radial walls of the bundle-sheath cells. By contrast, crystals were lacking in the walls of neighbouring mesophyll cells, suggesting that the suberin lamella in the bundle-sheath walls effectively inhibited the apoplastic movement of ferrous ions and possibly may impede, or restrict the movement of water across the bundle-sheath/mesophyll interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01280209
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  • 10
    Electronic Resource
    Electronic Resource
    Free-space marker studies on the leaf ofZea mays L. (1985)
    Springer
    Protoplasma 126 (1985), S. 62-73 
    Details
    ISSN: 1615-6102
    Keywords: Zea mays ; Free-space markers ; Grass leaf anatomy ; Lanthanum ; Prussian blue ; Suberin lamella
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Two free-space marker procedures (Prussian blue and lanthanum nitrate) were employed to determine the pathway(s) followed by water and solutes in the transpiration stream after their introduction into the xylem of small and intermediate bundles, and the effectiveness of the suberin lamellae of the bundle-sheath cells as a barrier to the movement of tracer ions (Fe3+ and La3+). Judged from the distribution of Prussian-blue crystals (insoluble, crystalline deposits resulting from the precipitation of ferric ions by ferrocyanide anions) and lanthanum deposits, water and the tracer ions moved readily from the lumina of the vessels into the apoplast (cell wall continuum) of the phloem and bundle-sheath cells via portions of vessel primary walls not bearing lignified secondary wall thickenings. Prussian blue and lanthanum deposits were abundant on the bundlesheath cell side of the bundle sheath/mesophyll interface but few occurred on that of the mesophyll, indicating that the suberin lamella is an effective barrier to apoplastic movement of both ferric and lanthanum ions. The presence of Prussian-blue crystals and lanthanum deposits in the compound middle lamella of the radial wall of the bundle-sheath cells indicates that the compound middle lamella provides an apoplastic pathway for transpirational water from the xylem to the evaporating surfaces of the mesophyll and epidermal cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01287674
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