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  • 1
    Electronic Resource
    Electronic Resource
    Seasonal changes in the ultrastructure of the vascular cambium of Robinia pseudoacacia (1997)
    Springer
    Trees 11 (1997), S. 191-202 
    Details
    ISSN: 0931-1890
    Keywords: Key words Endoplasmic reticulum ; Robinia pseudoacacia ; Storage materials ; Vacuole ; Vascular cambium ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The ultrastructure of the vascular cambium of Robinia pseudoacacia L. was examined in trunk tissues collected over a 2 1/2 year period. During dormancy, fusiform cells are densely cytoplasmic with many small vacuoles and centrally located nuclei. Mitochondria are round to oval in sectional view. The plastids are variable in shape, have few internal membranes, and generally lack starch grains. The plasmalemma is smooth in outline. Proteinaceous material occurs in the vacuoles and many lipid droplets are scattered throughout the ground substance. Smooth tubular ER, often highly dilated, predominates, but short segments of rough ER are also present. Abundant free ribosomes are evenly distributed throughout the ground substance and the dictyosomes are inactive. Microtubules are parietal and have various orientations. During reactivation, the plasmalemma becomes irregular in outline and begins to form invaginations. Concurrently, the proteinaceous material disappears, the vacuoles begin to fuse, polysomes appear, and the dictyosomes begin to produce vesicles. During the period of cambial activity, fusiform cells are highly vacuolate, and the nuclei are centrally located. The mitochondria are round, oval, or elongate. Now the plastids contain phytoferritin, starch grains, or both. Many large invaginations of the plasmalemma intrude into the vacuole, pushing the tonoplast inward and pinching off into the vacuole, which lacks proteinaceous material. Lipid droplets are scarce. Most ER is rough, and ribosomes are generally aggregated as polysomes. Dictyosomes are actively producing vesicles. During the transition to dormancy, the fusiform cells gradually assume the appearance typical of the dormant cambium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009667
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  • 2
    Electronic Resource
    Electronic Resource
    Ultrastructure of cell division in the fusiform cells of the vascular cambium of Robinia pseudoacacia (1997)
    Springer
    Trees 11 (1997), S. 203-215 
    Details
    ISSN: 0931-1890
    Keywords: Key words Cell division ; Cytokinesis ; Fusiform cells ; Mitosis ; Robinia pseudoacacia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The ultrastructure of periclinally dividing fusiform cells was studied in the vascular cambium of Robinia pseudoacacia. Fusiform cell division begins in April at Madison, Wisconsin, when the cambial cells still have many characteristics of a dormant cambium. Soon afterward, the cambial cells acquire the appearance typical of an active cambium. Sequential phases of the microtubule cycle were documented: cortical microtubules bordering the cell wall during interphase, perinuclear microtubules preceding formation of the mitotic spindle, spindle microtubules, and phragmoplast microtubules. A preprophase band of microtubules was not encountered. An extended phragmosome was not encountered in periclinally dividing fusiform cells. During cytokinesis, the phragmosome is represented by a broad cytoplasmic plate which precedes the developing phragmoplast and cell plate as they migrate toward the ends of the cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00009668
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  • 3
    Electronic Resource
    Electronic Resource
    KATHERINE ESAU, 1898-1997 (1998)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Phytopathology 36 (1998), S. 27-40 
    Details
    ISSN: 0066-4286
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.phyto.36.1.27
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  • 4
    Electronic Resource
    Electronic Resource
    Structure and development of the sieve-cell protoplast in leaf veins ofWelwitschia (1973)
    Springer
    Protoplasma 76 (1973), S. 1-21 
    Details
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Tissue of one-year-old leaves ofWelwitschia mirabilis was fixed in glutaraldehyde and postfixed in osmium tetroxide for electron microscopy. Mature sieve cells contain nuclei composed of peripherally-distributed chromatin material and an intact envelope with pores. During sieve-cell development many mitochondria become closely associated spatially with the nucleus. In addition to a nucleus and mitochondria, the mature, plasmalemma-lined sieve cell contains plastids and abundant smooth endoplasmic reticulum, which generally occurs in massive aggregates at the sieve areas. Dictyosomes and ribosomes are lacking and a tonoplast is not discernible in mature sieve cells. P-protein is not present at any stage of development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01279669
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  • 5
    Electronic Resource
    Electronic Resource
    Structure and development of sieve areas in leaf veins ofWelwitschia (1973)
    Springer
    Protoplasma 76 (1973), S. 23-34 
    Details
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The sieve areas inWelwitschia are essentially similar to those of coniferous sieve cells, consisting of groups of plasmalemma-lined pores, which are joined in the middle of the wall by a median cavity. The median cavity contains membranes which apparently are connected with aggregates of endoplasmic reticulum bordering the sieve areas. The median cavity is formed through union of smaller median enlargements, the median nodules, each initially associated with a plasmodesma, during perforation of the young sieve area. Callose platelets are not associated with developing pores. All fully-developed pores were lined with callose. The sieve cells are connected with only one other cell type, the albuminous cell. On the sieve-cell side of the wall these connections are similar to sievearea pores, on the albuminous-cell side to plasmodesmata. These connections are also characterized by median enlargements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01279670
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  • 6
    Electronic Resource
    Electronic Resource
    Ultrastructure of metaphloem sieve elements inZea mays (1975)
    Springer
    Protoplasma 83 (1975), S. 365-388 
    Details
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Metaphloem sieve elements from various parts of the plant body ofZea mays L. were examined with the electron microscope. No qualitative differences were found among sieve elements from sources, sinks, and intermediate regions of the plant. At maturity all sieve elements are lined with a parietal layer of cytoplasm, consisting of a plasmalemma, an anastomosing network of endoplasmic reticulum (ER), occasional stacks of ER, mitochondria, and plastids with protein crystalloids. Many mature sieve elements contained persistent, although apparently degenerated nuclei. In addition, in many mature sieve elements the vacuoles apparently continued to be delimited from the parietal cytoplasm by the tonoplast. In most relatively uninjured sieve elements the plasmalemma-lined sieve-plate pores contained little callose and cytoplasmic components and, hence, were largely unoccluded. P-protein was not encountered in any sieve elements at any stage of development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01418595
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  • 7
    Electronic Resource
    Electronic Resource
    Microautoradiographic studies of phloem loading and transport in the leaf of Zea mays L. (1983)
    Springer
    Planta 159 (1983), S. 193-206 
    Details
    ISSN: 1432-2048
    Keywords: Assimilate transport ; Leaf (14C transport) ; Phloem loading ; Sieve tube ; Vascular bundle ; Zea (14C transport)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Microautoradiographs showed that [14C]sucrose taken up in the xylem of small and intermediate (longitudinal) vascular bundles of Zea mays leaf strips was quickly accumulated by vascular parenchyma cells abutting the vessels. The first sieve tubes to exhibit 14C-labeling during the [14C]sucrose experiments were thick-walled sieve tubes contiguous to the more heavily labeled vascular parenchyma cells. (These two cell types typically have numerous plasmodesmatal connections.) With increasing [14C]sucrose feeding periods, greater proportions of thick- and thin-walled sieve tubes became labeled, but few of the labeled thin-walled sieve tubes were associated with labeled companion cells. (Only the thin-walled sieve tubes are associated with companion cells.) When portions of leaf strips were exposed to 14CO2 for 5 min, the vascular parenchyma cells-regardless of their location in relation to the vessels or sieve tubes-were the most consistently labeled cells of small and intermediate bundles, and label (14C-photosynthate) appeared in a greater proportion of thin-walled sieve tubes than thick-walled sieve tubes. After a 5-min chase with 12CO2, the thin-walled sieve tubes were more heavily labeled than any other cell type of the leaf. After a 10-min chase with 12CO2, the thin-walled sieve tubes were even more heavily labeled. The companion cells generally were less heavily labeled than their associated thin-walled sieve tubes. Although all of the thick-walled sieve tubes were labeled in portions of leaf strips fed 14CO2 for 5 min and given a 10-min 12CO2 chase, only five of 72 vascular bundles below the 14CO2-exposed portions contained labeled thick-walled sieve tubes. Moreover, the few labeled thick-walledsieve tubes of the “transport region” always abutted 14C-labeled vascular parenchyma cells. The results of this study indicate that (1) the vascular parenchyma cells are able to retrieve at least sucrose from the vessels and transfer it to the thick-walled sieve tubes, (2) the thick-walled sieve tubes are not involved in long-distance transport, and (3) the thin-walled sieve tubes are capable themselves of accumulating sucrose and photosynthates from the apoplast, without the companion cells serving as intermediary cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397525
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  • 8
    Electronic Resource
    Electronic Resource
    The cell wall-plasmalemma interface in sieve tubes of barley (1989)
    Springer
    Planta 177 (1989), S. 24-34 
    Details
    ISSN: 1432-2048
    Keywords: Brush border ; Cell wall ; Hordeum (cell wall-plasmalemma interface) ; Leaf veins ; Plasmalemma ; Sieve tubes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Both thick- and thin-walled sieve tubes in leaf-blade veins of Hordeum vulgare L. exhibit a distinct, electron-opaque inner wall layer after fixation in glutaraldehyde-osmium tetroxide and staining with uranyl acetate and lead citrate. This inner wall layer is thickest at the sieve plates and lateral sieve areas where it is permeated by a labyrinth of tubules formed by the plasmalemma. Along the lateral walls between sieve areas the inner wall layer apparently is penetrated by numerous microvilli-like evaginations of the plasmalemma, giving the cell wall-plasmalemma interface the appearance of a brush border. It is suggested that a similar brush-border-like structure may occur at the cell wall-plasmalemma interface of sieve elements in a wide variety of vascular plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392151
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  • 9
    Electronic Resource
    Electronic Resource
    Loading and transport of assimilates in different maize leaf bundles (1989)
    Springer
    Planta 178 (1989), S. 1-9 
    Details
    ISSN: 1432-2048
    Keywords: Leaf (assimilate transport) ; Phloem loading ; Phloem transport ; Sieve tube ; Vascular bundle ; Zea (assimilate transport)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The loading and transport functions of vascular bundles in maize (Zea mays L.) leaf strips were investigated by microautoradiography after application of 14CO2. The concentrations of 14C-contents in thin-walled sieve tubes of individual bundles in the loading and transport regions were determined by digital image analysis of silver-grain density over the sieve tubes and compared. In the loading region, relatively high concentrations of 14C-contents were found in the thin-walled sieve tubes of small bundles and in the small, thin-walled sieve tubes of the intermediate bundles; the concentration of 14C-label in large bundles was very low. In the transport region, at a transport distance of 2 cm, all of the small bundles contained 14C-assimilates, but generally less than the same bundles did in the loading region; by comparison, at that distance intermediate and large bundles contained two-to threefold more 14C-assimilates than the same bundles in the loading region. The lateral transfer of assimilates from smaller to larger bundles via transverse veins could be demonstrated directly in microautoradiographs. A reverse transport from larger to smaller bundles was not found. At a transport distance of 4 cm, all large and intermediate bundles were 14C-labeled, but many of the small bundles were not. Although all longitudinal bundles were able to transport 14C-asimilates longitudinally down the blade, it was the large bundles that were primarily involved with longitudinal transport and the small bundles that were primarily involved with loading.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392520
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  • 10
    Electronic Resource
    Electronic Resource
    Observations on albuminous cells in Pinus (1967)
    Springer
    Planta 78 (1967), S. 93-97 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Albuminous cells were examined in seasonal collections of secondary phloem of Pinus banksiana, P. resinosa and P. strobus. It was determined that the only reliable criterion for the identification of albuminous cells is their conspicuous connections with sieve cells. Discrete bodies, which give positive protein reactions, were encountered in young albuminous cells. These bodies, which have been interpreted as slime bodies, eventually elongate in the cytoplasm and disappear. During periods of high starch content in other parenchymatous elements, albuminous cells may also contain starch.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00406643
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