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  • 1
    Electronic Resource
    Electronic Resource
    Differentiation of wound vessel members without DNA synthesis, mitosis or cell division (1975)
    [s.l.] : Nature Publishing Group
    Nature 257 (1975), S. 806-808 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] WVM are highly specialised elements of the xylem which differentiate in parenchyma tissue as a response to wounding. They are characterised by the deposition of a patterned cellulose secondary wall which becomes lignified and remains as a resistant structure when the cell contents undergo autolysis ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/257806a0
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  • 2
    Electronic Resource
    Electronic Resource
    Current perspectives on plasmodesmata: structure and function (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 83 (1991), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Recent studies on plasmodesmata have shown that these important intercellular passages for communication and transport are much more sophisticated in both structure and regulatory abilities than previously imagined. A complex, but not well understood, substructure has been revealed by a variety of increasingly reliable ultrastructural techniques. Proteinaceous particles are seen within the cytoplasmic sleeve surrounding the desmotubule. Dye-coupling studies have provided experimental evidence for the physical pathway of solute movement, supporting conclusions about substructural dimensions within plasmodesmata drawn from the ultrastructural studies. Calcium has been identified as a major factor in the regulation of intercellular communication via plasmodesmata. Evidence from studies on virus movement through plasmodesmata suggests a direct interaction between virallycoded movement proteins and plasmodesmata in the systemic spread of many viruses. There is increasing evidence, albeit indirect, that in some plant species phloem loading may involve transport of photoassimilate entirely within the symplast from mesophyll cells to the sieve element-companion cell complexes of minor veins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1991.tb01301.x
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  • 3
    Electronic Resource
    Electronic Resource
    Raffinose oligosaccharide concentrations measured in individual cell and tissue types in Cucumis melo L. leaves: implications for phloem loading (1996)
    Springer
    Planta 198 (1996), S. 614-622 
    Details
    ISSN: 1432-2048
    Keywords: Cucumis ; Galactinol ; Phloem loading ; Raffinose ; Stachyose ; Sucrose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Raffinose, stachyose, and galactinol are synthesized in intermediary cells (specialized companion cells) of the minor-vein phloem of cucurbits. To better understand the role of these carbohydrates and the regulation of their synthesis and transport, we measured the concentrations of each of the components of the raffinose oligosaccharide synthetic pathway in mesophyll and sieve element-intermediary cell complexes (SE-ICCs) in the leaves of melon (Cucumis melo L. cv. Hale's Best Jumbo). These concentrations are consistent with a polymer-trapping mechanism for phloem loading, with sucrose diffusing from mesophyll into intermediary cells and being made into raffinose and stachyose, which are too large to diffuse back to the mesophyll. To determine carbohydrate concentrations, we developed a method involving microdissected tissues. Blind endings of areoles, and mesophyll surrounding these veins, were separately removed from lyophilized leaf tissue. Carbohydrates were quantitated by high-performance liquid chromatography with pulsed amperometric detection. A small amount of mesophyll remained attached to the blind endings; the carbohydrate contribution of these cells to the vein sample was eliminated by subtraction, based on the amount of chlorophyll. Volumes of cells and subcellular compartments were calculated by morphometric analysis and were used to calculate carbohydrate concentrations. Assuming no subcellular compartmentation, the additive concentration of sugars in the SE-ICCs of minor veins is about 600 mM. Stachyose and raffinose concentrations are about 330 mM and 70 mM, respectively, in SE-ICCs; concentrations of these sugars are much lower in mesophyll (0.2 and 0.1 mM). This is consistent with the view that stachyose and raffinose are unable to pass through the plasmodesmata between intermediary cells and bundle-sheath cells. Sucrose levels appear to be higher in the SE-ICC (about 130mM) than in the mesophyll (about 10 mM), but if compartmentation is taken into account the gradient for sucrose is probably downhill from mesophyll to intermediary cells. Flux through plasmodesmata between the bundle sheath and intermediary cells was calculated and was found to be within the range of values of flux through plasmodesmata reported in the literature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00262649
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  • 4
    Electronic Resource
    Electronic Resource
    Structure of grafted crown-gall teratoma shoots of tobacco: Regulation of transformed cells (1981)
    Springer
    Planta 153 (1981), S. 42-48 
    Details
    ISSN: 1432-2048
    Keywords: Crown gall ; Hyperplasia ; Hypertrophy ; Teratoma ; Nicotiana
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Crown-gall teratomas are tumors of higher plants with an intrinsic capacity for organogenesis. The growth pattern of tobacco (Nicotiana tabacum L.) teratoma shoots, which is highly aberrant in primary tumors, becomes normal when the shoots are grafted to healthy stock plants. However, certain abnormalities commonly persist; tumors form at the graft junctions, leaves are small, apical dominance is incomplete, the stem and proximal region of the leaf midribs swell excessively, and localized eruptions of neoplastic growth occur on the swollen tissue. Swelling of the shoots is primarily the result of cell hypertrophy in the cortex. Neoplastic divisions do not occur as a general rule; they are restricted, with the exception of tumor formation at the graft junctions, to localized eruptions of teratoid growth on the nodes and leaf midribs where cell hypertrophy is most evident. The histology of the apical meristem and histogenesis of primary tissues is normal, even in grossly distorted shoots. Similarly, there is no evidence of unregulated division in the vascular cambium. It is concluded that cell expansion and division are tightly regulated in meristematic regions of teratoma shoots whereas post-meristematic tissue is prone to excessive hypertrophy and eventual initiation of neoplastic cell division.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00385316
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  • 5
    Electronic Resource
    Electronic Resource
    Sugar synthesis and phloem loading in Coleus blumei leaves (1992)
    Springer
    Planta 187 (1992), S. 388-394 
    Details
    ISSN: 1432-2048
    Keywords: Coleus ; Galactinol ; 3-O-methyl glucose ; Phloem loading ; Plasmodesma (transport) ; Raffinose ; Stachyose
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sugar-synthesis and -transport patterns were analyzed in Coleus blumei Benth. leaves to determine where galactinol, raffinose, and stachyose are made and whether phloem loading includes an apoplastic (extracellular) step or occurs entirely within the symplast (plasmodesmata-connected cytoplasm). To clarify the sequence of steps leading to stachyose synthesis, a pulse (15 s) of 14CO2 was given to attached leaves followed by a 5-s to 20-min chase: sucrose was rapidly labeled while galactinol, raffinose and stachyose were labeled more slowly and, within the first few minutes, to approximately the same degree. Leaf tissue was exposed to either 14CO2 or [14C]glucose to identify the sites of synthesis of the different sugars. A 2-min exposure of peeled leaf tissue to [14C]glucose resulted in preferential labeling of the minor veins, as opposed to the mesophyll; galactinol, raffinose and stachyose were more heavily labeled than sucrose in these preparations. In contrast, when leaf tissue was exposed to 14CO2 for 2 min for preferential labeling of the mesophyll, sucrose was more heavily labeled than galactinol, raffinose or stachyose. We conclude that sucrose is synthesized in mesophyll cells while galactinol, raffinose and stachyose are made in the minorvein phloem. Competition experiments were performed to test the possibility that phloem loading involves monosaccharide uptake from the apoplast. Two saturable monosaccharide carriers were identified, one for glucose, galactose and 3-O-methyl glucose, and the other for fructose. Washing the apoplast of peeled leaf pieces with buffer or saturating levels of 3-O-methyl glucose, after providing a pulse of 14CO2, did not inhibit vein loading or change the composition of labeled sugars, and less than 0.5% of the assimilated label was recovered in the incubation medium. These and previous results (Turgeon and Gowan, 1991, Plant Physiol. 94, 1244–1249) indicate that the phloem loading pathway in Coleus is probably symplastic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195663
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  • 6
    Electronic Resource
    Electronic Resource
    Minor vein structure and sugar transport in Arabidopsis thaliana (2000)
    Springer
    Planta 211 (2000), S. 105-111 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Arabidopsis (sucrose transport) – Minor vein – Phloem loading – Plasmodesmata – Raffinose – Sucrose transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Leaf and minor vein structure were studied in Arabidopsis thaliana (L.) Heynh. to gain insight into the mechanism(s) of phloem loading. Vein density (length of veins per unit leaf area) is extremely low. Almost all veins are intimately associated with the mesophyll and are probably involved in loading. In transverse sections of veins there are, on average, two companion cells for each sieve element. Phloem parenchyma cells appear to be specialized for delivery of photoassimilate from the bundle sheath to sieve element-companion cell complexes: they make numerous contacts with the bundle sheath and with companion cells and they have transfer cell wall ingrowths where they are in contact with sieve elements. Plasmodesmatal frequencies are high at interfaces involving phloem parenchyma cells. The plasmodesmata between phloem parenchyma cells and companion cells are structurally distinct in that there are several branches on the phloem parenchyma cell side of the wall and only one branch on the companion cell side. Most of the translocated sugar in A. thaliana is sucrose, but raffinose is also transported. Based on structural evidence, the most likely route of sucrose transport is from bundle sheath to phloem parenchyma cells through plasmodesmata, followed by efflux into the apoplasm across wall ingrowths and carrier-mediated uptake into the sieve element-companion cell complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250000268
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  • 7
    Electronic Resource
    Electronic Resource
    Leaf development and phloem transport in Cucurbita pepo: Maturation of the minor veins (1976)
    Springer
    Planta 129 (1976), S. 265-269 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Young leaves of Cucurbita pepo L. were examined by whole-leaf autoradiography and serial paradermal sections were examined by light microscopy to determine whether commencement of sugar export depends upon the minor vein phloem achieving structural maturity. Maturation of these veins develops progressively from the largest toward the smallest elements with the minor veins in the distal region of the leaf maturing before those in the proximal region. Commencement of sugar export is coincident with maturation of the abaxial phloem of the minor veins delimiting the areoles. The abaxial phloem elements of the larger minor veins, which are probably capable of vein loading too but border only relatively few areoles, mature before export starts. The adaxial phloem surrounding the areoles and the xylem elements, mature in advance of the abaxial phloem and well before the beginning of sugar export. It is therefore considered unlikely that structural development alone directly governs the initiation of export. The results suggest that some other rate controlling step is involved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00398269
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  • 8
    Electronic Resource
    Electronic Resource
    Leaf development and phloem transport in Cucurbita pepo: Carbon economy (1975)
    Springer
    Planta 123 (1975), S. 53-62 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Net photosynthesis, dark respiration and growth for leaf 5 of Cucurbita pepo L. plants grown under controlled conditions were measured and the data used for an assessment of the changes in carbon balance during growth of the leaf through expansion to maturity. The blade is first capable of net CO2 fixation when ca. 8% expanded but the initial rapid growth during this period is sustained almost entirely through imported nutrients. When the growth rate starts to decline rapidly the net photosynthetic capacity of the blade begins to increase. This increase is accompanied by an expansion of the intercellular spaces and by decreasing dark respiration measured at night and in dark periods during the day. The blade becomes completely independent of phloem imported nutrients and begins to export excess photosynthate when the phase of rapid decrease in relative growth rate is almost complete at about 45% expansion. Maximum net photosynthesis of ca. 11 mg CO2 h-1 dm-2 is achieved at 70% expansion. The first detectable synthesis of the transport sugars stachyose and raffinose in the blade coincides with the beginning of intralaminar phloem transport from the tip to the base of the leaf. The synthesis of sucrose, the other major transport sugar, is detectable at all stages of leaf development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00388060
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  • 9
    Electronic Resource
    Electronic Resource
    Leaf development and phloem transport in Cucurbita pepo: Transition from import to export (1973)
    Springer
    Planta 113 (1973), S. 179-191 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The capacity of a growing leaf blade of Cucurbita pepo L. to import 14C-labelled photoassimilate is lost in a basipetal direction. Import into the lamina tip stops when the blade is 10% expanded. Development of the leaf progresses linearly with time and the lamina base stops importing when the blade is 45% expanded. Export capacity also develops basipetally and follows immediately the loss of import capacity, at least in the lamina base. The small amount of material initially exported from the leaf tip is redistributed to the still-importing leaf base, delaying export from the lamina until the blade is 35% expanded. Loss of import capacity by the petiole is both basipetal and dorsoventral. The proximal, adaxial portion of the petiole is the last region to cease importing 14C. Leaves of Beta vulgaris L. and Nicotiana tabacum L. also lose import capacity in a basipetal direction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00388202
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  • 10
    Electronic Resource
    Electronic Resource
    Localization of galactinol, raffinose, and stachyose synthesis in Cucurbita pepo leaves (1992)
    Springer
    Planta 188 (1992), S. 354-361 
    Details
    ISSN: 1432-2048
    Keywords: Cucurbita (stachyose synthesis) ; Galactinol synthase (immunolocalization) ; Phloem loading ; Raffinose ; Stachyose synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The biochemical pathway of stachyose synthesis was localized by immunocytochemical and 14C-labeling techniques in mature Cucurbita pepo L. leaves. Galactinol synthase (GaS; EC 2.4.1.123), the first unique enzyme in this pathway, was immunolocalized within the intermediary cells of minor veins in conventionally fixed and cryo-fixed, resin-embedded sections using polyclonal anti-GaS antibodies and protein A-gold. Intermediary cells are specialized companion cells with extensive symplastic connections to the bundle sheath. Gold particles were not seen over the non-specialized companion cells of larger veins or over intermediary cells in young leaves prior to the sink-source transition. In another approach to localization, radiolabel was measured in isolated mesophyll tissue and whole tissue of leaves that were lyophilized following a 90-s exposure to 14CO2. Mesophyll, obtained by abrasion of the leaf surface, contained labeled sucrose, galactinol, raffinose and stachyose. However, the latter three labeled compounds constituted a smaller proportion of the neutral fraction than in whole-tissue samples, which also contained minor veins. We conclude that synthesis of galactinol, raffinose, and stachyose occurs in both mesophyll and intermediary cells, predominantly the latter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192802
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