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  • 1
    Monographie ausleihbar
    Monographie ausleihbar
    Ottawa : NRC Press
    Signatur: M 15.89279
    Materialart: Monographie ausleihbar
    Seiten: IX, 154 S. , Ill., graph. Darst. , 1 CD-ROM (12 cm) , 28 cm
    ISBN: 9780660197982 , 0660197987
    Sprache: Englisch
    Standort: Kompaktmagazin oben
    Zweigbibliothek: GFZ Bibliothek
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Journal of agricultural and food chemistry 17 (1969), S. 898-899 
    ISSN: 1520-5118
    Quelle: ACS Legacy Archives
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 28 (2005), S. 0 
    ISSN: 1365-3040
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Hypoxia can stimulate the development of a suberized exodermis in aquatic plants; however, its influence on this aspect of terrestrial root development is sparsely documented. To determine the effects of hypoxia on maize (Zea mays cv. Seneca Horizon) roots, seedlings were grown in vermiculite (VERM), aerated hydroponics (AER), stagnant hydroponics with agar (STAG), or aerated hydroponics with agar (AERAG). The endo- and exodermis were examined for wall modifications. Lateral root emergence and aerenchyma formation were documented qualitatively. The endodermal Casparian band formation was unaffected by treatment. Endodermal and exodermal suberin lamella formation was earliest and most extensive in VERM. Suberization, especially in the exodermis of aerated treatments, was depressed in all hydroponic media. In comparison with AER, STAG exodermal lamellae were increased, but endodermal lamellae were decreased. Since the suberized exodermis forms a barrier to radial oxygen loss from roots to the medium, its stimulation in STAG roots (which also developed extensive aerenchyma) would help retain oxygen in the root. The reduction of endodermal lamellae should facilitate oxygen diffusion into the stele. Clearly, the response to environmental conditions is variable within individual cortical cell layers. Additionally, the observed patterns of lamellae, aerenchyma and lateral root development indicate a tight radial co-ordination of root development.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 97 (1996), S. 0 
    ISSN: 1399-3054
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Passage cells frequently occur in the endodermis and exodermis but are not ubiquitous in either layer. Passage cells occur in the form of short cells in the dimorphic type of exodermis. In both layers, Casparian bands are formed in all cells, but the subsequent development of suberin lamellae and thick, cellulosic walls are delayed or absent in the passage cells. Available evidence suggests that passage cells of the endodermis are important for the transfer of calcium and magnesium into the stele and thus into the transpiration stream. They become the only cells which present a plasmalemma surface to the soil solution (and are thus capable of ion uptake) when the epidermis and central cortex die. This occurs naturally in some herbaceous and woody species and is known to be promoted by drought. Most evidence indicates that the development of suberin lamellae in both the endodermis and exodermis increases the resistance of the root to the radial flow of water. Passage cells thus provide areas of low resistance for the movement of water, and the position of these cells in the endodermis (i.e., in close proximity to the xylem) is explained in terms of function. Exodermal passage cells have a cytoplasmic structure suggesting an active role in ion uptake. This may be related to the tendency of the epidermis to die, leaving the passage cells as the only ones with their membranes exposed to the soil solution. Passage cells in the exodermis attract endomycorrhizal fungi while those in the endodermis do not. It is clear that passage cells of the endodermis and exodermis play a variety of roles in the plant root system.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 92 (1994), S. 0 
    ISSN: 1399-3054
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Bulbs of Allium cepa L., which had developed short, adventitious roots, were transferred to various conditions, i.e. vermiculite watered to saturation, vermiculite watered to half saturation, immersed in hydroculture, and immersed in hydroculture except for the proximal 20 mm which was continuously exposed to air. The development of the exodermis occurred in a patchy fashion in many roots but was not influenced by the growing conditions. The vitality of the epidermis declined under all conditions, the rate of decline being inversely related to the ambient moisture level. The differences between the treatments were most evident at the oldest region sampled (120 mm from the root tip) where 4% of the epidermal cells were dead in roots grown in hydroponics. This compared with 62% dead cells in saturated vermiculite, 78% in half-saturated vermiculite and 92% in roots exposed to air. Death of the epidermal cells was not accelerated by the maturation of the underlying exodermis. Epidermal cells which did not overlie a short cell of the exodermis (i.e. were only in contact with long cells) died earlier than the others: this trend was evident even prior to the maturation of the exodermis. These results suggest that the epidermal cells are not well connected symplasmically to the long cells or to the neighbouring epidermal cells. The large majority of epidermal cells (98% of the total) were in contact with a short cell of the exodermis. These epidermal cells tended to die off slowly, even under very favourable ambient conditions. Since these cells provide the major site for ion uptake in roots with a mature exodermis. their death may reduce the efficiency of the root for this activity.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 72 (1988), S. 0 
    ISSN: 1399-3054
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The roots of many angiosperm species possess two Casparian bands, one in the endodermis and one in the outermost layer of the cortex. Over most of the root surface in these species, ions are taken up by the epidermis and may be transported symplastically to the xylem.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Protoplasma 211 (2000), S. 103-115 
    ISSN: 1615-6102
    Schlagwort(e): Allium cepa ; Endodermis ; Exodermis ; Plasmodesmata ; Suberin lamellae ; Transmission electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Onion (Allium cepa L. cv. Ebeneezer) roots from vermiculite culture were examined with transmission electron microscopy to detect the plasmodesmata in all tissues. In young root regions, plasmodesmata linked all living cells together in all directions. In old zones, the plasmodesmatal connections of the endodermis to its neighbor tissues were not interrupted by later suberin lamella and cellulosic wall deposition. Moreover, plasmodesmata in the fully mature endodermis usually exhibited a large central cavity. In the exodermis, however, upon deposition of suberin lamellae in long cells, all plasmodesmata that initially linked them to their adjacent cells were severed. Afterwards, the long cells lost the capability of forming wound pit callose and their protoplasts began to degenerate. The mature exodermal layer was symplastically bridged to its neighbors only by the short (passage) cells that lacked suberin lamellae. Compared to the long cells, the short cells not only had thicker cytoplasm surrounding their central vacuoles but also a higher density of mitochondria and rough endoplasmic reticulum, consistent with an active involvement in the transport processes of the root. The above results were obtained by an improved, extended transmission electron microscopy procedure devised to analyze plasmodesmata in cells with suberin lamellae. By prefixing root tissues in glutaraldehyde and acrolein, all cells were well preserved. Postfixation was carried out in osmium tetroxide at a low concentration (0.5%). Following dehydration in acetone and transfer to propylene oxide, infiltration with Spurr's resin was accomplished by incubating samples in the accelerator-free mixture for 4 days, then infiltrating samples in the accelerator-amended mixture for additional 4 days.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    ISSN: 1615-6102
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Cell walls of mature epidermal and hypodermal cells are autofluorescent when viewed under ultraviolet or blue light. This autofluorescence develops in a centripetal direction, beginning in the outer tangential wall of the epidermis and ending in the inner tangential wall of the hypodermis. The intercellular regions between the epidermis and hypodermis and between the hypodermis and the cortex are dense and also become autofluorescent. Although the walls of the hypodermis provide a barrier to the movement of a high molecular weight fluorescent dye, the walls of the epidermis are permeable. Histochemical studies indicate that lipids and polyphenolics are components of the epidermal and hypodermal cell walls. Both layers are resistant to the wall-degrading enzyme Driselase and to concentrated sulphuric acid, whereas the cortex is digested with both treatments. Observations with the transmission electron microscope show that a complex suberin lamella encases each hypodermal cell but is absent from the epidermis. However, the outer tangential wall and radial walls of the epidermal cells are complex in that layers of different densities are present. Some of these layers, as well as the intercellular regions and the radial walls of the hypodermal cells, bind ferric ions when tissue is fixed in ferric chloride-glutaraldehyde indicating the presence of poly-phenolics in these regions. An extracellular layer covering the outer tangential wall of the epidermis stained positively with a number of histochemical tests for polyphenolics.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Planta 190 (1993), S. 127-136 
    ISSN: 1432-2048
    Schlagwort(e): Casparian band ; Endodermis ; Hydraulic conductivity ; Root pressure ; Wound reaction ; Zea
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The main barriers to the movement of water and ions in young roots of Zea mays were located by observing the effects of wounding various cell layers of the cortex on the roots' hydraulic conductivities and root pressures. These parameters were measured with a root pressure probe. Injury to the epidermis and cortex caused no significant change in hydraulic conductivity and either no change or a slight decline in root pressure. Injury to a small area of the endodermis did not change the hydraulic conductivity but caused an immediate and substantial drop in root pressure. When large areas of epidermis and cortex were removed (15–38% of total root mass), the endodermis was always injured and root pressure fell. The hydraulic conductance of the root increased but only by a factor of 1.2–2.7. The results indicate that the endodermis is the main barrier to the radial movement of ions but not water. The major barrier to water is the membranes and apoplast of all the living tissue. These conclusions were drawn from experiments in which hydrostatic-pressure differences were used to induce water flows across young maize roots which had an immature exodermis and an endodermis with Casparian bands but no suberin lamellae or secondary walls. The different reactions of water and ions to the endodermis can be explained by the huge difference in the permeability of membranes to these substances. A hydrophobic wall barrier such as the Casparian band should have little effect on the movement of water, which permeates membranes and, perhaps, also the Casparian bands easily. However, hydrophobic wall depositions largely prevent the movement of ions. Several hours after wounding the endodermis, root pressure recovered to some extent in most of the experiments, indicating that the wound in the endodermis had been partially healed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Digitale Medien
    Digitale Medien
    Springer
    Planta 189 (1993), S. 288-297 
    ISSN: 1432-2048
    Schlagwort(e): Hydraulic conductivity ; Pit (membrane, hydraulic conductivity) ; Root ; Xylem ; Zea
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The hydraulic conductivity of the lateral walls of early metaxylem vessels (Lpx in m · s−1 · MPa−1) was measured in young, excised roots of maize using a root pressure probe. Values for this parameter were determined by comparing the root hydraulic conductivities before and after steam-ringing a short zone on each root. Killing of living tissue virtually canceled its hydraulic resistance. There were no suberin lamellae present in the endodermis of the roots used. The value of Lpx ranged between 3 · 10−7 and 35 · 10−7 m · s−1 · MPa−1 and was larger than the hydraulic conductivity of the untreated root (Lpr = 0.7 · 10−7 to 4.0 · 10−7 m · s−1 · MPa−1) by factor of 3 to 13. Assuming that all flow through the vessel walls was through the pit membranes, which occupied 14% of the total wall area, an upper limit of the hydraulic conductivity of this structure could be given(Lppm=21 · 10−7 to 250 · 10−7 m · s−1 · MPa−1). The specific hydraulic conductivity (Lpcw) of the wall material of the pit membranes (again an upper limit) ranged from 0.3 · 10−12 to 3.8 · 10−12 m2 · s−1 · MPa−1 and was lower than estimates given in the literature for plant cell walls. From the data, we conclude that the majority of the radial resistance to water movement in the root is contributed by living tissue. However, although the lateral walls of the vessels do not limit the rate of water flow in the intact system, they constitute 8–31% of the total resistance, a value which should not be ignored in a detailed analysis of water flow through roots.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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