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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 109 (1981), S. 317-334 
    ISSN: 1615-6102
    Keywords: Acid phosphatase ; Cellular necrosis ; Cytochemistry ; Grafting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In order to elucidate the events that lead to cellular autolysis, and thus better understand the mechanism of cellular incompatibility betweenSedum telephoides andSolanum pennellii stems, we have followed the appearance and fate of the hydrolytic enzyme acid phosphatase in both the compatibleSedum autograft and the incompatibleSedum/Solanum heterograft. Acid phosphatase was localized by a modified Gomori-type reaction. Following an initial association with the endoplasmic reticulum and dictyosomes by 6–10 hours after grafting, acid phosphatase activity in the compatibleSedum autograft was associated primarily with the plasmalemma, tonoplast, and vacuole. This strict compartmentation in membranes or organelles and absence of enzyme from the cytosol was maintained throughout the development of the compatible autograft inSedum. Although acid phosphatase activity in the incompatible heterograft betweenSedum andSolanum was initially similar to the compatible autograft inSedum, a marked difference in enzyme localization occurred in the two graft partners over time.Solanum cells accumulated increased amounts of acid phosphatase, but the enzyme remained sequestered in the plasmalemma, tonoplast, and vacuole. In comparableSedum cells, however, there was a dramatic increase in acid phosphatase activity in the cytosol, often without any prior compartmentation within the vacuole. This high activity of acid phosphatase in theSedum cytosol was correlated with cellular autolysis, death, and eventual cell collapse to form the characteristic necrotic layer that insulates the stock from the scion. These results suggest that the lethal cellular senescence associated withSedum cells of the incompatible heterograft is correlated with a cytoplasmic release of acid phosphatase. A similar release of the enzyme does not occur in theSolanum stock or in the compatibleSedum autograft. Thus, while acid phosphatase synthesis and/or activation is induced in both the compatible and incompatible grafts, incompatibility betweenSedum andSolanum involves a failure ofSedum cells to isolate hydrolytic enzymes from the cytosol, which subsequently leads to cellular necrosis.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Protoplasma 115 (1983), S. 114-121 
    ISSN: 1615-6102
    Keywords: Compatibility ; Grafting ; Incompatibility ; Sedum telephoides ; Solanum pennellii ; Tissue culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In order to determine whether graft incompatibility betweenSedum telephoides andSolanum pennellii required a prior wounding of tissues, we monitored the cellular events that occurred during grafting of intact (i.e., non-wounded) surfaces ofSedum andSolanum callus tissuein vitro. The only cytological events that occurred in response to autografting ofSedum callusin vitro were (1) dilation of the endoplasmic reticulum in cells adjacent to the graft interface, and (2) the formation of a conspicuously thickened cell wall between the grafted cells. The only cytological event that occurred in callus cells ofSolanum that were heterografted to callus cells ofSedum was a slightly reduced staining intensity of the cytoplasm.Sedum cells of the heterograft, on the other hand, underwent a progressive cellular necrosis when grafted toSolanum in vitro. These results indicate that (1) a prior wounding of tissues is not necessary to elicit the incompatibility response betweenSedum andSolanum, although the wounding induced from an initial graft incision acts to exaggerate and accelerate incompatibility, and (2) graft incompatibility betweenSedum andSolanum occursin vitro between callus cells as it doesin vivo between stems. Thus, the incompatibility factor is probably a normal component of the ground tissue and not the exclusive product of more highly differentiated tissues. Finally, the mechanism of autografting of non-wounded callus cells is compared to the known mechanism of postgenital tissue fusions.
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  • 3
    ISSN: 1432-2048
    Keywords: Catharanthus (Vinca) ; Differentiation ; Epidermis ; Morphogen, diffusible ; Postgenital fusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract During postgenital fusion of the distal adaxial surfaces of the two originally separate carpel primordia of Catharanthus roseus (L.) G. Don, approx. 400 epidermal cells undergo rapid dedifferentiation into parenchymatous cells. To characterize the mechanism of the induction of dedifferentiation, various types of both water-permeable and water-impermeable barriers were placed between pre-fusion carpels. Barriers which did not allow the passage of water-soluble agents blocked dedifferentiation. Barriers which allowed passage of water-soluble agents did not block dedifferentiation of the contacting epidermal cells, implicating a diffusible agent or “morphogen” as the factor responsible for dedifferentiation. Experiments with barriers of known pore size demonstrated that the molecular weight of this morphogen was less than 1000. The two cell walls and thin cuticle present at the site of this postgenital fusion do not block the movement of some substances between the fusing carpels. Tracer studies with tritium-labeled asparagine confirmed that substances can be transported across the fusion plane.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 5415-5422 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The time-dependent behavior of above-all-band-edges resonant propagating structures is presented. The results obtained are compared to those for the extensively studied double-barrier resonant tunneling structure for reference. It was found that for structures with the same resonant energies and resonance widths, the time-dependent characteristics are very similar. The structures were compared using two analytic approaches. The first is based on linear systems theory and the second on a finite-differences approach. It was found that for both structures, the quasibound state builds up at a rate determined by the parameters of the incident packet and decays with a time constant which corresponds to the lifetime.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 1983-04-22
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
    Publication Date: 2012-01-11
    Description: We assess the impact of transport of pollution from midlatitudes on the abundance of ozone in the Arctic in summer 2006 using the GEOS-Chem global chemical transport model and its adjoint. We find that although the impact of midlatitude emissions on ozone abundances in the Arctic is at a maximum in fall and winter, in July transport from North America, Asia, and Europe together contributed about 25% of surface ozone abundances in the Arctic. Throughout the summer, the dominant source of ozone in the Arctic troposphere was photochemical production within the Arctic, which accounted for more than 50% of the ozone in the Arctic boundary layer and as much as 30%–40% of the ozone in the middle troposphere. An adjoint sensitivity analysis of the impact of NOx emissions on ozone at Alert shows that on synoptic time scales in both the lower and middle troposphere, ozone abundances are more sensitive to emissions between 50°N and 70°N, with important influences from anthropogenic, biomass burning, soil, and lightning sources. Although local surface NOx emissions contribute to ozone formation, transport of NOx in the form of peroxyacetyl nitrate (PAN) from outside the Arctic and from the upper troposphere also contributed to ozone production in the lower troposphere. We find that in late May and June the release of NOx from PAN decomposition accounted for 93% and 55% of ozone production at the Arctic surface, respectively.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Publication Date: 1970-06-01
    Print ISSN: 0044-0604
    Electronic ISSN: 2041-4811
    Topics: Geosciences
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