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  • Articles: DFG German National Licenses  (3)
  • High tropical mountains  (2)
  • 3H Thymidine incorporation  (1)
  • Brain lesions  (1)
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  • Articles: DFG German National Licenses  (3)
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Years
  • 1
    ISSN: 1432-1939
    Keywords: Cold resistance mechanisms ; Supercooling ; Life forms ; High tropical mountains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Freezing tolerance and avoidance were studied in several different sized species of the tropical high Andes (4200 m) to determine whether there was a relationship between plant height and cold resistance mechanisms. Freezing injury and supercooling capacity were determined in ground level plants (i.e. cushions, small rosettes and a perennial herb), intermediate height plants (shrubs and perennial herbs) and arborescent forms (i.e. giant rosettes and small trees). All ground-level plants showed tolerance as the main mechanism of resistance to cold temperatures. Arborescent forms showed avoidance mechanisms mainly through supercooling, while intermediate plants exhibited both. Insulation mechanisms to avoid low temperatures were present in the two extreme life-forms. We suggest that a combination of freezing tolerance and avoidance by insulation is least expensive and is a more secure mechanism for high tropical mountain plants than supercooling alone.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 75 (1988), S. 156-160 
    ISSN: 1432-1939
    Keywords: Draba chionophila ; Freezing tolerance ; Cold resistance ; High tropical mountains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Freezing tolerance as a cold resistance mechanism is described for the first time in a plant growing in the tropical range of the Andean high mountains. Draba chionophila, the plant in which freezing tolerance was found, is the vascular plant which reaches the highest altitudes in the Venezuelan Andes (approximately 4700m). Night cycles of air and leaf temperature were studied in the field to determine the temperature at which leaf freezing began. In the laboratory, thermal analysis and freezing injury determinations were also carried out. From both field and laboratory experiments, it was determined that freezing of the leaf tissue, as well as root and pith tissue, initiated at a temperature of approximately-5.0°C, while freezing injury occurred at approximately-12.0°C for the pith, and below-14.0°C for roots and leaves. This difference in temperature suggests that the plant still survives freezing in the-5.0 to-14.0°C range. Daily cycles of leaf osmotic potential and soluble carbohydrate concentration were also determined in an attempt to explain some of the changes occurring in this species during the nighttime temperature period. A comparison between Andean and African high mountain plants from the point of view of cold resistance mechanisms is made.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 242 (1985), S. 17-23 
    ISSN: 1432-0878
    Keywords: Brain lesions ; 3H Thymidine incorporation ; Astrocytes ; Monocytes/Macrophages ; Capillaries ; Ischemia ; Mongolian gerbil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Tritiated thymidine autoradiography was used to measure cellular proliferation after ischemic injury in gerbil brain. Gerbils were subjected to bilateral occlusion of the common carotid arteries which resulted in areas of necrosis, or infarcts, in the posterior thalamus or midbrain. From 12 h to 10 days following the ischemia, gerbils were injected with 3H thymidine, sacrificed 4 h later, and the brains sectioned. In order to identify astrocytes and monocytes/macrophages, immunocytochemistry was performed prior to autoradiography, using antisera against glial fibrillary acidic protein and endothelial-monocyte reticuloendothelial antigen, respectively. Immunocytochemistry was also used to visualize microvessel laminin, myelin, and leakage of serum albumin. Lastly, a histochemical procedure for acid phosphatase activity was employed to verify cellular phagocytic activity in the wound. A reproducible sequence of reactions took place during the first 10 days after ischemia. Early changes included leakage of albumin and myelin breakdown, followed by arrival of monocytes at 2 days and their differentiation into macrophages by 5 days. These cells exhibited intense proliferation from 2 to 6 days post-ischemia. Microvessel endothelial cells were maximally labeled at 4 days post-ischemia. Hypertrophied astrocytes were apparent at 2 days and proliferated from 3 to 7 days post-ischemia, and by 10 days the wound was replaced by a “glial scar”.
    Type of Medium: Electronic Resource
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