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  • 1
    Electronic Resource
    Electronic Resource
    Thymopoietin, a Thymic Polypeptide, Specifically Interacts at Neuronal Nicotinic α-Bungarotoxin Receptors (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 53 (1989), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: α-Bungarotoxin (α-BGT), a snake venom polypeptide, interacts potently and specifically with a nicotinic receptor population in neuronal tissue. However, the identity of this site is unclear, because, unlike at the neuromuscular junction and in electroplax, in nervous tissue the toxin does not block nicotinic cholinergic responses. Therefore, we sought endogenous compounds other than acetylcholine that could interact with the neuronal α-BGT site. In the present experiments, thymopoietin, a polypeptide isolated from the thymus, is shown to inhibit potently α-BGT binding to brain membranes in a dose-dependent manner (IC50= 3.1 nM). This effect was not shared by a wide variety of other peptides, including thysplenin, a closely related polypeptide. Thymopoietin did not inhibit the binding of other radioligands known to interact with different populations of cholinergic receptors, such as [3H]nicotine and [3H]methylcarbachol, which bind to nicotinic receptors, or [3H]quinuclidinylbenzilate, which binds to muscarinic receptors. These results show that thymopoietin potently and specifically affects l25I-α-BGT binding to brain membranes and suggest that thymopoietin might be an endogenous ligand for α-BGT receptors in neuronal tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1989.tb07431.x
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  • 2
    Electronic Resource
    Electronic Resource
    Specialized Properties and Solute Transport in Brain Capillaries (1986)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 48 (1986), S. 241-250 
    Details
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.ph.48.030186.001325
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  • 3
    Electronic Resource
    Electronic Resource
    Freezing avoidance in Andean giant rosette plants (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 8 (1985), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Frost avoidance mechanisms were studied in Espeletia spicata and Espeletia timotensis, two Andean giant rosette species. The daily courses of soil, air and tissue temperatures were measured at a site at circa 4000 m. Only the leaves were exposed to subzero temperatures; the apical bud and stem pith tissues were insulated by surrounding tissues. The leaf tissues avoided freezing by supercooling rather than by undergoing active osmotic changes. The temperatures at which ice formed in the tissues (the supercooling points) coincided with injury temperatures indicating that Espeletia tissue does not tolerate any kind of ice formation. For insulated tissue (apical bud, stem pith, roots) the supercooling point was around - 5°C coinciding with the injury temperature. Supercooling points of about –13 to - 16°C were observed for leaves. These results contrast with those reported for Afroalpine giant rosettes which tolerate extracellular freezing. The significance of different adaptive responses of giant rosettes to similar cold tropical environments is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1985.tb01685.x
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  • 4
    Electronic Resource
    Electronic Resource
    Thymopoietin: A Marker of the Human Nicotinic Acetylcholine Receptor (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 540 (1988), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1988.tb27080.x
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  • 5
    Electronic Resource
    Electronic Resource
    Gas exchange and water balance of a mistletoe species and its mangrove hosts (1989)
    Springer
    Oecologia 78 (1989), S. 176-183 
    Details
    ISSN: 1432-1939
    Keywords: Mistletoes ; Mangrove trees ; Gas exchange ; Water relations ; Carbon isotope ratios
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The gas exchange and water relations of the hemiparasite Pthirusa maritima and two its mangrove host species, Conocarpus erectus and Coccoloba uvifera, were studied in an intertidal zone of the Venezuelan coast. Carbon uptake and transpiration, leaf osmotic and total water potential, as well as nutrient content in the xylem sap and leaves of mistletoes and hosts were followed through the dry and wet season. In addition, carbon isotope ratios of leaf tissue were measured to further evaluate water use efficiency. Under similar light and humidity conditions, mistletoes had higher transpiration rates, lower leaf water potentials, and lower water use efficiencies than their hosts. Potassium content was much higher in mistletoes than in host leaves, but mineral nutrient content in the xylem sap of mistletoes was relatively low. The resistance of the liquid pathway from the soil to the leaf surface of mistletoes was larger than the total liquid flow resistance of host plants. Differences in the daily cycles of osmotic potential of the xylem sap also indicate the existence of a high resistance pathway along the vascular connection between the parasite pathway along the vascular connection between the parasite and its host. P. maritima mistletoes adjust to the different physiological characteristics of the host species which it parasitizes, thus ensuring an adequate water and carbon balance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00377153
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  • 6
    Electronic Resource
    Electronic Resource
    Morphological changes along an altitude gradient and their consequences for an andean giant rosette plant (1985)
    Springer
    Oecologia 67 (1985), S. 601-601 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00790036
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  • 7
    Electronic Resource
    Electronic Resource
    Cold hardiness and supercooling along an altitudinal gradient in andean giant rosette species (1985)
    Springer
    Oecologia 68 (1985), S. 147-152 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Factors affecting supercooling capacity and cold hardiness were investigated in leaves of ten giant rosette species of the genus Espeletia (Compositae). These species grow along a 2,800–4,200 m elevation gradient in the Venezuelan Andes. In this high tropical environment, freezing frequently occurs every night, particularly above 3,300 m, but lasts for only a few hours. Supercooling capacty is linearly related to leaf water potential (Ψ L ) in all species; however supercooling is more responsive to Ψ L changes in Espeletia species from high paramos. The rate of change in the species-specific supercooling point and the rate of change of average annual minimum temperature along the elevation and climatic gradient follow the same trend (approximately -0.6 K per 100 m elevation). At a given elevation, the expanded leaves of the different species tend to supercool 8–10 K below minimum air temperatures. Experimentally-induced freezing was accompanied by the formation of intracellular ice and tissue damage. The relative apoplastic water content (RAWC) of the leaves, which may influence the ice nucleation rate or the facility by which ice propagates, was determined by pressure-volume methods. Species from higher sites tend to exhibit lower RAWC (2%–7%) than species from lower sites (7%–36%). A causal relationship between supercooling capacity and RAWC is suggested. In the high tropical Andes, the temperature oxotherm plateau of Espeletia leaves seems to be sufficiently fow to avoid freezing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379487
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  • 8
    Electronic Resource
    Electronic Resource
    Morphological changes along an altitude gradient and their consequences for an andean giant rosette plant (1985)
    Springer
    Oecologia 65 (1985), S. 278-283 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Selected morphological features were measured in five populations of the giant rosette plant Espeletia schultzii occurring along an elevation gradient from 2600 to 4200 m in the Venezuelan Andes. Pith volume per amount of leaf area increases with elevation resulting in significantly larger water storage capacity at higher elevations. Thickness of leaf pubescence and, therefore, leaf boundary layer resistance, also increases with elevation resulting in both potentially higher leaf temperatures relative to air temperature and higher leaf to air vapor pressure gradients. The net effect on transpiration rate would depend on ratios of stomatal to boundary layer resistance and leaf energy balance. At higher elevations the central rosette leaves are more vertically oriented and the leaf bases show a pronounced curvature as the intersection with the main axis is approached. This gives these rosettes a distinctly paraboloid appearance and probably enhances capture and retention of incident long and shortwave radiation by the apical bud and expanding leaves. Features which result in enhanced water storage capacity and higher plant temperatures relative to air temperature without greatly increasing water loss are adaptive in high altitude paramo habitats where water availability and growth are limited by year round low temperatures (mean 2–3° C).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379230
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  • 9
    Electronic Resource
    Electronic Resource
    Freezing tolerance in Draba chionophila, a ‘miniature’ caulescent rosette species (1988)
    Springer
    Oecologia 75 (1988), S. 156-160 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00378830
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  • 10
    Electronic Resource
    Electronic Resource
    Phosotynthesis in hemiepiphytic species of Clusia and Ficus (1987)
    Springer
    Oecologia 74 (1987), S. 339-346 
    Details
    ISSN: 1432-1939
    Keywords: Clusia ; Ficus ; Strangler ; CAM ; Photosynthesis ; Hemiepiphyte
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Hemiepiphytic species in the genera Clusia and Ficus were investigated to study their mode of photosynthetic metabolism when growing under natural conditions. Despite growing sympatrically in many areas and having the same growth habit, some Clusia species show Crassulacean acid metabolism (CAM) whereas all species of Ficus investigated are C3. This conclusion is based on diurnal CO2 fixation patterns, diurnal stomatal conductances, diurnal titratable acidity fluctuations, and δ13C isotope ratios. Clusia minor, growing in the savannas adjacent to Barinas, Venezuela, shows all aspects of Crassulacean acid metabolism (CAM) on the basis of nocturnal gas exchange, stomatal conductance, total titratable acidity, and carbon isotope composition when measured during the dry season (February 1986). During the wet season (June 1986), the plants shifted to C3-type gas exchange with all CO2 uptake occurring during the daylight hours. The carbon isotope composition of new growth was-28 to-29‰ typical of C3 plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00378927
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