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  • Articles  (46)
  • Biology  (46)
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  • Articles  (46)
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  • 1
    Electronic Resource
    Electronic Resource
    POPULATION BIOLOGY OF HIV-1 INFECTION: Viral and CD4+ T Cell Demographics and Dynamics in Lymphatic Tissues (1999)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Immunology 17 (1999), S. 625-656 
    Details
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Human immunodeficiency virus-1 (HIV-1) is usually transmitted through sexual contact and in the very early stages of infection establishes a persistent infection in lymphatic tissues (LT). Virus is produced and stored at this site in a dynamic process that slowly depletes the immune system of CD4+ T cells, setting the stage for AIDS. In this review, I describe the changes in viral and CD4+ T cell populations in LT over the course of infection and after treatment. I present recent evidence that productively infected CD4+ T cells play an important role in establishing persistent infection from the onset, and that the LT are the major reservoir where virus is produced and stored on follicular dendritic cells (FDCs). I discuss the methods used to define the size of viral and CD4+ T cell populations in LT and the nature of virus-host cell interactions in vivo. These experimental approaches have identified populations of latently and chronically infected cells in which virus can elude host defenses, perpetuate infection, and escape eradication by highly active antiretroviral treatment (HAART). I discuss the dramatic impact of HAART on suppressing virus production, reducing the pool of stored virus, and restoring CD4+ T cell populations. I discuss the contributions of thymopoiesis and other renewal mechanisms, lymphatic homeostasis and trafficking to these changes in CD4+ T cell populations in LT, and conclude with a model of immune depletion and repopulation based on the limited regenerative capacity of the adult and the uncompensated losses of productively infected cells that treatment stems. The prediction of this model is that immune regeneration will be slow, variable, and partial. It is nonetheless encouraging to know that even in late stages of infection, control of active replication of HIV-1 provides an opportunity for the immune system to recover from the injuries inflicted by infection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.immunol.17.1.625
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  • 2
    Electronic Resource
    Electronic Resource
    Xylem pressure response in maize roots subjected to osmotic stress: determination of radial reflection coefficients by use of the xylem pressure probe (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 18 (1995), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The absolute pressure in conducting xylem vessels of roots of 2-week-old, slowly transpiring intact maize plants (bathed in nutrition medium) was determined to be +0·024 ± 0·044 MPa using the xylem pressure probe. When the roots were subjected to osmotic stress (NaCI, KCI or sucrose), the xylem pressure decreased immediately and became more negative. However, the response of xylem pressure to osmotic stress was considerably attenuated, indicating that the radial reflection coefficients, σ13 of the maize root for these solutes were rather low (between 0·2 and 0·4 depending on the concentration of the osmoticum). The low values of a, may be caused (partly) by unstirred layer effects. In repeated osmoticum/nutrition regimes a complex pattern of changes in xylem pressure was observed which was apparently linked to the interplay between transpiration and (passive and/or active) solute loading of the xylem. These processes were not observed when the roots were subjected to osmotic stress after excision. In this case, a biphasic response was observed comparable to that found for excised roots using the root pressure probe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1995.tb00599.x
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  • 3
    Electronic Resource
    Electronic Resource
    Xylem water transport: is the available evidence consistent with the cohesion theory? (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 17 (1994), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Since its introduction in the late 19th century, the so-called cohesion theory has become widely accepted as explaining the mechanism of the ascent of sap. According to the cohesion theory, the minimum standing vertical xylem tension gradient should be 0·01 MPa m−1. When transpiration is occurring, frictional resistances are expected to make this gradient considerably steeper. The results of numerous pressure chamber measurements reported in the literature are generally regarded as corroborating the cohesion theory. Nevertheless, several reports of pressure chamber measurements in tall trees appear to be incompatible with predictions of the cohesion theory. Furthermore, the pressure chamber is an indirect method for inferring xylem pressure, which, until recently, has not been validated by comparison against a direct method. The xylem pressure probe provides a means of testing the validity of the pressure chamber and other indirect techniques for estimating xylem pressure. We discuss here the results of concurrent measurements made with the pressure chamber and the xylem pressure probe, particularly recent measurements made at the top of a tall tropical tree during the rainy season. These measurements indicate that the pressure chamber often substantially overestimates the tension previously existing in the xylem, especially in the partially dehydrated tissue of droughted plants. We also discuss other evidence obtained from classical and recent approaches for studying water transport. We conclude that the available evidence derived from a wide range of independent approaches warrants a critical reappraisal of tension-driven water transport as the exclusive mechanism of long-distance water transport in plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1994.tb02015.x
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  • 4
    Electronic Resource
    Electronic Resource
    Simultaneous measurement of water flow velocity and solute transport in xylem and phloem of adult plants of Ricinus communis over a daily time course by nuclear magnetic resonance spectrometry (2001)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 24 (2001), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A new method for simultaneously quantifying rates of flow in xylem and phloem using the FLASH imaging capabilities of nuclear magnetic resonance (NMR) spectrometry was applied in this study. The method has a time resolution of up to 4 min (for the xylem) and was used to measure the velocity of flows in phloem and xylem for periods of several hours to days. For the first time, diurnal time course measurements of flow velocities and apparent volume flows in phloem and xylem in the hypocotyl of 40-d-old Ricinus communis L were obtained. Additional data on gas exchange and the chemical composition of leaves, xylem and phloem sap were used to assess the role of leaves as sinks for xylem sap and sources for phloem. The velocity in the phloem (0·250 ± 0·004 mm s−1) was constant over a full day and not notably affected by the light/dark cycle. Sucrose was loaded into the phloem and transported at night, owing to degradation of starch accumulated during the day. Concentrations of solutes in the phloem were generally less during the night than during the day but varied little within either the day or night. In contrast to the phloem, flow velocities in the xylem were about 1·6-fold higher in the light (0·401 ± 0·004 mm s−1) than in the dark (0·255 ± 0·003 mm s−1) and volume flow varied commensurately. Larger delays were observed in changes to xylem flow velocity with variation in light than in gas exchange. The relative rates of solute transport during day and night were estimated on the basis of relative flow and solute concentrations in xylem and phloem. In general, changes in relative flow rates were compensated for by changes in solute concentration during the daily light/dark cycle. However, the major solutes (K+, NO3−) varied appreciably in relative concentrations. Hence the regulation of loading into transport systems seems to be more important to the overall process of solute transport than do changes in mass flow. Due to transport behaviour, the chemical composition of leaves varied during the day only with regard to starch and soluble carbohydrates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2001.00704.x
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  • 5
    Electronic Resource
    Electronic Resource
    Uptake, subcellular distribution and metabolism of the phospholipid analogue hexadecylphosphocholine in MDCK cells
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Lipids and Lipid Metabolism 1211 (1994), S. 14-22 
    Details
    ISSN: 0005-2760
    Keywords: (Canine) ; Alkylphosphocholine ; Madin-Darby kidney cell ; Metabolism ; Phospholipid analogue ; Uptake
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0005-2760(94)90133-3
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  • 6
    Electronic Resource
    Electronic Resource
    Androgen receptor complex binding in murine skeletal muscle nuclei
    Amsterdam : Elsevier
    Biochemical and Biophysical Research Communications 105 (1982), S. 1554-1560 
    Details
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0006-291X(82)90965-2
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  • 7
    Electronic Resource
    Electronic Resource
    Structure of the invertebrate fauna in salt marshes of the Wadden Sea coast of Schleswig-Holstein influenced by sheep-grazing (1995)
    Springer
    Helgoland marine research 49 (1995), S. 563-589 
    Details
    ISSN: 1438-3888
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Results of investigations on the influence of five different sheep grazing intensities on the invertebrate fauna of two mainland salt marsh sites of the German Wadden Sea coast are presented for the years 1990 and 1991. The investigation of the invertebrate fauna has been carried out since 1989 in thePuccinellia maritima zone, and theFestuca-Puccinellia as well as theFestuca-Armeria zones, with trapping transects arranged along an inundation gradient. Apart from specific biotic effects, grazing causes changes in environmental characteristics. Effects on microclimate comprise higher ranges of variance in soil-surface temperature on grazed sites. Decreasing food resources caused by grazing bring disadvantages to herbivores, the major part of the invertebrate fauna, due to merotope destruction (e. g. inflorescences ofAster tripolium) and the decline of host plant stands (e. g.A. tripolium, Plantago ssp.). Flower visitors and pollen feeding species that depend onA. tripolium have become extinct. Increasing food resources, caused by grazing, lead to higher population densities of a few specialized grass-feeding and surface-grazing invertebrates (e. g.Mayetiola ssp.,Psammotettix putoni, Bledius tricornis). Soil characteristics in the lower salt marsh have not been altered significantly by grazing; hence, the direct effect of grazing and trampling leads to a decrease in population density of many species such asAssiminea grayana, Orchestia gammarellus and collembolans. The biomass and abundance of detritivores and many herbivores increased from 1990 to 1991 on the totally grazed fields, whereas predators diminished in numbers at the same time. A descriptive model is presented, involving grazing, winter temperature, and precipitation as basic factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02368383
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  • 8
    Electronic Resource
    Electronic Resource
    Nuclear-magnetic-resonance imaging of leaves ofMesembryanthemum crystallinum L. plants grown at high salinity (1989)
    Springer
    Planta 178 (1989), S. 524-530 
    Details
    ISSN: 1432-2048
    Keywords: Crassulacean acid metabolism ; Leaf (water binding) ; Mesembryanthemum ; Mesophyll (water binding) ; Nuclear magnetic resonance microscopy ; Water, free and bound
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Differences in water binding were measured in the leaf cells ofMesembryanthemum crystallinum L. plants grown under high-salinity conditions by using nuclear-magnetic-resonance (NMR) imaging. The 7-Tesla proton NMR imaging system yielded a spatial resolution of 20·20·100 μm3. Images recorded with different spin-echo times (4.4 ms to 18 ms) showed that the water concentrations in the bladder cells (located on the upper and lower leaf surface), in the mesophyll cells and in the water-conducting vessels were nearly identical. All of the water in the bladder cells and in the water-conducting vessels was found to be mobile, whilst part of the water in the mesophyll cells was bound. Patches of mesophyll cells could be identified which bound water more strongly than the surrounding mesophyll cells. Optical investigations of leaf cross-sections revealed two types of mesophyll cells of different sizes and chloroplast contents. It is therefore likely that in the small-sized mesophyll cells water is strongly bound. A long-term asymmetric water exchange between the mesophyll cells and the bladder cells during Crassulacean acid metabolism has been described in the literature. The high density of these mesophyll cells in the lower epidermis is a possible cause of this asymmetry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00963822
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  • 9
    Electronic Resource
    Electronic Resource
    Resistivity of Red Blood Cells Against High-Intensity, Short-Duration Electric Field Pulses Induced by Chelating Agents (1999)
    Springer
    The journal of membrane biology 170 (1999), S. 121-133 
    Details
    ISSN: 1432-1424
    Keywords: Key words: Erythrocytes — Deformability — DTPA — Electropermeabilization — Electrodeformation — Electrorotation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract. The interaction of human red blood cells (RBCs) with diethylenetriamine-pentaacetic acid (DTPA) or its Gd-complex (Magnevist, a widely used clinical magnetic resonance contrast agent containing free DTPA ligands) led to the following, obviously interrelated phenomena. (i) Both compounds protected erythrocytes against electrohemolysis in isotonic solutions caused by a high-intensity DC electric field pulse. (ii) The inhibition of electrohemolysis was observed only when cells were electropulsed in low-conductivity solutions. (iii) The uptake of Gd-DTPA by electropulsed RBCs was relatively low. (iv) (Gd-) DTPA reduced markedly deformability of erythrocytes, as revealed by the electrodeformation experiments using high-frequency electric fields. Taken together, the results indicate that (Gd-) DTPA produce stiffer erythrocytes that are more resistant to electric field exposure. The observed effects of the chelating agents on the mechanical properties and the electropermeabilization of RBCs must have an origin in molecular changes of the bilayer or membrane-coupled cytoskeleton, which, in turn, appear to result from an alteration of the ionic equilibrium (e.g., Ca2+ sequestration) in the vicinity of the cell membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002329900542
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  • 10
    Electronic Resource
    Electronic Resource
    Nuclear magnetic resonance microscopy ofAncistrocladus heyneanus (1997)
    Springer
    Protoplasma 198 (1997), S. 210-217 
    Details
    ISSN: 1615-6102
    Keywords: Nuclear magnetic resonance micro-imaging ; Chemical-shift imaging ; Fluorescence microscopy ; Ancistrocladus heyneanus ; Ancistrocladaceae ; Naphthylisoquinoline alkaloids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The tropical lianaAncistrocladus heyneanus, which is known for its biologically active naphthylisoquinoline alkaloids, has been studied by nuclear magnetic resonance (NMR) microscopy for the first time. The spatial resolution of the cross-sectional NMR images was of the order of 20 μm. Quantitative NMR relaxation time images of the root and the shoot show great contrast between different tissue regions. In addition, we observed the regional distribution of chemical compounds inAncistrocladus heyneanus by chemical-shift NMR microscopy. The NMR imaging results were compared with light and fluorescence microscopic images and reveal the excellent tissue characterization using NMR technology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01287570
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