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  • 1
    Electronic Resource
    Electronic Resource
    Sequential extraction procedure for the speciation of particulate trace metals (1979)
    s.l. : American Chemical Society
    Analytical chemistry 51 (1979), S. 844-851 
    Details
    ISSN: 1520-6882
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ac50043a017
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  • 2
    Electronic Resource
    Electronic Resource
    Turgor regulation in the salt-tolerant alga Chara longifolia (2000)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Chara longifolia is a salt-tolerant Charophyte which regulates its turgor inresponse to osmotic stress. Membrane depolarization, in creased membrane conductance, and cessation of cytoplasmic streaming (due to increase in cytoplasmic Ca2+) precede regulation in response to hypotonic stress. Measurements of these three parameters are presented here with simultaneous turgor measurements. Variability in the occurrence, rate and extent of turgor regulation in individual cells was correlated with magnitude of the stress. Hypertonic stress showed the same slow time course as was found previously, requiring several days for complete regulation. Fifty μM nifedipine, a Ca2+ channel blocker, inhibited turgor regulation. In the presence of 5 μM nifedipine, turgor regulation was delayed. An increase in conductance preceded regulation, but membrane depolarization was less and no detectable change in cytoplasmic streaming was observed, requiring modifications to a previously presented model for turgor regulation. There was no significant difference in 45Ca2+ influx under control and stress conditions. However, the control flux was insensitive to nifedipine, whereas under stress the flux is inhibited 54% by nifedipine. We suggest that osmotic stress results in a rapid increase in a nifedipine-sensitive Ca2+ entry mechanism, followed very quickly by a decrease in the control entry mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2000.00571.x
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  • 3
    Electronic Resource
    Electronic Resource
    The effect of divalent cations on Na+ tolerance in Charophytes. II: Chara corallina (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 11 (1988), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The freshwater Charophyte Chora corallina dies when subjected to 70 molm−3 NaCl if the Ca2+ concentration is 0.1 mol m −3. This stress is accompanied by a depolarization of the cell to a membrane potential more positive than EK, a net influx of Na+ into the vacuole, and a net loss of K+ from the vacuole. Raising the Ca2+ concentration to 7 mol m −3 in the presence of elevated Na+ restores the Na+ to Ca2+ ratio to 10: 1 as in the control solution, and results in enhanced survival even though turgor is not regulated. Mg2+ is not a good substitute for Ca2+. It is suggested that the main reason that C. corallina fails to occupy saline habitats is its failure to regulate turgor, not sensitivity to Na +, since the latter is similar to that seen in C. buckellii, which is found in saline habitats.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1988.tb01785.x
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of divalent cations on Na+ tolerance in Charophytes. I: Char a buckellii (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 11 (1988), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract The comparative Na+ tolerance of Chora buckellii cultured in freshwater (FW) or artificial Waldsea water (AWW, which contains about 110 mol m−3 each Na +, Mg2+, Cl− and SO2-4 was tested with respect to the external Na+ to Ca2+ ratio (Na: Ca). Fifty per cent of FW cells subjected to 70 mol m−3 NaCl, which raised Na:Ca from 10: 1 to 700: 1 and the external osmotic pressure from 0.024 to 0.402 MPa, died within 6 d. Death was associated with the loss of Na/K selectivity, H+ -pump activity and turgor. Restoration of Na:Ca to 10:1 in high Na+ medium with CaCl2 ensured 100% survival and maintained H+-pump activity and Na/K selectivity of FW cells. Turgor was regulated within 3 d with net uptake of Na +, K+ and Cl− in the vacuolc. Mg2+ was not as effective as Ca2+ in enhancing survival or maintaining H+ -pump activity and Na/K selectivity of FW cells in the presence of elevated Na+. However, turgor was regulated within 3 d by accumulation of Cl− and an unknown cation in the vacuole. All AWW cells subjected to an increase of 70 mol m −3 NaCl, which raised Na: Ca from 16:1 to 25: 1 and the external osmotic pressure from 0.915 to 1.22 MPa, survived and maintained H + -pump activity. Turgor was regulated within 6d by accumulating Na +, K+ and Cl− in the vacuole. All AWW cells subjected to 70molm−3 NaCl in a medium in which Na:Ca was equal to 700:1 survived and maintained H + -pump activity, but showed loss of Na/K selectivity. Turgor was regulated with an unknown osmoticum(a) within 6 d.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1988.tb01784.x
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  • 5
    Electronic Resource
    Electronic Resource
    The role of calcium in turgor regulation in Chara longifolia (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 salt-tolerant alga Chara longifolia (Robinson) is capable of regulating its turgor in response to hypotonic stress resulting from a decrease in the osmotic pressure of the medium. This regulatory process takes only 40 min in small cells (length ≤ 10 mm), but requires 3d in large cells (length ≥30mm). Turgor regulation in small cells is comprised of two phases, a fast phase reducing the increased turgor by about 25% in the First 5 min, and a second phase reducing the turgor to near the original value within 40 min. The second phase is inhibited by reducing the concentration of Ca2+ in the external medium from 4.6 to 0.01 mol m−3; the first phase is less affected by the reduction of Ca2+. In the first 5 min of stress, the membrane depolarizes in a voltage-dependent fashion, electrical conductance of the membrane increases transiently and cytoplasmic streaming is inhibited. When the external Ca2+ concentration is lowered, conductance does not increase and streaming continues unaffected. In a low ionic strength medium, Ca2+ is not required in the medium for turgor regulation.To test the hypothesis that there is increased Ca2+ entry from the medium during turgor regulation, we measured the influx of 45Ca2+ into the cell. We found an increased influx of Ca2+, from 18 to 36 nmol m−2 s−1 during the first 30 to 90 s following osmotic stress. This increase was evident only in cells below about 7 mm in length, and was more marked in smaller cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1995.tb00346.x
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  • 6
    Electronic Resource
    Electronic Resource
    ATP-driven proton pumping in two species of Chara differing in salt tolerance (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 15 (1992), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Chara corallina is an obligate freshwater alga, while C. buckellii can be grown in salt and freshwater culture. When grown in fresh water, C. buckellii has electrophysiological properties similar to C. corallina, but when cultured in salt water, it has a less negative membrane potential and has a higher conductance. We show in internally perfused, tonoplast-free cells that the ATP-dependence of the two species cultured in fresh water is similar, although C. buckellii hyperpolarizes at lower ATP concentrations. We determined the pump parameters in perfused and intact cells. Using both techniques, C. corallina and C. buckellii cultured in fresh water show similar values of Ep, Gp and Ip. However, there is a significant difference between the two techniques: Ep is more negative (–400 to –700 mV) in perfused cells than in intact cells (–220 to –260mV); Gp is lower (0·1–0·2 versus 0·3–0·9 S m−2); and Ip is higher (40–60 versus 10–18 mA m−2). Salt-cultured C. buckellii was compared with freshwater C. buckellii using intact cells; Gp and Ep were similar, but Ip was much higher in salt-cultured cells (60 versus 15mA m−2). This higher pump rate is due to the depolarization of the membrane of salt-cultured algae, which is caused by a higher passive conductance. The significance of the less negative membrane potential and the higher rate of proton pumping is discussed with respect to the banding pattern and salt stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1992.tb01474.x
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  • 7
    Electronic Resource
    Electronic Resource
    Trace Metal Speciation of USGS Reference Sample MAG-I (1980)
    Oxford, UK : Blackwell Publishing Ltd
    Geostandards and geoanalytical research 4 (1980), S. 0 
    Details
    ISSN: 1751-908X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The USGS reference sample marine mud MAG-1 has been subjected to a sequential extraction procedure designed to partition the constituent trace metals into five fractions: I-exchangeable; II- bound to carbonates; III-bound to Fe-Mn oxides; IV- bound to organic matter; V- residual. The analytical approach involved successive chemical extractions and the subsequent determination of trace metal concentrations (Co, Cu, Ni, Pb, Zn; Fe, Mn) in the leachates by atomic absorption spectrophotometry. The chemical speciation results obtained on four replicate sub-samples demonstrate that the coefficients of variation for metal concentrations in the individual fractions are generally better than + 10%. Comparison with published values for total trace metal concentrations in the MAG-1 sample suggests that the overall accuracy of the chemical extraction procedure is satisfactory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1751-908X.1980.tb00279.x
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  • 8
    Electronic Resource
    Electronic Resource
    Vacuolar and cytoplasmic pH, ion composition, and turgor pressure in Lamprothamnium as a function of external pH (1982)
    Springer
    Planta 155 (1982), S. 287-295 
    Details
    ISSN: 1432-2048
    Keywords: Charophyta ; Ion composition ; Lamprothamnium ; pH (internal) ; Salinity ; Turgor pressure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Ionic responses to alteration in external and internal pH were examined in an organism from a marine-like environment. Vacuolar pH (pHv) is about 4.9–5.1, constant at external pH (pHo) 5–8, while cytoplasmic pH (pHc) increases from 7.3 to 7.7. pHc regulation fails above pHo 9, and this is accompanied by failure of turgor regulation. Na+ increases above pHo 9, while K+ and Cl− decrease. These changes alone cannot however explain the alterations in turgor. Agents known to affect internal pH are also tested for their effect on ion relations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00429453
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  • 9
    Electronic Resource
    Electronic Resource
    Calcium effects on electrogenic pump and passive permeability of the plasma membrane ofChara corallina (1984)
    Springer
    The journal of membrane biology 81 (1984), S. 59-67 
    Details
    ISSN: 1432-1424
    Keywords: Chara ; calcium ; protons ; potassium ; electrogenic pump ; conductance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Removal of Ca2+ from the medium results in depolarization of theChara internodal cell and an increase in membrane conductance (G m). The increase in conductance is associated with an increase in K+ conductance, as judged by Ca2+ effects on the K+ dependence of clamp current. The voltage dependence ofG m is also affected by Ca2+, as is the time course of the response of clamp current to a step change in voltage. Mg2+ restores the low conductance and the fast response to a voltage change, but not hyperpolarization at neutral pH, suggesting that there is an additional, independent effect on the electrogenic pump. The membrane does not show the normal ability to increase proton conductance at high pH in the absence of Ca2+; this is also restored by Mg2+ as well as by Ca2+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868810
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  • 10
    Electronic Resource
    Electronic Resource
    TheChara plasmalemma at high pH. Electrical measurements show rapid specific passive uniport of H+ or OH− (1980)
    Springer
    The journal of membrane biology 56 (1980), S. 1-7 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Above a critical external pH (about 10.5), theChara membrane acquires new propertes. In this state the membrane potential is close to the equilibrium potentials for H+ and OH−, hyperpolarizing as external pH increases with a slope of −59 mV/pH unit. The membrane conductance increases by an average factor of 2.4 above the critical pH. These changes are explained by an increase in permeability to OH− (or H+). The establishment of a OH− (or H+ permeable membrane at high pH suggests that the large fluxes of OH− (or H+ which occur in the alkaline band in photosynthesizing cells are passive.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869346
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