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  • 1985-1989  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    Operation of contractile vacuoles in the euryhaline green flagellate Chlamydomonas pulsatilla (Chlorophyceae) as a function of salinity (1989)
    Springer
    Marine biology 100 (1989), S. 373-379 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Chlamydomonas pulsatilla Wollenweber, a euryhaline, marine flagellate (isolated from rockpool at St. Andrew's, New Brunswick, Canada in 1980 by J. A. Hellebust), shows decreasing rates of activity of its four contractile vacuoles in the salinity range of 0 to 15% artificial seawater (ASW). Electron microscopy shows that the contractile vacuole complex persists as a spongiome (collection of small vesicles or tubules) in cells grown at salinities above the range for operation of contractile vacuoles. From calculations of rates of water expulsion, based on size and frequency of contraction of individual vacuoles determined by light microscopy, the time necessary to empty one cell volume increased from ca 20 min at 1% ASW to ca 600 min at 15% ASW. Analysis of inorganic and organic solute contents of cells grown at 1 and 5% ASW allowed the calculation of internal osmotic pressures. Estimates of hydraulic conductivities based on rates of water expulsion via contractile vacuoles and differences in internal and external osmotic pressures resulted in values ranging from 1.1 to 1.4×10-14 m s-1 Pa-1 for individual cells. Growth experiments at low photon flux densities over a salinity range of 1 to 15% ASW, over which contractile vacuole activity varied by a factor of 30, showed little difference in growth rates. This indicates that the cost for operation of contractile vacuoles must be very low. The secretion of large molecular weight organic substances does not appear to be associated with the functioning of contractile vacuoles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00391153
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of methionine sulfoximine on growth and nitrogen assimilation of the marine microalga Chlorella autotrophica (1985)
    Springer
    Marine biology 86 (1985), S. 85-91 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Chlorella autotrophica Shihira and Krauss (clone 580), a euryhaline microalga from the marine coastal environment is subject to large fluctuations in external salinity and nitrogen supply. The alga exhibits maximum growth at salinities lower than 100% ASW (artificial seawater). Cells divide faster and show higher cell yields when the supply of either NH 4 + or NO 3 - is increased above 0.2 mM. Cells growing on NH 4 + show high levels of NADPH-glutamate dehydrogenase (GDH) activity, and the levels of glutamine synthetase (GS) are decreased to very low levels under these conditions. Methionine sulfoximine (MSX), an inhibitor of GS, has little effect on cell division and nitrogen assimilation of cells growing on NH 4 + . Cells growing on NO 3 - , however, show marked inhibition (65%) in nitrogen assimilation in the presence of 5 mM MSX. This MSX concentration also causes growth retardation and a progressive decrease in cell protein and nitrogen content. GS is almost completely inhibited by 5 mM MSX in both NH 4 + and NO 3 - -grown cells. Cells growing on NH 4 + maintain high levels of NADPH-GDH activity in the presence of MSX. NADPH-GDH activity in MSX-treated NO 3 - -grown cells increases, and, in the presence of 5 mM MSX, reaches 40% of the level found in NH 4 + -grown cells. These results are consistent with NADPH-GDH providing an alternate pathway for NH 4 + assimilation by this marine Chlorella species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392582
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  • 3
    Electronic Resource
    Electronic Resource
    Osmoregulation in the euryhaline flagellate Brachiomonas submarina (Chlorophyceae) (1985)
    Springer
    Marine biology 87 (1985), S. 245-250 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Brachiomonas submarina Bohlin (Chlorophyceae), a euryhaline marine flagellate, can osmoregulate over a wide range of external salinity. The alga exhibits maximum water content at 100% artificial seawater (ASW), and shows only a small water loss (〈15%) when salinity is increased to 300% ASW. The non-aqueous volume of the cells is increased at salinities higher than 100% ASW. This is partially attributable to the accumulation of glycerol. Glycerol is the major osmoregulatory organic solute in this flagellate. The alga also shows an accumulation of amino acids in response to increased salinity. The contribution of glycerol and amino acids to intracellular osmolarity is only 9% at 10% ASW, but accounts for 49% at 300% ASW. The remainder of the osmotic balance is due to uptake and accumulation of inorganic ions, particularly sodium, potassium and chloride.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00397801
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Regulation of glycerol and starch metabolism in Chlamydomonas pulsatilla in response to changes in salinity (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 12 (1989), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. Chlamydomonas pulsatilla rapidly adjusts its level of osmoregulatory solute, glycerol, when exposed to increased (upshock) or decreased (downshock) salinities. Rates of degradation, or loss, of glycerol are similar in light and dark, while rates of net synthesis proceed about 20% faster in the light than in the dark. Synthesis of glycerol in the dark is correlated with degradation of starch, and starch appears also to be utilized for glycerol synthesis in response to extensive salinity upshocks in the light, where photosynthesis is strongly inhibited. Under conditions of moderate upshocks in the light, photosynthesis is not affected, and net increases in both glycerol and starch were observed. Glycerol turnover takes place both under iso-osmotic conditions, and during period of adjustments to osmotic downshocks, where there is a rapid net decrease in the glycerol pool. Half times for glycerol turnover were estimated from rates of incorporation of photoassimilated 14C into glycerol and glycerol pool sizes to be 20 and 74 min for cells incubated at 50 and 100% artificial seawater, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1989.tb01230.x
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