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  • 1
    Digitale Medien
    Digitale Medien
    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
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-3040.1989.tb01230.x
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  • 2
    Digitale Medien
    Digitale Medien
    Osmoregulation in the euryhaline flagellate Brachiomonas submarina (Chlorophyceae) (1985)
    Springer
    Marine biology 87 (1985), S. 245-250 
    Details
    ISSN: 1432-1793
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00397801
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  • 3
    Digitale Medien
    Digitale Medien
    Utilization of glutamate and glucose for heterotrophic growth by the marine pennate diatom Nitzschia laevis (1978)
    Springer
    Marine biology 47 (1978), S. 1-7 
    Details
    ISSN: 1432-1793
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Nitzschia laevis Hustedt grew in the dark in the presence of either glutamate or glucose as substrate. Complex mixtures of yeast extract or tryptone plus lactate also supported good heterotrophic growth, while tryptone alone only supported very slow growth in the dark. The observed growth rates of N. laevis in the dark at different concentrations of glutamate or glucose could be accounted for by the measured uptake rates of these compounds. The affinity of the uptake systems for glutamate and glucose (K s =0.03 mM for each) was quite high, and similar for dark- and light-grown cells. The lack of a lag-phase when cells were transferred from photoautotrophic to heterotrophic growth conditions can be explained by the presence of uptake systems for glutamate and glucose in ligh--grown cells, as well as in dark-grown cells. However, the uptake capacity was generally higher in the latter than the former. N. laevis also took up alanine and lactate according to Michaelis-Menten kinetics, with a K s for alanine of 0.02 mM and for lactate of 0.4 mM. Malate and glycerol were not taken up to a significant extent by the cells. Cells grown in continous light had a doubling time of 18 h. The shortest doubling time observed in the dark on glutamate was 48 h and on glucose 24 h. Glutamate was used for heterotrophic growth with an efficiency of 43% and glucose with an efficiency of 48%.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00397012
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  • 4
    Digitale Medien
    Digitale Medien
    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
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00391153
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  • 5
    Digitale Medien
    Digitale Medien
    Heterotrophic nutrition of the marine pennate diatom Nitzschia angularis var. affinis (1976)
    Springer
    Marine biology 36 (1976), S. 313-320 
    Details
    ISSN: 1432-1793
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The nutritional pattern for heterotrophic growth of Nitzschia angularis var. affinis (Grun.) Perag. is more complex than for other diatom species studied previously. This species grew slowly in the dark in the presence of single amino acids, either glutamate or alanine; other amino acids when supplied singly were not used as substrates. Carbon from glutamate was converted to cell carbon with an efficiency of 43%. Glutamine was inhibitory both in the light and in the dark, and aspartate inhibited heterotrophic growth on glutamate. Glucose and tryptone supplied singly did not support heterotrophic growth, but when combined, together they allowed for rapid growth of N. angularis (generation time of 16 h). Glucose in combination with glutamate, alanine, aspartate, or asparagine (but not with any other amino acids) also supported growth in the dark, at a rate considerably more rapid than with glutamate alone. In the presence of excess glucose and limiting concentrations of glutamate, approximately 50% of the cell carbon for heterotrophic growth came from glucose, while in combination with tryptone about 25% of the cell carbon came from glucose. Amino acids were taken up by cells grown either photoautrophically or in the dark in the presence or absence of organic substrates; uptake rates were some-what higher for dark-grown than for light-grown cells. Glucose was taken up only by dark-grown cells; induction of a glucose uptake system in the dark required the presence of glutamate but not of glucose. The rates of uptake of glutamate and glucose by cells incubated in the dark with glutamate were sufficiently high to account for the observed rates of growth on these substrates in the dark. The uptake systems of N. angularis have relatively high affinities for glucose (K s =0.03 mM) and glutamate (K s =0.02 mM).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00389192
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  • 6
    Digitale Medien
    Digitale Medien
    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
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00392582
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