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  • 1
    ISSN: 1432-072X
    Keywords: Anabaena ; Cyanobacteria ; Ammonium release ; Photorespiration ; Glycollate pathway
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A release of ammonium by non-nitrogen-fixing Anabaena cylindrica (grown on NH4Cl) in the presence of MSX (methionine sulfoximine) and absence of any external nitrogen source was found. In the light the release was maximal at 0.2 mM MSX, a concentration which did not affect net CO2 fixation nor the glycollate excretion, but inhibited the glutamine synthetase activity and the reassimilation of ammonium. It is suggested that the major source of the ammonium released is the photorespiratory conversion of glycine to serine as (1) the release was stimulated by increase in light intensity, (2) high CO2 (3%) lowered the release, if not given as a longer pretreatment (as CO2 or HCO 3 - ) when a stimulation was observed, (3) glyoxylate and glutamate stimulated the release, the latter compound particularly under nitrogen-deficient conditions and (4) isonicotinic acid hydrazide caused a reduced release of ammonium. Furthermore, a substantial part of the ammonium released by N2-fixing A. cylindrica in presence of MSX may thus originate from the glycollate pathway. The data show that in the light the glycine to serine conversion is active in cyanobacteria with a concomitant production of ammonium which is assimilated by glutamine synthetase.
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  • 2
    ISSN: 1432-2048
    Keywords: Cyanobacteria ; Fe-protein (immuno-gold localization) ; Nitrogenase ; Nitrogen fixation ; Oscillatoria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The filamentous non-heterocystous cyanobacterium Oscillatoria limosa was subjected to Western blot analyses using two antisera raised against the small subunit (Fe-protein) of the nitrogenase complex. Two polypeptides were recognized in nitrogen-fixing cultures irrespective of the antiserum used while no bands were detectable in nitrate-grown cultures. The apparent molecular weights of the two polypeptides were approximately 40.5 and 39.5 kDa respectively, with the former, probably an inactive form, dominating. In situ immunogold electron microscopy was used to reveal the cellular and subcellular localization on the Fe-protein. All cells of the trichomes of nitrogen-fixing O. limosa showed a dense label. The label was homogeneously distributed throughout the cytoplasm including the thylakoid area. Nitrate-grown cultures contained a very low label.
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  • 3
    ISSN: 1432-2048
    Keywords: Anabaena ; C2H2 reduction ; CO2 fixation ; Cyanobacteria ; Glyoxylate ; Nitrogenase Photorespiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Raising the pO2 reduced nitrogenase activity (C2H2 reduction) of Anabaena cylindrica for both glyoxylate-treated (5 mM) and untreated cells. The stimulation caused by glyoxylate, however, increased with increases of pO2 from 2 to 99 kPa. As the pO2 increased the net CO2 fixation was lowered (Warburg effect) while the CO2 compensation point increased. Glyoxylate partly relieved this sensitivity of net photosynthesis to oxygen and reduced the compensation point considerably. The cells used were preincubated in the dark to exhaust photosynthetic pools. A more pronounced reduction in sensitivity of nitrogenase to oxygen for glyoxylate-treated cells was evident when a preincubation in air with reduced pCO2 (13 μl l-1) was used. This was, however, not evident until after a 10-h incubation in air. Before this point 2 kPa O2 sustained the highest nitrogenase activity. Addition of 0.5 and 5 mM of HCO 3 - to Anabaena cultures preincubated at low CO2 levels (29 μl l-1) abolished the stimulatory effect of glyoxylate on the nitrogenase. Thus, the results sustain the suggestion that glyoxylate may act as an inhibitor of photorespiratory activities in cyanobacteria and can be used as a means of increasing their nitrogen and CO2 fixation capacities.
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  • 4
    ISSN: 1432-2048
    Keywords: Ammonium ; Cyanobacteria ; Lichen ; Nitrate ; Nitrogenase ; Photosynthesis (lichens)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Uptake of NH 4 + and NO 3 - by the N2-fixing lichens Peltigera praetextata (two-component lichen) and P. aphthosa (three-component lichen) was studied. In addition, the effects of these ions, separately and in combination, on C2H2 reduction and CO2 exchange were examined. Both NH 4 + and NO 3 - were utilized by the lichens. NH4NO3 caused an increased liberation of NO 3 - from the lichens as compared to the release observed in untreated lichen thalli. NH 4 + and NO 3 - led to reduced C2H2 reduction by P. praetextata, which, however, was less pronounced than when the two ions were given in combination. In P. aphthosa the C2H2 reduction was inhibited by NH 4 + and NH4NO3, but not by NO 3 - alone. NH 4 + and NO 3 - had no effect on the net photosynthesis of P. praetextata, while, in combination, they led to inhibition, although only at a concentration higher than that inhibitory to the C2H2 reduction of P. aphthosa. The photsynthesis was inhibited by all salts, but only initially, probably a “salt effect”. Effects of NH 4 + on the membrane potential of the cyanobiont are suggested as an important factor causing the depression of net photosynthesis.
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  • 5
    ISSN: 1432-2048
    Keywords: Anabaena ; Cyanobacteria ; Glutamine synthetase ; Immuno-gold localization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Localization of glutamine synthetase in thin sections of nitrogen-fixing Anabaena cylindrica was performed using immuno-gold/transmission electronmicroscopy. The enzyme was present in all of the three cell types possible; vegetative cells, heterocysts and akinetes. The specific gold label was always more pronounced in heterocysts compared with vegetative cells, and showed a uniform distribution in all three types. No specific label was associated with subcellular inclusions such as carboxysomes, cyanophycin granules and polyphosphate granules. When anti-glutamine synthetase antiserum was omitted, no label was observed.
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  • 6
    ISSN: 1432-2048
    Keywords: Anabaena ; Azolla ; Cyanobacteria ; Heterocyst ; Nitrogenase localization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Transmission electron microscopy and immunocytological labeling were used to study the distribution and ontological occurrence of dinitrogenase reductase (Fe-protein) of nitrogenase in cyanobacterial symbionts within young leaves of the water-ferns Azolla filiculoides Lamarck, A. caroliniana Willdenow, and A. pinnata R. Brown. Rabbit anti-dinitrogenase reductase antisera and goat anti-rabbit-immunoglobulin G antibody conjugated to colloidal gold were used as probes. Western blot analyses showed that a polypeptide of approx. 36 kDa (kdalton) was recognized in the symbionts of all three Azolla species and that the polyclonal sera used were monospecific. In all symbionts, nitrogenase was immunologically recognizable within heterocysts. It was absent from vegetative cells, and also from the akinetes of the A. caroliniana and A. pinnata symbionts. The differentiation of vegetative cells into heterocysts in all three symbionts was initiated by formation of additional external cell-wall layers and narrowing of the neck followed by loss of glycogen, mild vesiculation of thylakoid membranes, and the appearance of polar nodules. No nitrogenase was detected at these early stages, but it appeared in the intermediate proheterocyst stage concomitantly with the formation of contorted membranes, and reached the strongest labeling in mature heterocysts, containing extensive tightly packed membranes. Nitrogenase was evenly distributed throughout heterocysts except at the polar regions, which contained honey-comb configurations and large polar nodules. With increased age of the A. caroliniana and A. pinnata symbionts, heterocysts became highly vesiculated, with a concomitant decrease in the amount of nitrogenase detected.
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