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  • 1
    ISSN: 1615-6102
    Keywords: Immunogold labeling ; Iron-superoxide dismutase ; Cyanobiont ; Azolla filiculoides ; Heterocysts ; Nitrogenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Immunogold labeling and transmission electron microscopy were used to localize iron-superoxide dismutase (Fe-SOD) in the different cells of nitrogen-fixing cyanobacterial symbiont present within different leaf cavity groups ofAzolla filiculoides Lam. As evidenced by Western blotting and immunoprecipitation, Fe-SOD antibody fromAnabaena cylindrica recognized Fe-SOD in extracts of the cyanobiont and showed the same electrophoretic mobility and pattern as purifiedA. cylindrica Fe-SOD. In vegetative cells of the cyanobiont, Fe-SOD was mainly localized in the thylakoidal membranes and in the outer membrane. The labeling pattern was similar in vegetative cells of the various groups of leaf cavities examined except at the apex where a lower gold particle density was seen. In heterocysts of the leaf cavity groups containing high nitrogenase activity, Fe-SOD labeling was most pronounced and more intense than in vegetative cells. The Fe-SOD label was preferentially located throughout the heterocyst cytoplasm and in the honeycomb regions. In accordance with the decline in nitrogenase activity, the Fe-SOD gold particle density decreased significantly in heterocysts of basal leaf cavity group. The presence of Fe-SOD in regions of high nitrogenase protein levels, and the fact that the pattern of Fe-SOD label parallels that of nitrogenase activity support a role of Fe-SOD in the protection of nitrogenase against superoxide radicals.
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  • 2
    ISSN: 1615-6102
    Keywords: Cell differentiation ; Immunolocalisation ; Nitrogenase ; Non-heterocystous cyanobacteria ; Trichodesmium ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Trichodesmium is the first described example of a filamentous cyanobacterium without heterocysts that contains cells specialised for nitrogen fixation. The ultrastructure of cells with and without nitrogenase were compared using primarilyTrichodesmium tenue Wille, but alsoT. thiebautii Gomont andT. erythraeum Ehrenberg et Gomont. Immunohistochemistry demonstrated that the cytoplasm of certain cells was densely labelled with antibodies against Fe-protein (dinitrogenase reductase). Comparative TEM-image analysis revealed that these cells were also distinguished by a denser thylakoid network, dividing the vacuole-like space into smaller units. The nitrogenase-containing cells also exhibited less extensive gas vacuoles as well as fewer and smaller cyanophycin granules compared to cells which lacked nitrogenase. Carboxysomes were present in both cell types in equal proportion. Longitudinal sections showed that cells with nitrogenase were arranged adjacent to each other, and that groups of cells with and without nitrogenase may coexist in the same trichome. The correlation between modifications in ultrastructure and the presence of nitrogenase suggests a new type of cyanobacterial cell specialisation related to nitrogen fixation. The results obtained also question the systematic affiliation of the genusTrichodesmium.
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  • 3
    ISSN: 1432-2048
    Keywords: Anabaena ; Chaperonin localization ; GroEL protein ; Nitrogenase ; Ribulose-1,5-bisphosphate carboxylase/oxygenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The occurrence and distribution of a multifunctional chaperonin-60 (cpn60), the GroEL protein, was demonstrated in the cyanobacterium Anabaena PCC 7120 by using a rabbit anti-GroEL (Escherichia coli) antibody. Western-blot analysis showed a distinct cross-reaction with a protein of approx. 65 kilodaltons, analogous to the Mr of the E. coli homologue. Immunocyto-chemical studies of vegetative cells showed that a chaperonin was localized in both vegetative cells and heterocysts. In vegetative cells cpn60 was primarily detected both in the carboxysomes, and in the cytoplasm, though mainly in the thylakoid region of the latter. In heterocysts, specialized cells for nitrogen fixation, the cpn60 label was prominent and was evenly distributed throughout the cell. These results support recent findings that chaperonins are multifunctional proteins, and extend those findings by demonstrating the occurrence of cpn60 in a prokaryotic cyanobacterium and by raising the possibility of the involvement of this chaperonin in the assembly of heterocystous proteins.
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  • 4
    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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  • 5
    ISSN: 1432-2048
    Keywords: Cyanobacterium ; Gunnera ; Heterocyst ; Nitrogenase ; Nostoc ; Symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Developmental patterns related to nitrogen fixation in the heterocystous cyanobacteriumNostoc harboured in distinct colonies along the stem ofGunnera magellanica Lam. plantlets were examined using successive plant sections. Pronounced morphological, physiological and biochemical alterations in the cyanobacterium were demonstrated. Close to the growing apex the cyanobacterial biomass, contained in smallGunnera cells, was low and consisted mostly of vegetative cells showing a high density of different storage structures except for cyanophycin granules. In contrast, both the total and specific nitrogenase activity and the relative nitrogenase protein level were at maximum within this part; while the frequency of heterocysts increased from zero to 30% within the same area. The nitrogenase protein was localized only in the heterocysts throughout the plant. Further down theGunnera stem there was a progressive increase in both the cyanobacterial biomass and the heterocyst frequency, which finally constituted about 60% of the cyanobacterial cell population. Throughout this part of the stem, cyanophycin granules were frequent in the vegetativeNostoc cells. At the base of the stem, degeneratedNostoc cells dominated and the nitrogenase activity was close to zero, although the nitrogenase protein remained. Degeneration of theNostoc cells and leaf shedding coincided. Both intact plants (approx. 20 mm in height) and plant stem sections (2 mm in length) showed substantial nitrogenase activity, although sectioning caused a 30% reduction in total nitrogenase activity.
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  • 6
    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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