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  • Articles  (204)
  • Nitrogen fixation
  • Springer  (204)
  • 2005-2009
  • 1990-1994  (88)
  • 1980-1984  (116)
  • 1965-1969
  • 1925-1929
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Biology and fertility of soils 18 (1994), S. 231-236 
    ISSN: 1432-0789
    Keywords: A-value ; Bradyrhizobium ; Genotype ; Growth stage ; 15N ; Nitrogen fixation ; Nodulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract TheA-value method, involving the application of a higher15N rate to a reference non-N2-fixing plant, was used to assess the magnitude of N2 fixation in two bambara groundnut cultivars at four growth stages [vegetative, 0–47 days after planting (DAP); early pod-filling, 47–99 DAP; mid-pod-filling, 99–120 DAP; physiological maturity, 120–148 DAP). The cultivars were Ex-Ada, a bunchy type, and CS-88-11, a slightly spreading type. They were grown on a loamy sand. Uninoculated Ex-Ada and CS-88-11 were used as reference plants to measure the N2 fixed in the inoculated bambara groundnuts. In this greenhouse study, soil was the major source of N in bambara groundnuts during vegetative growth, and during this period it accounted for over 80% of the N accumulaed in the plants. However, N2 fixation became the major source of plant N during reproductive growth. There were significant differences between the two cultivars in the ability to fix N2, and at physiological maturity, almost 75% of the N in CS-88-11 was derived from the atmosphere compared to 55% in Ex-Ada. Also, the total N fixed in CS-88-11 at physiological maturity was almost double that in Ex-Ada. Our data indicate that the higher N2 fixation in CS-88-11 was due to two factors, a higher intensity of N2 fixation and a longer active period of N2 fixation. The results also suggest that bambara groundnut genotypes could be selected for higher N2 fixation in farining systems.
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  • 2
    ISSN: 1432-0789
    Keywords: Acacia mangium ; Acacia auriculiformis ; Bradyrhizobium spp. ; Rhizobium spp. ; Nitrogen fixation ; Nodule efficiency ; Tree legumes ; Agroforestry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Two Australian Acacia species, A. mangium and A. auriculiformis were inoculated in vitro with eight strains of Bradyrhizobium spp. and two strains of Rhizobium spp. On the two plant species, only Bradyrhizobium spp. strains formed effective N2-fixing nodules. A. mangium, which nodulates effectively with a restricted range of Bradyrhizobium spp. strains, is a specific host compared to A. auriculiformis. A. auriculiformis is assumed to be a promiscuous host because it nodulates effectively with a wide range of Bradyrhizobium spp. strains. Nodule efficiency as expressed by the ratio of N2 fixed to nodule dry weight appeared to be higher in A. auriculiformis (0.44–0.81) than in A. mangium (0.23–0.55).
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  • 3
    ISSN: 1432-0789
    Keywords: Nitrogen fixation ; Atriplex spp. ; Root-associated diazotrops ; Acetylene reduction assy (ARA) ; Saline sodic soils ; Enterobacter agglomerans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary TwoAtriplex spp. growing in low-fertility saline sodic soils were assayed for root-associated nitrogenase activity. The excised washed and unwashed root of the two species.A. lentiformis andA. amnicola, showed high root-associated nitrogenase activity. Acetylene-reducing activity seemed to be directly influenced by moisture. The highest number of diazotrophs, enumerated using a most probable number technique was observed on the root surface. Most of the isolated diazotrophs were identified asEnterobacter agglomerans. Root-associated nitrogenase activity inAtriplex spp. may explain the high protein and biomass content of these plants growing in low-fertility saline sodic soils.
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  • 4
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    Journal of molecular evolution 21 (1984), S. 19-32 
    ISSN: 1432-1432
    Keywords: Leghemoglobin ; Gene duplication ; Gene linkage ; Concerted evolution ; Nitrogen fixation ; Soybean
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have analyzed the sequences of soybean leghemoglobin genes as an initial step toward understanding their mode of evolution. Alignment of the sequences of plant globin genes with those of animals reveals that (i) based on the proportion of nucleotide substitutions that have occurred at the first, second, and third codon positions, the time of divergence of plant and animal globin gene families appears to be extremely remote (between 900 million and 1.4 billion years ago, if one assumes constancy of evolutionary rate in both the plant and animal lineages) and (ii) in addition to the normal regulatory sequences on the 5′ end, an approximately 30-base-pair sequence, specific to globin genes, that surrounds the cap site is conserved between the plant and animal globin genes. Comparison of the leghemoglobin sequences with one another shows that (i) the relative amount of sequence divergence in various coding and noncoding regions is roughly similar to that found for animal globin genes and (ii) as in animal globin genes, the positions of insertions and deletions in the intervening sequences often coincide with the locations of direct repeats. Thus, the mode of evolution of the plant globin genes appears to resemble, in many ways, that of their animal counterparts. We contrast the overall intergenic organization of the plant globin genes with that of animal genes, and discuss the possibility of the concerted evolution of the leghemoglobin genes.
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  • 5
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    Trees 8 (1993), S. 99-103 
    ISSN: 1432-2285
    Keywords: Robinia pseudoacacia L. ; Hydrogen uptake ; Hydrogenase ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Hydrogen uptake is thought to increase the efficiency of nitrogen fixation by recycling H2 produced by nitrogenase that would otherwise be lost by diffusion. Here we demonstrate the capacity of eight Rhizobium strains to take up molecular hydrogen. Uptake by nodule homogenates from Robinia pseudoacacia was measured amperometrically under nitrogenase repression. Markedly lower activities were found than in soybean nodules. In addition hydrogenase activity was detected by the ability of bacteroids to reduce methylene blue in the presence of hydrogen. It was demonstrated that hydrogenase structural genes are present in the black locust symbiont, Rhizobium sp. strain R1, using hybridization with a plasmid, which contained hydrogenase genes from R. leguminosarum bv. viceae.
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  • 6
    ISSN: 1432-2048
    Keywords: Alnus ; Ammonium ; Carbon translocation ; Endophyte damage ; Nitrogen fixation ; Root nodule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cloned plants of Alnus incana (L.) Moench were inoculated and grown without combined nitrogen for seven weeks. The effects of ammonium on the function and structure of the root nodules were studied by adding 20 mM NH4Cl (20 mM KCl=control) for four days. Nitrogenase activity decreased to ca. 50% after one day and to less than 10% after two days in ammonium treated plants, but was unaffected in control plants. The results were similar at photon flux densities of 200 and 50 μmol m-2 s-1. At the higher light level the effect was concentration dependent between 2 and 20 mM NH4Cl. The recovery was slow, and more than 11 d were needed for plants treated with 20 mM ammonium to reach initial activity. The distribution of 14C to the root nodules after assimilation of 14CO2 by the plants was not changed by the ammonium treatment. Microscopical studies of root nodules showed high frequencies of endophyte vesicles being visually damaged in nodules from ammonium-treated plants, but not in nodules from control plants. When nitrogenase activity was restored, visually damaged vesicles were again few, whereas young developing vesicles were numerous. The slow recovery, the 14C-translocation pattern, and the structural changes of the endophyte indicate a more complex mechanism of ammonium influence than simply a short-term reduction in supply of carbon compounds to the nodules.
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  • 7
    ISSN: 1432-2048
    Keywords: Ammonia ; Nitrogen fixation ; Nodule ; Senescence (root nodules) ; Ureide ; Vigna
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract During early development (up to 18 d after sowing) of nodules of an “effective” cowpea symbiosis (Vigna unguiculata (L.) Walp cv. Vita 3: Rhizobium strain CB756), rapidly increasing nitrogenase (EC 1.7.99.2) activity and leghaemoglobin content were accompanied by rapid increases in activities of glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 2.6.1.53), enzymes of denovo purine synthesis (forming inosine monophosphate) xanthine oxidoreductase (EC 1.2.3.2), urate oxidase (EC 1.7.3.3), phosphoenolpyruvate carboxylase (EC 4.1.1.31) and led to increased export of ureides (allantoin and allantoic acid) to the shoot of the host plant in the xylem. Culturing plants with the nodulated root systems maintained in the absence of N2 (in 80 Ar: 20 O2, v/v) had little effect on the rates of induction and increase in nitrogenase activity and leghaemoglobin content but, in the absence of N2 fixation and consequent ammonia production by bacteroids, there was no stimulation of activity of enzymes of ammonia assimilation or of the synthesis of purines or ureides. Addition of NO 3 - (0.1–0.2 mM) relieved host-plant nitrogen deficiency caused by the Ar: O2 treatment but failed to increase levels of enzymes of N metabolism in either the bacteroid or the plant-cell fractions of the nodule. Premature senescence in Ar: O2-grown nodules occurred at 18–20 d after sowing, and resulted in reduced levels of nitrogenase activity and leghaemoglobin but increased the activity of hydroxybutyrate oxidoreductase (EC 1.1.1.30).
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  • 8
    ISSN: 1432-2048
    Keywords: β-1,4-Glucan ; Nitrogen fixation ; Phaseolus (root nodules) ; Rhizobium (mutant) ; Root nodules ; produced by mutantRhizobium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Root nodules induced inPhaseolus vulgaris L. by the wild-type (WT) and a C4-dicarboxylic-acid mutant strain ofRhizobium leguminosarum biovar.phaseoli were compared on the basis of ultrastructure and cytochemistry of cellulose subunits. The mutant bacteroids failed to colonize infected host cells in a normal manner, and presented a premature degenerative appearance. Starch granules, rough endoplasmic reticulum and mitochondria were found to accumulate in the ineffective nodules. The most striking difference between effective and ineffective nodules was the presence of unusual spherical, laminated structures in plastids of mutant-infected host cells only. Cytochemical observations showed that these structures containβ-1,4-glucans. The presence ofβ-1,4-glucans within such structures may be caused by the activity of a cellulase which is produced by either the bacteroids or the host cell and is locally hydrolyzing the host cell-wall, thus releasing cellulose subunits into the cytoplasm. Another possibility is denovo synthesis ofβ-1,4-glucans in the host cell.
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  • 9
    ISSN: 1432-2048
    Keywords: Carbohydrate and nitrogen distribution ; Nitrate ; Nitrogenase activity ; Nitrogen fixation ; Respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This study was undertaken to determine how carbon utilization of fruit production might affect symbiotic activity in hydroponically cultured white bean (Phaseolus vulgaris L.) cv. Rico and its supernodulating genotype R32-BS15 (abbreviated as RBS15). Total plant biomass production of both genotypes was similar. Nodule dry weight of RBS15 consistently scored approximately twice the amount recorded for Rico, while nodule numbers in the mutant were almost six times as high. Nodule respiration on a per-plant basis and specific respiration was initially (day 37) disproportionally higher in the mutant, reaching up to three times the values recorded for Rico, while plant N2 fixation estimated by 15N dilution was almost identical. This indicates a lower fixation efficiency of RBS15 nodules, which we suggest to be a result of the larger number of smaller nodules with a higher proportion of growth and maintenance respiration per unit nodule mass. During reproductive development, specific respiration of the mutant dropped below that of Rico without a reduction in fixation, indicating a change in relative efficiency of fixation. Continuous removal of fruits from day 37 onwards stimulated respiration of nodules in both genotypes with highest values per plant being documented for RBS15, while specific activity was higher for Rico. The results indicate that symbiotic activity was not detrimentally affected by competition for carbohydrates between fruits and nodules. It appeared that nodules did not possess excess N2-fixation capacity which could be stimulated by additional provision of photosynthate. Hence, the early onset of reproduction during the life cycle of P. vulgaris is unlikely to be responsible for inadequate fixation performance in the field.
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  • 10
    ISSN: 1432-2048
    Keywords: Aspartate aminotransferase (immunocytochemistry, subcellular fractionation) ; Glutamate oxaloacetic transaminase ; Medicago (root nodules, N2 fixation) ; Nitrogen fixation ; Root nodule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Aspartate aminotransferase (AAT; EC 2.6.1.1) catalyzes the synthesis of the amino acid aspartate which, in alfalfa root nodules, serves as the immediate precursor of the primary N-transport compound, asparagine. The enzyme AAT may also be important in providing substrates for host-plant and bacteroid respiration. The enzyme occurs as two isoenzymes, AAT-1 and AAT-2, with AAT-1 more abundant in roots and AAT-2 predominant in root nodules. To further elucidate the role of AAT in root-nodule metabolism, subcellular fractionation and immunocytochemical methods were used to determine the intra- and intercellular localization of these two isozymes. Fractionation of nodule subcellular components showed that AAT-2 was localized in amyloplasts. Immunogold labelling with AAT-2 antibodies unequivocally confirmed this, showing that AAT-2 was localized in nodule amyloplasts and leaf chloroplasts. In root nodules, the density of immunogold labelling of infected cell plastids was almost four times that of uninfected cell plastids. The data suggest that aspartate biosynthesis in alfalfa root nodules occurs primarily in the plastids of infected cells.
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  • 11
    ISSN: 1432-2048
    Keywords: Ammonium assimilation ; Glycine ; Nitrogen fixation ; Proplastid ; Purine synthesis ; Root nodule ; Ureide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Subcellular organelle fractionation of nitrogen-fixing nodules of soybean (Glycine max (L.) Merr.) indicates that a number of enzymes involved in the assimilation of ammonia into amino acids and purines are located in the proplastids. These include asparagine synthetase (EC 6.3.1.1), phosphoribosyl amidotransferase (EC 2.4.2.14), phosphoglycerate dehydrogenase (EC 1.1.1.95), serine hydroxymethylase (EC 2.1.2.1), and methylene-tetrahydrofolate dehydrogenase (EC 1.5.1.5). Of the two isoenzymes of asparate aminotransferase (EC 2.6.1.1) in the nodule, only one was located in the proplastid fraction. Both glutamate synthase (EC 1.4.1.14) and triosephosphate isomerase (EC 5.3.1.1) were associated at least in part with the proplastids. Glutamine synthetase (EC 6.3.1.2) and xanthine dehydrogenase (EC 1.2.1.37) were found in significant quantities only in the soluble fraction. Phosphoribosylpyrophosphate synthetase (EC 2.7.6.1) was found mostly in the soluble fraction, although small amounts of it were detected in other organelle fractions. These results together with recent organelle fractionation and electron microscopic studies form the basis for a model of the subcellular distribution of ammonium assimilation, amide synthesis and uredie biogenesis in the nodule.
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  • 12
    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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  • 13
    ISSN: 1432-2048
    Keywords: Bradyrhizobium ; Dicarboxylate transport ; Glycine ; Nitrogen fixation ; Peribacteroid membrane ; Zhizobium ; Root nodule ; Symbiosis (soybean-Bradyrhizobium)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Malate and succinate were taken up rapidly by isolated, intact peribacteroid units (PBUs) from soybean (Glycine max (L.) Merr.) root nodules and inhibited each other in a competitive manner. Malonate uptake was slower and was severely inhibited by equimolar malate in the reaction medium. The apparent Km for malonate uptake was higher than that for malate and succinate uptake. Malate uptake by PBUs was inhibited by (in diminishing order of severity) oxaloacetate, fumarate, succinate, phthalonate and oxoglutarate. Malonate and butylmalonate inhibited only slightly and pyruvate,isocitrate and glutamate not at all. Of these compounds, only oxaloacetate, fumarate and succinate inhibited malate uptake by free bacteroids. Malate uptake by PBUs was inhibited severely by the uncoupler carbonylcyanidem-chlorophenyl hydrazone and the respiratory poison KCN, and was stimulated by ATP. We conclude that the peribacteroid membrane contains a dicarboxylate transport system which is distinct from that on the bacteroid membrane and other plant membranes. This system can catalyse the rapid uptake of a range of dicarboxylates into PBUs, with malate and succinate preferred substrates, and is likely to play an important role in symbiotic nitrogen fixation. Energization of both the bacteroid and peribacteroid membranes controls the rate of dicarboxylate transport into peribacteroid units.
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  • 14
    ISSN: 1432-2048
    Keywords: Allantoin ; Amino acids ; Bleeding sap ; Nitrogen fixation ; Phaseolus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Dwarf french beans, Phaseolus vulgaris L., were grown with or without inoculation with rhizobia (strain 3644), and with or without a combined nitrogen source (nitrate or ammonium ions). The distribution of radioactivity into products of dark 14CO2 assimilation was studied in roots or nodules from these plants. A detailed study was also made of the distribution and rates of excretion of nitrogen in xylem bleeding sap in 28 day old plants grown on the various sources of nitrogen. Whereas detached nodules accumulated radioactive glycine, serine and glutamate when incubated with 14CO2, bleeding sap from plants root fed 14CO2 contained low levels of radioactivity in these compounds but higher levels in allantoin. Chemical analysis showed allantoin to be the major compound transported in the xylem of nodulated plants, whether or not they were fed on combined nitrogen. In contrast uninoculated plants accumulated mainly amino acids in the bleeding sap, the amount and chemical composition of which depended on the combined nitrogen source.
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  • 15
    ISSN: 1432-2048
    Keywords: Glyoxylate ; Isonicotinic acid hydracide ; Medicago ; Nitrogen fixation ; Photorespiration ; Rhizobium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nitrogen fixation (measured as acetylene reduction) by whole nodulated alfalfa plants was stimulated when the plants were treated with isonicotinic acid hydracide (INH) and glyoxylate, both inhibitors of the glycolate pathway of carbohydrate metabolism, at concentrations of 300 and 100 mM, respectively. Reducing energetic loses caused by photorespiration results in an increase in the symbiotic nitrogen fixation.
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  • 16
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    Planta 152 (1981), S. 544-552 
    ISSN: 1432-2048
    Keywords: Ammonium assimilation ; Lichens ; Nitrogen fixation ; Peltigera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Nostoc in the cephalodia of the lichen Peltigera aphthosa Willd. fixed 15N2 and the bulk of the nitrogen fixed was continuously transferred from it to its eukaryotic partners (a fungus and a green alga, Coccomyxa sp.). Kinetic studies carried out over the first 30 min, after exposure of isolated cephalodia to 15N2, showed that highest initial 15N2-labelling was into NH 4 + . After 12 min little further increase in the NH 4 + label occurred while that in the amide group of glutamine and in glutamate continued to increase. The 15N-labelling of the amino group of glutamine and of aspartate increased more slowly, followed by an increase in the labelling of alanine. When total incorporation of 15N-label was calculated, the overall pattern was found to be rather similar except that, throughout the experiment, the total 15N incorporated into glutamate was about six times greater than that into the amide group of glutamine. Pulse chase experiments, in which 14N2 was added to cephalodia previously exposed to 15N2, showed that the NH 4 + pool rapidly became depleted of 15N-label, followed by decreases in the labelling of glutamate, the amide group of glutamine and aspartate. The 15N-labelling of alanine, however, continued to increase for a period. When isolated cephalodia were treated with L-methionine-SR-sulphoximine, an inhibitor of glutamine synthetase (EC 6.3.1.2), and azaserine, an inhibitor of glutamate synthase (EC 2.6.1.53), there was no detectable labelling in glutamine although the 15N-labelling of glutamate increased unimpaired. On treating the cephalodia with amino-oxyacetate, an inhibitor of aminotransferase activity, the alanine pool decreased. Evidence was obtained that glutamine synthetase and glutamate synthase were located in the Nostoc, and that glutamate dehydrogenase (EC 1.4.1.4) and various amino-transferases were located in the cephalodial fungus. Possible implications of these findings are discussed.
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  • 17
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    Oecologia 84 (1990), S. 176-185 
    ISSN: 1432-1939
    Keywords: Prosopis glandulosa ; Mesquite ; Nodulation ; Nitrogen fixation ; Vegetation change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We report the recovery of root nodules from P. glandulosa var. glandulosa in the eastern portion of its range, where the species reaches its greatest vegetational development. Single cores 4.7 cm in diameter and up to 250 cm deep yielded from 0 to over 250 nodules. Nodules were found at all depths below 10 cm, with the highest concentration often around 100 cm. Detailed studies of three trees revealed relatively small volume densities of about 0.02 nodules cm−3, high surface area densities of 2–4 nodules cm−2, and high nodule biomass of 8–23 g m−2, when compared to cultivated legumes. Nodules are small, weakly attached to roots that are seldom over 0.5 mm in diameter, and not easily observed under field conditions. No nodules were recovered from cores from the more arid western portion of P.glandulosa's range, although seedlings nodulated readily in these soils in the glasshouse as well as in most unamended soils from throughout mesquite's geographical range. Local differences in nodulating potential of soils included a negative association with mesquite canopies and a positive association with depth. These results suggest a significant role for biological fixation in the nitrogen regime and vegetation dynamics of Prosopis-dominated ecosystems.
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  • 18
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    Oecologia 85 (1990), S. 241-246 
    ISSN: 1432-1939
    Keywords: Plant-soil interactions ; Nutrient cycling ; Nitrogen fixation ; Decomposition ; Primary succession
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Plant nutrient status and physiological processes were examined in relation to soil nutrient characteristics under individuals of five species colonizing a young cinder deposit in Hawaii Volcanoes National Park. Two exotic species, Buddeleja asiatica and Myrica faya, had high photosynthetic rates and high nitrogen concentrations and relatively easily decomposed leaves; soils under them had high concentrations of nitrogen, cations, and organic matter and high rates of net nitrogen mineralization. At the other extreme, the natives Metrosideros polymorpha and Vaccinium reticulatum had low plant concentrations and photosynthetic rates, and low concentrations and turnover rates of N in the soil. Thus, a strong correlation exists between soil processes and plant processes, suggesting a positive feedback cycle.
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  • 19
    ISSN: 1432-1939
    Keywords: Plant defenses ; Polyphenols ; Herbivory ; Savanna ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In East African savanna we found that leaves of mature tree species with symbiotic N2 fixation contained lower concentrations of polyphenols than leaves of species without this symbiosis. We suggest that the root symbiosis is costly to the plant in terms of photosynthate that otherwise could be used in chemical defense. Further, a negative relationship between concentration of polyphenols and the height of the species was found, independent of their ability to fix N2. These findings suggest that root symbioses and apparency to herbivory are important factors mediating the production of chemical defenses in plants.
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  • 20
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    Oecologia 88 (1991), S. 451-455 
    ISSN: 1432-1939
    Keywords: Nitrogen fixation ; Carbon isotope ratio ; Nitrogen isotope ratio ; Acacia ; Namibia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Nitrogen (N2) fixation was estimated along an aridity gradient in Namibia from the natural abundance of 15N (δ15N value) in 11 woody species of the Mimosacease which were compared with the δ15N values in 11 woody non-Mimosaceae. Averaging all species and habitats the calculated contribution of N2 fixation (N f ) to leaf nitrogen (N) concentration of Mimosaceae averaged about 30%, with large variation between and within species. While in Acacia albida N f was only 2%, it was 49% in Acacia hereroensis and Dichrostachys cinerea, and reached 71% in Acacia melifera. In the majority of species N f was 10–30%. There was a marked variation in background δ15N values along the aridity gradient, with the highest δ15N values in the lowland savanna. The difference between δ15N values of Mimosaceae and non-Mimosaceae, which is assumed to result mainly from N2 fixation, was also largest in the lowland savanna. Variations in δ15N of Mimosaceae did not affect N concentrations, but higher δ15N-values of Mimosaeae are associated with lower carbon isotope ratios (δ13C value). N2 fixation was associated with reduced intrinsic water use efficiency. The opposite trends were found in non-Mimosaceae, in which N-concentration increased with δ15N, but δ13C was unaffected. The large variation among species and sites is discussed.
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  • 21
    ISSN: 1432-1939
    Keywords: Actinorhizal plants ; Evolutionary tradeoffs ; Nitrogen fixation ; Nutrient resorption ; Phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nutrient resorption was measured in an actinorhizal nitrogen-fixing shrub,Comptonia peregrina, for five years in the understory of a deciduous oak forest in Rhode Island, USA. Mean resorption of nitrogen was extremely inefficient (11%) compared to most deciduous species (50%+), yet resorption of phosphorus was efficient (53%) and comparable to other species. Of the seven additional nutrients studied, only copper (6%) and zinc (10%) were resorbed from senescing leaves. Resorption of nitrogen (5%–20%) and phosphorus (40%–71%) varied significantly among years. Copper was resorbed from leaves in three years and accreted into leaves in two years. Five-year resorption means differed among individual genets by as much as a factor of 2.5 for nitrogen, and 1.3 for phosphorus. Resorption of nitrogen, copper, and zinc were highly correlated, yet resorption of phosphorus remained autonomous from other nutrients. The ecophysiological tradeoffs inComptonia which have resulted in the cooccurence of actinorhizal nitrogen fixation, inefficient nitrogen resorption, and efficient phosphorus resorption suggest that plant nutrient status does have an impact on resorption efficiency and that the evolution of nutrient conservation strategies is nutrient-specific.
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  • 22
    ISSN: 1432-0789
    Keywords: Phosphorus fertilizer ; vesicular-arbuscular mycorrhizal fungus ; Azospirillum brasilense ; Glomus versiforme ; Barley ; Nitrogen fixation ; Nitrogen-15 ; Hordeum vulgare
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Pot-culture studies were carried out to examine the response of barley (Hordeum vulgare L.) to inoculation with Azospirillum brasilense and Glomus versiforme, singly and/or in combination, under varying levels of nitrogenous [(15NH4)2SO4] and soluble phosphatic (single superphosphate) fertilizers. The interaction between both the endophytes led to increased growth and nutrition of the barley plants. Roots from plants inoculated with Azospirillum brasilense and Glomus versiforme exhibited very low acetylene reduction activity. N2 fixation in the plants increased with the increase in plant growth but the mycorrhiza alone gave a low level of N2 fixation in the plants compared to combined inoculation with both the endophytes.
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  • 23
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    Biology and fertility of soils 11 (1991), S. 210-215 
    ISSN: 1432-0789
    Keywords: Rhizosphere ; Maize ; Bacillus circulans ; Enterobacteriaceae ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary We studied the dominant diazotrophs associated with maize roots and rhizosphere soil originating from three different locations in France. An aseptically grown maize plantlet, the “spermosphere model”, was used to isolate N2-fixing (acetylene-reducing) bacteria. Bacillus circulans was the dominant N2-fixing bacterium in the rhizosphere of maize-growing soils from Ramonville and Trogny, but was not found in maize-growing sandy soil from Pissos. In the latter soil, Enterobacter cloacae, Klebsiella terrigena, and Pseudomonas sp. were the most abundant diazotrophs. Azospirillum sp., which has been frequently reported as an important diazotroph accociated with the maize rhizosphere, was not isolated from any of these soils. The strains were compared for their acetylene-reducing activity in the spermosphere model. The Bacillus circulans strains, which were more frequently isolated, also exhibited significantly greater acetylene-reducing activity (3100 nmol ethylene day-1 plant-1) than the Enterobacteriaceae strains (180 nmol ethylene day-1 plant-1). This work indicates for the first time that Bacillus circulans is an important maizerhizosphere-associated bacterium and a potential plant growth-promoting rhizobacterium.
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  • 24
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    Biology and fertility of soils 11 (1991), S. 273-278 
    ISSN: 1432-0789
    Keywords: Genetic variability ; N-15 methods ; Nitrogen fixation ; Provenances ; Rhizobium strains ; Gliricidia sepium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Variation in nodulation and N2 fixation by the Gliricidia sepium/Rhizobium spp. symbiosis was studied in two greenhouse experiments. The first included 25 provenances of G. sepium inoculated with a mixture of three strains of Rhizobium spp. N2 fixation was measured using the 15N isotope dilution method 12 weeks after planting. On average, G. sepium derived 45% of its total N from atmospheric N2. Significant differences in fixation were observed between provenances. The percentage of N derived from atmospheric N2 ranged from 26 to 68% (equivalent to 18–62 mg N plant-1) and was correlated with total N in the plant (r=0.70; P=0.05). The second experiment included six strains of Rhizobium spp. and two methods of inoculation and the plants were harvested 14,35 and 53 weeks after planting. In the first harvest significant differences were found between the number of nodules and the percentage and amount of N2 fixed. There was also a significant correlation between the number of nodules and the amount of N2 fixed (r=0.92; P=0.05). In the final harvest no correlation was observed, although there were significant differences between the number of nodules and the percentage of N derived from the atmosphere. The amount of N2 fixed increased with time (from an average of 27% at the first harvest to 58% at the final harvest) and was influenced by the Rhizobium spp. strain and the method of inoculation. It ranged from 36% for Rhizobium sp. strain SP 14 to 71% for Rhizobium SP 44 at the last harvest. Values for the percentage of atmosphere derived N2 obtained by soil inoculation were slightly higher than those obtained by seed inoculation.
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  • 25
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    Biology and fertility of soils 11 (1991), S. 306-312 
    ISSN: 1432-0789
    Keywords: Alkali soil ; Blue-green algae ; Calcium carbonate ; Gypsum ; Nitrogen fixation ; Organic matter ; Soil reclamation ; Sodic soil ; Waterlogged soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Virgin alkali (sodic) soils have a high pH and high exchangeable Na and are often barren. Blue-green algae, however, tolerate excess Na and grow extensively on the soil surface in wet seasons. Experiments using a highly degraded alkali soil (silt loam, pH 10.3, electrical conductivity 3.5 dS m-1, 90% exchangeable Na) were conducted in soil columns, with or without gypsum, in order to study the influence of waterlogging on the growth of indigenous and inoculated blue-green algae and hence, soil reclamation. The growth of indigenous blue-green algae was initially slow in alkali soil, due to the high pH and exchangeable Na, and depressed in gypsum-amended soil, due to excess Ca. Inoculation hastened the establishment of blue-green algae in both the unamended alkali soil and the gypsum-amended soil, overcoming the adverse influence of excess Na in the former and excess Ca in the latter. Gypsum was effective in amelioration (pH 9.05, electrical conductivity 1.2 dS m-1, 41% exchangeable Na after 11 weeks) but blue-green algae were ineffective even after 17 weeks. In combination with gypsum, blue-green algae had no additional effect, and the C and N increases due to the growth of indigenous or inoculated blue-green algae were insignificant. Alkali soil reclamation by biological methods requires mobilization of Ca from native soil calcite and the exchange of Ca for Na in the exchange complex. The ineffectiveness of blue-green algae was ascribed to their inability to mobilize Ca. It is argued that current theories favouring blue-green algae as a biological amendment to bring about alkali soil reclamation are untenable and are not comparable with an effective chemical amendment such as gypsum.
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  • 26
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    Biology and fertility of soils 12 (1991), S. 100-106 
    ISSN: 1432-0789
    Keywords: Azospirillum ; 15N-isotope dilution ; Nitrogen fixation ; Acetylene reduction activity ; ARA ; Rhizosphere ; Mineral nitrogen ; Oxygen tension
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Acetylene reduction activity by Azospirillum brasilense, either free-living in soils or associated with wheat roots, was determined in a sterilised root environment at controlled levels of O2 tension and with different concentrations of mineral N. In an unplanted, inoculated soil nitrogenase activity remained low, at approximately 40 nmol C2H4 h-1 per 2kg fresh soil, increasing to 300 nmol C2H4 h-1 when malic acid was added as a C source via a dialyse tubing system. The N2 fixation by A. brasilense in the rhizosphere of an actively growing plant was much less sensitive to the repressing influence of free O2 than the free-living bacteria were. An optimum nitrogenase activity was observed at 10 kPa O2, with a relatively high level of activity remaining even at an O2 concentration of 20 kPa. Both NO inf3 sup- and NH inf4 sup+ repressed nitrogenase activity, which was less pronounced in the presence than in the absence of plants. The highest survival rates of inoculated A. brasilense and the highest rates of acetylene reduction were found in plants treated with azospirilli immediately after seedling emergence. Plants inoculated at a later stage of growth showed a lower bacterial density in the rhizosphere and, as a consequence, a lower N2-fixing potential. Subsequent inoculations with A. brasilense during plant development did not increase root colonisation and did not stimulate the associated acetylene reduction. By using the 15N dilution method, the affect of inoculation with A. brasilense in terms of plant N was calculated as 0.067 mg N2 fixed per plant, i.e., 3.3% of the N in the root and 1.6% in the plant shoot were of atmospheric origin. This 15N dilution was comparable to that seen in plants inoculated with non-N2-fixing Psudomonas fluorescens.
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  • 27
    ISSN: 1432-0789
    Keywords: Ulex gallii ; Legume ; Nitrogenase activity ; Nitrogen fixation ; Acetylene reduction activity ; Phosphorus fertilizer ; Forest soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary N2(C2H2) fixation by Ulex gallii Planchon (dwarf or autumn flowering gorse/furze) seedlings was determined following 8 months of growth (December-August) in the glasshouse in a very acid, N- and P-deficient forest soil. Application of Na2HPO4·12H2O or North African ground rock phosphate fertilizer was essential for growth, nodulation and C2H2 reduction activity. Overall, both the sodium phosphate and the rock phosphate were equally effective P sources and the maximum acetylene reduction by intact roots was measured as 4.09 and 4.69 μmol C2H4g-1 fresh weight nodule h-1, respectively. Applied NH4Cl severely inhibited nodulation and restricted acetylene reduction activity but not seedling growth. The results are discussed in relation to the spread of U. gallii in the south of Ireland and its potential as a leguminous nurse crop for Sitka spruce on the very impoverished forest soils of the region.
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  • 28
    ISSN: 1432-0789
    Keywords: Typic cryoboroll ; N yield ; 15N ; Root length ; Grass-legume intercrop ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Barley-field pea intercrops have been shown to increase N yield when grown under cryoboreal subhumid conditions. In this study, we extended previous research by testing the hypotheses that (1) the intercropped field pea fixes a greater proportion of its shoot and root N than does sole-cropped field pea; (2) N is transferred from the annual legume to the cereal during the growing season; and (3) root production is greater under intercropped than sole-cropped conditions. Unconfined microplots seeded to barley, field peas, or a barley-field pea intercrop were fertilized with N at 10 kg ha-1 as (NH4)2SO4 (5.21 atom % 15N excess). Both the intercropped and sole-cropped barley derived more than 93% of their N from the soil. In contrast, 40% of N in the intercropped field pea was derived from soil. This study provided no evidence for transfer of N from the legume to the cereal. On average, the proportion of N derived from air by both pea intercrops was 39% higher than that derived by the sole-cropped pea. Root length determined by a grid intersection method following digitization using an image analyzer tended to be higher under intercropping than in sole crops. We conclude that even on fertile soils benefits may accrue from annual intercropping that includes a legume. The benefits arise from (1) increased N production, (2) greater N-fixation efficiency, and/or (3) more shoot and root residue-N mineralization for subsequent crops.
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  • 29
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    Biology and fertility of soils 13 (1992), S. 165-172 
    ISSN: 1432-0789
    Keywords: Azospirillum brasilense ; 15N-isotope enrichment ; Nitrogen fixation ; Auxine ; 2,4-dichlorphenoxy acetic acid ; 3,5-dichlor-phenoxy acetic acid ; Acetylene reduction assay ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Wheat seedlings, treated with the auxine 2,4-dichlor-phenoxy acetic acid (2,4-D) during germination developed only a residual root system. Root elongation was extremely restricted and root tips were deformed to thick club-shaped tumours. When 2,4-D was added in a later stage of plant growth the plants developed additional nodule-like knots along primary roots. Root and shoot dry-matter production was slightly repressed in all 2,4-D treatments and N translocation from roots to shoots was repressed as well. When transferred to an auxine-free growth medium, the 2,4-D-affected roots were not capable of complete recovery. In plants inoculated gnotobiotically with Azospirillum brasilense, either with the wild type or with the NH 4 + -excreting mutant strain C3, a 2,4-D addition increased rhizosphere acetylene-reduction activity at pO2 1.5 kPa. The O2 sensitivity of root-associated nitrogenase activity tended to be reduced. The number of root-colonizing bacteria, at approximately 108 colony-forming units (cfu) per g dry root, was similar in the 2,4-D treatments and untreated controls. Plant treatment with high concentrations of the chemical isomer 3,5-dichlor-phenoxy acetic acid (3,5-D) did not have comparable effects, either on plant development or on rhizosphere-associated nitrogenase activity. Root-tumour tissue inhabited by A. brasilense showed purple staining when subjected to a tetrazolium chloride solution, which may indicate intensive local nitrogenase activity in this tissue. Exposed to an 15N2-enriched atmosphere, plants treated with 2,4-D and with A. brasilense incorporated significantly higher amounts of 15N than untreated controls. In all cases the highest values of 15N enrichment were found following inoculation with the NH 4 + -excreting mutant strain C3.
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  • 30
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    Biology and fertility of soils 15 (1993), S. 35-38 
    ISSN: 1432-0789
    Keywords: Nitrogen fixation ; Eucalyptus saligna ; Albizia falcataria ; Pontoscolex corethrurus ; Litterfall
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Tree species differ in the quantity and quality of litter produced, and these differences may significantly affect ecosystem structure and function. I examined the importance of tree species in determining earthworm densities in replicated stands of Eucalyptus saligna Sm. and Albizia falcataria (L.) Fosberg, and in mixed stands (25% albizia and 75% eucalyptus). Mean earthworm densities ranged from 92 m-2 in the pure eucalyptus, to 281 m-2 in the mixture, and a maximum of 469 m-2 in the pure albizia stands. Only two earthworm species were present, Pontoscolex corethrurus and Amynthas gracilis. Leaf biomass on the forest floor was highest in the pure eucalyptus and lowest in the pure albizia stands, whereas the annual fine litterfall production was lowest in the pure eucalyptus and highest in the albizia stands. The N content of fine litterfall was correlated positively with earthworm density, and the fine litterfall biomass: N ratio was correlated negatively with earthworm density. Greater leaf biomass on the forest floor under eucalyptus stands despite lower rates of litterfall suggests that litter quality, rather than litter quantity, was primarily responsible for the greater earthworm density in the albizia stands. Some biogeochemical effects of tree species in the tropics may be mediated through effects on earthworm populations.
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  • 31
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    Biology and fertility of soils 15 (1993), S. 73-78 
    ISSN: 1432-0789
    Keywords: Firewood crops ; Green-leaf manure ; Macronutrients ; Nodulation ; Nitrogen fixation ; Sesbania spp. ; Acetylen reduction assay ; ARA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary In three field trials conducted during the summer season of 1986, 1987 and 1989 in an alkaline soil, 17 accessions of annual Sesbania spp. were evaluated for nodulation, N2 fixation (acetylene reduction assay), dry weight of roots and shoots, woody biomass production, and nutrient uptake. At 50 days after sowing all the accessions were effectively nodulated (average 36.4 root nodules plant-1) with a high nodule score (3.4). There was a lot of variation in nodule volume and mass and in acetylene reduction activity but not in N content (5.2%). N uptake in shoots, roots and nodules averaged 639, 31, and 13 mg plant-1, respectively, and much of the fixed N remained in shoots. Accessions of ‘S. cannabina’ complex performed better than others. S. rostrata had poor root nodulation but exhibited excellent stem nodulation (300 nodules plant-1) even though not inoculated with Azorhizobium sp. Average concentrations of N, P, K, S, Ca, and Mg in the shoots were high, at 3.2, 0.28, 1.5, 0.28, 1.5, and 0.4% respectively, and Na was low (0.15%), reflecting the usefulness of Sesbania spp. as an integrated biofertilizer source. Green matter production was 26.0 Mg ha-1 (5.9 Mg dry matter) and N uptake was 158 kg ha-1, 54 days after sowing. Average woody biomass of six accessions at maturity, 200 days after sowing, was high (19.9 Mg ha-1), showing its potential for shortterm firewood production. Total nutrient uptake for production of woody biomass (200 days of growth) was no more demanding than growing the plant to the green-manuring stage of 50–60 days' growth.
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  • 32
    ISSN: 1432-0789
    Keywords: δ 15N ; Elevation ; Nitrogen fixation ; Non-nodulating ; Glycine max ; Soybeans ; Isolines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Dissimilarities in soil N uptake between N2-fixing and reference non-N2-fixing plants can lead to inaccurate N2 fixation estimates by N difference and 15N enrichment methods. The natural 15N abundance (δ 15N) method relies on a stabilized soil 15N pool and may provide reliable estimates of N2 fixation. Estimates based on the δ 15N and differences in N yield of nodulating and non-nodulating isolines of soybean were compared in this study. Five soybeans from maturity groups 00, IV, VI, and VIII and their respective non-nodulating isolines were grown at three elevations differing in ambient temperature and soil N availability. Despite large differences in phenological development and N yield between the non-nodulating isolines, the δ 15N values measured on seeds were relatively constant within a site. The δ 15N method consistently produced lower N2 fixation estimates than the N difference method, but only in three of the 15 observations did they differ significantly. The average crop N derived from N2 fixation across sites and maturity groups was 81% by N difference compared to 71% by δ 15N. The magnitude of difference between the two methods increased with increasing proportions of N derived from N2 fixation. These differences between the two methods were not related to differences in total N across sites or genotypes. The low N2 fixation estimates based on δ 15N might indicate that the nodulating isolines had assimilated more soil N than the non-nodulating ones. A lower variance indicated that the estimates by N difference using non-nodulating isolines were more precise than those by δ 15N. Since the differences between the estimates were large only at high N2 fixation levels (low soil N availability), either method may be used in most situations when a non-nodulating isoline is used as the reference plant. The δ 15N method may have a comparative advantage over N difference and 15N enrichment methods in the absence of a suitable non-N2-fixing reference plant such as a non-nodulating isoline.
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  • 33
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    Biology and fertility of soils 15 (1993), S. 275-278 
    ISSN: 1432-0789
    Keywords: Peanuts ; Arachis hypogaea ; Continuous cropping ; Nitrogen fixation ; Bradyrhizobium spp. ; Effectiveness of rhizobia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The objective of this study was to assess the number and effectiveness of peanut rhizobia in soils of the major peanut-growing areas of Thailand. Three cropping areas, (1) continuously cropped with peanuts, (2) continuously cropped with non-legumes, and (3) non-cultivated fields, were chosen in each region. Peanut rhizobia were found in the soil at 38 to 55 sites sampled. Cultivated fields with a peanut cultivation history contained (as estimated by most probable numbers) an average of 1.6×103 cells g-1 of soil. The numbers of peanut rhizobia in most of the fallow fields and some of the noncultivated shrub or forest locations were much the same as at the sites where Arachis hypogaea was cultivated. In contrast, there were no or few (28–46 cells g-1 soil) peanut rhizobia in the majority of fields continuously cultivated with sugarcane, cassava, corn, and pineapple. It appears that in these areas the indigenous peanut rhizobial populations are not adequate in number for a maximal nodulation of peanuts. A total of 343 Bradyrhizobium isolates were tested for effectiveness and were found to vary widely in their ability to fix N2. In some areas the majority of rhizobia were quite effective while in others they were less effective than the inoculum strain THA 205 recommended in Thailand.
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  • 34
    ISSN: 1432-0789
    Keywords: Fertilizer use efficiency ; Intercropping ; Natural 15N abundance ; Nitrogen fixation ; Pigeonpea ; Sorghum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A field experiment was conducted to obtain the N balance sheet for sole crops and intercrops of sorghum [Sorghum bicolor (L.) Moench] and pigeonpeas [Cajanus cajan (L.) Millsp.]. Intercropping gave a significant advantage over sole cropping in terms of dry matter production and grain yield, as calculated on the basis of the land equivalent ratio and area-time equivalent ratio. The N fertilizer use efficiency and atmospheric N2 fixation by pigeonpea were estimated using 15N-labeling and natural abundance methods. The N fertilizer use efficiency of sorghum was unaltered by the cropping system, while that of the pigeonpea was greatly reduced by intercropping. Although intercropping increased the fractional contribution of fixed N to the pigeonpeas, no significant difference was observed between the cropping systems in total symbiotically fixed N. There was no evidence of a significant transfer of N from the pigeonpea to the sorghum. This study showed that use of soil N and fertilizer N by pigeonpeas was almost the same as that by sorghum in sole cropping, indicating the potential competence of pigeonpeas to exploit soil N. However, when N was exhausted by a companion crop in intercropping, the pigeonpea crop increased its dependency on atmospheric N2 fixation. We conclude that knowledge of how N from different sources is shared by companion crops is a prerequisite to establishing strategies to increase N use, and consequently land productivity, in intercropping systems.
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  • 35
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    Biology and fertility of soils 16 (1993), S. 299-301 
    ISSN: 1432-0789
    Keywords: A N value ; 15N ; Nitrogen fixation ; Glycine max ; Hordeum vulgare
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Pot experiments were conducted with two soils, from Rottenhaus and Seibersdorf in Austria, to ascertain whether the rate of fertilizer N application and the test crop would influence the amount of N available in the soil as assessed by the A-value method. 15N-labelled fertilizer was applied at rates of 10, 25, 40, 60, and 100 mg N kg-1 soil, corresponding approximately to 20, 50, 80, 120 and 200 kg N ha-1 respectively, and two crop species, barley (Hordeum vulgareL.) and non-nodulating soybean (Glycine max L.) were used to determine the soil A N value under the various fertilizer regimes. The results showed that the Rottenhaus soil had a higher A N value than the Seibersdorf soil, suggesting that the former was more fertile than the latter. The A N values of both soils were significantly affected by the level of N application. When grown in the same soil, the two test crops showed significantly different fertilizer use efficiency and per cent N derived from fertilizer when the rate of N application exceeded 20 kg ha-1. Thus, the A N value as determined by the two test crops differed significantly for the same soil when the rate of N application was greater than 20 kg/ha. The difference was greater when the soil fertility level was high. The dependence of the A N value on the level of N application and the species of crop seriously compromises the suitability of this method for determining plant-associated N2 fixation. Hence, considerable caution is required when using this method to estimate plant-associated N2 fixation.
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  • 36
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    Biology and fertility of soils 17 (1994), S. 1-8 
    ISSN: 1432-0789
    Keywords: Ammonium excretion ; Azospirillum brasilense ; Auxine ; 2,4-Dichlor-phenoxy-acetic acid ; Nitrogen fixation ; Paranodulation ; Maize ; Zea mays ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Maize seedlings develop nodule-like tumour knots (para-nodules) along primary roots when treated with the auxin 2,4-dichlor-phenoxy-acetic acid (2,4-D). Inoculated NH 4 + -excreting Azospirillum brasilense cells were shown to colonize these tumours, mostly intracellularly, promoting a high level of N2 fixation when microaerophilic conditions were imposed. The nitrogenase activity inside the para-nodules was less sensitive to free O2 than in non-para-nodulating roots. Both light and electron microscopy showed a dense bacterial population inside intact tumour cells, with the major part of the cell infection along a central tumour tissue. The bacteria colonized the cytoplasm with a close attachment to inner cell membranes. In an auxin-free growth medium, young 2,4-D-induced para-nodules grew further to become mature differentiated root organs in which introduced bacteria survived with a stable population. These results provide evidence that gramineous plants are potentially able to create a symbiosis with diazotrophic bacteria in which the NH 4 + -excreting symbiont will colonize para-nodule tissue intracellularly, thus becoming well protected.
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  • 37
    ISSN: 1432-0789
    Keywords: Nitrogen fixation ; Photosynthetic bacteria ; Stem nodules ; Aeschynomene scabra ; Sesbania rostrata ; Azorhizobium caulinodans ; Erythrobacter sp. ; Roseobacter denitrificans
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Bradyrhizobial strain BTAi 1 nodulates both stems and roots of Aeschynomene spp. Previous work has shown that it contains bacteriochlorophyll a and forms photosynthetic reaction centers, and has provided indirect evidence of photosynthesis by bacteroids within stem nodules. Here we report physiological and biochemical characteristics of BTAi 1 ex planta, which also suggest the presence of photosynthetic activity. Light-stimulated uptake of 14CO2 by BTAi 1 was detected at all stages of growth. Inhibitors of photosynthesis, 1,10-orthophenanthroline and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), and the uncoupler NH4Cl, immediately suppressed light-driven 14CO2 uptake and increased O2 uptake. BTAi 1 is strictly aerobic and was unable to grow without organic C even in the light; also, it was unable to grow chemoautotrophically in an atmosphere enriched with H2 and CO2. In micro-aerobic conditions, strain BTAi 1 expressed acetylene reducing activity ex planta in an N-free medium. The highest rates of light-stimulated 14CO2 uptake and acetylene-reducing activity occurred during the exponential and early stationary phases of growth. Acetylene-reducing rates at a low glucose concentration were increased following a light-dark cycle in comparison with continuous dark conditions.
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  • 38
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    Biology and fertility of soils 18 (1994), S. 37-41 
    ISSN: 1432-0789
    Keywords: Available nutrients ; Insecticides ; Microortanisms ; Nitrogen fixation ; Phosphate solubilization ; Rhizosphere soil ; Rice yield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A field experiment was conducted to investigate the effects of 1,2,3,4,5,6-hexachlorocyclohexane (BHC), phorate, carbofuran, and fenvalerate, at their recommended doses, on some chemical and microbiological properties of the rhizosphere soil in relation to rice yields. In general, the insecticides had a beneficial effect on rhizosphere soil properties. Carbofuran strongly stimulated the mineralization of organic C. BHC and phorate led to the retention of less total N in the soil. BHC released more NH inf4 sup+ -N than the other insecticides. Phorate, however, liberated the most NO inf3 sup- -N. Phorate and fenvalerate released more available P than BHC and carbofuran did. All the insecticides stimulated the proliferation of aerobic non-symbiotic N2-fixing and phosphate-solubilizing microorganisms, resulting in an overall increase in rice yield. BHC had the greatest effect on rice yields, followed by phorate.
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  • 39
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    Environmental management 7 (1983), S. 177-187 
    ISSN: 1432-1009
    Keywords: Nitrogen ; Model ; Agriculture ; Mass balance ; Ground-water ; Denitrification ; Immobilization ; Dry deposition ; Nitrogen fixation ; Nitrate ; Florida
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract A detailed nitrogen budget was devised for agricultural activities in the Florida peninsula, based on routine data published by state agricultural agencies. The model demonstrates that important unmonitored fluxes of nitrogen can often be calculated by mass balance on individual model compartments, and that the reasonability of poorly quantified fluxes can be assessed. The results of such models can be very useful in designing and assessing the results of field experiments and in prioritizing environmental monitoring programs.
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  • 40
    ISSN: 1432-072X
    Keywords: Nitrogen fixation ; Regulation ; Guanosine 5′-diphosphate 3′-diphosphate (ppGpp)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Addition of ammonium to N2 fixing cultures of Azotobacter vinelandii, Klebsiella pneumoniae and Clostridium pasteurianum rapidly reduced the intracellular levels of guanosine 5′-diphosphate 3′-diphosphate (ppGpp) by 70–90%. This change might reflect a regulatory role of ppGpp in nitrogen metabolism.
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  • 41
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    Archives of microbiology 136 (1983), S. 20-25 
    ISSN: 1432-072X
    Keywords: Hydrogen production ; Nitrogen fixation ; Hydrogen recycling ; Hydrogenase
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    Topics: Biology
    Notes: Abstract Mutants of Rhodopseudomonas capsulata lacking uptake hydrogenase activity have been isolated among those unable to grow photoautotrophically. Studies with these mutants showed increases in nitrogenase mediated H2 production from all substrates tested. In addition, photosynthetic synthetic growth on N2 with malate as carbon source was not affeced by the block in H2 uptake even under low light. Under these growth conditions hydrogen was observed to accumulate in mutant but not in wild-type cultures. This finding suggested that H2 was evolved by nitrogenase during N2 fixation by this photosynthetic bacterium and was efficiently recycled in the wild type.
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  • 42
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    Archives of microbiology 135 (1983), S. 287-292 
    ISSN: 1432-072X
    Keywords: Cyanobacteria ; Respiration ; Nitrogen fixation ; Heterocysts ; K m for O2 ; Anabaena variabilis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Simultaneous measurements of acetylene reduction by Anabaena variabilis and the concentration of dissolved oxygen in the suspension were made using a specially designed vessel which allowed measurements under steady-state conditions. The rate of acetylene reduction in the dark increased with increasing oxygen concentrations until a maximum value was reached at 300 μM O2 (corresponding to 30% O2 in the gas phase at 35°C). This presumably results from a requirement for energy provided by respiration. Measurements of the dependence of respiration rate on dissolved oxygen concentration were made under comparable conditions using an open system to allow conditions close to steady-state to be obtained. The respiration rate of diazotrophically grown Anabaena variabilis had a dependence on oxygen concentration corresponding to the sum of two activities. These had K m values of 1.0 μM and 69 μM and values of V max of similar magnitude. Only the high affinity activity was observed in nitrate-grown cyanobacteria lacking heterocysts, and this presumably represent activity in the vegetative cells. The oxygen concentration dependence of the low affinity activity resembled that for the stimulation of acetylene reduction. We interpret this as the result of oxygen uptake by the heterocysts. The results are consistent with the idea that in intact filaments of cyanobacteria O2 enters heterocysts much more slowly than it enters the vegetative cells.
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  • 43
    ISSN: 1432-072X
    Keywords: Ammonium export ; Ammonium assimilation ; Glutamine synthetase ; Nitrogen fixation ; Rhizobium sp. 32H1
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    Topics: Biology
    Notes: Abstract The relationship between ammonium assimilation and ammonium export has been studied in free-living, N2-fixing Rhizobium sp. 32H1. After 55 to 67 h of microaerobic growth under a gas phase of 0.2% O2 – 1.0% CO2 – 98.8% Ar high levels of nitrogenase were observed concomitant with a slightly adenylylated glutamine synthetase (GSI) and some glutamine synthetase (GSII) activity. However, after growth of 89 h, or longer, GSI became adenylylated and the level of GSII had decreased. When the gas phase was shifted to 0.2% O2 – 1.0% CO2 – 98.8% N2, a lag was observed before ammonium export could be detected in the 55 to 67 h cultures. No lag in ammonium export was observed in the cultures previously grown for 89 h. The onset of ammonium export in the 55 to 67 h cultures was found to correlate with the adenylylation state of GSI. There appeared to be no correlation between the level of GSII and the export of ammonium. Neither an increase in the adenylylation level of GSI nor ammonium export was observed when the 55 to 67 h cultures were maintained under the Ar gas mixture.
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  • 44
    ISSN: 1432-072X
    Keywords: Propionic fermentation ; Fermentation of aspartate ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract From estuarine mud a rod-shaped, motile, gram-negative, anaerobic bacterium was isolated (strain asp 66). Asp 66 fermented several substrates including glucose, fructose, malate, fumarate, citrate and aspartate. Fermentation products were acetate, propionate and presumably CO2. Hydrogen was never formed nor utilized. Succinate conversion to propionate was catalyzed by cell suspensions but did not support growth. Asp 66 did not require vitamins and grew well in mineral media with a fermentable substrate. The pH range for growth was from 6.5 to 8.5. Temperature optimum was 27 to 30°C. The strain was able to fix N2 as evidenced by its growth with N2 as sole nitrogen source and its ability to reduce acetylene to ethylene. Cell-free extracts of cultures grown under air without shaking contained cytochrome(s) with absorption peaks at 523 nm and at 553 nm. The G+C content of the DNA was 60.8+-1 mol%. The taxonomic position of strain asp 66 is discussed.
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  • 45
    ISSN: 1432-072X
    Keywords: Klebsiella pneumoniae ; Nitrogen fixation ; Regulation
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    Topics: Biology
    Notes: Abstract The nifL gene product of Klebsiella pneumoniae inhibits the activity of the positive activator protein NifA in response to increased levels either of fixed nitrogen or of oxygen in the medium. In order to demonstrate that the responses to these two effectors are discrete we have subjected nifL to hydroxylamine mutagenesis and isolated nifL mutants that are impaired in their ability to respond to oxygen but not to fixed nitrogen. Two such mutations were sequenced and shown to be single base pair changes located in different parts of nifL. The amino acid sequence of NifL shows limited homology to the histidine protein kinases which comprise the sensing component of bacterial two-component regulatory systems. In the light of the location of one of the oxygen-insensitive mutations (Leu294Phe) we have reassessed this homology and we suggest that the Gln273-Leu317 region of NifL may facilitate interactions between NifL and NifA.
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  • 46
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    Archives of microbiology 127 (1980), S. 163-165 
    ISSN: 1432-072X
    Keywords: Nitrogen fixation ; Arthrobacter ; Corynebacterium ; Anabaena azollae
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    Topics: Biology
    Notes: Abstract Coryneform bacteria were found associated with the nitrogen fixing blue-green alga, Anabaena azollae in the leaf cavity of Azolla caroliniana. Plate counts indicated ca. 7,400±1,900 bacterial cells per mature leaf cavity or approximately 1 bacterial cell for every algal cell. No other type of bacterium was found in these cavities.
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  • 47
    ISSN: 1432-072X
    Keywords: Fluorescent antibody staining ; Nitrogen fixation ; Symbiosis ; Anabaena azollae ; Azolla caroliniana
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    Topics: Biology
    Notes: Abstract Fluorescent antibody staining indicated differences in surface antigenicity in Anabaena azollae cells fresh from the leaf cavities of the fern, Azolla caroliniana, and algae which were isolated and subcultured from this fern. Such results suggest that either changes in antigenicity occur in this phycobiont during culturing or that isolation selects for an antigenically different mutant strain capable of in vitro growth.
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  • 48
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    Archives of microbiology 129 (1981), S. 238-239 
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    Keywords: Rhizobium ; Disaccharide ; Bacteroid ; Transport ; Nitrogen fixation
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    Topics: Biology
    Notes: Abstract Slow growing strains of rhizobia appear to lack both uptake systems and catabolic enzymes for disaccharides. In the fast-growing strains of rhizobia there are uptake mechanisms and catabolic enzymes for disaccharide metabolism. In Rhizobium leguminosarum WU 163 and WU235 and R. trifolii WU290, sucrose and maltose uptake appears to be constitutive whereas in R. meliloti WU60 and in cowpea Rhizobium NGR234 uptake of these disaccharides is inducible. There is evidence that there are at least two distinct disaccharide uptake systems in fast-growing rhizobia, one transporting sucrose, maltose and trehalose and the other, lactose. Disaccharide uptake is via an active process since uptake is inhibited by azide, dinitrophenol and carbonyl cyanide m-chlorophenylhydrazone but not by arsenate. Bacteroids of R. leguminosarum WU235 and R. lupini WU8 are unable to accumulate disaccharides.
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  • 49
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    Archives of microbiology 130 (1981), S. 38-43 
    ISSN: 1432-072X
    Keywords: Nitrogen fixation ; Gene expression ; Regulation ; Messenger RNA ; Transcription ; Klebsiella pneumoniae
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    Topics: Biology
    Notes: Abstract Nitrogenase messenger RNA synthesis in Klebsiella pneumoniae was determined by labelling cells with (3H)uracil and isolating total RnA, which was then hybridized to filterbound recombinant plasmid pSA30 DNA carrying the nitrogenase structural genes nifH, D, and K. Derepression of nitrogenase mRNA starts 1.5 h before the onset of nitrogenase activity (as measured by acetylene reduction). Exposure of nif-derepressed cultures to either NH 4 + , air, or high temperatures (39° C) results in a rapid decrease of the synthesis rates both of nitrogenase mRNA and nitrogenase polypeptides. Nitrogenase mRNA is remarkably stable. After blocking transcription with rifampicin, hybridizable and actively translatable nitrogenase mRNA survives with an average half-life of 18 min. Half-lives are considerably shorter when rifampicin-inhibited cultures are simultaneously shifted to conditions which are non-permissive for nitrogenase synthesis, pointing to some posttranscriptional influence on nitrogenase mRNA stability. In all experiments performed there was no evidence for uncoupling of nitrogenase mRNA synthesis from nitrogenase mRNA translation, indicating that nitrogenase synthesis is regulated solely by transcriptional control.
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  • 50
    ISSN: 1432-072X
    Keywords: Rhizobium trifolii ; Symbiosis ; Nodulation ; Nitrogen fixation ; Symbiotic genes ; Reiterated sequences ; Plasmid
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    Notes: Abstract A Rhizobium trifolii symbiotic plasmid specific gene library was constructed and the physical organisation of regions homologous to nifHDK, nifA and nod genes was determined. These symbiotic gene regions were localised to u 25 kb region on the sym-plasmid, pPN1. In addition four copies of a reiterated sequence were identified on this plasmid, with one copy adjacent to nifH. No rearrangement of these reiterated sequences was observed between R. trifolii bacterial and bacteroid DNA. Analysis of a deletion derivative of pPN1 showed that these sequences were spread over a 110 kb region to the left of nifA.
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  • 51
    ISSN: 1432-072X
    Keywords: Ammonia assimilation ; Lichen symbioses ; Nitrogen fixation ; 15N kinetics ; Peltigera canina
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    Topics: Biology
    Notes: Abstract On following N2-incorporation and subsequent metabolism in the lichen Peltigera canina using 15N as tracer, it was found, over a 30 min period, that greatest initial labelling was into NH 4 + followed by glutamate and the amide-N of glutamine. Labelling of the amino-N of glutamine, aspartate and alanine increased slowly. Pulse-chase experiments using 15N confirmed this pattern. On inhibiting the GS-GOGAT pathway using l-methionine-dl-sulphoximine and azaserine, 15N enrichment of glutamate, alanine and aspartate continued although labelling of glutamine was undetectable. From this and enzymic data, NH 4 + assimilation in the P. canina thallus appears to proceed via GS-GOGAT in the cyanobacterium and via GDH in the fungus; aminotransferases were present in both partners. The cyanobacterium assimilated 44% of the 15N2 fixed; the remainder was liberated almost exclusively as NH 4 + and then assimilated by fungal GDH.
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  • 52
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    Archives of microbiology 135 (1983), S. 103-109 
    ISSN: 1432-072X
    Keywords: RNA polymerase ; Transcription ; Nitrogen fixation ; Symbiosis ; Rhizobium
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    Topics: Biology
    Notes: Abstract DNA-dependend RNA polymerase (EC 2.7.7.6) from Rhizobium japonicum was purified. The subunit structure was found to be ββ′α2σ, with the following apparent molecular weights determined by electrophoresis: M r (β and β') 150,000 each, M r (σ) 96,000, M r (α) 40,000, M r (holoenzyme) 490,000, M r (core enzyme) 380,000. The recovery of σ was 28%. RNA polymerase from aerobically grown R. japonicum cells and from nitrogen-fixing cells have the same electrophoretic properties suggesting that no chemical modification of the enzyme occurs when cells undergo this metabolic differentiation. The enzyme is Mg2+-dependent, rifampicin-sensitive, and has optimal activity at alkaline pH (8–10) and at 35–40° C. It binds strongly to bacteriophage T7 promoters, weakly to antibiotic resistance genes, and not at all to cloned R. japonicum nif DNA. Preliminary in vitro transcription experiments, including nif DNA as template, revealed that additional factors may be required for selective transcription from promoters.
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  • 53
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    Archives of microbiology 136 (1983), S. 219-221 
    ISSN: 1432-072X
    Keywords: Xanthobacter ; Nitrogen fixation ; Oxygen sensitivity ; Nitrogen metabolism ; Glutamine synthetase ; Glutamate synthase
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    Topics: Biology
    Notes: Abstract N2-fixation was investigated in the chemoautotrophic hydrogen bacterium Xanthobacter H4-14. N2-fixing batch cultures of this organism could only be grown at pO2 values of around 0.02 bar, and in continuous culture dissolved oxygen tensions above 16 μM were found to inhibit N2-fixation. Xanthobacter H4-14 utilized a variety of amino acids, nitrate and ammonia as nitrogen sources. Cell-free extracts from steady-state continuous cultures of ammonia grown, nitrate grown and N2-fixing Xanthobacter were assayed for the presence of ammonia assimilation enzymes. No alanine dehydrogenase or glutamate dehydrogenase activity was detected. Ammonia was assimilated exclusively via the glutamine synthetase/glutamate synthase pathway, irrespective of the extracellular concentration of ammonia.
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  • 54
    ISSN: 1432-072X
    Keywords: Selenium ; Hydrogenase ; Bradyrhizobium japonicum ; Nitrogen fixation
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    Notes: Abstract It has been established that the hydrogenase from autotrophically cultured Bradyrhizobium japonicum contains selenium as a bound constituent. About 80% of the enzyme selenium remains bound during precipitation with 5% trichloroacetic acid (TCA). However, 85% of the selenium bound to the enzyme is released by a combined treatment of urea, heat and TCA. Neither selenomethionine nor selenocysteine could be detected on analysis of anaerobically hydrolyzed enzyme. These results are consistent with the report showing that the structural genes for this enzyme do not contain a TGA codon (Sayavedra-Soto et al. 1988) which has been reported to code for selenocysteine incorporation into several proteins (Chambers et al. 1986; Zinoni et al. 1986; Stadtman 1987). We have demonstrated that 75Se from the labeled hydrolyzed enzyme forms the derivative' selenodicysteine. The form of selenium resulting in the synthesis of this derivative apparently is SeO inf3 sup= or a compound such as Se= which is easily oxidized to SeO inf3 sup= . In a separate approach it was established that 12–16% of the total 75Se in the native enzyme reacted with 2,3-diaminonaphthalene indicating that this fraction was present as SeO inf3 sup= . The remaining 75Se was bound to the enzyme protein. From this research, we concluded that Se in Bradyrhizobium japonicum hydrogenase is present in a labile bound form. In this respect, this enzyme is similar to xanthine dehydrogenase and nicotinic acid hydroxylase, both of which contain labile Se constituents that have not been defined.
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  • 55
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    Archives of microbiology 158 (1992), S. 256-261 
    ISSN: 1432-072X
    Keywords: Frankia ; Amino acids ; Glutamine synthetase ; Nitrogen fixation
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    Topics: Biology
    Notes: Abstract The utilization of some amino acids, added at 1 mM and 10 mM concentrations, as the sole combined nitrogen sources by Frankia sp. strain CpI1, has been investigated. Glutamine, like NH 4 + , provided rapid growth without N2 fixation. Histidine at 1 mM yielded poor N2-fixing activity but better cell growth than N2. Aspartate, glutamate, alanine, proline, each at 1 mM concentration, supported similar levels of N2 fixation and growth. Growth on 10 mM glutamate, proline, or histidine resulted in poor N2-fixing activity and poor cell growth. Cells grown on 10 mM alanine had about half the N2-fixing activity of cells grown on N2 but growth was good. Aspartate at 10 mM concentration, however, stimulated N2-fixing activity dramatically and promoted faster growth. Enzyme analysis suggested that asparate is catabolized by glutamate-oxaloacetate transaminase (GOT), since GOT specific activity was induced, and aspartase activity was not detected, in cells grown on aspartate as the sole combined nitrogen source. Thinlayer chromatography (TLC) of metabolites extracted from N2-grown cells fed with [14C]-aspartate showed that label was rapidly accumulated mainly on aspartate and/or glutamate, depending on the cells' physiological state, without detectable labeling on fumarate or oxaloacetate (OAA). These findings provide evidence that aspartate is catabolized by GOT to OAA which, in turn, is rapidly converted to α-ketoglutarate through the TCA cycle and then to glutamate by GOT or by glutamate synthase (GOGAT). The stimulation of N2 fixation and growth by aspartate is probably caused by an increased intracellular glutamate pool.
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  • 56
    ISSN: 1432-072X
    Keywords: Rhizobium leguminosarum biovar phaseoli ; nifA ; nifB ; nifH ; Nitrogen fixation ; nif Gene ; fix Gene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We report the isolation, mutational analysis and the nucleotide sequence of the Rhizobium leguminosarum bv. phaseoli nifA gene. Comparison of the deduced amino acid sequence with other NifA sequences indicated the presence of the conserved central activator and the C-terminal DNA-binding domains. Nodules elicited by a R. leguminosarum bv. phaseoli nifA mutant were symbiotically ineffective. The expression of a nifA-gusA fusion was shown to be independent on the oxygen status of the cell. We cloned the three nifH copies of R. leguminosarum bv. phaseoli and determined the nucleotide sequence of their promoter regions. The expression of nifH-gusA fusions is induced under microaerobic conditions and is dependent on the presence of NifA.
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  • 57
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    Keywords: Synechococcus sp. ; Nitrogen fixation ; Photosynthetic oxygen evolution ; Light-dark cycle ; Light-response curve
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    Notes: Abstract When nitrogen fixing cell cultures of Synechococcus RF-1 were subjected to an alternating lightdark regime (12 h:12 h), a cyclic decrease in the photosynthetic oxygen evolution potential was observed during the dark periods. This rhythm of net photosynthesis rate was maintained for at least two days after transition to continuous light. The decrease in net photosynthesis was accompanied by a stimulation of dark respiration. However, the magnitude of oxygen uptake was considerably smaller than the observed decrease in oxygen evolution. The photosynthetic activity of cells taken from the dark period was characterized by (i) a significantly lower quantum yield and (ii) a strong reduction in the light-saturated rate of photosynthesis. Growing the cultures on nitrate or under continuous light completely suppressed this rhythm. Protein synthesis was not necessary for the recovery of the light-saturated rate of photosynthesis during the light period. The cellular content of chlorophyll a and of phycobiliproteins did not vary between light and dark period, indicating that quantitative changes in the composition of the photosynthetic apparatus are not the basis for the observed oscillations. Regulatory modifications of the photosynthetic efficiency are proposed as an adaptation mechanism to adjust the intracellular oxygen concentration to the needs for nitrogenase activity.
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  • 58
    ISSN: 1432-072X
    Keywords: Aromatic catabolism ; Free-living diazotrophs ; Nitrogen fixation ; catechol dioxygenases ; Protocatechuate dioxygenases
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    Notes: Abstract Six species of free-living nitrogen fixing bacteria, Azomonas agilis, Azospirillum brasilense, Azospirillum lipoferum, Azotobacter chroococcum, Azotobacter vinelandii, and Beijerinckia mobilis, were surveyed for their ability to grow and fix N2 using aromatic compounds as sole carbon and energy source. All six species grew and expressed nitrogenase activity on benzoate, catechol, 4-hydroxybenzoate, naphthalene, protocatechuate, and 4-toluate. In many cases, growth rates on one or more aromatic compounds were comparable to or greater than those on the non-aromatic substrates routinely used for cultivation of the organisms. Specific activity of nitrogenase in extracts of aromatic-grown cells often exceeded that in cells grown on non-aromatic substrates. All six species growing on substrates typically converted to catechol expressed inducible catechol 1,2-dioxygenase and/or catechol 2,3-dioxygenase. When grown on substrates typically converted to protocatechuate, inducible protocatechuate 3,4-dioxygenase and/or protocatechuate 4,5-dioxygenase was expressed. A. chroococcum expressed only ortho cleavage dioxygenases during growth on naphthalene and 4-toluate and only meta cleavage dioxygenases on the other aromatics. B. mobilis expressed only ortho cleavage dioxygenases. The other four species examined expressed both ortho and meta cleavage enzymes.
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  • 59
    ISSN: 1432-072X
    Keywords: Rhodobacter capsulatus ; Nitrogen fixation ; Nitrogenase activity ; Nitrogenase expression ; Aerobiosis ; Oxygen ; Light ; Modification of the Fe protein
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract Rhodobacter capsulatus was grown chemotrophically in the dark in oxygen-regulated chemostat culture and in the presence of limiting amounts of fixed N. When the oxygen partial pressure was varied, in situ nitrogen fixation occurred only at 1% of air saturation of the medium. By contrast, nitrogenase proteins and their activity measured in the absence of oxygen could be detected up to 30% of air saturation. This revealed that expression of nitrogenase is much less sensitive toward oxygen than the in situ function of the enzyme. At oxygen partial pressures 〉 1% of air saturation, the degree of modification of the Fe protein of nitrogenase was increased. Light was of no stimulatory effect on both the activity and the expression of nitrogenase. This holds true for growth at 1% or 5% of air saturation. At 5% of air saturation, however, high illumination enhanced the inhibitory effect of oxygen on nitrogenase formation.
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  • 60
    ISSN: 1432-072X
    Keywords: Calcium ; Nitrogen fixation ; Nodulation ; Periplasmic proteins ; Rhizobium fredii
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    Notes: Abstract Calcium is essential for the growth of rhizobia and the formation of nitrogen-fixing root-nodules on legumes, but its precise role in these processes remains unknown. We have found that Rhizobium fredii USDA208 accumulates a major 38 kDa protein when grown in media supplemented with 0.3–2 μmM CaCl2. We have purified this protein and raised polyclonal antibodies against it. The protein initially is synthesized as a 40 kDa precursor which subsequently undergoes calcium-dependent processing to give rise to the mature polypeptide. Subcellular and immunocytochemical localization studies indicate that the 38 kDa protein accumulates preferentially in the periplasmic space. Its N-terminal sequence, AETIKIGVAGPMTG, shows significant homology to the N-termini of amino acid binding proteins from the periplasm, including leucine-, isoleucine-, and valine-specific binding proteins of Pseudomonas aeruginosa and Escherichia coli and a leucine-specific binding protein of E. coli. The R. fredii protein does not, however, bind [3H]-leucine. The 38 kDa protein is encoded by the bacterial chromosome. It is absent in several rhizobia other than R. fredii, but antigenically related polypeptides are present in Escherichia coli and Erwinia carotovora subsp. carotovora.
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  • 61
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    Archives of microbiology 124 (1980), S. 161-167 
    ISSN: 1432-072X
    Keywords: Nitrogen fixation ; Photosynthesis ; Green alga ; Chl a and b ; DCMU ; Light and O2 dependency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A unicellular alga which can grow in the light without a combined nitrogen source was isolated from a hot spring. The cells were almost spherical, usually 5–10 μm in diameter. Absorption spectra of the watersoluble pigments and of the acetone-extracted ones revealed the existence of chlorophyll a and b and the absence of phycobilins. Thin sections examined by electron microscopy revealed an eukaryotic organization with features typical of the coccoid green algae (the Chlorococcales). Cells divided by internal cytokinesis and subsequent liberation of daughter cells from the parental wall, in a way similar to Chlorella. The alga reduced acetylene to ethylene and incorporated 15N2 into cell protoplasm when incubated in a low oxygen atmosphere. Nitrogenase activity was light-dependent, microaerophilic and thermophilic. Although the association of symbiotic nitrogen fixing prokaryotes with the cells may still be possible, any such organisms have not so far been detected.
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  • 62
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    Archives of microbiology 127 (1980), S. 115-118 
    ISSN: 1432-072X
    Keywords: Proteus mirabilis ; Serratia marcescens ; Erwinia herbicola ; Nitrogen fixation ; nif genes ; his genes ; Plasmids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Plasmid pRD1, an R plasmid of the P incompatibility group which carries his and nif genes from Klebsiella pneumoniae in addition to drug resistance markers derived from RP4, was transferred to His- mutants of Serratia marcescens, Erwinia herbicola and Proteus mirabilis. His+ transconjugants were obtained at low but different frequencies according to recipient genus. Transconjugants all acquired the drug resistance, and were Nif+ in S. marcescens and E. herbicola, having acetylene-reducing activities of the same order of magnitude as the parent K. pneumoniae and fixing 15N2. No evidence for nif expression in P. mirabilis transconjugants was obtained though the nif genes were present.
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  • 63
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    Archives of microbiology 132 (1982), S. 219-224 
    ISSN: 1432-072X
    Keywords: Rhizobium ; Nitrogen fixation ; Nodules ; Soybean
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Several mutants defective in nodulation were isolated from Rhizobium japonicum strains 3I1b110 and 61A 76. Mutants of class I do not form nodules after incubation with soybean [Glycine max (L.) Merrill] for 17 days, but will do so by 28 days. When host plants other than G. max are infected with several of these strains, there is no detectable difference in the time of nodulation or size of nodules as compared to the wild type. Two mutants of class I (i. e., SM1 and SM2) have been shown previously to be altered in the lipopolysaccharide portion of their cell wall. Mutants of class II are not slow to nodulate but form fewer nodules than the wild type on all the host plants tested. Mutants of class III are unable to form nodules. Some bacteriophage-resistant mutants, altered in cell surface structure, fall into this class. Two mutants of class III do not bind to soybean roots.
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  • 64
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    Archives of microbiology 133 (1982), S. 172-177 
    ISSN: 1432-072X
    Keywords: Beggiatoa ; Nitrogen fixation ; Acetylene reduction ; Nitrate assimilation ; Microaerobic ; Isolation of marine strains
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Four newly isolated marine strains of Beggiatoa and five freshwater strains were tested for nitrogen fixation in slush agar medium. All strains reduced acetylene when grown microaerobically in media containing a reduced sulfur source and lacking added combined nitrogen. The addition of 2 mmol N, as nitrate or ammonium salts, completely inhibited this reduction. Although not optimized for temperature or cell density, acetylene reduction rates ranged from 3.2 to 12 nmol·mg prot-1 min-1. Two freshwater strains did not grow well or reduce acetylene in medium lacking combined nitrogen if sulfide was replaced by thiosulfate. Two other strains grew well in liquid media lacking both combined nitrogen and reduced sulfur compounds but only under lowered concentrations of air. All freshwater strains grew well in medium containing nitrate as the combined nitrogen source. Since they did not reduce acetylene under these conditions, we infer that they can assimilate nitrate.
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    Archives of microbiology 133 (1982), S. 312-317 
    ISSN: 1432-072X
    Keywords: Rhizobium japonicum ; Rhizobium leguminosarum ; Formate metabolism ; Formate dehydrogenase ; Nitrogen fixation ; Nitrogenase ; Bacteroids ; Symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Formate metabolism supported nitrogen-fixation activity in free-living cultures of Rhizobium japonicum. However, formate0dependent nitrogense activity was observed only in the presence of carbon sources such as glutamate, ribose or aspartate which by themselves were unable to support nitrogenase activity. Formate-dependent nitrogenase activity was not detected in the presence of carbon sources such as malate, gluconate or glycerol which by themselves supported nitrogenase activity. A mutant strain of R. japonicum was isolated that was unable to utilise formate and was shown to lack formate dehydrogenase activity. This mutant strain exhibited no formate-dependent nitrogenase activity. Both the wild-type and mutant strains nodulated soybean plants effectively and there were no significant differences in the plant dry weight or total nitrogen content of the respective plants. Furthermore pea bacteroids lacked formate dehydrogenase activity and exogenously added formate had no stimulatory effect on the endogenous oxygen uptake rate. The role of formate metabolism in symbiotic nitrogen fixation is discussed.
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  • 66
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    Keywords: Nitrogen fixation ; Nitrogenase regulation ; Glutamine synthetase ; Methionine suofoximine ; Rhodospirillaceae
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    Notes: Abstract Methionine sulfoximine (MSX), an irreversible inhibitor of glutamine synthetase of Rhodopseudomonas palustris restored nitrogenase activity to cells in which nitrogenase had been completely inhibited by ammonia switch-off. After addition of MSX, there was a lag period before nitrogenase activity was fully restored. During this lag, glutamine synthetase activity progressively decreased, and near the time of its complete inhibition, nitrogenase activity resumed. Nitrogenase switch-off by ammonia thus required active glutamine synthetase. Glutamine itself caused nitrogenase inhibition whose reversal by MSX depended on the relative ratio of MSX to glutamine. Unlike ammonia, glutamine inhibited nitrogenase under conditions where glutamine synthetase activity was absent. This indicates that glutamine is the effector molecule in nitrogenase switch-off, for instance by interacting with the enzymatic system for Fe protein inactivation. The effects of glutamine and MSX were also dependent on the culture age. Possible explanation for this and for the competitive effects are a common binding site within the regulatory apparatus for nitrogenase, or, in part, within a common transport system. Some observations with MSX were extended to Rhodopseudomonas capsulata and agreed with those in R. palustris.
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  • 67
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    Keywords: Azotobacter vinelandii ; Continuous culture ; Oxygen control ; Nitrogen fixation ; Respiratory protection
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    Notes: Abstract Azotobacter vinelandii strain OP was grown in continuous culture at various dissolved oxygen concentrations of air (100% air saturation of the medium=225 ±14 μM O2). Sucrose was added as carbon source and either dinitrogen or ammonia as nitrogen sources. Irrespective of the nitrogen source steady state cultures showed the following general responses with dissolved oxygen concentrations increasing from about 1% to 30% air saturation: (i) cell protein levels, (ii) the amount of cell protein formed per sucrose consumed as well as (iii) nitrogenase activity decreased by at least a factor of two while (iv) cellular respiration increased. At higher oxygen concentrations the parameters changed only slightly, if at all. Increasing the sucrose concentration in the inflowing medium (s R) from 3 g/l to 15 g/l increased the total level of cellular respiration with nitrogen-fixing cultures but was more pronounced with ammonium-assimilating cultures. With nitrogen-fixing cultures cell protein levels increased five-fold while the ratio of protein formed per sucrose consumed as well as cellular nitrogenase activity remained unaffected. With ammonium-assimilating cultures the cell protein level was only doubled and the level of cell protein formed per sucrose consumed was decreased at the higher s R. Increasing the dilution rate at a constant oxygen concentration of 45% air saturation resulted in an almost parallel increase of both cellular respiratory and nitrogenase activity at low and moderate dilution rates. At high dilution rates nitrogenase activity increased steeply over the respiratory activity. Nitrogen-fixing cultures adapted to various oxygen concentrations were subjected to oxygen stress by increasing the oxygen concentration for 7 min. In all cases, this resulted in a complete inhibition (‘switch-off’) of nitrogenase activity. Upon restoration of the original oxygen concentration nitrogenase activity returned to a decreased level. The discussion arrives at the conclusion that some of the results are incompatible with the concept of respiratory protection of nitrogenase.
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  • 68
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    Archives of microbiology 136 (1983), S. 81-83 
    ISSN: 1432-072X
    Keywords: Ammonia production ; Anabaena ; Cyanobacteria ; Nitrate reductase ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In the filamentous heterocystous cyanobacterium Anabaena sp. strain ATCC 33047 dinitrogen fixation and nitrate reduction are mutually exclusive processes. Nitrate promotes nitrate reductase synthesis and represses nitrogenase formation. Inhibition of ammonium assimilation by l-methionine-d,l-sulfoximine (MSX) alleviates the repressive effect of nitrate on nitrogenase synthesis, thus indicating that the nitrate effect is indirect through metabolites generated from the ammonium derived from nitrate reduction. In MSX-treated cells both nitrate reduction and dinitrogen fixation take place simultaneously, although at different sites of the filament, without any apparent competition for the required reducing power. The MSX-treated Anabaena cells generate ammonium from both nitrate and dinitrogen, simultaneously.
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  • 69
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    Archives of microbiology 138 (1984), S. 212-216 
    ISSN: 1432-072X
    Keywords: Denitrification ; Nitrate respiration ; Nitrous oxide reduction ; Nitrogen fixation ; Azospirillum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nitrous oxide reduction can consistently be demonstrated with high activities in cells of Azospirillum brasilense Sp 7 which are grown anaerobically in the presence of low amounts of nitrite. Azospirillum can even grow anaerobically with nitrous oxide in the absence of any other respiratory electron acceptor. Nitrous oxide reduction by Azospirillum is inhibited by acetylene, amytal and weakly by carbon monoxide. Azospirillum converts nitrous oxide to molecular nitrogen without the formation of ammonia. The cells must, therefore, be supplied with ammonia from nitrogen fixation during anaerobic growth with nitrous oxide. When no other nitrogen compound besides nitrous oxide is available in the medium, the bacteria synthesize nitrogenase from protein reserves in about 2 h. Nitrogenase synthesis is blocked by chloramphenicol under these conditions. In contrast, the addition of nitrate or nitrite to the medium represses the synthesis of nitrogenase. Nitrous oxide reduction by Azospirillum and other microorganisms is possibly of ecological significance, because the reaction performed by the bacteria may remove nitrous oxide from soils.
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  • 70
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    Archives of microbiology 130 (1981), S. 96-100 
    ISSN: 1432-072X
    Keywords: Nitrogen fixation ; Nitrate respiration ; Denitrification ; Assimilatory nitrate reduction ; Dissimilatory nitrate reduction ; Acetylene reduction ; Azospirillum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Azospirillum spp. participate in all steps of the nitrogen cycle except nitrification. They can fix molecular nitrogen and perform assimilatory nitrate reduction and nitrate respiration. Culture conditions have been defined under which nitrate is used both as terminal respiratory electron acceptor and as nitrogen source for growth. Nitrate and, possibly to a very limited extent, nitrite, but not sulfate, iron or fumarate support anaerobic respiration. Under anaerobic conditions, nitrate can also supply energy for nitrogen fixation but without supporting growth. Nitrate-dependent nitrogenase activity lasts only for 3–4 h until the enzymes of assimilatory nitrate reduction are synthesized. Nitrite accumulates during this period and inhibits nitrogenase activity at concentrations of about 1 mM.
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  • 71
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    Archives of microbiology 140 (1984), S. 215-217 
    ISSN: 1432-072X
    Keywords: Glutathione reductase ; Cyanobacteria ; Nostoc muscorum ; O2 protection ; Glutathione ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Glutathione reductase activity was detected and characterized in heterocysts and vegetative cells of the cyanobacterium Nostoc muscorum. The activity of the enzyme varied between 50 and 150 nmol reduced glutathione· min-1·mg protein-1, and the apparent Km for NADPH was 0.125 and 0.200 mM for heterocysts and vegetative cells, respectively. The enzyme was found to be sensitive to Zn+2 ions, however, preincubation with oxidized glutathione rendered its resistance to Zn+2 inhibition. Nostoc muscorum filaments were found to contain 0.6–0.7mM glutathione, and it is suggested that glutathione reductase can regenerate reduced glutathione in both cell types. The combined activity of glutathione reductase and isocitrate dehydrogenase in heterocysts was as high as 18 nmol reduced glutathione·min-1·mg protein-1. A relatively high superoxide dismutase activity was found in the two cell types; 34.2 and 64.3 enzyme units·min-1·mg protein-1 in heterocysts and vegetative cells, respectively. We suggest that glutathione reductase plays a role in the protection mechanism which removes oxygen radicals in the N2-fixing cyanobacterium Nostoc muscorum.
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  • 72
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    Archives of microbiology 158 (1992), S. 155-161 
    ISSN: 1432-072X
    Keywords: Anoxygenic phototrophic bacteria ; Photosynthesis ; Heliobacteria ; Nitrogen fixation
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    Topics: Biology
    Notes: Abstract Three species of anoxygenic phototrophic heliobacteria, Heliobacterium chlorum, Heliobacterium gestii, and Heliobacillus mobilis, were studied for comparative nitrogen-fixing abilities and regulation of nitrogenase. Significant nitrogenase activity (acetylene reduction) was detected in all species grown photoheterotrophically on N2, although cells of H. mobilis consistently had higher nitrogenase activity than did cells of either H. chlorum or H. gestii. Nitrogen-fixing cultures of all three species of heliobacteria were subject to “switch-off” of nitrogenase activity by ammonia; glutamine also served to “switch-off” nitrogenase activity but only in cells of H. mobilis and H. gestii. Placing photosynthetically grown heliobacterial cultures in darkness also served to “switch-off” nitrogenase activity. Dark-mediated “switch-off” was complete in lactate-grown heliobacteria but in pyruvate-grown cells substantial rates of nitrogenase activity continued in darkness. In all heliobacteria examined ammonia was assimilated primarily through the glutamine synthetase/glutamate synthase (GS/GOGAT) pathway although significant levels of alanine dehydrogenase were present in extracts of cells of H. gestii, but not in the other species. The results suggest that heliobacteria, like phototrophic purple bacteria, are active N2-fixing bacteria and that despite their gram-positive phylogenetic roots, heliobacteria retain the capacity to control nitrogenase activity by a “switch-off” type of mechanism. Because of their ability to fix N2 both photosynthetically and in darkness, it is possible that heliobacteria are significant contributors of fixed nitrogen in their paddy soil habitat.
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  • 73
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    Archives of microbiology 132 (1982), S. 333-337 
    ISSN: 1432-072X
    Keywords: Anabaena variabilis Kütz ; 14C-prelabeled blue-green algae ; Interaction respiration/photosynthesis ; CO2 exchange ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Prelabeled Anabaena variabilis Kütz. evolves 14CO2 in the light with KCN and DCMU (2,4-dichlorophenyl-1,1-dimethylurea) present, comparable to the dark control without inhibitors added. Double-reciprocal plots of CO2 release vs. light intensity with either KCN or KCN+DCMU present result in two straight lines intersecting at the ordinate. Apparently, reducing equivalents originating from carbohydrate catabolism are channeled into the photosynthetic electron-transport chain, competing for electrons from photosystem II. Under these conditions, the CO2 release is accompanied by a light-dependent oxygen uptake, presumably due to oxygen-reducing photosystem-I activity while ribulose-bisphosphate carboxylase is inhibited by KCN. Comparing nine blue-green algae it was shown that only nitrogen-fixing species release substantial amounts of CO2 in the light with KCN or KCN+DCMU present. This release is particularly obvious with Anabaena variabilis Kütz. under nitrogen-fixing conditions, but small when the alga is grown with combined nitrogen. We conclude that nitrogen-fixing species share a common link between respiratory and photosynthetic electron transport. The physiological role may be electron supply of nitrogenase by photosystem I.
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  • 74
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    Archives of microbiology 133 (1982), S. 6-10 
    ISSN: 1432-072X
    Keywords: Rhodospirillaceae ; Rhodopseudomonas globiformis ; Nitrogen metabolism ; Nitrogen fixation ; Glutamine synthetase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Rhodopseudomonas globiformis strain 7950 grew with a variety of amino acids, urea, or N2 as sole nitrogen sources. Cultures grown on N2 reduced acetylene to ethylene; this activity was absent from cells grown on nonlimiting NH 4 + . Glutamate dehydrogenase could not be detected in extracts of cells of strain 7950, although low levels of an alanine dehydrogenase were present. Growth ofR. globiformis on NH 4 + was severely inhibited by the glutamate analogue and glutamine synthetase inhibitor, methionine sulfoximine. High levels of glutamine synthetase (as measured in the γ-glutamyl transferase assay) were observed in cell extracts of strain 7950 regardless of the nitrogen source, although N2 and amino acid grown cells contained somewhat higher glutamine synthetase contents than cells grown on excess NH 4 + . Levels of glutamate synthase inR. globiformis were consistent with that reported from other phototrophic bacteria. Both glutamate synthase and alanine dehydrogenase were linked to NADH as coenzyme. We conclude thatR. globiformis is capable of fixing N2, and assimilates NH 4 + primarily via the glutamine synthetase/glutamate synthase pathway.
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  • 75
    ISSN: 1432-072X
    Keywords: Cyanobacteria ; Ultrastructure ; Nitrogen fixation ; Water stress ; Taxonomy ; DNA ; Plasmids
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    Topics: Biology
    Notes: Abstract Two strains of desiccation-tolerant coccoid cyanobacteria, Chroococcus S24, a marine form, and Chroococcus N41, a cryptoendolith isolated from a hot-desert rock, have been characterized. The mol % DNA base compositions of the strains are 47.1 and 48.9% respectively. Plasmid DNA was not detected in either strain. The pigment contents and nutritional characteristics of the strains are identical. Both lack phycoerythrinoid pigments and, in culture, behave as slow-growing halotolerant marine forms with elevated requirements for Na+, Cl−, Mg2+ and Ca2+. Sucrose was the only carbon source of those tested that supported photoheterotrophic growth. Each strain synthesizes nitrogenase under anaerobic conditions but not in air. Morphologically the two strains are indistinguishable. They are considered to be independent isolates of the same cyanobacterial species. Chroococcus N41 was studied in detail with the electron microscope. When brought to equilibrium at matric water potentials of-168 MPa and lower (to-673 MPa=c0.12a w) the protoplast shrinks, but the cells maintain the same size and diameter as those at-2,156 kPa (MN medium; control); the sheath expands and remains attached to the cell wall outer membrane by fibrils. The cell wall, cell membrane, thylakoid membranes, cyanophycin granules and carboxysomes appeared intact in desiccated cells.
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  • 76
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    Keywords: Plectonema ; Nitrogen fixation ; Nitrogen starvation ; Cyanobacteria ; Glycogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nitrogen-starved cells of the filamentous, nonheterocystous cyanobacterium, Plectonema boryanum 581, were cultured microaerophilically in the presence and absence of exogenous, organic substrates (fructose, glucose, sucrose, and CO2) to determine the effect of an external carbon source on nitrogenase activity. In unsupplemented and in fructose-, glucose-, and sucrose-enriched cultures, nitrogenase activity was detected 75 min after the exclusion of oxygen, compared to 90 min for the CO2-supplemented cultures. Nitrogenase activity increased for more than 40 h at levels unique to each carbon-supplemented and unsupplemented culture. The relationship between nitrogenase activity, carbon source, and glycogen content is discussed.
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  • 77
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    Archives of microbiology 156 (1991), S. 270-276 
    ISSN: 1432-072X
    Keywords: Coding regions ; Codon frequency table ; IS-like elements ; Nitrogen fixation ; Nodulation ; Repeated sequence ; Bradyrhizobium japonicum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To date, the sequences of 45 Bradyrhizobium japonicum genes are known. This provides sufficient information to determine their codon usage and G+C content. Surprisingly, B. japonicum nodulation and NifA-regulated genes were found to have a less biased codon usage and a lower G+C content than genes not belonging to these two groups. Thus, the coding regions of nodulation genes and NifA-regulated genes could hardly be identified in codon preference plots whereas this was not difficult with other genes. The codon frequency table of the highly biased genes was used in a codon preference plot to analyze the RSRjα9 sequence which is an insertion sequence (IS)-like element. The plot helped identify a new open reading frame (ORF355) that escaped previous detection because of two sequencing errors. These were now corrected. The deduced gene product of ORF355 in RSRjα9 showed extensive similarity to a putative protein encoded by an ORF in the T-DNA of Agrobacterium rhizogenes. The DNA sequences bordering both ORFs showed inverted repeats and potential target site duplications which supported the assumption that they were IS-like elements.
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  • 78
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    Archives of microbiology 154 (1990), S. 510-513 
    ISSN: 1432-072X
    Keywords: Frankia ; Nitrogen fixation ; Glutamine synthetase ; Ammonium assimilation ; Serine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nitrogen-starved cells of Frankia strain HFPArl3 incorporated [13N]-labeled ammonium into glutamine ≫ serine ≫ (glutamate, alanine, aspartate), after five-minute radioisotope exposures. High initial endogenous pools of glutamate were reduced, while total glutamine increased, during short term NH inf4 sup+ incubation. Preincubation of cells in methionine sulfoximine (MSX) resulted in [13N]glutamine reduced by more than 80%, while [13N]glutamate and [13N]alanine levels increased. The results suggest that glutamine synthetase is the primary enzyme of ammonium assimilation, and that glutamate dehydrogenase and alanine dehydrogenase may also function in ammonium assimilation at low levels. Efflux of [13N]serine and lesser amounts of [13N]glutamine was detected from the Frankia cells. The identity of both Ser and Gln in the extracellular compartment was confirmed with gas chromatography/mass spectrometry. Serine efflux may be of significance in nitrogen transfer in Frankia.
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  • 79
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    Archives of microbiology 156 (1991), S. 362-366 
    ISSN: 1432-072X
    Keywords: Peribacteroid membrane ; Symbiosomes ; Grycine max ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Addition of ATP to intact symbiosomes isolated from soybean nodules, resulted in generation of a membrane potential (positive inside) across the peribacteroid membrane (PBM). This energisation was monitored as oxonol fluorescence quenching. The rate of fluorescence quenching was inhibited by the inclusion of permeant anions in the reaction medium. Using this inhibition as a measure of anion uptake across the PBM, the presence of a phthalonate-sensitive dicarboxylate carrier on the PBM was confirmed. Following dissipation of the membrane potential by a permeant anion, a pH gradient, measured using [14C]methylamine uptake, was slowly established across the PBM. This ΔpH was abolished by addition of an uncoupler but was insensitive to inhibitors of bacteroid respiration. The difference in pH between the external medium and the symbiosome interior was estimated to be in the range of 1–1.6 pH units. The magnitude in planta will depend on the concentrations of ATP and permeant anions in the cytosol of the host cell.
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  • 80
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    Archives of microbiology 157 (1992), S. 361-366 
    ISSN: 1432-072X
    Keywords: Rhodobacter capsulatus ; Ammonium assimilation ; Nitrogen fixation ; Glutamate synthase
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract Nitrogen assimilation in Rhodobacter capsulatus has been shown to proceed via the coupled action of glutamine synthetase (GS) and glutamate synthase (GOGAT) with no measurable glutamate dehydrogenase (GDH) present. We have recently isolated a novel class of mutants of R. capsulatus strain B100 that lacks a detectable GOGAT activity but is able to grow at wild type rates under nitrogen-fixing conditions. While NH 4 + -supported growth in the mutants was normal under anaerobic/photosynthetic conditions, the growth rate was decreased under aerobic conditions. Ammonium and methylammonium uptake experiments indicated that there was a clear difference in the ammonium assimilatory capabilities in these mutants under aerobic versus anaerobic growth. Regulation of expression of a nifH : : lacZ fusion in these mutants was not impaired. The possible existence of alternative ammonium assimilatory pathways is discussed.
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  • 81
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    Archives of microbiology 157 (1992), S. 431-435 
    ISSN: 1432-072X
    Keywords: Nitrogen fixation ; Nitrogenase ; “Switchoff” ; Metabolic regulation ; Rhodospirillum rubrum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effect of NAD(P) and analogs of this nucleotide on nitrogenase activity in Rhodospirillum rubrum has been studied. Addition of NAD+ to nitrogen fixing Rsp. rubrum leads to inhibition of nitrogenase. NADP+ has the same effect but NADH or analogs modified in the nicotinamide portion do not cause inhibition. In contrast to ammonium ions, addition of NAD+ leads to inhibition of nitrogenase in cells that have been N-starved under argon. The inhibitory effect of NAD+ is more pronounced at lower light intensities. Addition of NAD+ also leads to inhibition of glutamine synthetase, a phenomenon also occurring when “switchoff” is produced by the addition of effectors such as ammonium ions or glutamine. It is also shown that NAD+ is taken up by Rsp. rubrum cells.
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  • 82
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    Archives of microbiology 159 (1993), S. 423-427 
    ISSN: 1432-072X
    Keywords: Chlorogloeopsis ; Continuous culture ; Cyanobacterium ; Nitrogen fixation ; Oxygen effects ; Photosynthesis ; Respiration ; Temperature effects ; Thermophile
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract The effect of temperature and oxygen on diazotrophic growth of the thermophilic cyanobacterium HTF (High Temperature Form) Chlorogloeopsis was investigated using cells grown in light-limited continuous culture at a dilution rate of 0.02 h-1. Diazotrophy was more sensitive to elevated temperatures than growth with combined nitrogen. The maximum temperature for growth of cultures gassed with CO2-enriched air was more than 55 °C but less than 60 °C with N2 as the sole nitrogen source, but between 60°C and 65°C when nitrate was present in the medium. The effect of temperature on nitrogenase activity, photosynthesis and respiration in the dark was determined using cells grown at 55°C. Maximal rates of all three processes were observed at 55°C and rates at 60°C during shortterm incubations were not less than 75% of the maximum. However, nitrogenase activity at 60°C was unstable and decayed at a rate of 2.2 h-1 under air and at 0.3 h-1 under argon. Photosynthesis and respiration were more stable at 60°C than anoxic nitrogen fixation. The upper temperature limits for diazotrophic growth thus seem to be set by the stability of nitrogenase.
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  • 83
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    Keywords: Carbohydrate ; Cell cycle ; Hydrogen production ; Marine ; Synechococcus sp. ; Nitrogen fixation ; Synchronous culture ; Unicellular cyanobacterium
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    Notes: Abstract Synchronously growing cells of nitrogen-fixing Synechococcus sp. Miami BG 043511 were harvested periodically and the capability for hydrogen photoproduction in closed vessels was measured under hydrogen production conditions. The capability for hydrogen photoproduction in cells was correlated with that of cellular carbohydrate content. Cells with a high carbohydrate content exhibited a high capacity for hydrogen production and those with low carbohydrate content exhibited low capacity for hydrogen production. Nitrogenase activity at the onset of incubation did not coincide with a capability for the cells to produce hydrogen during the subsequent incubation period. Interestingly, when cells with a high capacity for hydrogen photoaccumulation were incubated, alternate periods of hydrogen and oxygen accumulation were observed at 12 hour intervals. About 0.5 ml of hydrogen per ml of cell suspension was accumulated in flasks during the initial 12-h incubation period. These observations indicate that the use of synchronous culture can be one of the ways of provide materials suitable not only for basic studies but also for applied aspects of hydrogen photoproduction.
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  • 84
    ISSN: 1432-072X
    Keywords: Key words     Synechococcus sp. ; Nitrogen fixation ; Photosynthetic oxygen evolution ; Light-dark cycle ; Light-response curve
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    Notes: Abstract      When nitrogen fixing cell cultures of Synechococcus RF-1 were subjected to an alternating light-dark regime (12 h : 12 h), a cyclic decrease in the photosynthetic oxygen evolution potential was observed during the dark periods. This rhythm of net photosynthesis rate was maintained for at least two days after transition to continuous light. The decrease in net photosynthesis was accompanied by a stimulation of dark respiration. However, the magnitude of oxygen uptake was considerably smaller than the observed decrease in oxygen evolution. The photosynthetic activity of cells taken from the dark period was characterized by (i) a significantly lower quantum yield and (ii) a strong reduction in the light-saturated rate of photosynthesis. Growing the cultures on nitrate or under continuous light completely suppressed this rhythm. Protein synthesis was not necessary for the recovery of the light-saturated rate of photosynthesis during the light period. The cellular content of chlorophyll a and of phycobiliproteins did not vary between light and dark period, indicating that quantitative changes in the composition of the photosynthetic apparatus are not the basis for the observed oscillations. Regulatory modifications of the photosynthetic efficiency are proposed as an adaptation mechanism to adjust the intracellular oxygen concentration to the needs for nitrogenase activity.
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  • 85
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    Keywords: Nitrogen fixation ; Vanadium ; anf Azotobacter ; nif ; Sigma(σ)54 ; Sigma(σ)N ; Molybdenum ; vnf ; ntrC ; rpoN
    Source: Springer Online Journal Archives 1860-2000
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    Notes: Abstract Several regulatory gene mutants of Azotobacter vinelandii were tested for ability to synthesize functional nitrogenase-1 (Nif phenotype), nitrogenase-2 (Vnf), or nitrogenase-3 (Anf). While nifA mutants were Nif-, Vnf+, and Anf+/-, and ntrC mutants were Nif+, Vnf+, and Anf+, nifA ntrC double mutants were Nif-, Vnf-, and Anf-. A vnfA mutant was Nif+, Vnf+/-, and Anf+/-, and an anfA strain was Nif+, Vnf+, and Anf-. lacZ fusions in the nifH, vnfH, vnfD, anfH, and nifM genes of Azotobacter vinelandii were constructed and introduced into wild-type and regulatory mutants of A. vinelandii. Expression of these operons correlated with the growth phenotype of the regulatory mutants. Apparently either NifA or NtrC can activate expression of nifM. Also, expression of the anf operon required the NifA transcriptional activator, although there are no NifA binding sites at appropriate locations upstream of anfH (or anfA). The results confirm previous reports that VnfA and AnfA are required for expression of vnf and anf genes, respectively, and that VnfA is involved in repression of the nifHDK operon in the absence of molybdenum and of the anfHDGK operon in the presence of vanadium.
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    Trees 5 (1991), S. 227-231 
    ISSN: 1432-2285
    Keywords: Robinia pseudoacacia L. ; Nitrate ; Nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Experiments with black locust (Robinia pseudoacacia L.) seedlings grown under strictly controlled laboratory conditions indicated that the availability of nitrate has a marked impact on nitrogen fixation. When nitrate concentrations were very low, both nodulation and seedling growth were impaired, whereas nitrate concentrations high enough to promote plant growth strongly inhibited symbiotic nitrogen fixation. When nitrate was added to the growth medium after infection, nodulation and nitrogen fixation of the seedlings decreased. This effect was even more marked when nitrate was applied before infection with rhizobia. Higher nitrogen concentrations also reduced nodule number and nodule mass when applied simultaneously with the infecting bacteria. The contribution of symbiotic nitrogen fixation to black locust shoot mass by far exceeded its effects on shoot length and root mass. When nitrate availability was very low, specific nitrogen fixation (i. e. nitrogenase activity per nodule wet weight) was improved with increasing nitrogen supply, but rapidly decreased with higher nitrogen concentrations.
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    Theoretical chemistry accounts 60 (1982), S. 579-587 
    ISSN: 1432-2234
    Keywords: Nitrogen fixation ; Nitrogen complexes ; Carbon monoxide complexes ; Electronic effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract MNDO method is used to study the interaction of nitrogen and carbon monoxide molecules with a proton, hydrogen atom, hydride ion, hydrogen molecule ion and hydrogen molecule. Predicted geometries and heats of reaction of different complexes are presented. The wave functions are analyzed in terms of ground state charge distributions and overlap populations. Electronic effects accompanying complexation are also discussed.
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  • 88
    ISSN: 1573-1561
    Keywords: Nitrogen fixation ; glyceollin ; phytoalexin ; Bradyrhizobium japonicum ; nodulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Nitrogen fixation in root nodules formed by strain 2143 ofBradyrhizobium japonicum andGlycine max (L.) Merr. cv Williams 82 reaches a maximum at 21 to 28 days postinoculation and then begins to decline. The phytoalexin, glyceollin, accumulates in nodules coincident with the decline in nitrogen fixation. Nodules formed by strain 3122, which are unable to fix nitrogen, accumulate even higher levels of glyceollin and do so beginning 21 days postinoculation even though these nodules contain no recoverable bacteria. The typical phytoalexin response occurs within days of infection. The mechanism by which this response in theBradyrhizobium japonicum-soybean combination is delayed 2 to 3 weeks after infection is presently unknown but phytoalexin accumulation could contribute to the inability of the soybean-Bradyrhizobium japonicum combination to maintain high levels of nitrogen fixation throughout the growing season.
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  • 89
    ISSN: 1432-2048
    Keywords: Nitrogen fixation ; Nodule development ; Senescence (nodules) ; Vigna
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cowpea (Vigna unguiculata (L.) Walp cv. Vita 3) seedlings inoculated with Rhizobium strain CB756 were cultured with their root systems maintained in air or in Ar: O2 (80:20, v/v) during early nodule development (up to 24 d after sowing). Compared with those in air, seedlings in Ar:O2 showed progressive N deficiency with inhibited shoot growth, reduced ribulose-1,5-bisphosphate carboxylase and total protein levels and loss of chlorophyll in the leaves. Nodule initiation, differentiation of infected and uninfected nodule tissues and the ultrastructure of bacteriod-containing cells were similar in the air and Ar: O2 treatments up to 16 d after sowing. Thereafter the Ar: O2 treatment caused cessation of growth and development of nodules, reduced protein levels in bacteroids and nodule plant cells, and progressive degeneration of nodule ultrastructure leading to premature senescence of these organs. Provision of NO 3 - (0.1–0.2 mM) to Ar: O2-grown seedlings overcame the abovementioned consequences of N2 deficiency on nodule and plant growth, but merely delayed the degenerative effects of Ar: O2 treatment on nodule structure and senescence. Treatment of Ar: O2-grown seedlings with NO 3 - greatly increased the protein level of nodules but the increase was largely restricted to the plant cell fraction as opposed to the bacteroids. By contrast, NO 3 - treatment of air-grown seedlings increased protein of bacteroid and host nodule fractions to the same relative extents when compared with air-grown plants not supplemented with NO 3 - . These findings, taken together with studies of the distribution of N in nodules of symbiotically effective plants grown from 15N-labeled seed, indicate that direct incorporation of fixation products by bacteroids may be a critical feature in the establishment and continued growth of an effective symbiosis in the cowpea seedling.
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  • 90
    ISSN: 1432-2048
    Keywords: Glutamine synthetase ; Leghaemoglobin ; Nitrogenase ; Nitrogen fixation ; Phaseolus ; Rhizobium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The activities of glutamine synthetase (GS), nitrogenase and leghaemoglobin were measured during nodule development in Phaseolus vulgaris infected with wild-type or two non-fixing (Fix-) mutants of Rhizobium phaseoli. The large increase in GS activity which was observed during nodulation with the wild-type rhizobial strain occurred concomitantly with the detection and increase in activity of nitrogenase and the amount of leghaemoglobin. Moreover, this increase in GS was found to be due entirely to the appearance of a novel form of the enzyme (GSn1) in the nodule. The activity of the form (GSn2) similar to the root enzyme (GSr) remained constant throughout the experiment. In nodules produced by infection with the two mutant strains of Rhizobium phaseoli (JL15 and JL19) only trace amounts of GSn1 and leghaemoglobin were detected.
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  • 91
    ISSN: 1432-2048
    Keywords: β-1,4-Glucan ; Nitrogen fixation ; Phaseolus (root nodules) ; Rhizobium (mutant) ; Root nodules ; produced by mutant Rhizobium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Root nodules induced in Phaseolus vulgaris L. by the wild-type (WT) and a C4-dicarboxylic-acid mutant strain of Rhizobium leguminosarum biovar. phaseoli were compared on the basis of ultrastructure and cytochemistry of cellulose subunits. The mutant bacteroids failed to colonize infected host cells in a normal manner, and presented a premature degenerative appearance. Starch granules, rough endoplasmic reticulum and mitochondria were found to accumulate in the ineffective nodules. The most striking difference between effective and ineffective nodules was the presence of unusual spherical, laminated structures in plastids of mutant-infected host cells only. Cytochemical observations showed that these structures contain β-1,4-glucans. The presence of β-1,4-glucans within such structures may be caused by the activity of a cellulase which is produced by either the bacteroids or the host cell and is locally hydrolyzing the host cell-wall, thus releasing cellulose subunits into the cytoplasm. Another possibility is denovo synthesis of β-1,4-glucans in the host cell.
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  • 92
    ISSN: 1432-2048
    Keywords: Flavin ; Glycine (nitrogen fixation) ; Leghemoglobin ; Nitrogen fixation ; Oxygen (activated) ; Pyridine nucleotides ; Symbiosis (legume-Rhizobium)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The reduction of ferric leghemoglobin (Lb3+) from soybean (Glycine max (L.) Merr.) nodules by riboflavin, FMN and FAD in the presence of NAD(P)H was studied in vitro. The system NAD(P)H + flavin reduced Lb3+ to oxyferrous (Lb2+ · O2) or deoxyferrous (Lb2+) leghemoglobin in aerobic or anaerobic conditions, respectively. In the absence of O2 the reaction was faster and more effective (i.e. less NAD(P)H oxidized per mole Lb3+ reduced) than in the presence of O2; this phenomenon was probably because O2 competes with Lb3+ for reductant, thus generating activated O2 species. The flavin-mediated reduction of Lb3+ did not entail production of superoxide or peroxide, indicating that NAD(P)H-reduced flavins were able to reduce Lb3+ directly. The NAD(P)H + flavin system also reduced the complexes Lb3+ · nicotinate and Lb3+ · acetate to Lb2+ · O2, Lb2+ or Lb2+ · nicotinate, depending on the concentrations of ligands and of O2. In the presence of 200 μM nitrite most Lb remained as Lb3+ in aerobic conditions but the nitrosyl complex (Lb2+ · NO) was generated in anaerobic conditions. The above-mentioned characteristics of the NAD(P)H + flavin system, coupled with its effectiveness in reducing Lb3+ at physiological levels of NAD(P)H and flavins in soybean nodules, indicate that this mechanism may be especially important for reducing Lb3+ in vivo.
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  • 93
    ISSN: 1432-2048
    Keywords: Aspartate aminotransferase (immunocytochemistry, subcellular fractionation) ; Glutamate oxaloacetic transaminase ; Medicago (root nodules, N2 fixation) ; Nitrogen fixation ; Root nodule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Aspartate aminotransferase (AAT; EC 2.6.1.1) catalyzes the synthesis of the amino acid aspartate which, in alfalfa root nodules, serves as the immediate precursor of the primary N-transport compound, asparagine. The enzyme AAT may also be important in providing substrates for host-plant and bacteroid respiration. The enzyme occurs as two isoenzymes, AAT-1 and AAT-2, with AAT-1 more abundant in roots and AAT-2 predominant in root nodules. To further elucidate the role of AAT in root-nodule metabolism, subcellular fractionation and immunocytochemical methods were used to determine the intra- and intercellular localization of these two isozymes. Fractionation of nodule subcellular components showed that AAT-2 was localized in amyloplasts. Immunogold labelling with AAT-2 antibodies unequivocally confirmed this, showing that AAT-2 was localized in nodule amyloplasts and leaf chloroplasts. In root nodules, the density of immunogold labelling of infected cell plastids was almost four times that of uninfected cell plastids. The data suggest that aspartate biosynthesis in alfalfa root nodules occurs primarily in the plastids of infected cells.
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  • 94
    ISSN: 1432-2048
    Keywords: Blue-green alga ; Cyanobacterium ; Nitrate (reduction, uptake) ; Nitrogen fixation ; Nodularia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nitrogen fixation and nitrate-reduction activities were determined in photoautotrophic cultures of two wild-type strains of cyanobacterium Nodularia, spp. M1 and M2. Air could support growth of the two strains at a similar rate in the presence or absence of exogenous nitrate, ammonium and/or bicarbonate. Nitrogenase activity in air-grown cultures varied with culture age, and totally disappeared after 6 h of darkness. Recovery took place upon culture re-illumination. Ammonium at a concentration of 1 mM resulted in the total disappearance of nitrogenase activity and of heterocysts. In contrast, 20 mM nitrate hardly affected nitrogenase activity and heterocyst formation after ten generations. Under the same conditions, either ammonium or nitrate completely abolished nitrogenase activity and heterocyst formation in Anabaena sp. PCC 7119, a typical heterocystous strain. The inefficiency of nitrate in inhibiting nitrogen fixation in Nodularia M1 and M2 seemed to be caused by a low nitrate-reductase activity, and not by an impairment of nitrate-uptake activity. On the other hand, the presence of nitrate was not required for uptake activity to be expressed in Nodularia.
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  • 95
    ISSN: 1432-2242
    Keywords: Genetics ; Symbiosis ; Nitrogen fixation ; Coevolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary To determine the relationship between nodulation restriction by the Rj4 allele of soybean, rhizobitoxine-induced chlorosis, and taxonomic grouping of bradyrhizobia, 119 bradyrhizobial isolates were tested in Leonard jar culture for nodulation response and chlorosis induction. In addition to strain USDA 61, the strain originally reported as defining the Rj4 response, eight other isolates (i.e., USDA 62, 83, 94, 238, 252, 259, 260, and 340) were discovered to elicit the nodulation interdiction of the Rj4 allele. Only 16% of all the bradyrhizobial strains tested induced chlorosis, but seven of the nine strains (78%) interdicted by the Rj4 allele were chlorosis-inducing strains. Furthermore, in tests for antibiotic resistance profile, eight of the nine interdicted strains (89%) were classed in DNA homology group II. This evidence suggests that the Rj4 allele has a positive value to the host plant in shielding it from nodulation by certain chlorosis-inducing bradyrhizobia of a DNA homology group with impaired efficiency of nitrogen fixation with soybean.
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  • 96
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    Theoretical and applied genetics 80 (1990), S. 223-227 
    ISSN: 1432-2242
    Keywords: Selection index ; Nitrogen fixation ; Peanut ; Nonparametric method ; Stepwise regression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Eight characters related to nitrogen fixation and pod development measured 30 days after flowering were evaluated for their correct grading of the relative yield performance of 17 genetically diverse lines of groundnut (Arachis hypogaea L.). Each line was assigned a high or low yield status based on its pod yield, shelling percentage, and 100-kernel weight. Seventeen character combinations were examined for their relative merit in correct identification of the yield status of lines. The character sets, nitrogenase activity alone or in combination with nitrogen percent or shoot weight identified the status of 77% of lines correctly. The extent to which various characters accounted for the variation in pod yield was also checked by multiple regression analysis. While the character combination, nitrogen percent plus leaf area explained 75% of variation in pod yield, nodule mass, nitrogenase activity, and leaf area occurred in some other combinations that explained yield variation to a lesser extent. These analyses point to the profitability of involving crop physiological traits such as leaf area and nitrogen percent in selecting for relative yield performance in groundnut.
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  • 97
    ISSN: 1432-2242
    Keywords: Glutamate oxalate transaminase ; Isozymes ; Nitrogen fixation ; Medicago sativa L. ; Rhizobium meliloti
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The enzyme aspartate aminotransferase (AAT) plays a key role in the assimilation of fixed-N in alfalfa (Medicago sativa L.) root nodules. AAT activity in alfalfa nodules is due to the activity of two dimeric isozymes, AAT-1 and AAT-2, that are products of two distinct genes. Three forms of AAT-2 (AAT-2a, -2b, and-2c) have been identified. It was hypothesized that two alleles occur at the AAT-2 locus, giving rise to the three AAT-2 enzymes. In a prior study bidirectional selection for root nodule AAT and asparagine synthetase (AS) activities on a nodule fresh weight basis in two diverse alfalfa germ plasms resulted in high nodule enzyme activity subpopulations with about 20% more nodule AAT activity than low enzyme activity subpopulations. The objectives of the study presented here were to determine the inheritance of nodule AAT-2 production and to evaluate the effect of bidirectional selection for AAT and AS on AAT-2 allelic frequencies, the relative contributions of AAT-1 and AAT-2 to total nodule activity, nodule enzyme concentration, and correlated traits. Two alleles at the AAT-2 locus were verified by evaluating segregation of isozyme phenotypes among F1 and S1 progeny of crosses or selfs. Characterization of subpopulations for responses associated with selection was conducted using immunoprecipitation of in vitro nodule AAT activity, quantification of AAT enzyme protein by ELISA, and AAT activity staining of native isozymes on PAGE. Results indicate that selection for total AAT activity specifically altered the expression of the nodule AAT-2 isozyme. AAT-2 activity was significantly greater in high compared to low activity subpopulations, and high AAT subpopulations from both germ plasms had about 18% more AAT-2 enzyme (on a nodule fresh weight basis). No significant or consistent changes in AAT-2 genotypic frequencies in subpopulations were caused by selection for AAT activity. Since changes in AAT activity were not associated with changes in AAT-2 genotype, selection must have affected a change(s) at another locus (or loci), which indirectly effects the expression of nodule AAT.
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  • 98
    ISSN: 1432-2242
    Keywords: Medicago sativa ; Nodulation (spontaneous) ; Nitrogen fixation ; Symbiosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Rhizobium nodulation genes can produce active extracellular signals for legume nodulation. The R. meliloti host-range nodH gene has been postulated to mediate the transfer of a sulfate to a modified lipo-oligosaccharide, which in its sulfated form is a specific nodulation factor for alfalfa (Medicago sativa L.). We found that alfalfa was capable of effective nodulation with signal-defective and non-nodulating nodH mutants (Nnr) defining a novel gene-for-gene interaction that conditions nodulation. Bacteria-free nodules that formed spontaneously at about a 3–5% rate in unselected seed populations of alfalfa cv ‘Vernal’ in the total absence of Rhizobium (Nar) exhibited all the histological, regulatory and ontogenetic characteristics of alfalfa nodules. Inoculation of such populations with nodH mutants, but not with nodA or nodC mutants, produced a four- to five-fold increase in the percentage of nodulated plants. Some 10–25% of these nodulated plants formed normal pink nitrogen-fixing nodules instead of white empty nodules. About 70% of the S1 progeny of such Nnr+ plants retained the parental phenotype; these plants were also able to form nodules in the absence of Rhizobium. If selected Nar+ plants were self-pollinated almost the entire progeny exhibited the parental Nar+ phenotype. Segregation analysis of S1 and S2 progeny from selected Nar+ plants suggests that the Nar character is monogenic dominant and that the nodulation phenotype is controlled by a gene dose effect. The inoculation of different S1 Nar+ progeny with nodH mutant bacteria gave only empty non-fixing nodules. Our results indicate that certain alfalfa genotypes can be selected for suppression of the non-nodulation phenotype of nodH mutants. The fact that the Nnr plant phenotype behaved as a dominant genetic trait and that it directly correlated with the ability of the selected plants to form nodules in the absence of Rhizobium suggests that the interaction of plant and bacterial alleles occurs early during signal transduction through the alteration of a signal reception component of the plant so that it responds to putative signal precursors.
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  • 99
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    Molecular genetics and genomics 239 (1993), S. 435-440 
    ISSN: 1617-4623
    Keywords: Enterobacter agglomerans ; nifQ gene ; FeMo-cofactor ; Nitrogen fixation ; Overexpression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The nifQ gene, involved in early stages of iron-molybdenum cofactor (FeMo-co) biosynthesis, was identified downstream of the nijB and nijF genes of Enterobacter agglomerans. This gene was cloned and its nucleotide sequence determined. The amino acid sequence, as deduced from the nucleotide sequence, revealed an accumulation of cysteine amino acid residues at the C-terminal end of the protein. The cysteine cluster showed the following consensus sequence Cys-X4-Cys-X2-Cys-X5-Cys, which is a typical characteristic of metal-binding proteins. Further, the nifQ gene was cloned downstream of strong transcriptional (bacteriophage λpLpR) and translational (atpE) signals of the expression vector pCYTEXP1 and expressed as an unfused, soluble protein in Escherichia coli. The molecular mass of 19 kDa, as deduced by SIDS-PAGE, is in good agreement with the molecular mass deduced from the nucleotide sequence. The availability of high-level expression clones should facilitate purification of large quantities of the recombinant NifQ protein and elucidation of its properties.
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  • 100
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    Protoplasma 182 (1994), S. 32-38 
    ISSN: 1615-6102
    Keywords: Rhizobium sp. (Cicer) CC 1192 ; Cicer arietinum ; Nitrogen fixation ; Root nodules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Developing and senescing chickpea (Cicer arietinum L.) nodules formed byRhizobium sp. (Cicer) CC 1192 have been shown by light and electron microscopy to have general morphological and ultrastructural features that are characteristic of indeterminate nodules. These features included the presence of persistent meristematic tissue at the distal ends of the multi-lobed nodules, and a gradient of cells at different stages of development towards the proximal point of attachment of the nodules to the parent root. The cytoplasm of infected cells in the nitrogen-fixing region of the nodules was densely packed with symbiosomes, most of which contained a single bacteroid. Infection threads containing bacteria were noted in invaded cells from the nitrogen-fixing region of the nodules. Other features that were observed in chickpea nodules included the presence of electron-dense occlusions in intercellular spaces in the nitrogen-fixing region, and plasmodesmata that connected infected cells with other infected cells and with uninfected cells. No poly-β-hydroxybutyrate granules were noted in the bacteroids. In later stages of development, infected cells became enlarged and highly vacuolated, and eventually lost their contents. Uninfected cells in the central region were smaller than infected cells and were also highly vacuolated. Some of the degenerative processes that take place in senescing bacteroids were noted.
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