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  • 1
    ISSN: 1420-9071
    Keywords: Arbuscular mycorrhiza ; abscisic acid ; carotenoid ; Glomus ; nitrate reductase ; mycorradicin ; sterols ; yellow pigment in mycorrhiza
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract This communication compares some biochemical methods for quantifying colonization by arbuscular mycorrhizal (AM) fungi. The degree of mycorrhizal colonization can conveniently be measured by determining fungal specific sterols. AM-colonized plants show a specific synthesis of 24-methylene cholesterol and an enhanced level of campesterol (=24-methyl cholesterol). A gene probe for nitrate reductase, the key enzyme for nitrogen assimilation, has been developed, which allows the monitoring of the distribution of this enzyme in fungi. Among the phytohormones tested, only abscisic acid (ABA) is found at a considerably higher level in AM-colonized plants than in controls. The concentration of ABA is about twenty times higher in spores and hyphae of the AM fungusGlomus than in maize roots. Other phytohormones (auxins, cytokinins) do not show such alterations after mycorrhizal colonization. The roots of gramineous plants become yellow as a result of mycorrhizal colonization. The yellow pigment(s) formed is (are) deposited in larger quantities in the vacuole(s) of the root parenchyma and endodermis cells during the development of the gramineous plants. A substance isolated from such roots has now been identified as a C-14 carotenoid with two carboxylic groups, and named mycorradicin.
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  • 2
    ISSN: 0168-9452
    Keywords: Abscisic acid ; Anabaena variabilis ; Arbuscular mycorrhizal fungi ; Azospirillum brasilense ; Conjugated abscisic acid ; Glomus ; Nitrogen-fixing cyanobacteria
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2048
    Keywords: Cyanobacteria ; Hydrogenase ; Hydrogen Evolution ; Nitrogenase ; Nitrogen Fixation ; Inhibitors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nitrogen-fixingAnabaena cylindrica cells are found to evolve hydrogen in high quantities in the presence of CO plus C2H2. Studies with the inhibitors dichlorophenyldimethylurea (DCMU), disalicylidenepropanediamine (DSPD), dibromothymoquinone (DBMIB), undecylbenzimidazole (UDB) and chloro-carbonyl-cyanide-phenylhydrazone (CCCP) and also withAnabaena grown on nitrate- and ammonia-nitrogen show that the H2-formation is due to the ATP-dependent H3O+-reduction catalysed by nitrogenase. In control experiments CO plus C2H2 inhibited the activities of a cell-free hydrogenase fromClostridium pasteurianum. It is concluded that Anabaena has a hydrogenase whose natural function is to recycle the H2 lost by the action of nitrogenase.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 118 (1978), S. 177-184 
    ISSN: 1432-072X
    Keywords: Cyanobacteria ; Knallgas reaction ; Hydrogenase ; Hydrogen utilization ; Nitrogenase ; Nitrogen fixation ; Isolated heterocysts ; Anabaena cylindrica ; Nostoc muscorum ; Anabaena variabilis ; Anacystis nidulans ; Cyanophora paradoxa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Several blue-green algae were surveyed for the occurrence of the hydrogenase which was assayed by the oxyhydrogen or Knallgas reaction in the intact organisms. In aerobically grown cultures, the reaction was detectable in Anabaena cylindrica, Nostoc muscorum and in two Anabaena variabilis species, whereas virtually no activity was observed in Anacystis nidulans and Cyanophora paradoxa. In these latter two algae, the reaction was, however, found after growth under molecular hydrogen for several days, which drastically increased the activity levels with all the algae tested. In the nitrogen fixing species, the activity of the Knallgas reaction was enhanced when all combined nitrogen was omitted from the media. H2 and hydrogenase could not significantly support the CO2-fixation in photoreduction experiments with all blue-green algae investigated here. Hydrogenase was assayed by the dithionite and methyl viologen dependent evolution of hydrogen and was found to be present with essentially the same specific activity levels in preparations of both heterocysts and vegetative cells from Anabaena cylindrica. Na2S2O4 as well as H2 supported the C2H2-reduction of the isolated heterocysts. The H2-dependent C2H2-reduction did not require the presence of oxygen but was strictly light-dependent where H2 served as an electron donor to photosystem I of these cells. It is concluded that hydrogen can be utilized by two different pathways in blue-green algae.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 114 (1977), S. 43-49 
    ISSN: 1432-072X
    Keywords: Cyanobacteria ; Anabaena ; Hydrogenase ; Hydrogen-uptake ; Nitrogenase ; Nitrogen fixation ; Protection mechanism ; Inhibitors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The blue-green alga Anabaena cylindrica is found to consume molecular hydrogen in a hydrogenase dependent reaction. This hydrogen uptake proceeds in the dark and is strictly dependent on oxygen, thus representing a Knallgas reactions. Its rate is almost as high as that of the endogenous respiration in Anabaena. Studies with inhibitors reveal that hydrogen is utilized via the complete respiratory chain providing additional energy for the alga. CO plus C2H2 completely block the Knallgas reaction which explains the previously reported considerable increase in the total H2 formation representing the difference between the nitrogenase-dependent H2-evolution and the reutilization of the gas catalysed by the hydrogenase in intact Anabaena. H2 is able to support the C2H2-reduction in the dark in a reaction again strictly dependent on oxygen. Moreover, H2 is also consumed in experiments carried out under far red light and in the presence of dichlorophenyl-dimenthyl-urea (DCMU) where the energy for nitrogen fixation is no longer provided by respiration but by cyclic photophosphorylation. Under these conditions, H2 is found to supply electrons for the formation of C2H4 from C2H2 in a reaction no longer dependent on the presence of oxygen. Moreover, in these experiments, the presence of H2 stabilizes the C2H2-reduction activity against the deleterious effect of oxygen. Thus, this communication provides evidence for a triplicate function of the H2-uptake catalysed by hydrogenase in intact Anabaena which is (a) to provide energy by the Knallgas reaction, (b) to supply reducing equivalents for nitrogenase, (c) to protect nitrogenase from damage by oxygen.
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  • 6
    ISSN: 1615-6102
    Keywords: Arbuscular mycorrhiza ; Carotenoids ; Mycorradicin ; Mycorrhizal symbiosis ; Glomus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Many plants form yellow coloured roots when colonized by arbuscular mycorrhizal (AM) fungi. In maize, a yellow pigment is first visible as small droplets in parenchyma cells of roots in the vicinity of arbuscules, 3–4 weeks after mycorrhizal colonization. During the course of the development of the plants, the yellow pigment spreads all over the cells of the cortex (with the exception of the exodermis) and of the endodermis, whereas the other stelar elements remain uncoloured. Other gramineous plants (wheat, barley, millet) show the same pattern of pigment formation. In contrast, the deposition of this pigment is not detected in roots ofTagetes, garden bean, onion, or leek. Weak yellow fluorescence is also seen in the fungal structures, particularly in the arbuscules of the investigated probes. This is, however, clearly different from the intense yellow colour of the pigment formed in root cells of grasses. The yellow pigment is even detected in such cells which are never colonized by fungal structures (e.g., endodermal cells). A major constituent of the yellow pigment of AM-colonized root cells has been identified as a carotenoid with 14 carbon atoms and two carboxylic groups and termed mycorradicin. This carotenoid is likely deposited in the vacuoles of root cells as a result of the colonization specifically by arbuscular fungi.
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