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  • 1
    Electronic Resource
    Electronic Resource
    Effect of low rhizosphere oxygen on growth, nitrogen fixation and nodule morphology in lucerne (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 89 (1993), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Oxygen shortage in soils can occur following a wide range of natural circumstances, affecting the plant's physiology. In this paper the performance of nodulated lucerne plants under severe hypoxia is examined and the mechanisms involved to achieve this adaptation are discussed. Nodulated lucerne plants (Medicago sativa L.) were grown with their rooting medium exposed to 1 or 21 kPa oxygen. Final yield, as expressed on a shoot dry weight basis, was unaffected but root and nodule dry weights were reduced by 50%. Water content in roots and nodules was higher at 1 kPa as a result of the formation of aerenchyma. Specific acetylene reduction activity was higher in hypoxic nodules as a consequence of modified nodule structure, although they were more sensitive to the presence of acetylene or nitrate. Root respiration was insensitive to changes in external oxygen supply, therefore providing adequate support for mineral uptake. Nodule respiration rates were 5 times higher in control plants when measured as CO2 evolution, whereas no differences were observed in O2 uptake. It is suggested that adaptation of nodulated lucerne to low oxygen concentrations involves changes in photosynthate allocation and nodule morphology, which provide a more efficient nitrogen fixation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1993.tb01786.x
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  • 2
    Electronic Resource
    Electronic Resource
    Denitrification in lucerne nodules and bacteroids supplied with nitrate (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 84 (1992), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Nodulated lucerne plants (Medicago sativa L. cv. Aragón) were supplied with 20 mM nitrate. Anaerobically isolated bacteroids of Rhizobium meliloti from these plants were able to denitrify after 48 h treatment. R. meliloti bacteroids behave as total denitrifiers, reducing nitrate to dinitrogen: when acetylene was omitted from the assay medium very little nitrous oxide was recovered. The onset of denitrification activity was coincident with the induction of nitrite reductase activity (EC 1.7.99.3) whereas nitrate reductase activity (EC 1.7.99.4) was constitutive. Whole nodules from plants receiving several doses of nitrate were assayed, in a nitrate-free medium, to monitor denitrification activity dependent on nitrate within the nodules. Denitrification activity was detected after 2 days of 20 mM nitrate supply or after 3 days in the presence of 10 or 5 mM nitrate. These results are discussed in relation to current controversy about nitrate entry into the infection region of nodules. It is concluded that this process occurs more rapidly than suggested in recent research.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1992.tb04701.x
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of low nitrate supply to nodulated lucerne on time course of activites of enzymes involved in inorganic nitrogen metabolism (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 80 (1990), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Plants of lucerne (Medicago sativa L. cv. Aragón) inoculated with several strains of Rhizobium meliloti were supplied with a low level of nitrate (5 mM). After 1 week, normalised nodule mass, obtained by dividing nodule weight by shoot weight, was decreased by one-fourth. This result closely paralleled the bacteroid protein content of nodules, whereas the cytosolic content remained constant. Nitrate reductase activity (NRA, EC 1.7.99.4) of bacteroids increased rapidly after nitrate supply, with actual rates being highly dependent on the Rhizobium strain. The expression of cytosolic NR (EC 1.6.6.1) also varied depending on the bacterial strain but was largely insensitive to nitrate feeding. Nitrite reductase activity (NiRA, EC 1.7.2.2) of either bacteroid or plant origin was independent of the R. meliloti strain. Activation occurred after 3 and 7 days, respectively, of nitrate feeding. Significant amounts of nitrite were obtained throughout the experimental period from buffered extracts of both bacteroids and cytosol of nodules. However, when these nodules were ground in the presence of inhibitors of enzyme activity, nitrite was only found in nodules containing strain 102-F-51 after 1 week of treatment. These results agree with the recent hypothesis that nitrite plays a role in a secondary stage of nodule damage by nitrate. We propose that NiRA rather than NRA can be used as an internal probe of nitrate access to the infected region of nodules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1990.tb04394.x
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  • 4
    Electronic Resource
    Electronic Resource
    Nitrate and hydrogen peroxide metabolism in Medicago sativa nodules and possible effect on leghaemoglobin function (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 72 (1988), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effect of NO3 (0–20 mM for 7 days) upon NO3 and H2O2 metabolism in lucerne (medicago sativa L. ev. Aragón) nodules initiated by Rhizobium meliloti strain 102F51 has been examines. Ty;pical nitrate reductase, (NR) activities of bacteroids (EC 1.7.99.4) and cytosol (EC 1.6.6.1) of nodules not treated with NO3 were 60 and 45 nmol NO2 formed (mg protein)1h−1 respectively, Inductin of bacteroid NR took place in nodules exposed ot concentrations above 5 mM No3 whereas cytosol NR was induced at 5 mM No3 decreasint at greater NO3 concentrations. In resonse to NO3 additin, NO2 increasingly accumulated in the nodule cytosol at quantities commensurate with those needed to oxidise leghaemoglobin (Lb) in vitro. A comparison of patterns of NO2 accumulation and activities of NRs expressed on a nodule weight basis indicates that plant NR contributes decisively to NO2 production at the earlier phass of nodule senescence (5–10mM No3 while bacteroid NR becomes increasingly important in generating NO2 at nore advanced stages (10–20mM NO3). Specific superoxide dismutase (SOD; EC 1.15.1.1) and catalase (EC 1.11.1.6) activities of bacteroids remained constant during the NO3 induced senescence of nodules whereas SOD activity of cytosol increased 1.5-fold and catalase activity ws inhibited by 20% at 20 mM NO3 substantial peroxidase (EC 1.11.1.7) activity was found in the plant but none in the bacteroid fraction of nodules. Peroxidase activity increased significantly only at 20 mM NO3 concomitantly with malondialdephyde content. concentrations. Free H2O2 interferes wihjt Lb function in vivo is suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1988.tb06375.x
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  • 5
    Electronic Resource
    Electronic Resource
    Nitrate and nitrite reduction by alfalfa root nodules: Accumulation of nitrite in Rhizobium melioti bacteroids and senescence of nodules (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 64 (1985), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Addition of NO−3 rapidly induced senescence of root nodules in alfalfa (Medicago sativa L. cv. Aragon). Loss of nodule dry matter began at the lowest NO−3 concentration (10 mM) but degradation of bacteroid proteins was only detected when nodules were supplied with NO−3 concentrations above 20 mM.Bacteroids from Rhizobium meliloti contained high specific activities of nitrate reductase (NR) and nitrite reductase (NiR). Both enzymes were presumably substrate-induced although substantial enzyme activities were present in the absence of NO−3 Typical specific activities for soluble NR and NiR of bacteroids under NO−3 free conditions were 1.2 and 1.4 μmol (mg protein)−1h−1, respectively. In the presence of NO−3, the specific activity of NR was considerably greater than that of NiR, thus causing NO−2 accumulation in bacteroids. Nitrite levels in the bacteroids were linearly correlated with specific activities of NR and NiR, indicating that NO−2 is formed by bacteroid NR and that this NO−2 in turn, induces bacteroid NiR. Accumulation of NO−2 within bacteroids also indicates that NO−2 inhibits nodule activity after feeding plants with NO−3
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1985.tb03352.x
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of water stress on enzymes of ammonia assimilation in root nodules of alfalfa (Medicago sativa) (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 61 (1984), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Protein content and activities of the enzymes glutamine synthetase (EC 6.3.1.2), NADH-glutamate synthase (EC 1.4.1.14), NADH-glutamate dehydrogenase (reductive amination (EC 1.4.1.2) and NAD+-glutamate dehydrogenase (oxidative deamination) (EC 1.4.1.2) from the plant fraction of root nodules of alfalfa (Medicago sativa L. cv. Aragon) were determined under water stress. Only NADH-glutamate synthase activity was inhibited during drought. The results indicate that the glutamine synthetase/NADH-glutamate synthase cycle was fully operational in alfalfa nodules of control or even mildly stressed plants when N2-fixation was not inhibited, but that the coupling between glutamine synthetase and NADH-glutamate synthase was lost as drought progressed. Patterns of glutamine synthetase and NADH-/NAD+-gluta-mate dehydrogenase activities reflect changes in ammonia content of nodules and/or availability of carbon substrates, and indicate that nodules maintain sufficient enzyme activity for ammonia assimilation throughout water stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1984.tb05186.x
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  • 7
    Electronic Resource
    Electronic Resource
    Nitrate and nitrite reduction in the plant fraction of alfalfa root nodules (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 65 (1985), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The plant fraction of alfalfa (Medicago sativa L. cv. Aragon) nodules contained both nitrate reductase (NR) and nitrite reductase (NiR). Specific activity of NADH-NR from the cytosol of nodules not treated with NO3- was about 30 nmol (mg protein)-1-h-1 and was not basically affected by NO3 addition. In contrast, typical specific activity for cytosolic NiR was 1.5 umol (mg protein)-1h-1 using methyl viologen as electron donor. This activity strongly increased with NO3 concentration, probably due to substrate induction. Maximal activity was 3.5 μmol (mg protein)-1h-1 at 50 to 200 mM NO3.Estimates indicate that the contribution of cytosol to the overall NR and NiR activities of alfalfa nodules is distinctly different: less than 10% and about 70%, respectively. The increasing amounts of NO2 accumulating in the cytosol upon NO3, supply, and the different response to NO3 of bacteroid and cytosolic NRs support the concept that most of this NO2 comes from the bacteroids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1985.tb02380.x
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  • 8
    Electronic Resource
    Electronic Resource
    The effect of NaCl salinity and water stress with polyethylene glycol on nitrogen fixation, stomatal response and transpiration of Medicago sativa, Trifolium repens and Trifolium brachycalycinum (subclover) (1982)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 54 (1982), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The objective of this study was to investigate the behaviour of different legumes against salinity and water stress, thus trying to discover simultaneous adaptations to both stresses. The nitrogen fixation, transpiration, predawn leaf water potential, and stomatal response of Medicago sativa L. (cvs. Tierra de Campos and Aragon), Trifolium repens L. (cv. Aberystwyth S-184) and T. brachycalycinum Katzn. et Morley (=T. subterraneum L. cv. Clare) were compared at three levels of stress (0.05, 0.3 and 0.5 MPa of either NaCl or polyethylene glycol 6000) in nutrient solution. The plants were stressed for three days and then returned to control nutrient solution. The changes in the parameters analyzed were dependent on the proportion of stress treatments and the nature of the species, always being greater in plants from PEG than from NaCl solutions. Transfer of lucerne and subclover plants from NaCl at 0.05 MPa to a non-saline medium resulted in an increase of nitrogen fixation above the level of the non-salinized control plants, especially significant in lucerne. Analysis of possible inorganic impurities in commercial PEG suggest that such type of impurities are not responsible for the toxic effects reported. Plant damage resulting from PEG treatment was apparently due to penetrations of PEG (as determined qualitatively by using the tetraiodinebismuthic acid technique) or low-molecular organic impurities into the plant. – The results are discussed as part of the adaptation of the different species to salinity and water stress. The best performance was given by “Tierra de Campos”.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1982.tb00271.x
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  • 9
    Electronic Resource
    Electronic Resource
    Distribution of nitrate reductase activity in nodulated lucerne plants (1991)
    Springer
    Plant and soil 131 (1991), S. 107-113 
    Details
    ISSN: 1573-5036
    Keywords: lucerne ; nitrate ; nitrate reductase ; Rhizobium meliloti
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Nitrogen fixing plants of lucerne (Medicago sativa L. cv. Aragón) were grown in a glasshouse for three months in the absence of nitrate, and then supplied with 5 mM KNO3 for a week. In control (non-nitrate fed) plants, nitrate reductase activity (NRA EC 1.6.6.1) was detected only in nodules. After nitrate supply, root NRA showed a transient increase. Shoot NRA increased with time, paralleling changes in nitrate distribution; stem NRA represented nearly 50% of total NRA in plant tissues. Total nitrogen, expressed on a dry weight basis, tended to decrease in shoots upon nitrate supply. Bacteroid NRA (EC 1.7.99.4) showed a great variation depending on Rhizobium meliloti strains, ranging from 5 to 40% of total plant NRA. However, different Rhizobium strains did not give different results in terms of plant growth parameters, nitrate or organic nitrogen content.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00010425
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  • 10
    Electronic Resource
    Electronic Resource
    Denitrification in lucerne nodules is not involved in nitrite detoxification (1996)
    Springer
    Plant and soil 182 (1996), S. 149-155 
    Details
    ISSN: 1573-5036
    Keywords: denitrification ; lucerne ; Medicago sativa ; nitrite detoxification ; Rhizobium meliloti
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Dissimilatory reduction of ionic nitrogen oxides to gaseous forms such as nitrous oxide or nitrogen can be carried out by free living or symbiotic forms of some strains of Rhizobium meliloti. In this paper we investigate whether bacteroid denitrification plays a role in the alleviation of the inhibitory effects of nitrate on nitrogen fixation both in bacteroid incubations as in whole nodules. The presence of a constitutive nitrate reductase (NR) activity in isolated bacteroids caused nitrite accumulation in the incubation medium, and acetylene reduction activity in these bacteroids was progressively inhibited, since nitrite reductase (NiR) activity was unable to reduce all the nitrite produced by NR and denitrification occurred slowly. Even nodules infiltrated with nitrate and nitrite failed to increase gaseous forms of nitrogen substantially, indicating that nitrite availability was not limiting denitrification by bacteroids. In spite of the low rates of bacteroidal denitrification, the effect of nodule denitrification on the inhibition of nitrogen fixation by nitrate in whole plants was tested. For that purpose, lucerne plants (Medicago sativa L. cv. Aragon) were inoculated with two Rhizobium meliloti strains: 102-F-65 (non denitrifying) and 102-F-51 (a highly denitrifying strain). After a seven days nitrate treatment, both strains showed the same pattern of inhibition, and it occurred before any nitrate or nitrite accumulation within the nodules could be detected. This observation, together with the lack of alleviation of the ARA inhibition in the denitrifying strain, and the limited activity of dissimilatory nitrogen reduction present in these bacteroids, indicate a role other than nitrite detoxification for denitrification in nodules under natural conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00011003
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