Nitrogen Fixation by Native Australian Legumes

1981 ◽  
Vol 29 (2) ◽  
pp. 143 ◽  
Author(s):  
AC Lawrie
Keyword(s):  
Nitrogen Fixation ◽  
Acetylene Reduction ◽  
Sand Dune ◽  
Nitrogenase Activity ◽  
Root Nodules ◽  
Sand Dunes ◽  
Late Summer ◽  
Open Forest ◽  
Seasonal And Diurnal Variations ◽  
Major Factors

Nitrogen fixation was studied by the acetylene-reduction technique in root nodules of 10 native Australian legumes in three habitats in Victoria: low open-forest. sandy heathland and coastal sand dunes. Nodular activity reached a maximum in spring (and in autumn in sand-dune species), declined to a minimum in late summer and continued at a low level throughout winter. Mean nitrogenase activity was 1.73 μmol C2H2 reduced g-1 fresh wt nodules h-1, with spring maxima 8-250 times summer minima. It is suggested that variations in rainfall and temperature were the major factors influencing seasonal variations in nodular activity. Estiniates of minimum acetylene reduction per hectare per year were derived from measurements of seasonal and diurnal variations in acetylene reduction and abundance of nodules per hectare, and were used to derive approximate minimum values for nitrogen fixation of 0.004-0.746 kg ha-1 yr-1. The quantities of nitrogen fixed are compared with other reports and the significance of nitrogen fixation by these native legumes is discussed.

The role of oxygen diffusion from the shoots and nodule roots in nitrogen fixation by root nodules of Myrica gale

1978 ◽  
Vol 56 (11) ◽  
pp. 1365-1371 ◽  
Author(s):  
John Tjepkema
Keyword(s):  
Nitrogen Fixation ◽  
Oxygen Uptake ◽  
Aqueous Phase ◽  
Acetylene Reduction ◽  
Nitrogenase Activity ◽  
Root Nodules ◽  
Myrica Gale ◽  
Before And After ◽  
Whole Plants

Nitrogenase activity (acetylene reduction) and oxygen uptake by root nodules of Myrica gale L. were measured before and after removal of nodule roots. There was no significant effect of nodule root removal when respiration was measured in the gas phase (0.05–0.2 atm pO2 (1 atm = 101.325 kPa)) or acetylene reduction in a stirred aqueous phase at 0.2 atm pO2. However, when acetylene reduction was measured in 0.05 atm pO2 in an unstirred aqueous phase, there was a 66 to 76% reduction in activity. These results indicate that nodule roots are important for oxygen uptake when the nodules are present in an aqueous phase at low pO2, which is probably the normal environmental conditions for many of the nodules. Other measurements showed that diffusion of oxygen from the shoot to the root nodules is not important for nitrogen fixation. These measurements were done on whole plants with the shoots in air (0.20 atm pO2) and the roots in water at the desired pO2 value. With 0.0 atmpO2 in the root environment, the rate of acetylene reduction was only 4% of the rate at 0.2 atmpO2. Thus, only small amounts of oxygen are transported from the shoot to the nodules.

Nitrogen fixation (acetylene reduction) by Klebsiella pneumoniae in association with 'Park' Kentucky bluegrass (Poa pratensis L.)

1981 ◽  
Vol 27 (1) ◽  
pp. 52-56 ◽  
Author(s):  
L. V. Wood ◽  
R. V. Klucas ◽  
R. C. Shearman
Keyword(s):  
Nitrogen Fixation ◽  
Klebsiella Pneumoniae ◽  
Ethylene Production ◽  
Acetylene Reduction ◽  
Nitrogenase Activity ◽  
Poa Pratensis ◽  
Kentucky Bluegrass ◽  
Surface Sterilization ◽  
Reducing Activity ◽  
Acetylene Reducing Activity

Turfs of 'Park' Kentucky bluegrass reestablished in the greenhouse and inoculated with Klebsiella pneumoniae (W6) showed significantly increased nitrogen fixation (acetylene reduction) compared with control turfs. Mean ethylene production rates per pot were 368 nmol h−1 for K. pneumoniae treated turfs, 55 nmol h−1 for heat-killed K. pneumoniae treated turfs, and 44 nmol h−1 for untreated turfs. Calculated lag periods before activity was observed were generally very short (less than 1 h).When 'Park' Kentucky bluegrass was grown from seed on soil-less medium of Turface, a fired aggregate clay, inoculation with K. pneumoniae (W6) resulted in 9 of 11 turfs showing nitrogenase activity (mean ethylene producion rate per pot was 195 nmol h−1). Only 3 of 11 turfs treated with heat-killed K. pneumoniae showed any activity and their mean rate of ethylene production (40 nmol h−1 per pot) was significantly lower than that for turfs treated with K. pneumoniae.Using the 'Park'–Turface soil-less model system it was shown that acetylene reducing activity was (i) root associated, (ii) generally highest at a depth of 1–4 cm below the surface, (iii) enhanced by washing excised roots, and (iv) inhibited by surface sterilization of excised roots. Klebsiella pneumoniae was recovered from Turface and roots showing acetylene reducing activity.

scholarly journals Factors Influencing Nitrogenase Activity (Acetylene Reduction) by Root Nodules of Groundnut, Arachis hypogaea L.

1983 ◽  
Vol 10 (1) ◽  
pp. 26-29 ◽  
Author(s):  
P. T. C. Nambiar ◽  
P. J. Dart
Keyword(s):  
Soil Moisture ◽  
Environmental Factors ◽  
Acetylene Reduction ◽  
Nitrogenase Activity ◽  
Root Nodules ◽  
Activity Period ◽  
Diurnal Fluctuation ◽  
Factors Influencing ◽  
Arachis Hypogaea L ◽  
Reduction Assay

Abstract Acetylene reduction assay, used to measure nitrogenase activity of legume root nodules, is influenced by environmental factors, which limit its application. The effects of some of the environmental factors on acetylene reduction by groundnut root nodules are described. The activity was nonlinear during the first hour of incubation. Assay temperature above 25 C decreased the activity. Washing the nodulated roots prior to the assay also decreased the activity. The activity was influenced by light intensity, soil moisture, and moisture content in the incubation bottle. Diurnal fluctuation with one maximum and one minimum activity period during a 24 hour cycle was observed. Nitrogenase activity was higher during the postrainy season compared to that of the rainy season. A virginia cultivar Kadiri-71 had higher nitrogenase activity than a dwarf valencia cultivar, MH 2.

Potential for nitrogen fixation in the rhizosphere and habitat of natural stands of the wild rice Zizania aquatica

1979 ◽  
Vol 57 (11) ◽  
pp. 1285-1291 ◽  
Author(s):  
M. T. Ogan
Keyword(s):  
Nitrogen Fixation ◽  
Water Column ◽  
Acetylene Reduction ◽  
Wild Rice ◽  
Heterotrophic Bacteria ◽  
Nitrogenase Activity ◽  
Early Summer ◽  
Zizania Aquatica ◽  
Natural Stands ◽  
Root Surfaces

The potential for nitrogen fixation in the rhizosphere and habitat of natural stands of Zizania aquatica (L) was studied by the acetylene reduction method. The data obtained suggested that this potential exists in the water column, the rhizosphere soil of the wild rice habitat, and on the root surfaces of the plants.In situ determination of rates of nitrogen fixation in the water column showed low but significant levels only in late spring – early summer and the rate was thought to be dependent on the presence of the blue-green algae Aphanizomenon. Laboratory experimental evidence showed that acetylene reduction by rhizosphere surface soil was attributable to Oscillatoria species while bacteria were more active in the subsurface soil and on the root surfaces. The bacteria-mediated nitrogenase activity was often preceded by a long lag period. The heterotrophic bacteria involved were enumerated, isolated, and characterised and they belong to the genera Azotobacter and Clostridium. Algal components of blooms occurring within the stands of Zizania at various times were identified.

Ineffectiveness of viomycin-resistant mutants of Rhizobium meliloti

1969 ◽  
Vol 15 (7) ◽  
pp. 671-675 ◽  
Author(s):  
G. S. Hendry ◽  
D. C. Jordan
Keyword(s):  
Cell Wall ◽  
Nitrogen Fixation ◽  
Parent Strain ◽  
Rhizobium Meliloti ◽  
Nitrogenase Activity ◽  
Root Nodules ◽  
Effective Strain ◽  
One Step ◽  
Increased Sensitivity ◽  
Resistant Mutants

Under clearly defined conditions one-step acquisition of viomycin resistance by a normally effective strain of Rhizobium meliloti resulted in one-step acquisition of ineffectiveness in nitrogen fixation, which probably occurred with a one-gene change in the R. meliloti genome. Two-step mutants retained their ability to produce root nodules but such nodules also were ineffective. Increased sensitivity of the viomycin-resistant mutants to glycine and D-alanine was not noted. Bacteroids were not seen in nodules formed by the viomycin-resistant mutants on their homologous host plant. Nitrogenase activity was not detected, by acetylene reduction, in detached ineffective nodules, whereas effective nodules formed 10.6 μmoles of ethylene per hour per gram of nodules. Growth of the effective parent strain in a low concentration of viomycin resulted in elongation and swelling of the cells so that they appeared as artificially produced bacteroids. Viomycin-resistant mutants did not undergo this transformation. Antigens could be readily extracted by hot- and cold-saline extraction of wet packed cells of both resistant and sensitive cultures but antigenic differences, which may have indicated cell wall differences, were not noted.

scholarly journals Effects of Engineered Sinorhizobium meliloti on Cytokinin Synthesis and Tolerance of Alfalfa to Extreme Drought Stress

2012 ◽  
Vol 78 (22) ◽  
pp. 8056-8061 ◽  
Author(s):  
Ji Xu ◽  
Xiao-Lin Li ◽  
Li Luo
Keyword(s):  
Nitrogen Fixation ◽  
Drought Stress ◽  
Sinorhizobium Meliloti ◽  
Nitrogenase Activity ◽  
Root Nodules ◽  
Severe Drought ◽  
Control Strain ◽  
Free Living ◽  
Content Type ◽  
Host Tolerance

ABSTRACTCytokinin is required for the initiation of leguminous nitrogen fixation nodules elicited by rhizobia and the delay of the leaf senescence induced by drought stress. A few free-living rhizobia have been found to produce cytokinin. However, the effects of engineered rhizobia capable of synthesizing cytokinin on host tolerance to abiotic stresses have not yet been described. In this study, two engineeredSinorhizobiumstrains overproducing cytokinin were constructed. The tolerance of inoculated alfalfa plants to severe drought stress was assessed. The engineered strains, which expressed theAgrobacterium iptgene under the control of different promoters, synthesized more zeatins than the control strain under free-living conditions, but their own growth was not affected. After a 4-week inoculation period, the effects of engineered strains on alfalfa growth and nitrogen fixation were similar to those of the control strain under nondrought conditions. After being subjected to severe drought stress, most of the alfalfa plants inoculated with engineered strains survived, and the nitrogenase activity in their root nodules showed no apparent change. A small elevation in zeatin concentration was observed in the leaves of these plants. The expression of antioxidant enzymes increased, and the level of reactive oxygen species decreased correspondingly. Although theiptgene was transcribed in the bacteroids of engineered strains, the level of cytokinin in alfalfa nodules was identical to that of the control. These findings suggest that engineeredSinorhizobiumstrains synthesizing more cytokinin could improve the tolerance of alfalfa to severe drought stress without affecting alfalfa nodulation or nitrogen fixation.

Renodulation and nitrogen fixing potential of Acacia nilotica inoculated with Rhizobium isolates

1993 ◽  
Vol 39 (1) ◽  
pp. 87-91 ◽  
Author(s):  
Banwari Lal ◽  
Sunil Khanna
Keyword(s):  
Nitrogen Fixation ◽  
Dry Matter ◽  
Nitrogenase Activity ◽  
Root Nodules ◽  
Acacia Nilotica ◽  
Resistance Pattern ◽  
Dry Matter Yield ◽  
Native Population ◽  
Rhizobium Isolate ◽  
Matter Production

Renodulation and nitrogen fixation potential of indigenous and exotic isolates of Rhizobium were studied in a field experiment with Acacia nilotica from July 1990 to June 1991. The inoculum isolates belonged to different serotypes and did not show cross-reaction with the native population of Rhizobium. Nitrogenase activity of root nodules observed at 4-month intervals covering three seasons snowed a decline during winter months, which corresponded with the senescence of the nodules. Maximal renodulation as checked by serotyping and antibiotic resistance pattern was observed with isolate AB 3 followed by AD 4 and USDA 3325. The highest nitrogenase activity was exhibited in plants inoculated with AD 4 at 12 months. Plants inoculated with Rhizobium isolate USDA 3325 showed the highest increase in dry-matter yield at 12 months. Except for AB 3, dual inoculation with Rhizobium isolates and Glomus fasciculatum did not enhance dry matter production as compared with uninoculated controls or single inoculation of either Rhizobium isolate or G. fasciculatum.Key words: Rhizobium, Acacia nilotica, nitrogenase activity, renodulation.

Effect of elevated carbon dioxide in the root atmosphere on nitrogenase activity in three actinorhizal plant species

2001 ◽  
Vol 79 (9) ◽  
pp. 1010-1018 ◽  
Author(s):  
Christa R Schwintzer ◽  
John D Tjepkema
Keyword(s):  
Carbon Dioxide ◽  
Acetylene Reduction ◽  
Nitrogenase Activity ◽  
Root Nodules ◽  
Alnus Glutinosa ◽  
Repeated Measurements ◽  
Myrica Gale ◽  
Black Alder ◽  
Low Concentrations ◽  
Speckled Alder

In wet soils, nitrogen-fixing root nodules are subjected to elevated CO2. Only a few studies have examined the effect of elevated CO2 on nitrogenase activity, and the results have been mixed. We examined intact black alder (Alnus glutinosa (L.) Gaertn.) and sweet gale (Myrica gale L.) seedlings and field-collected speckled alder (Alnus incana ssp. rugosa (Du Roi) Claus.) nodules to clarify the effects of elevated CO2. Nitrogenase activity was measured via acetylene reduction in an open, flow-through system. We found that repeated measurements of the peak rate of nitrogenase activity, the only reliable measure of nitrogenase activity, could be made on the same plant via 150-s exposures to acetylene separated by 20 min without acetylene. Our results for elevated CO2 consistently showed that it had little effect on nitrogenase activity at low concentrations and increasingly inhibited nitrogenase activity as the CO2 concentration increased. In black alder, 0.5 kPa CO2 had little effect, whereas 3.0 kPa CO2 reduced nitrogenase activity 31–35%. Sweet gale, was less sensitive to elevated CO2 and was unaffected by 1.5 kPa CO2. Black alder grown with the roots, but not the shoots, in 1.3 kPa CO2 showed only minimal acclimation to elevated CO2.Key words: acetylene reduction technique, actinorhizal plants, Alnus, carbon dioxide, Myrica gale, nitrogen fixation.

Relative contributions to nitrogenase (acetylene reducing) activity of stem and root nodules in Sesbania rostrata

1992 ◽  
Vol 38 (6) ◽  
pp. 577-583 ◽  
Author(s):  
J. K. Ladha ◽  
Minviluz Garcia ◽  
R. P. Pareek ◽  
G. Rarivoson
Keyword(s):  
Acetylene Reduction ◽  
Root Nodule ◽  
Nitrogenase Activity ◽  
Root Nodules ◽  
Dry Weight ◽  
Acetylene Reduction Activity ◽  
Sesbania Rostrata ◽  
Reduction Activity ◽  
Acetylene Reducing Activity ◽  
Aerial Stem

Six experiments, two each in the phytotron, greenhouse, and field, were conducted to assess the contribution of nitrogenase activity (acetylene reduction) by stem nodules in the presence and absence of root nodules of Sesbania rostrata (Brem & Oberm). In a greenhouse experiment, the effect of detaching already formed aerial stem nodules on the restoration of root nodules and nitrogenase activity was studied. The field experiment compared nodulation and acetylene-reduction activity by dual-nodulating S. rostrata and root-nodulating Sesbania cannabina. Acetylene-reduction activity expressed per gram of nodule dry weight was higher for stem nodules than for root nodules. Root nodule dry weight and acetylene-reduction activity failed to increase after stem inoculation, but root nodule dry weight and acetylene-reduction activity increased several fold within 15 days of detachment of aerial stem nodules. Stem nodulation, which occurred without inoculation under lowland field condition, suppressed root nodulation, thus accounting for more than 75% of total nitrogenase activity. Sesbania rostrata showed higher acetylene-reduction activity than S. cannabina. In dual-nodulating plants, root and stem nodules appeared to strike a balance in competition for energy, which may be controlled by stem nodulation. Key words: Sesbania rostrata, Azorhizobium caulinodans, stem nodule, root nodule, acetylene-reducing activity.

Nitrogen Fixation (Acetylene Reduction) Associated with Sea Urchins (Strongylocentrotus droebachiensis) Feeding on Seaweeds and Eelgrass

1977 ◽  
Vol 34 (3) ◽  
pp. 416-420 ◽  
Author(s):  
M. L. Guerinot ◽  
W. Fong ◽  
D. G. Patriquin
Keyword(s):  
Nitrogen Fixation ◽  
Acetylene Reduction ◽  
Sea Urchins ◽  
Nitrogenase Activity ◽  
Average Rate ◽  
Strongylocentrotus Droebachiensis ◽  
Molar Ratio ◽  
Laminaria Digitata ◽  
Bare Rock ◽  
Nitrogenase Activities

Sea urchins feeding in different macrophyte zones in St. Margaret's Bay, Nova Scotia, in November and December 1975 were examined for nitrogenase activity using the acetylene reduction technique. For sea urchins feeding on Laminaria digitata and L. longicruris, the average rate of acetylene reduction was equivalent to N2 fixation of 55 μg N2 per sea urchin per day assuming a 3:1 molar ratio of C2H2 reduction to N2 fixation. Lower nitrogenase activities were observed for sea urchins feeding on Agarum cribrosum and Zostera marina, and no nitrogenase activity was observed for sea urchins taken from bare rock substrate on which kelp had been absent for 4 yr. Samples of separated digestive tracts but not the degutted bodies of sea urchins exhibited nitrogenase activity, suggesting that the digestive tract is the site of nitrogen fixation in whole sea urchins.

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