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1.
It is unclear to what extent oxygen diffusion pathways through the cortex of the nitrogen-fixing zone of indeterminate nodules are liquid filled and whether a blockage of these pathways is involved in varying nodule oxygen permeability to control nitrogenase activity. We examined the proportion of water-filled intercellular spaces of lucerne (Medicago sativa L.) nodules with cryo-scanning electron microscopy. This technique allows for direct observation of water accumulation. Thirty percent of all intercellular spaces in the inner cortex of lucerne nodules were liquid filled. Decreasing the nodule oxygen permeability by detopping of the plant or by increasing the rhizospheric oxygen partial pressure to 80 kPa had no statistically significant effect on the water distribution in the intercellular spaces. Therefore, the hypothesis of a continuous aqueous diffusion barrier in the inner cortex could not be supported. The abundance of glycoproteins in intercellular spaces of the inner cortex was investigated with immunoelectron microscopy. No alteration due to detopping or after increase of the rhizospheric oxygen partial pressure was observed. Therefore, our results do not support the hypothesis of a short-term regulation of oxygen permeability by blockage of diffusion pathways through morphological changes in the cortex region of the nitrogen-fixing zone of lucerne nodules. 相似文献
2.
When excised root nodules ofCoriaria arborea are assayed for nitrogenase activity at various pO2 they show a broad optimum between 20 and 40 kPa O2, with some evidence for adaptation. Continuous flow assays of nodulated root systems of intact plants indicate that Coriaria shows an acetylene induced decline in nitrogenase activity. When root systems were subject to step changes in pO2 nitrogenase activity responded with a steep decline followed by a slower rise in activity both at lower and higher than ambient pO2. Thus Coriaria nodules are able to adapt rapidly to oxygen levels well above and well below ambient. Measurement of nodule diffusion resistance showed that the adaptation is accompanied by rapid increase in resistance at above ambient pO2 and decrease in resistance at below ambient pO2. Plants grown with root systems at pO2 from 5–40 kPa O2 did not differ in growth or nodulation. The anatomy of Coriaria nodules shows they have a dense periderm which encircles the nodule and also closely invests the infected zone. The periderm is both thicker and more heavily suberised in nodules grown at high pO2 than at low pO2. Vacuum infiltration of India ink indicates that oxygen diffusion is entirely through the lenticel and via a small gap adjacent to the stele. 相似文献
3.
Nitrogen fixation and respiration by root nodules ofAlnus rubra Bong.: Effects of temperature and oxygen concentration 总被引:1,自引:1,他引:0
Summary Using a root nodule cuvette and a continuous flow gas exchange system, we simultaneously measured the rates of carbon dioxide evolution, oxygen uptake and acetylene reduction by nodules ofAlnus rubra. This system allowed us to measure the respiration rates of single nodules and to determine the effects of oxygen concentration and temperature on the energy cost of nitrogen fixation. Energy cost was virtually unchanged (2.8–3.5 moles of carbon dioxide or oxygen per mole of ethylene) from 16 to 26°C (pO2=20 kPa) while respiration and nitrogenase activity were highly temperature dependent. At temperatures below 16°C, nitrogenase activity decreased more than did respiration and as a result, energy cost rose sharply. Acetylene reduction ceased below 8°C. Inhibition of nitrogenase activity at low temperatures was rapidly reversed upon return to higher temperatures. At high temperatures (above 30°C) nitrogenase activity declined irreversibly, while respiration and energy cost increased.Energy cost was nearly unchanged at oxygen partial pressures of 5 to 20 kPa (temperature of 20°C). Respiration and nitrogenase activity were strongly correlated with oxygen tension. Below 5 kPa, acetylene reduction and oxygen uptake decreased sharply while production of carbon dioxide increased, indicating fermentation. Fermentation alone was unable to support nitrogenase activity. Acetylene reduction was independent of oxygen concentration from 15 to 30 kPa. Nitrogenase activity decreased and energy cost rose above 30 kPa until nearly complete inactivation of nitrogenase at 70–80 kPa. Activity declined gradually, such that acetylene reduction at a constant oxygen concentration was stable, but showed further inactivation when oxygen concentration was once again increased. Alder nodules appear to consist of a large number of compartments that differ in the degree to which nitrogenase is protected from excess oxygen.Supported by United States Department of Agriculture Grant 78-59-2252-0-1-005-1 相似文献
4.
Effect of low rhizosphere oxygen on growth, nitrogen fixation and nodule morphology in lucerne 总被引:1,自引:0,他引:1
C. Arrese-Igor M. Royuela C. de Lorenzo M. R. de Felipe P. M. Aparicio-Tejo 《Physiologia plantarum》1993,89(1):55-63
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. 相似文献
5.
Intercellular location of glycoprotein in soybean nodules: effect of altered rhizosphere oxygen concentration 总被引:5,自引:4,他引:5
Abstract. A glycoprotein which occludes intercellular spaces in the inner cortex of legume nodules may be involved in controlling oxygen diffusion into rhizobial-infected cells. Here we investigated this possibility by localizing the glycoprotein using monoclonal antibodies and immunogold labelling in nodulated roots of soybean cv. Clarke inoculated with Bradyrhizobium japonicum strain RCR3442 exposed to atmospheres with either 10, 21 (control) or 40% oxygen for 28d. Infected cells showed evidence of premature senescence when grown in above or below ambient pO2 particularly at 10% oxygen, although cortical cells appeared to be little altered by oxygen treatment. In the inner cortical cells, more glycoprotein was seen to be occluding intercellular spaces of those nodules subjected to 40% oxygen and less in those nodules exposed to 10% oxygen, when compared to controls. This observation, made at the light microscope level (using silver enhancement) was confirmed under the TEM using immunogold labelling. Therefore, it is suggested that intercellular space glycoprotein is one of the structural components of the diffusion resistance in the cortex of legume nodules. 相似文献
6.
H P Holzmann H A Berghammer M Ortner K Haselwandter 《Canadian journal of microbiology》1991,37(10):775-779
The objective of this study was to analyse in vivo the effect of oxygen on the nitrogenase of Bacillus polymyxa. The culture technique employed in this study prevented spore formation by B. polymyxa during the entire period of exposure to acetylene. Under these conditions the acetylene-reduction assay allowed quantification of nitrogenase activity over long incubation periods (44 h). Nitrogenase activity was highest in cells harvested in the late logarithmic phase. At PO2 of 0.19 and 0.37 kPa, acetylene reduction was inhibited by 80 and 100%, respectively. This switch-off effect could be reversed through oxygen exhaustion, either by flushing the culture with N2 or by cellular respiration, suggesting a respiratory protection mechanism for the nitrogenase complex in B. polymyxa. Oxygen consumption measured by a closed-chamber respirometer showed a linear increase up to a PO2 of 0.2 kPa. Above 0.3 kPa a saturation in oxygen consumption was observed. Exposure to high oxygen pressures resulted in an irreversible loss of nitrogenase activity. The oxygen inhibition pattern was shown to be similar to that in other microaerophilic and anaerobic nitrogen-fixing microorganisms. 相似文献
7.
Tolerance to water stress was studied in plants of grey alder, Alnus incana (L.) Moench, grown in a climate chamber in pots of sand supplied with a nitrogen-free nutrient solution. The plants were subjected to a single drying and recovery cycle, during which acetylene reduction, transpiration and stomatal resistance were measured. At different stress levels the plants were placed in a closed system to equilibrate the water potential in the plant-soil system. The water potential of the plants was determined, after which they were watered and their recovery studied. Nitrogenase activity showed low tolerance to water deficit. At moderate stress (−0.6 to −0.8 MPa) acetylene reduction was reduced by half, and at more severe stress, (< −1 MPa) activity was near zero. There was a rapid decrease in nitrogenase activity coincident with stomatal closure, which indicates a continuous need for photoassimilates for nitrogenase activity. Nodules or nitrogenase activity seemed to be weak sinks for assimilates compared with root pressure bleeding. Measurements of nitrogenase activity in root nodule homogenates supplied with ATP and reductant suggested a loss of active nitrogenase in the nodules in response to water stress. The recovery from moderate stress or long dark treatment took several days, and recovery from severe stress took still longer. Shortage of assimilates and disturbances in oxygen and nitrogen balances in the nodules are discussed as reasons for the reduced nitrogenase activity in response to water stress. 相似文献
8.
为了解非豆科固氮树种的固氮酶和N_2O还原酶(Nos)活性,采用乙炔还原法和乙炔抑制技术对细枝木麻黄(Casuarina cunninghamiana)和江南桤木(Alnus trabeculosa)离体根瘤及立地土壤的两种酶活性进行了研究。结果表明,离体根瘤只在厌氧条件下有固氮酶活性,在好氧条件下有Nos活性。根瘤区根际土和非根瘤区根际土的固氮酶活性在好氧条件大于厌氧条件,Nos活性只表现在厌氧条件下。在好氧条件下,根瘤区根际土和非根瘤区根际土的固氮酶活性无显著差异;根瘤区根际土的Nos活性显著大于非根瘤区根际土。除离体根瘤在好氧条件下不表现固氮酶活性外,细枝木麻黄和桤木的离体根瘤、根瘤区根际土和非根瘤区根际土的固氮酶活性均都大于Nos活性。好氧条件下根瘤区根际土的固氮酶活性与非根瘤区根际土的呈极显著正相关,而厌氧条件下根瘤的固氮酶活性与好氧条件下根瘤区根际土和非根瘤区根际土固氮酶活性、好氧条件下根瘤的Nos活性与厌氧条件下根瘤区根际土和非根瘤区根际土Nos活性均呈极显著负相关。这为研究弗兰克氏菌结瘤植物共生固氮体系对N2O汇强度的影响和调控奠定基础。 相似文献
9.
Growth, acetylene reduction, and respiration rate were studied in batch and continuous cultures of Arthrobacter fluorescents at different oxygen partial pressures. The optimum pO2 values for growth and acetylene reduction were 0.05 and 0.025 atm, respectively, but microorganisms can tolerate higher pO2 values. The growth of cultures provided with combined nitrogen was dependent on oxygen availability, and strict anaerobic conditions did not support growth. Acetylene reduction of a population grown in continuous culture and adapted to low pO2 (0.02 atm) was much more sensitive to oxygenation than that of a population adapted to high pO2 (0.4 atm). Their maximum nitrogenase activity, at their optimal pO2 values, were quite different. The respiratory activity of nitrogen-fixing cultures increased with increasing oxygen tensions until a pO2 of 0.2 atm. At higher pO2 values, the respiration rate began to decrease. 相似文献
10.
《Annals of botany》1997,79(5):493-503
The development of the N2-fixing symbiosis between white lupin (Lupinus albusL.) cv. Multolupa andBradyrhizobiumstrain ISLU16 was followed using the acetylene reduction assay (ARA), immunoblots of protein extracts, and microscopy/immunogold labelling at 0, 8, 12, 17 and 20 d after infection. There was no ARA at 0, 8 and 12 d, although macroscopically visible nodule primordia had formed on roots by 8 d. The lack of nitrogenase at these times was confirmed by a negative signal to immunogold labelling with nitrogenase-specific antibodies. At 17 d three out of six plants had ARA, and nodules from these gave a positive signal with the nitrogenase antibody. By contrast, ARA−(fix−) nodules at 17 d were smaller (mean radius of 0.49 mm compared to 1.01 mm with fix+nodules) and gave a negative signal with the nitrogenase antibody. Western blots of nodule protein extracts using the monoclonal antibodies MAC236 and MAC265 (which recognize two epitopes on a glycoprotein which is considered to be involved in both rhizobial infection and the regulation of nodule oxygen diffusion) gave a strong signal with nodules (fix+) from 20 d plants and with 17 d fix+plants. The signal with MAC236/MAC265 was substantially weaker with nodules from 17 d fix−plants, and there was no signal apparent from nodules/nodulated roots from the 0, 8 and 12 d harvests. However, further investigation using immunogold labelling revealed that not only were MAC236 and MAC265 expressed within cortical intercellular spaces in 20 d and 17 d fix+/fix−nodules, but they were also strongly expressed in the developing cortex surrounding the newly-infected tissue in 8 d nodules, as well as in intercellular spaces within the cortex and infected tissue of 12 d nodules. These data demonstrate that the glycoprotein recognized by MAC236 and MAC265 is present before the onset of nitrogenase expression and function, but expression of the epitopes appears to be enhanced from the onset of N2fixation. Nodules at all harvests were investigated for the presence of infection threads, as the MAC236/MAC265-recognized glycoprotein is also a component of the infection thread matrix in nodules from other legumes. Infection threads were not seen in nodules from any of the harvests except for the 20 d nodules, and then only after serial sectioning. The latter revealed occasional short wide infection threads entering and releasing rhizobia into small pockets of uninfected cells, within the infected tissue, but not within the meristems. The matrix of these infection threads labelled weakly, or not at all, with MAC236 and MAC265, and it was concluded that the majority of the MAC236/MAC265 detected in lupin nodule extracts originated from glycoprotein within cortical intercellular spaces. 相似文献
11.
The aim of this study was to test the effect of oxygen partialpressure as a possible limiting factor of nitrogen fixationfollowing defoliation. The response of nitrogenase activity(C2H2-reduction) of defoliated and undefoliated white and redclover plants (Trifolium repens L. and Trifolium pratense L.)to either 19 kPa oxygen or 55 kPa oxygen was investigated. Priorto defoliation, white clover plants were grown for five weeksin a growth chamber, and red clover plants for 7 or 11 weeksin a glasshouse. The results included measurements of 16N2-uptake. Increasing oxygen partial pressure from 19 to 55 kPa severelyrestricted nitrogenase activity of undefoliated white cloverplants; however, 2 h after complete defoliation, the same treatmentcaused a significant increase. A fivefold increase in nitrogenaseactivity upon exposure to the elevated oxygen partial pressurewas found at the end of a 24 h period. This beneficial effectdecreased gradually from 1 to 5 d after defoliation. The responseof recently defoliated red clover plants to 55 kPa oxygen partialpressure was similar to that of white clover, independentlyof plant age. The gradual recovery of nitrogenase activity duringthree weeks of regrowth was associated with a simultaneous changein the response to increased oxygen partial pressure, leadingagain to the response of undefoliated plants. These data suggested that lack of oxygen at the site of nitrogenfixation, resulting from a dramatic increase in oxygen-diffusionresistance, is the main factor limiting nitrogenase activityfollowing defoliation. Trifolium repens L., Trifolium pratense L., white clover, red clover, defoliation, regrowth, nodules, nitrogen fixation, nitrogenase activity, oxygen limitation 相似文献
12.
A flow-through gas system was used to study the effects of disturbanceon nitrogenase (acetylene reduction) activity of nodulated rootsystems of soyabean (Glycine max) and white clover (Trifoliumrepens). Detopping plus removal of the rooting medium (by shaking)produced a substantial decrease in maximum nitrogenase activity.This response is due to a reduction in oxygen flux to the bacteroidscaused by an increase in the oxygen diffusion resistance ofthe nodule. The decrease in maximum nitrogenase activity wasmuch smaller for roots subjected to detopping only. Thus, theeffect of root shaking is more important than that of shootremoval. The effect of detopping plus root shaking on nitrogenase activityoccurred whether the plants were equilibrated and assayed at25°C or 15°C. However, the effect of disturbance onthe oxygen diffusion resistance of the nodules, and thus onnitrogenase activity, was greater at the higher temperature.At the lower temperature the oxygen diffusion resistance ofthe nodules had already been increased in response to the reducedrequirement for oxygen. These nodules were less susceptibleto the effects of disturbance. Thus, comparisons of the effectsof equilibration temperature on nitrogenase activity produceddifferent results depending on whether intact or disturbed systemswere used. With intact systems activity was lower at the lowertemperature but with detopped/shaken roots the lowest activityoccurred at the higher temperature. It is concluded that the use of detopped/shaken roots can producesubstantial errors in the acetylene reduction assay, which makesthe assay invalid even when used for comparative purposes. However,comparisons with rates of 15N2 fixation and H2 production showthat accurate measurements of nitrogenase activity can be obtainedfrom maximum rates of acetylene reduction by intact plants ina flow-through gas system. The continued use of assay proceduresin which cumulated ethylene production from disturbed systemsis measured in closed vessels must be questioned. Key words: Nodules, acetylene, nitrogenase activity 相似文献
13.
The effects of increasing rhizosphere pO2on nitrogenase activity and nodule resistance to O2diffusion were investigated in soybean plants [Glycine max (L.) Merr. cv. Harosoy 63] in which nitrogenase (EC 1.7.99.2) activities were inhibited by (a) removal of the phloem tissue at the base of the stem (stem girdling), (b) exposure of roots to 10 mM NO3over 5 days (NO3-treated), or (c) partial inactivation of nitrogenase activity by an exposure of nodulated roots to 100 kPa O2(O2-inhibitcd). In control plants and in plants which had been treated with 100 kPa O2, increasing rhizosphere O2concentrations in 10 kPa increments from 20 to 70 kPa did not alter the steady-state nitrogenase activity. In contrast, in plants in which nitrogenase activities were depressed by stem girdling or by exposure to NO3, increasing rhizosphere pO2resulted in a recovery of 57 or 67%, respectively, of the initial, depressed rates of nitrogenase activity. This suggests that the nitrogenase activity of stem-girdled and NO3-treated soybeans was O2-limited. For each treatment, theoretical resistance values for O2diffusion into nodules were estimated from measured rates of CO2exchange, assuming a respiratory quotient of 1.1 and 0 kPa of O2in the infected cells. At an external partial pressure of 20 kPa O2, the stem-girdled and NO3--treated plants displayed resistance values which were 4 to 8.6 times higher than those in the nodules of the control plants. In control and O2-inhibited plants, increases in pO2from 20 to 70 kPa in 10 kPa increments resulted in a 2.5- to 3.9-fold increase in diffusion resistance to O2, and had little effect on either respiration or nitrogenase activity. In contrast, in stem-girdled and NO3--treated plants, increases in external pO2had little effect on diffusion resistance to O2, but resulted in a 2.3- to 3.2-fold increase in nodule respiration and nitrogenase activity. These results are consistent with stem-girdling and NO3--inhibition treatments limiting phloem supply to nodules causing an increase in diffusion resistance to O2at 20 kPa and an apparent insensitivity of diffusion resistance to increases in external pO2. 相似文献
14.
缺硼对大豆根瘤结构和功能的影响 总被引:3,自引:1,他引:2
在营养液培养条件下以普通结结瘤大豆Braggcv.「Glycinemax(L.)Merr」及其超结瘤突变体nts382为实验材料,运用光学显微方法研究了硼对大豆根瘤结构的影响,并测定了根瘤固氮酶活性结果表明,缺硼使根瘤结构受到严重破坏,并使固氮酶活性显著下降,缺硼使根瘤结构受到破坏是导致固氮酶活性下降的可能原因。 相似文献
15.
Klucas RV 《Plant physiology》1974,54(4):612-616
Soybean Glycine max. L. Merr. nodule senescence was studied using the loss of acetylene reduction by intact tap root nodules as its indication. Tap root nodules from two varieties (Calland and Beeson) of field-grown soybeans were used. The specific activities of nitrogenase (micromoles/minute gram fresh weight of nodules) as measured by the acetylene reduction assay decreased abruptly between 58 to 65 and 68 to 75 days after planting the Beeson and Calland soybeans, respectively. Major changes were not detected in dry weight, total nitrogen, and leghemoglobin levels during the period when in vivo nitrogenase activity declined. Ammonium levels in the cytosol of nodules and poly-β-hydroxybutyrate increased moderately just prior to or coincidental with the loss of nitrogenase activity. Neither enzymes that have been postulated to be involved in ammonium assimilation nor NADP+-specific isocitrate dehydrogenase exhibited any large changes in specific activities during the initial period when nitrogenase activity declined. 相似文献
16.
The low gas permeability of a diffusion barrier in the cortex of soybean nodules plays a significant role in the protection
of nitrogenase from oxygen inactivation. It may also set an upper limit on nodule respiration and nitrogen fixation rates.
Two methods which have been used to quantify the gas permeability of leguminous nodules are reviewed and found to be unreliable.
A new assay technique for determining both the nodule activity and gas permeability is developed and tested. This ‘lag-phase’
assay is based on the time nodules require to reach steady-state ethylene production after being exposed to acetylene. The
technique is rapid, insensitive to errors in biochemical parameters associated with nitrogenase, and is non-destructive. The
method was tested with intact aeroponically grown soybean plants for which the mean nodule gas permeability was found to be
13.3×10−3 mms−1. This corresponds to a layer of cells approximately 35 um thick and is consistent with previously reported values. 相似文献
17.
18.
Mutagenesis provoked by exposure to increased concentration of antibiotics of five indigenous Rhizobium galegae strains resulted
in the generation of several antibiotic-resistant mutants. The mutants differed from the wild type and one from another in
respect to the nodulation capacity, the nitrogenase activity, the nodule ultrastructure, and the plant growth response. Galega
plants inoculated with mutants resistant to streptomycin and rifampicin formed nodules with higher nitrogenase activity and
accumulated more shoot dry biomass than plants inoculated with the parent strains. Resistance to kanamycin and nalidixic acid
was associated with significant decrease of nitrogenase activity. A correlation between nitrogen-fixing efficiency and nodule
infected cell ultrastructure was found. When the bacteroids occupied about 10 times higher area in infected cells of nodule
than peribacteroid spaces and host cytosol had electron dense and homogenous structure, the nitrogenase activity was the highest.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
Adaptation of Nodulated Soybean (Glycine max L. Merr.) to Growth in Rhizospheres Containing Nonambient pO(2) 总被引:3,自引:3,他引:0
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Nodulated soybean (Glycine max L. Merr. cv White Eye inoculated with Bradyrhizobium japonicum strain CB 1809) plants were cultured in the absence of combined N from 8 to 28 days with their root systems maintained continuously in 1, 2.5, 5, 10, 20, 40, 60, or 80% O2 (volume/volume) in N2. Plant dry matter yield was unaffected by partial pressure of oxygen (pO2) and N2 fixation showed a broad plateau of maximum activity from 2.5 to 40 or 60% O2. Slight inhibition of nitrogenase activity occurred at 1% O2 and as much as 50% inhibition occurred at 80% O2. Low pO2 (less than 10%) decreased nodule mass on plants, but this was compensated for by those nodules having higher specific nitrogenase activities. Synthesis and export of ureides in xylem was maintained at a high level (70-95% of total soluble N in exudate) over the range of pO2 used. Measurements of nitrogenase (EC 1.7.99.2) activity by acetylene reduction indicated that adaptation of nodules to low pO2 was largely due to changes in ventilation characteristics and involved increased permeability to gases in those grown in subambient pO2 and decreased permeability in those from plants cultured with their roots in pO2 greater than ambient. A range of structural alterations in nodules resulting from low pO2 were identified. These included increased frequency of lenticels, decreased nodule size, increased volume of cortex relative to the infected central tissue of the nodule, as well as changes in the size and frequency of extracellular voids in all tissues. In nodules grown in air, the inner cortex differentiated a layer of four or five cells which formed a band, 40 to 50 micrometers thick, lacking extracellular voids. This was reduced in nodules grown in low pO2 comprising one or two cell layers and being 10 to 20 micrometers thick in those from 1% O2. Long-term adaptation to different external pO2 involved changes which modify diffusive resistance and are additional to adjustments in the variable diffusion barrier. 相似文献
20.
Shigeyuki Tajima Hiroyuki Sasahara Hiroshi Kouchi Tadakatsu Yoneyama Junji Ishizuka 《Bioscience, biotechnology, and biochemistry》2013,77(12):3473-3479
Bacteroids retaining high acetylene reduction activity (nitrogenase activity) were prepared anaerobically from soybean nodules. Addition of succinate (or of both leghemoglobin and succinate) to the acetylene reduction assay system greatly increased the activity of the isolated bacteroids.When various organic acids were incubated with the bacteroids at 2% oxygen concentration, an optimum condition for bacteroid acetylene reduction, the organic acid degradation by bacteroids was very slow, and both lactate and acetate were accumulated in the incubation system, suggesting the operation of fermentative pathway in bacteroids under such low oxygen conditions.With 20% oxygen, the added organic acids were degraded rapidly by bacteroids without addition of leghemoglobin to the incubation system.With leghemoglobin in the incubation system, the organic acid degradation by bacteroids was accelerated extensively even at 2% oxygen, and the formation of lactate and acetate were negligible. No significant difference in the organic acid degradation rate was observed between the 2% and 20% oxygen concentrations when the leghemoglobin was present in the incubation system. Addition of acetylene to the assay system slightly inhibited the organic acid degradation.This data suggests that bacteroids are unable to oxidize organic acid in low oxygen concentration and that the leghemoglobin allows the rapid organic acid dagradation by bacteroids even in such low oxygen concentrations. 相似文献