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4.
In vivo CO 2 fixation activity and in vitro phosphoenolpyruvate carboxylase activity were demonstrated in effective and ineffective nodules of alfalfa ( Medicago sativa L.) and in the nodules of four other legume species. Phosphoenolpyruvate carboxylase activity was greatly reduced in nodules from both host and bacterially conditioned ineffective alfalfa nodules as compared to effective alfalfa nodules. Forage harvest and nitrate application reduced both in vivo and in vitro CO2 fixation activity. By day 11, forage harvest resulted in a 42% decline in in vitro nodule phosphoenolpyruvate carboxylase activity while treatment with either 40 or 80 kilograms nitrogen per hectare reduced activity by 65%. In vitro specific activity of phosphoenolpyruvate carboxylase and glutamate synthase were positively correlated with each other and both were positively correlated with acetylene reduction activity. The distribution of radioactivity in the nodules of control plants (unharvested, 0 kilograms nitrogen per hectare) averaged 73% into the organic acid and 27% into the amino acid fraction. In nodules from harvested plants treated with nitrate, near equal distribution of radioactivity was observed in the organic acid (52%) and amino acid (48%) fractions by day 8. Recovery to control distribution occurred only in those nodules whose in vitro phosphoenolpyruvate carboxylase activity recovered. The results demonstrate that CO2 fixation is correlated with nitrogen fixation in alfalfa nodules. The maximum rate of CO2 fixation for attached and detached alfalfa nodules at low CO2 concentrations (0.13-0.38% CO2) were 18.3 and 4.9 nanomoles per hour per milligram dry weight, respectively. Nodule CO2 fixation was estimated to provide 25% of the carbon required for assimilation of symbiotically fixed nitrogen in alfalfa. 相似文献
5.
Seedlings of grey alder ( Alnus incana Moench), nodulated or unnodulated, were investigated at varied relative addition rate of nitrogen. Nitrogen fixation alone, without addition of mineral nitrogen, resulted in an almost optimum nitrogen status but only about half the maximum relative growth rate, probably mainly because of energy costs of nodulation and fixation. The growth deficit due to nodulation was much more than can be explained by the theoretical energy requirement for the amount of nitrogen fixed. Thus, the nitrogen fixation process was not very efficiently used. The nitrogen fixation rate was strongly stimulated by increasing nitrogen addition rate up to high levels. The fixation rate decreased rapidly close to optimum (maximum relative growth rate) and was negligible at maximum growth. A feed-back of mineral nitrogen on photosynthesis increased fixation rate with time, and the relative importance of fixation over mineral nitrogen nutrition increased. However, nitrogen fixation, also at maximum rate, supplied only a small proportion of the nitrogen amount required for maximum growth. The optimum nutrient solutions contained comparatively high nitrogen concentrations to secure free access to nitrogen. The nodules were damaged by this treatment, and it is concluded that the nitrogen additions must be adjusted to the current consumption of the plants to avoid an increased external nitrogen concentration. Strong linear regressions were found between relative growth rate, nitrogen status expressed as percentage content of fresh weight, and relative growth rate in unnodulated seedlings. There was a greater variability in nodulated seedlings than in unnodulated ones, because of the nitrogen fixation. The reactions of unnodulated grey alder were largely the same as previously reported for birch seedlings, but the maximum growth capacity was lower in grey alder. During an initial period of change in the internal nitrogen status, deficiency symptoms appeared, especially in unnodulated seedlings. As in birch, the leaves turned green again at stable nitrogen status, independent of level. The results are in sharp contrast to data from the literature where the external nitrogen concentration was used as the driving variable for the internal nitrogen status. The measured fixation rates for grey alder are much higher than those previously reported. Still, the maximum fixation rate observed is small compared to the total nitrogen uptake rate required for maximum growth, in contrast to reported relationships. These comparisons indicate that increased external nitrogen concentration obscures the real relations between mineral and fixed nitrogen, on one hand because of rapid inhibition of nitrogen fixation and, on the other hand, because of failure to obtain stable optimum nutrition and maximum growth by means of this treatment variable. 相似文献
6.
Summary The alder has a perennial nodule cluster. The nodule amount on the roots increases with tree age. The N 2-fixing activity of nodules decreases with nodule age. Purple coloured soils with various soil pHs and CaCO 3 contents are, in the main, the ones which influence nodulation and N 2-fixing. Higher N 2-fixing capacity existed in the neutral and low calcium soils. High calcium soils and acid soils can restrain nodulation and
the N 2-fixing rate significantly. On the slope, where calcarous light loams are found, the annual nitrogen fixation capacity of
alder and cypress mixed plantations, less than 10 years old, is 16 or 17 kg/ha yr, but in the valley, a pure alder plantation
can reach 40 kg/ha yr. 相似文献
12.
The total metabolic cost of soybean ( Glycine max L. Mer Clark) nodule nitrogen fixation was empirically separated into respiration associated with electron flow through nitrogenase and respiration associated with maintenance of nodule function. Rates of CO2 evolution and H2 evolution from intact, nodulated root systems under Ar:O2 atmospheres decreased in parallel when plants were maintained in an extended dark period. While H2 evolution approached zero after 36 hours of darkness at 22°C, CO2 evolution rate remained at 38° of the rate measured in light. Of the remaining CO2 evolution, 62% was estimated to originate from the nodules and represents a measure of nodule maintenance respiration. The nodule maintenance requirement was temperature dependent and was estimated at 79 and 137 micromoles CO2 (per gram dry weight nodule) per hour at 22°C and 30°C, respectively. The cost of N2 fixation in terms of CO2 evolved per electron pair utilized by nitrogenase was estimated from the slope of H2 evolution rate versus CO2 evolution rate. The cost was 2 moles CO2 evolved per mole H2 evolved and was independent of temperature. In this symbiosis, nodule maintenance consumed 22% of total respiratory energy while the functioning of nitrogenase consumed a further 52%. The remaining respiratory energy was calculated to be associated with ammonia assimilation, transport of reduced N, and H2 evolution. 相似文献
13.
Five wild herb legumes (Trifolium resupinatum, Melilotus indica, Medicago intertexta, Trigonella hamosa, and Alhagi murarum)
were collected from cultivated lands of the Nile Valley, and compared with clover (Trifolium alexandrinum), a cultivated forage
legume. The wild herb legumes exhibited great variation in nodulation percentage, nodule number, nodule mass and acetylene
reduction activity with regard to locality. Nodulation of T. resupinatum and M. indica ranged between 50 - 100% and 33 - 100%,
respectively, compared to 50 - 100% for T. alexandrinum. The number of nodules formed on T. resupinatum was 9 - 128 and that
of M. indica 6 - 39, compared to 13 - 122 nodule per plant for T. alexandrinum. Nodule mass was correlated with nodule number.
In M. indica, a small number of nodules was compensated with high specific nitrogenase activity. The herb legumes formed nodules
of small size, varying shape (globose, cylindrical, branched, etc.), and of different types (crotalaroid and astragaloid).
Microscopic examination of root-nodules from T. resupinatum, M. indica and M. intertexta, showed that these legumes formed
indeterminate and effective nodules, containing apical meristems, central symbiotic tissue with characteristic zonation and
peripheral vascular bundles. The nodules harboured bacteroids with pleiomorphic morphology.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Summary The apparent K m(hydrogen) for uptake of hydrogen by pea root nodules was determined. This enabled the concentration gradient necessary for the evolution
of hydrogen to be calculated for nodules with no hydrogenase activity. This indicated that hydrogen inhibition of nitrogenase
is not likely to be the cause of the low relative efficiency of legume root nodules. The factors that affect electron allocation
between protons and nitrogen in nitrogenase are reviewed and it is concluded that there must be some as yet unknown factor
that affects electron distribution in Rhizobium nitrogenase. One possibility is put forward and considered. A strain of Rhizobium was used that was found to possess hydrogenase activity in combination with pea variety Feltham First but not with variety
Meteor. The control of this enzyme is briefly discussed. 相似文献
15.
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 CO 2 evolution, whereas no differences were observed in O 2 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
17.
Liver mitochondria from octanoate-treated rabbits showed an impaired ability to synthesize citrulline. Two methods were used to evaluate citrulline synthesis in rat liver mitochondria. Under these conditions octanoate inhibited citrulline synthesis by over 50%. When ATP was included in the assay medium the inhibitory effect of octanoate was prevented. In the absence of ATP in the suspending medium, octanoate did not significantly lower total adenine nucleotides in rat liver mitochondria. However, under these conditions octanoate caused a change in the adenine nucleotide profile such that ATP content was decreased and AMP content was increased. When ATP was present in the assay medium, octanoate caused a similar increase in AMP content. However, ATP decreased only slightly. The alterations in mitochondrial adenine nucleotide profile by octanoate and the reversal of the effect by exogenous ATP suggests that octanoate inhibits citrulline synthesis via reduced intramitochondrial ATP levels. The ability of octanoate to lower mitochondrial ATP and elevate mitochondrial AMP may be related to its intramitochondrial activation by the medium chain fatty acid activating enzyme. 相似文献
18.
The infected cells of soybean ( Glycine max) root nodules require ATP production for ammonia assimilation and purine synthesis under microaerobic conditions. It is likely that the bulk of this demand is supplied through mitochondrial oxidative phosphorylation. Mitochondria purified from root nodules respired and synthesized ATP in sub-micromolar oxygen concentrations as measured by leghaemoglobin spectroscopy and luciferase luminescence. Both oxygen uptake and the apparent ATP/O ratio declined significantly as the oxygen concentration fell below 100 μmol m ?3. Cytochrome-pathway respiration by root nodule mitochondria had a higher apparent affinity for oxygen (Km 50 μmol m ?3) than did mitochondria isolated from roots (Km 125 μmol m ?3). Electron micrographs showed that mitochondria predominated at the periphery of infected cells adjacent to gas-filled intercellular spaces, where the oxygen concentration is predicted to be highest. Calculations of oxygen concentration and nitrogen fixation rates on an infected cell basis suggest that the measured rates of ATP production by isolated mitochondria are sufficient for the quantifiable in vivo requirements of ammonia assimilation and purine synthesis. The possible roles of mitochondrial respiration in the control of infected cell metabolism are also discussed. 相似文献
19.
Summary Growth and N accumulation were assessed in pure and mixed plantings (2 years old) of hybrid poplar and black alder in southern Québec. Symbiotic dinitrogen fixation was evaluated by natural 15N dilution. Growth of hybrid poplar plants and N accumulation in their tissues increased with their decreasing contribution to species ratio whereas no differences among treatments were measured for black alder. Yield and N content per hectare of aboveground components increased with the proportion of black alder in the plantation. Symbiotic dinitrogen fixation was estimated at 68% of alder nitrogen in both pure and mixed treatments. The maximum rate of N-fixation was 53kg ha –1 yr –1 in pure alder plots. The amount of nitrogen accumulated in entire plants of black alder from symbiotic fixation could be sufficient to balance the N export in harvested stems and branches of short-rotation plantations containing at least 33% of alder. 相似文献
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