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61.
R. W. F. Hardy R. C. Burns R. R. Hebert R. D. Holsten E. K. Jackson 《Plant and Soil》1971,35(1):561-590
Summary 1. Characteristics and methodology of the C2H2-C2H4 assay forin situ measurement of N2 fixation are outlined.
2. Electron micrographic analysis of the developmental morphology of the natural soybean symbiosis and C2H2-C2H4 analysis indicate that increasing N2-fixing activity from 12–35 days of age is accompanied by an increase in bacteroid number per cell, bacteroid number per vesicle
and inclusions per bacteroid. The mole ratio of leghemoglobin to nitrogenase also increases from 50 to a relatively constant
plateau of 500 to 1500 during this period. The quantitative validity of the C2H2-C2H4 assay as a measure of N2 fixation during a complete growth cycle of soybeans on nitrogen-free medium is demonstrated by Σ (C2H2→C2H4)×28/3 values which are 75–95% of the values determined for N2 fixed by Kjeldahl analyses.
3. A technique for the establishment of the first callus N2-fixing symbiosis in mixed cultures ofRhizobium legume provides a defined experimental system for exploration of legume symbiosis. N2-fixing activity is about 1% of the natural system and is influenced by exogenous auxins and cytokinins. Morphology, including
infection threads and vesicle enclosed bacteroids, is similar to the nodule system.
4. N2-fixing activity of field-grown soybeans, including varieties which differed in flowering characteristics and maturity dates,
and of peanuts was determined biweekly with the C2H2-C2H4 assay. Activity extended from nodule initiation to senescence and correlated with the nitrogen demands of the plant and in
most cases >90% of the N2 fixed during the 60–70 day period of fruit formation and maturation. A logarithmic relationship between N2-fixing activity and age, and N2 fixed and age was demonstrated as a fundamental characteristic of these annual symbionts,i.e. log N2 fixed =k(t−t
0), wheret
0 is age at activity initiation. The resultant parameters: 1) age at activity initiation, 2) calculated rate of daily increase
(7–9% for soybeans and 7–10% for peanuts), 3) age at end of logarithmic phase (about 80 days for soybeans), and 4) total N2 fixed (about 250 mg per soybean plant) are useful bases for evaluation of environmental, bacterial and host effects on N2 fixation. Various N fertilizers applied at planting and flowering inhibited N2 fixation of soybeans by decreasing the rate of daily increase.
5. Physical and chemical characteristics of nitrogenase, including those of crystalline Mo-Fe protein, reactions of nitrogenase,
and model studies are consistent with a proposed mechanism.
6. Potential utilities of N2 fixation research include increased food protein production via initially enhanced N2 fixation of legumes such as soybeans and eventually extension of N2-fixing symbioses to non-legumes and new chemistry of N2, including the direct incorporation of aerial N2 into important organic compounds.
Contribution No. 1748. 相似文献
62.
A specific rabbit antibody against the 4-azido-2-nitrophenyl determinant was photo-labelled by the homologous hapten ε-(4-azido-2-nitrophenyl)-l-lysine, and by the close structural isomer ε-(5-azido-2-nitrophenyl)-l-lysine. The extents of covalent labelling of the antibody-binding site were assessed by using radioactive haptens and exhaustive displacement dialysis, which leaves the unlabelled sites empty but largely intact. A single photolysis of hapten–antibody complex suffices to label those sites that are capable of being labelled. Although there is considerable overlap among sub-populations of antibody that will bind the two haptens non-covalently, sites that can be covalently labelled by one reagent cannot be labelled by the other. 相似文献
63.
Propagation Speed in Myelinated Nerve: II. Theoretical Dependence on External Na+ and on Temperature 总被引:2,自引:1,他引:1 下载免费PDF全文
W. L. Hardy 《Biophysical journal》1973,13(10):1071-1089
The Hodgkin-Huxley (H.H.) equations modified by Dodge for Rana pipiens myelinated nerve have been solved to determine how well the theory predicts the effects of changes of temperature and [Na+]0 on propagation. Conduction speed θ was found to have an approximately exponential dependence on temperature as was found experimentally, but the theoretical temperature coefficient (Q10) was low; 1.5 compared with the experimental finding of 2.95. θ was found to be a linear function of log ([Na+]0) in contrast to the experimental finding of a square root dependence on [Na+]0. θ is 50% greater at one-fourth normal [Na+]0 than the theory predicts. The difference between the theoretical θ([Na+]0) and the experimental θ([Na+]0) is probably due to an imprecisely known variation of parameters and not to a fundamental inadequacy of the theory. 相似文献
64.
Experiments were performed to test the ability of macrophages from newborn mice to participate in immune reactions. It was found that peritoneal cells from 4-day-old mice injected at birth with thioglycollate did not reconstitute reactivity to Shigella in adult, irradiated mice, while normal adult macrophages did.The total yield of peritoneal exudate cells (PEC) was relatively low, yet the number of precursor cells of macrophages in the newborn spleen was found in significantly higher concentrations than in the adult. The number of precursor cells in the spleens of 0–3-day-old mice did not increase in response to antigenic stimulation, indicating that they too are unable at this stage to develop reactivity to immunological signals. 相似文献
65.
Summary Host-cell reactivation of gamma-irradiated phage T1 in strains of E. coli K-12 has been compared with HCR of UV-irradiated phage in these same strains and with the radiation sensitivities of these strains (Fig. 1–4). The pattern of the HCR of gammairradiated phage in these strains is like that of the HCR of UV-irradiated phage. HCR in strains whose genotype is uvr
+rec- is like that of the wild type; whereas, HCR is minimal in strains which are uvr
-. It is suggested that some type of gamma-ray-induced base damage in phage DNA is repaired in uvr
+ strains.This work was supported by the United States Atomic Energy Commission Contract No. AT(11-1)-1686. — This is report No. COO-1686-6.Supported in part by the United States Public Health Service Training Grant No. 5T1 RH-80-02(67). 相似文献
66.
Flavodoxin. Chemical and biological properties 总被引:3,自引:0,他引:3
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