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  • Chemical shift artefact  (1)
  • Glutamate oxalate transaminase  (1)
  • Host-Rhizobium strain interaction  (1)
  • 1
    Electronic Resource
    Electronic Resource
    STIR sequences in NMR imaging of the optic nerve (1987)
    Springer
    Neuroradiology 29 (1987), S. 238-245 
    Details
    ISSN: 1432-1920
    Keywords: NMR imaging ; Optic nerve ; Chemical shift artefact ; Contrast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Orbital fat surrounding the optic nerve causes considerable difficulties in NMR imaging due to its high image intensity and the chemical shift artefact. We have investigated the ability of inversion recovery seqeunces with short inversion times (STIR sequences) to suppress fat signals in imaging the optic nerve. We have also compared the contrast attainable with STIR sequences with that obtainable from other sequences. Measurements were made on 4 normal controls and 5 patients with multiple sclerosis (MS) to obtain typical values of relaxation times and proton densities for orbital fat, cerebral white matter and MS lesions. The fat T1 measurements were used to predict an appropriate inversion time for the STIR sequence and estimate how much residual fat signal might be expected as a result of natural variations in fat T1. STIR sequences can be used to suppress the signal from orbital fat with little residual signal. Measurements from white matter and MS lesions were used to predict the contrast between normal and pathological tissues that is attainable with STIR sequences. STIR contrast compares favourably with that obtainable from other sequences.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00451760
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular and whole-plant responses to selection for enzyme activity in alfalfa root nodules: evidence for molecular compensation of aspartate aminotransferase expression (1992)
    Springer
    Theoretical and applied genetics 84 (1992), S. 355-361 
    Details
    ISSN: 1432-2242
    Keywords: Glutamate oxalate transaminase ; Isozymes ; Nitrogen fixation ; Medicago sativa L. ; Rhizobium meliloti
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The enzyme aspartate aminotransferase (AAT) plays a key role in the assimilation of fixed-N in alfalfa (Medicago sativa L.) root nodules. AAT activity in alfalfa nodules is due to the activity of two dimeric isozymes, AAT-1 and AAT-2, that are products of two distinct genes. Three forms of AAT-2 (AAT-2a, -2b, and-2c) have been identified. It was hypothesized that two alleles occur at the AAT-2 locus, giving rise to the three AAT-2 enzymes. In a prior study bidirectional selection for root nodule AAT and asparagine synthetase (AS) activities on a nodule fresh weight basis in two diverse alfalfa germ plasms resulted in high nodule enzyme activity subpopulations with about 20% more nodule AAT activity than low enzyme activity subpopulations. The objectives of the study presented here were to determine the inheritance of nodule AAT-2 production and to evaluate the effect of bidirectional selection for AAT and AS on AAT-2 allelic frequencies, the relative contributions of AAT-1 and AAT-2 to total nodule activity, nodule enzyme concentration, and correlated traits. Two alleles at the AAT-2 locus were verified by evaluating segregation of isozyme phenotypes among F1 and S1 progeny of crosses or selfs. Characterization of subpopulations for responses associated with selection was conducted using immunoprecipitation of in vitro nodule AAT activity, quantification of AAT enzyme protein by ELISA, and AAT activity staining of native isozymes on PAGE. Results indicate that selection for total AAT activity specifically altered the expression of the nodule AAT-2 isozyme. AAT-2 activity was significantly greater in high compared to low activity subpopulations, and high AAT subpopulations from both germ plasms had about 18% more AAT-2 enzyme (on a nodule fresh weight basis). No significant or consistent changes in AAT-2 genotypic frequencies in subpopulations were caused by selection for AAT activity. Since changes in AAT activity were not associated with changes in AAT-2 genotype, selection must have affected a change(s) at another locus (or loci), which indirectly effects the expression of nodule AAT.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00229494
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    A multiple-trait breeding program for improving the symbiosis for N2 fixation betweenMedicago sativa L. andRhizobium meliloti (1984)
    Springer
    Plant and soil 82 (1984), S. 303-314 
    Details
    ISSN: 1573-5036
    Keywords: Acetylene reduction ; Disease resistance ; Host-Rhizobium strain interaction ; Nitrate reductase ; Nodule enzymes ; Nodule mass ; 15N evaluation ; Plant vigor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The goal of breeding alfalfa for increased N2 fixation potential is addressed. A chronological progression of breeding, physiological, microbiological, and plant pathological research is described. Studies describing the interrelationships among plant morphological, plant physiological, andRhizobium effectiveness traits are summarized. It was concluded that N2 fixation in alfalfa is affected by coordinated responses among many physiological and biochemical traits. The simultaneous improvement of many factors in the symbiosis requires a comprehensive multiple-step breeding program. The current program includes selection in the glasshouse for seedling vigor,Rhizobium preference, shoot growth, nodule mass, root growth, nitrogenase (as measured by acetylene reduction), and nodule enzyme activity. The inclusion of additional selection traits is anticipated. Field evaluations of N2 fixation potential of alfalfa populations are made with15N isotope dilution techniques. Plant germplasm sources used in the breeding program include several heterogeneous populations which have good combining ability and pest resistance when they are intercrossed. Significant progress has been made in achieving the goal of breeding alfalfa for improved N2 fixation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02184269
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    Paper (German National Licenses)
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