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  • 1990-1994  (10)
  • 1960-1964
  • Medicago sativa  (4)
  • Medicago sativa L.  (3)
  • Rhenium  (3)
  • 1
    Electronic Resource
    Electronic Resource
    The quadruply bondedbis-carboxylatescis-Re2(μ-O2CCH3)2X4L2 (X = halide;L = neutral donor) as synthons in dirhenium chemistry (1994)
    Springer
    Journal of cluster science 5 (1994), S. 173-184 
    Details
    ISSN: 1572-8862
    Keywords: Rhenium ; dimetal comptexes ; phosphine ligands ; carboxylatebridged complexes ; redox chemistry ; preparation ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The reactions of the quadruply bonded dirhenium(III) carboxylatescis-Re2(μ-O2CR)2X4L2 (X=CI or Br; L=a monodentate donor) with monodentate, bidentate, and tridentate phosphine donors result in several types of redox behavior, usually involving partial or complete reductive decarboxylation of the dirhenium unit. Examples of dirhenium(VI, II), dirhenium(IV, II), dirhenium(III, II), and dirhenium(II, II) complexes, in which Re-Re bond orders of 4, 3.5, 3, l, or zero are encountered, have been isolated and repre-sentative examples structurally characterized. The course of these reactions is dependent upon the nature of the phosphine. The scope of this remarkably rich chemistry is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01165498
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  • 2
    Electronic Resource
    Electronic Resource
    The oxidative addition of hydrogen sulfide to the electron-rich triple bond: The isolation and characterization of compounds that contain the Re2(μ-H)(μ-SH) cluster unit (1991)
    Springer
    Journal of cluster science 2 (1991), S. 259-270 
    Details
    ISSN: 1572-8862
    Keywords: Rhenium ; clusters ; hydrido-bridged ; hydrosulfido-bridged ; preparation ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The reactions of Re2X4(μ-dppm)2 (X=Cl or Br; dppm=Ph2PCH2PPh2) with H2S in THF afford the dirhenium (III) complexes Re2(μ-H)(μ-SH)X4(μ-dppm)2, the first examples of the oxidative addition of an S-H unit across an electron-rich metal-metal triple bond. The bromide complex Re2(μ-H)(μ-SH)Br4(μ-dppm)2 (C2H5)2O crystallizes in the space group P21/n witha=16.631(2) Å,b=15.967(3) Å,c=19.904(2) Å, β=92.698(7)°,V=5279(2) Å3, andZ=4. The structure which was refined toR=0.053 (R w=0.070) for 4903 data withI〉3.0σ(I), shows the presence of an edge-shared bioctahedral geometry with a very short Re-Re distance of 2.4566(7) Å. While the hydrogen atoms of the μ-H and μ-SH ligands were not located in the X-ray structure determination, their presence is confirmed by IR and1H NMR spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00702956
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  • 3
    Electronic Resource
    Electronic Resource
    The oxidative addition of diphenylphosphine and monophenylphosphine to the electron-rich rhenium-rhenium triple bond. The isolation and characterization of compounds that contain the four-center Re(μ-X)(μ-PR2)Re cluster (X=halide) (1992)
    Springer
    Journal of cluster science 3 (1992), S. 83-102 
    Details
    ISSN: 1572-8862
    Keywords: Rhenium ; dimetal clusters ; hydrido-complexes ; phosphidobridged ; preparation ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Diphenylphosphine oxidatively adds to the Re≡Re bonds of Re2 X 4(μ-dppm)2 (X=Cl or Br; dppm=Ph2PCH2PPh2) and Re2Cl4(μ-dpam)2 (dpam=Ph2AsCH2AsPh2) to afford the dirhenium(III) complexes Re2(μ-X)(μ-PPh2)HX 3(μ-LL)2. The dppm complexes have also been prepared from the reactions of Re2(μ-O2CCH3)X 4(μ-dppm)2 with Ph2PH, and a similar strategy has been used to prepare Re2(μ-Cl)(μ-PPh2)HCl3(μ-dmpm)2 (dmpm=Me2PCH2PMe2) from Re2(μ-O2CCH3)Cl4(dmpm)2. Phenylphosphine likewise reacts with Re2 X 4(μ-dppm)2 to give Re2(μ-X)(μ-PHPh)HX 3(μ-dppm)2. An X-ray crystal structure determination on Re2(μ-Cl)(μ-PPh2)HCl3(μ-dppm)2 confirms its edge-shared bioctahedral structure. This complex crystallizes in the space group $$R\bar 3$$ (No. 148) witha=21.699(3) Å, α=84.50(4)°,V=10084(5) Å3, andZ=6. The structure was refined toR=0.049 (R w 0.069) for 5770 data withI〉3.0σ(I). The Re-Re distance is 2.5918(7) Å. Oxidation of the bromide complex Re2(μ-Br)(μ-PPh2)HBr3(μ-dppm)2 with NOPF6 produces the unusual dirhenium(III, II) cation [Re2(μ-H)(μ-Br)[P(O)Ph2]Br2(NO)(μ-dppm)2]+ which has been structurally characterized as its perrhenate salt, [Re2(μ-H)(μ-Br)[P(O)Ph2]Br2(NO)(μ-dppm)2]ReO4 · 2CH2Cl2. This complex crystallizes in the space group $$P\bar 1$$ (No. 2) witha=14.187(7) Å,b=16.419(5) Å,c=16.729(5) Å, α=98.76(2)°, β=110.11(3)°, γ=104.66(3)°,V=3414(6) Å3,Z=2. The structure was refined toR=0.040 (R w =0.051) for 5736 data withI〉3.0σ(I). The presence of a phosphorus-bound [P(O)Ph2]− ligand, a linear nitrosyl and a bridging hydrido ligand has been confirmed. The Re-Re distance is 2.6273(8) Å.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00814613
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  • 4
    Electronic Resource
    Electronic Resource
    Sequence analysis and developmental expression of an alfalfa protein disulfide isomerase (1992)
    Springer
    Plant molecular biology 19 (1992), S. 319-321 
    Details
    ISSN: 1573-5028
    Keywords: Medicago sativa ; cell culture ; protein disulfide isomerase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00027354
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  • 5
    Electronic Resource
    Electronic Resource
    Molecular characterization and expression of an isocitrate dehydrogenase from alfalfa (Medicago sativa L.) (1992)
    Springer
    Plant molecular biology 20 (1992), S. 801-807 
    Details
    ISSN: 1573-5028
    Keywords: Medicago sativa L. ; cell suspension culture ; isocitrate dehydrogenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A putative isocitrate dehydrogenase (IDH) cDNA from alfalfa has been cloned and sequenced. The derived amino acid sequence of 433 residues contains the isocitrate and isopropylmalate dehydrogenase signatures, is 63% identical to yeast mitochondrial NADP-IDH and shares high sequence identity with peptides of pig heart NADP-IDH. The sequence contains a potential N-terminal leader with similarities to a thylakoid transit peptide. IDH transcripts and NADP-IDH activity were detected in all alfalfa tissues examined, their levels depending upon the tissue type and its developmental stage. Transcripts and enzymatic activity were not induced on exposure of cell suspension cultures to a fungal elicitor. IDH is encoded by a small gene family in alfalfa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00027151
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  • 6
    Electronic Resource
    Electronic Resource
    Sequence analysis of an alfalfa 25S rRNA (1992)
    Springer
    Plant molecular biology 18 (1992), S. 1189-1190 
    Details
    ISSN: 1573-5028
    Keywords: Medicago sativa ; cell culture ; rRNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00047724
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  • 7
    Electronic Resource
    Electronic Resource
    Stress responses in alfalfa (Medicago sativa L.) 11. Molecular cloning and expression of alfalfa isoflavone reductase, a key enzyme of isoflavonoid phytoalexin biosynthesis (1991)
    Springer
    Plant molecular biology 17 (1991), S. 653-667 
    Details
    ISSN: 1573-5028
    Keywords: fungal elicitor ; isoflavone reductase mRNA ; Medicago sativa ; phytoalexin biosynthesis ; stereochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The major phytoalexin in alfalfa is the isoflavonoid (−)-medicarpin (or 6aR, 11aR)-medicarpin. Isoflavone reductase (IFR), the penultimate enzyme in medicarpin biosynthesis, is responsible for introducing one of two chiral centers in (−)-medicarpin. We have isolated a 1.18 kb alfalfa cDNA (pIFRalf1) which, when expressed in Escherichia coli, converts 2′-hydroxyformononetin stereospecifically to (3R)-vestitone, as would be predicted for IFR from alfalfa. The calculated molecular weight of the polypeptide (35400) derived from the 954 bp open reading frame compares favorably to estimated M rs determined for IFR proteins purified from other legumes. The transcript (1.4 kb) is highly induced in elicited alfalfa cell cultures. The kinetics of induction are consistent with the appearance of IFR activity, the accumulation of medicarpin, and the observed induction of other enzymes in the pathway. Low levels of IFR transcripts were found in healthy plant parts (roots and nodules) which accumulate low levels of a medicarpin glucoside. IFR appears to be encoded by a single gene in alfalfa. The cloning of IFR opens up the possibility of genetic manipulation of phytoalexin biosynthesis in alfalfa by altering isoflavonoid stereochemistry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00037051
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  • 8
    Electronic Resource
    Electronic Resource
    Stress responses in alfalfa (Medicago sativa L.) III. Induction of medicarpin and cytochrome P450 enzyme activities in elicitor-treated cell suspension cultures and protoplasts (1990)
    Springer
    Plant cell reports 9 (1990), S. 38-41 
    Details
    ISSN: 1432-203X
    Keywords: Medicago sativa L. ; Cytochrome P450 ; Elicitor ; Phytoalexin ; Protoplasts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cell suspension cultures of alfalfa (Medicago sativa L.) accumulated phenolic secondary metabolites in a pattern similar to that seen in alfalfa roots. Upon treatment with a crude elicitor preparation from the bean pathogen Colletotrichum lindemuthianum, the pterocarpan phytoalexin medicarpin accumulated in cells and culture medium. The extractable activities of six enzymes involved in medicarpin biosynthesis (including three cytochrome P450 activities) were induced by treatment with elicitor, and their induction kinetics correlated with the rate of medicarpin accumulation. However, protoplasts prepared from these cultures accumulated neither medicarpin nor other secondary products after treatment with elicitor. The cytochrome P450 activities were induced during the preparation of the protoplasts, but could be further induced by treatment with fungal elicitor. The results are discussed in relation to the use of alfalfa protoplasts as a system for functional analysis of cloned defense genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00232132
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  • 9
    Electronic Resource
    Electronic Resource
    Stress responses in alfalfa (Medicago sativa L.) IV. Expression of defense gene constructs in electroporated suspension cell protoplasts (1990)
    Springer
    Plant cell reports 9 (1990), S. 42-46 
    Details
    ISSN: 1432-203X
    Keywords: Medicago sativa L. ; Protoplast ; Chalcone synthase ; Promoter ; Transient assay ; Antisense RNA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have investigated conditions for the uptake and expression of chimeric genes in protoplasts of alfalfa (Medicago sativa L.). Constructs containing the bacterial reporter gene chloramphenicol acetyltransferase (CAT) under the control of either the cauliflower mosaic virus 35S promoter or a bean chalcone synthase (CHS) promoter were introduced into protoplasts by electroporation in the presence of polyethyleneglycol. The extent of expression in the absence of added inducers depended on the conditions for isolation, electroporation and subsequent culture of the protoplasts. Expression of the CHS promoter construct was increased on exposure of the protoplasts to a fungal elicitor or reduced glutathione. The relative levels of induced expression in relation to either basal expression or the type of elicitor used depended on the age of the suspension cultures from which the protoplasts were isolated. Electroporation of protoplasts with a construct from which bean CHS antisense transcripts were synthesized under the control of the 35S promoter resulted in the inhibition of appearance of elicitor-induced endogenous alfalfa CHS activity. The suitability of the alfalfa protoplast system for analysis and potential identification of defense response genes is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00232133
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  • 10
    Electronic Resource
    Electronic Resource
    Regulation of isoflavonoid metabolism in alfalfa (1994)
    Springer
    Plant cell, tissue and organ culture 38 (1994), S. 213-220 
    Details
    ISSN: 1573-5044
    Keywords: Glomus versiforme ; isoflavone reductase ; medicarpin ; Medicago sativa ; phytoalexin ; Phoma medicaginis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Isoflavonoids are believed to play important roles in plant-microbe interactions. During infection of alfalfa (Medicago sativa) leaves with the fungal pathogen Phoma medicaginis, rapid increases in mRNA levels and enzyme activities of isoflavone reductase, phenylalanine ammonia-lyase, chalcone synthase and other defense genes are observed within 1 to 2 hours. The phytoalexin medicarpin and its antifungal metabolite sativan increase beginning at 4 and 8 hours, respectively, along with other isoflavonoids. In contrast, during colonization of alfalfa roots by the symbiotic mycorrhizal fungus Glomus versiforme, expression of the general phenylpropanoid and flavonoid genes phenylalanine ammonia-lyase and chalcone synthase increases while mRNA levels for the phytoalexin-specific isoflavone reductase decrease. The total isoflavonoid content of colonized roots increases with time and is higher than that of uninoculated roots, but the accumulation of the antifungal medicarpin is somehow suppressed. An isoflavone reductase genomic clone has been isolated, promoter regions have been fused to the reporter gene β-glucuronidase, and the promoter-reporter fusions have been transformed into tobacco and alfalfa. Using histological staining, we have studied the developmental and stress-induced expression of this phytoalexin-specific gene in whole plants at a more detailed level than other methods allow. The isoflavone reductase promoter is functional in tobacco, a plant which does not synthesize isoflavonoids. Infection of transgenic alfalfa plants by Phoma causes an increase in β-glucuronidase staining, as does elicitation of transgenic alfalfa cell cultures, indicating that this promoter fusion is a good indicator of phytoalexin biosynthesis in alfalfa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00033879
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