Search Results - (Author, Cooperation:R. Summons)

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  1. 1
    J. P. Grotzinger ; D. Y. Sumner ; L. C. Kah ; K. Stack ; S. Gupta ; L. Edgar ; D. Rubin ; K. Lewis ; J. Schieber ; N. Mangold ; R. Milliken ; P. G. Conrad ; D. DesMarais ; J. Farmer ; K. Siebach ; F. Calef, 3rd ; J. Hurowitz ; S. M. McLennan ; D. Ming ; D. Vaniman ; J. Crisp ; A. Vasavada ; K. S. Edgett ; M. Malin ; D. Blake ; R. Gellert ; P. Mahaffy ; R. C. Wiens ; S. Maurice ; J. A. Grant ; S. Wilson ; R. C. Anderson ; L. Beegle ; R. Arvidson ; B. Hallet ; R. S. Sletten ; M. Rice ; J. Bell, 3rd ; J. Griffes ; B. Ehlmann ; R. B. Anderson ; T. F. Bristow ; W. E. Dietrich ; G. Dromart ; J. Eigenbrode ; A. Fraeman ; C. Hardgrove ; K. Herkenhoff ; L. Jandura ; G. Kocurek ; S. Lee ; L. A. Leshin ; R. Leveille ; D. Limonadi ; J. Maki ; S. McCloskey ; M. Meyer ; M. Minitti ; H. Newsom ; D. Oehler ; A. Okon ; M. Palucis ; T. Parker ; S. Rowland ; M. Schmidt ; S. Squyres ; A. Steele ; E. Stolper ; R. Summons ; A. Treiman ; R. Williams ; A. Yingst
    American Association for the Advancement of Science (AAAS)
    Published 2013
    Staff View
    Publication Date:
    2013-12-11
    Publisher:
    American Association for the Advancement of Science (AAAS)
    Print ISSN:
    0036-8075
    Electronic ISSN:
    1095-9203
    Topics:
    Biology
    Chemistry and Pharmacology
    Computer Science
    Medicine
    Natural Sciences in General
    Physics
    Keywords:
    Bays ; Carbon/analysis ; *Exobiology ; *Extraterrestrial Environment ; Geologic Sediments/analysis/classification ; Hydrogen/analysis ; Hydrogen-Ion Concentration ; Iron/analysis/chemistry ; *Mars ; Nitrogen/analysis ; Oxidation-Reduction ; Oxygen/analysis ; Phosphorus/analysis ; Salinity ; Sulfur/analysis/chemistry ; *Water
    Published by:
    http://www.aaas.org/

    Latest Papers from Table of Contents or Articles in Press
  2. 2
    C. R. Webster ; P. R. Mahaffy ; G. J. Flesch ; P. B. Niles ; J. H. Jones ; L. A. Leshin ; S. K. Atreya ; J. C. Stern ; L. E. Christensen ; T. Owen ; H. Franz ; R. O. Pepin ; A. Steele ; C. Achilles ; C. Agard ; J. A. Alves Verdasca ; R. Anderson ; D. Archer ; C. Armiens-Aparicio ; R. Arvidson ; E. Atlaskin ; A. Aubrey ; B. Baker ; M. Baker ; T. Balic-Zunic ; D. Baratoux ; J. Baroukh ; B. Barraclough ; K. Bean ; L. Beegle ; A. Behar ; J. Bell ; S. Bender ; M. Benna ; J. Bentz ; G. Berger ; J. Berger ; D. Berman ; D. Bish ; D. F. Blake ; J. J. Blanco Avalos ; D. Blaney ; J. Blank ; H. Blau ; L. Bleacher ; E. Boehm ; O. Botta ; S. Bottcher ; T. Boucher ; H. Bower ; N. Boyd ; B. Boynton ; E. Breves ; J. Bridges ; N. Bridges ; W. Brinckerhoff ; D. Brinza ; T. Bristow ; C. Brunet ; A. Brunner ; W. Brunner ; A. Buch ; M. Bullock ; S. Burmeister ; M. Cabane ; F. Calef ; J. Cameron ; J. Campbell ; B. Cantor ; M. Caplinger ; J. Caride Rodriguez ; M. Carmosino ; I. Carrasco Blazquez ; A. Charpentier ; S. Chipera ; D. Choi ; B. Clark ; S. Clegg ; T. Cleghorn ; E. Cloutis ; G. Cody ; P. Coll ; P. Conrad ; D. Coscia ; A. Cousin ; D. Cremers ; J. Crisp ; A. Cros ; F. Cucinotta ; C. d'Uston ; S. Davis ; M. Day ; M. de la Torre Juarez ; L. DeFlores ; D. DeLapp ; J. DeMarines ; D. DesMarais ; W. Dietrich ; R. Dingler ; C. Donny ; B. Downs ; D. Drake ; G. Dromart ; A. Dupont ; B. Duston ; J. Dworkin ; M. D. Dyar ; L. Edgar ; K. Edgett ; C. Edwards ; L. Edwards ; B. Ehlmann ; B. Ehresmann ; J. Eigenbrode ; B. Elliott ; H. Elliott ; R. Ewing ; C. Fabre ; A. Fairen ; K. Farley ; J. Farmer ; C. Fassett ; L. Favot ; D. Fay ; F. Fedosov ; J. Feldman ; S. Feldman ; M. Fisk ; M. Fitzgibbon ; M. Floyd ; L. Fluckiger ; O. Forni ; A. Fraeman ; R. Francis ; P. Francois ; C. Freissinet ; K. L. French ; J. Frydenvang ; A. Gaboriaud ; M. Gailhanou ; J. Garvin ; O. Gasnault ; C. Geffroy ; R. Gellert ; M. Genzer ; D. Glavin ; A. Godber ; F. Goesmann ; W. Goetz ; D. Golovin ; F. Gomez Gomez ; J. Gomez-Elvira ; B. Gondet ; S. Gordon ; S. Gorevan ; J. Grant ; J. Griffes ; D. Grinspoon ; J. Grotzinger ; P. Guillemot ; J. Guo ; S. Gupta ; S. Guzewich ; R. Haberle ; D. Halleaux ; B. Hallet ; V. Hamilton ; C. Hardgrove ; D. Harker ; D. Harpold ; A. M. Harri ; K. Harshman ; D. Hassler ; H. Haukka ; A. Hayes ; K. Herkenhoff ; P. Herrera ; S. Hettrich ; E. Heydari ; V. Hipkin ; T. Hoehler ; J. Hollingsworth ; J. Hudgins ; W. Huntress ; J. Hurowitz ; S. Hviid ; K. Iagnemma ; S. Indyk ; G. Israel ; R. Jackson ; S. Jacob ; B. Jakosky ; E. Jensen ; J. K. Jensen ; J. Johnson ; M. Johnson ; S. Johnstone ; A. Jones ; J. Joseph ; I. Jun ; L. Kah ; H. Kahanpaa ; M. Kahre ; N. Karpushkina ; W. Kasprzak ; J. Kauhanen ; L. Keely ; O. Kemppinen ; D. Keymeulen ; M. H. Kim ; K. Kinch ; P. King ; L. Kirkland ; G. Kocurek ; A. Koefoed ; J. Kohler ; O. Kortmann ; A. Kozyrev ; J. Krezoski ; D. Krysak ; R. Kuzmin ; J. L. Lacour ; V. Lafaille ; Y. Langevin ; N. Lanza ; J. Lasue ; S. Le Mouelic ; E. M. Lee ; Q. M. Lee ; D. Lees ; M. Lefavor ; M. Lemmon ; A. Lepinette Malvitte ; R. Leveille ; E. Lewin-Carpintier ; K. Lewis ; S. Li ; L. Lipkaman ; C. Little ; M. Litvak ; E. Lorigny ; G. Lugmair ; A. Lundberg ; E. Lyness ; M. Madsen ; J. Maki ; A. Malakhov ; C. Malespin ; M. Malin ; N. Mangold ; G. Manhes ; H. Manning ; G. Marchand ; M. Marin Jimenez ; C. Martin Garcia ; D. Martin ; M. Martin ; J. Martinez-Frias ; J. Martin-Soler ; F. J. Martin-Torres ; P. Mauchien ; S. Maurice ; A. McAdam ; E. McCartney ; T. McConnochie ; E. McCullough ; I. McEwan ; C. McKay ; S. McLennan ; S. McNair ; N. Melikechi ; P. Y. Meslin ; M. Meyer ; A. Mezzacappa ; H. Miller ; K. Miller ; R. Milliken ; D. Ming ; M. Minitti ; M. Mischna ; I. Mitrofanov ; J. Moersch ; M. Mokrousov ; A. Molina Jurado ; J. Moores ; L. Mora-Sotomayor ; J. M. Morookian ; R. Morris ; S. Morrison ; R. Mueller-Mellin ; J. P. Muller ; G. Munoz Caro ; M. Nachon ; S. Navarro Lopez ; R. Navarro-Gonzalez ; K. Nealson ; A. Nefian ; T. Nelson ; M. Newcombe ; C. Newman ; H. Newsom ; S. Nikiforov ; B. Nixon ; E. Noe Dobrea ; T. Nolan ; D. Oehler ; A. Ollila ; T. Olson ; M. A. de Pablo Hernandez ; A. Paillet ; E. Pallier ; M. Palucis ; T. Parker ; Y. Parot ; K. Patel ; M. Paton ; G. Paulsen ; A. Pavlov ; B. Pavri ; V. Peinado-Gonzalez ; L. Peret ; R. Perez ; G. Perrett ; J. Peterson ; C. Pilorget ; P. Pinet ; J. Pla-Garcia ; I. Plante ; F. Poitrasson ; J. Polkko ; R. Popa ; L. Posiolova ; A. Posner ; I. Pradler ; B. Prats ; V. Prokhorov ; S. W. Purdy ; E. Raaen ; L. Radziemski ; S. Rafkin ; M. Ramos ; E. Rampe ; F. Raulin ; M. Ravine ; G. Reitz ; N. Renno ; M. Rice ; M. Richardson ; F. Robert ; K. Robertson ; J. A. Rodriguez Manfredi ; J. J. Romeral-Planello ; S. Rowland ; D. Rubin ; M. Saccoccio ; A. Salamon ; J. Sandoval ; A. Sanin ; S. A. Sans Fuentes ; L. Saper ; P. Sarrazin ; V. Sautter ; H. Savijarvi ; J. Schieber ; M. Schmidt ; W. Schmidt ; D. Scholes ; M. Schoppers ; S. Schroder ; S. Schwenzer ; E. Sebastian Martinez ; A. Sengstacken ; R. Shterts ; K. Siebach ; T. Siili ; J. Simmonds ; J. B. Sirven ; S. Slavney ; R. Sletten ; M. Smith ; P. Sobron Sanchez ; N. Spanovich ; J. Spray ; S. Squyres ; K. Stack ; F. Stalport ; T. Stein ; N. Stewart ; S. L. Stipp ; K. Stoiber ; E. Stolper ; B. Sucharski ; R. Sullivan ; R. Summons ; D. Sumner ; V. Sun ; K. Supulver ; B. Sutter ; C. Szopa ; F. Tan ; C. Tate ; S. Teinturier ; I. ten Kate ; P. Thomas ; L. Thompson ; R. Tokar ; M. Toplis ; J. Torres Redondo ; M. Trainer ; A. Treiman ; V. Tretyakov ; R. Urqui-O'Callaghan ; J. Van Beek ; T. Van Beek ; S. VanBommel ; D. Vaniman ; A. Varenikov ; A. Vasavada ; P. Vasconcelos ; E. Vicenzi ; A. Vostrukhin ; M. Voytek ; M. Wadhwa ; J. Ward ; E. Weigle ; D. Wellington ; F. Westall ; R. C. Wiens ; M. B. Wilhelm ; A. Williams ; J. Williams ; R. Williams ; R. B. Williams ; M. Wilson ; R. Wimmer-Schweingruber ; M. Wolff ; M. Wong ; J. Wray ; M. Wu ; C. Yana ; A. Yen ; A. Yingst ; C. Zeitlin ; R. Zimdar ; M. P. Zorzano Mier
    American Association for the Advancement of Science (AAAS)
    Published 2013
    Staff View
    Publication Date:
    2013-07-23
    Publisher:
    American Association for the Advancement of Science (AAAS)
    Print ISSN:
    0036-8075
    Electronic ISSN:
    1095-9203
    Topics:
    Biology
    Chemistry and Pharmacology
    Computer Science
    Medicine
    Natural Sciences in General
    Physics
    Published by:
    http://www.aaas.org/

    Latest Papers from Table of Contents or Articles in Press
  3. 3
    Staff View
    Publication Date:
    2018-06-08
    Publisher:
    American Association for the Advancement of Science (AAAS)
    Print ISSN:
    0036-8075
    Electronic ISSN:
    1095-9203
    Topics:
    Biology
    Chemistry and Pharmacology
    Geosciences
    Computer Science
    Medicine
    Natural Sciences in General
    Physics
    Keywords:
    Geochemistry, Geophysics, Planetary Science
    Published by:
    http://www.aaas.org/

    Latest Papers from Table of Contents or Articles in Press
  4. 4
    Summons, R. E., Erwin, D. H.
    American Association for the Advancement of Science (AAAS)
    Published 2018
    Staff View
    Publication Date:
    2018-09-21
    Publisher:
    American Association for the Advancement of Science (AAAS)
    Print ISSN:
    0036-8075
    Electronic ISSN:
    1095-9203
    Topics:
    Biology
    Chemistry and Pharmacology
    Geosciences
    Computer Science
    Medicine
    Natural Sciences in General
    Physics
    Published by:
    http://www.aaas.org/

    Latest Papers from Table of Contents or Articles in Press
  5. 5
    LAWLESS, J. G. ; ZEITMAN, B. ; PEREIRA, W. E. ; SUMMONS, R. E. ; DUFFIELD, A. M.

    [s.l.] : Nature Publishing Group
    Published 1974
    Staff View
    ISSN:
    1476-4687
    Source:
    Nature Archives 1869 - 2009
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Notes:
    [Auszug] The meteorite sample used for this study was prepared by removing the outer surface and reducing the interior piece to a fine powder with a mortar and pestle. A hot water extract of a 2-g sample was obtained by refluxing for 20 h with 6 ml of water. After centrifuging, the supernatant and ...
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1038/251040a0

    Articles: DFG German National Licenses
  6. 6
    Fike, D. A. ; Grotzinger, J. P. ; Pratt, L. L. ; Summons, R. R.

    [s.l.] : Nature Publishing Group
    Published 2007
    Staff View
    ISSN:
    1476-4687
    Source:
    Nature Archives 1869 - 2009
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Notes:
    [Auszug] Replying to: K. Grey & C. R. Calver Nature 450, doi: 10.1038/nature06360 (2007). Calver and Grey point out the difficulties of relating the Australian acritarch record to the global record of environmental change. This results from the ...
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1038/nature06361

    Articles: DFG German National Licenses
  7. 7
    Grotzinger, J. P. ; Pratt, L. M. ; Summons, R. E. ; Fike, D. A.

    [s.l.] : Nature Publishing Group
    Published 2006
    Staff View
    ISSN:
    1476-4687
    Source:
    Nature Archives 1869 - 2009
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Notes:
    [Auszug] Oxygenation of the Earth’s surface is increasingly thought to have occurred in two steps. The first step, which occurred ∼2,300 million years (Myr) ago, involved a significant increase in atmospheric oxygen concentrations and oxygenation of the surface ocean. A further increase in ...
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1038/nature05345

    Articles: DFG German National Licenses
  8. 8
    Staff View
    ISSN:
    0009-9120
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Medicine
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1016/S0009-9120(73)80039-6

    Articles: DFG German National Licenses
  9. 9
    Staff View
    ISSN:
    1435-8107
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes:
    Abstract The metabolism of zeatin and that of 6-benzylaminopurine (BAP) have been compared in oat leaf segments in relation to the markedly differing ability of these cytokinins to retard senescence of such segments. Free BAP and a highly active senescence-retarding metabolite of BAP were detected in oat leaf segments supplied with BAP. The metabolite was identified by mass spectrometry and chromatography as 3-β-D-glucopyranosyl-BAP. The major metabolite of BAP was the 9-glucoside, but this lacked significant senescence-retarding activity. In contrast, in leaf segments supplied with zeatin, no free zeatin and no senescence-retarding metabolite of zeatin were detectable. The major metabolites of zeatin were adenosine, adenine nucleotides, the 9-glucoside, and unidentified polar metabolites. The differing activities of zeatin and BAP in the oat-leaf senescence bioassay appear to be, at least partially, a consequence of their differing metabolism and are not attributable to differences in uptake.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF02042237

    Articles: DFG German National Licenses
  10. 10
    Simoneit, Bernd R. T. ; Summons, R. E. ; Jahnke, L. L.
    Springer
    Published 1996
    Staff View
    ISSN:
    1573-0875
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Biology
    Geosciences
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF02459903

    Articles: DFG German National Licenses
  11. 11
    Jackson, M. J. ; Powell, T. G. ; Summons, R. E. ; Sweet, I. P.

    [s.l.] : Nature Publishing Group
    Published 1986
    Staff View
    ISSN:
    1476-4687
    Source:
    Nature Archives 1869 - 2009
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Notes:
    [Auszug] Despite the occurrence of commercial Proterozoic oil and gas fields in the Soviet Union, Oman and China1'5, rocks of this age are not generally considered to be likely sources of petroleum6. The McArthur Basin (Fig. la) contains an unmeta-morphosed, structurally simple sedimentary sequence. A ...
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1038/322727a0

    Articles: DFG German National Licenses
  12. 12
    Staff View
    ISSN:
    1432-2048
    Keywords:
    Cytokinin metabolites ; Zea mays
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Biology
    Notes:
    Abstract The cytokinins in certain fractions prepared from extracts of immature sweet-corn (Zea mays L.) kernels using polystyrene ion-exchange resins have been further investigated. Cytokinins active in the radish cotyledon bioassay were purified from these fractions and identified as 9-β-D-glucopyranosylzeatin, 9-β-D-glucopyranosyldihydrozeatin, O-β-D-glucopyranosylzeatin. and O-β-D-glucopyranosyl-9-β-D-ribofuranosylzeatin. In addition, compounds which resemble zeatin and its glycosides in chromatographic behaviour and in ultraviolet absorption characteristics were purified from extracts of the same material by high-performance liquid chromatography. In addition to zeatin and zeatin riboside, the following compounds were identified unambiguously: O-β-D-glucopyranosyl-9-β-D-ribofuranosyldihydrozeatin, O-β-D-glucopyranosyldihydrozeatin, and hihydrozeatin riboside. A further compound was tentatively identified as O-β-D-glucopyranosylzeatin, and at least two unidentified compounds appeared to be new derivatives of zeatin. In identifying the above compounds, chemical-ionization mass spectrometry proved to be an invaluable complementary technique, yielding spectra showing intense protonated-molecular-ion peaks and also prominent structure-related fragmentation that was either not evident or very minor in the electron-impact spectra. An assessment of the relative importance of the various possible mechanisms for cytokinin modification and inactivation in mature sweet-corn kernels was made by supplying [3H]zeatin and [3H]zeatin riboside to such kernels after excision. The principal metabolites of zeatin were adenine nucleotides, adenosine and adenine, while little of the metabolite radioactivity was attributable to known O-glucosides. Adenine nucleotides and adenine were the principal metabolites of zeatin riboside, while lesser metabolites were identified as adenosine, dihydrozeatin, and the O-glucosides of dihydrozeatin and dihydrozeatin riboside. Side-chain cleavage, rather than side-chain modification, appears to be the dominant form of cytokinin metabolism in mature sweet-corn kernels.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00380183

    Articles: DFG German National Licenses
  13. 13
    Staff View
    ISSN:
    1432-2048
    Keywords:
    Cytokinin metabolism ; Phaseolus
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Biology
    Notes:
    Abstract 6-[3H]Benzylaminopurine was supplied through the transpiration stream to de-rooted Phaseolus vulgaris L. seedlings. The principal metabolite formed was identified as β-(6-benzylaminopurin-9-yl)alanine by comparison with the synthetic compound.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00381257

    Articles: DFG German National Licenses
  14. 14
    Staff View
    ISSN:
    1432-2048
    Keywords:
    Cytokinin metabolism ; O-glucosylzeatin ; Lupinic acid ; Lupinus
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Biology
    Notes:
    Abstract [3H]zeatin was supplied through the transpiration stream to de-rooted lupin (Lupinus angustifolius L.) seedlings. The following previously known metabolites were identified chromatographically: 5′-phosphates of zeatin riboside and dihydrozeatin riboside, adenosine-5′-phosphate, zeatin riboside, zeatin-7-glucopyranoside, zeatin-9-glucopyranoside, adenine, adenosine and dihydrozeatin. Five new metabolites were purified; four of these contain an intact zeatin moiety. Two were identified unequivocally, one as l-β-[6-(4-hydroxy-3-methylbut-trans-2-enylamino)-purin-9-yl]alanine, a metabolite now termed lupinic acid, and the second as O-β-d-glucopyranosylzeatin. These two compounds were the major metabolites formed when zeatin solution (100 μM) was supplied to the de-rooted seedlings. The radioactivity in the xylem sap of intact seedlings, supplied with [3H]zeatin via the roots, was largely due to zeatin, dihydrozeatin and zeatin riboside. When [3H]zeatin (5 μM) was supplied via the transpiration stream to de-rooted Lupinus luteus L. seedlings, the principal metabolite in the lamina was adenosine, while in the stem nucleotides of zeatin and adenine were the dominant metabolites. O-Glucosylzeatin and lupinic acid were also detected as metabolites. The level of the latter varied greatly in the tissues of the shoot, and was greatest in the lower region of the stem and in the expanding lamina. Minor metabolites also detected chromatographically were: (a) dihydrolupinic acid, (b) a partially characterized metabolite which appears to be a 9-substituted adenine (also formed in L. angustifolius), (c) glucosides of zeatin riboside and/or dihydrozeatin riboside, and (d) O-glucosyldihydrozeatin. While lupinic acid supplied exogenously to L. luteus leaves underwent little metabolism, chromatographic studies indicated that O-glucosylzeatin was converted to its riboside, the principal metabolite formed, and also to adenosine, zeatin and dihydrozeatin. A thinlayer chromatography procedure for separating zeatin, dihydrozeatin, zeatin riboside and dihydrozeatin riboside is described.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00385073

    Articles: DFG German National Licenses
  15. 15
    Staff View
    ISSN:
    1432-2048
    Keywords:
    Carbon dioxide fixation (dark) ; Crassulacean acid metabolism ; Fumarase ; Malic acid ; Phosphoenolpyruvate carboxylase ; Ribulose-1,5-bisphosphate carboxylase
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Biology
    Notes:
    Abstract The labeling patterns in malic acid from dark 13CO2 fixation in seven species of succulent plants with Crassulacean acid metabolism were analysed by gas chromatography-mass spectrometry and 13C-nuclear magnetic resonance spectrometry. Only singly labeled malic-acid molecules were detected and on the average, after 12–14 h dark 13CO2 fixation the ratio of [4-13C] to [1-13C] label was 2:1. However the 4-C carboxyl contained from 72 to 50% of the label depending on species and temperature. The 13C enrichment of malate and fumarate was similar. These data confirm those of W. Cockburn and A. McAuley (1975, Plant Physiol. 55, 87–89) and indicate fumarase randomization is responsible for movement of label to 1-C malic acid following carboxylation of phosphoenolpyruvate. The extent of randomization may depend on time and on the balance of malic-acid fluxes between mitochondria and vacuoles. The ratio of labeling in 4-C to 1-C of malic acid which accumulated following 13CO2 fixation in the dark did not change during deacidification in the light and no doubly-labeled molecules of malic acid were detected. These results indicate that further fumarase randomization does not occur in the light, and futile cycling of decarboxylation products of [13C] malic acid (13CO2 or [1-13C]pyruvate) through phosphoenolpyruvate carboxylase does not occur, presumably because malic acid inhibits this enzyme in the light in vivo. Short-term exposure to 13CO2 in the light after deacidification leads to the synthesis of singly and multiply labeled malic acid in these species, as observed by E.W. Ritz et al. (1986, Planta 167, 284–291). In the shortest times, only singly-labeled [4-13C]malate was detected but this may be a consequence of the higher intensity and better detection statistics of this ion cluster during mass spectrometry. We conclude that both phosphoenolpyruvate carboxylase (EC 4.1.1.32) and ribulose-1,5-biphosphate carboxylase (EC 4.1.1.39) are active at this time.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00392426

    Articles: DFG German National Licenses
  16. 16
    Palni, L. M. S. ; Summons, R. E.
    Springer
    Published 1987
    Staff View
    ISSN:
    1573-5087
    Keywords:
    Crown-gall ; gas chromatography-mass spectrometry ; genetic tumours ; indole-3-acetic acid ; stable isotope dilution
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes:
    Abstract Indole-3-acetic acid (IAA) was identified and quantified in three cultured tumour lines, which included crown-gall tissue of Datura (25.4 ng/g fresh wt.) and two genetic tumour lines of tobacco (4.6 and 8.0 ng/g fresh wt.). The analysis was carried out using a stable isotope dilution assay in combination with gas chromatography-mass spectrometry. This is the first unambiguous determination of endogenous IAA in genetic tumour tissues.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00035019

    Articles: DFG German National Licenses
  17. 17
    Simoneit, Bernd R. T. ; Summons, R. E. ; Jahnke, L. L.
    Springer
    Published 1998
    Staff View
    ISSN:
    1573-0875
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Biology
    Geosciences
    Notes:
    Abstract Biomarkers in geological samples are products derived from biochemical (natural product) precursors by reductive and oxidative processes (e.g., cholestanes from cholesterol). Generally, lipids, pigments and biomembranes are preserved best over longer geological times and labile compounds such as amino acids, sugars, etc. are useful biomarkers for recent times. Thus, the detailed characterization of biomarker compositions permits the assessment of the major contributing species of extinct and/or extant life. In the case of the early Earth, work has progressed to elucidate molecular structure and carbon isotopic signals preserved in ancient sedimentary rocks. In addition, the combination of bacterial biochemistry with the organic geochemistry of contemporary and ancient hydrothermal ecosystems permits the modeling of the nature, behavior and preservation potential of primitive microbial communities. This approach uses combined molecular and isotopic analyses to characterize lipids produced by cultured bacteria (representative of ancient strains) and to test a variety of culture conditions which affect their biosynthesis. On considering Mars, the biomarkers from lipids and biopolymers would be expected to be preserved best if life flourished there during its early history (3.5–4 × 109 yr ago). Both oxidized and reduced products would be expected. This is based on the inferred occurrence of hydrothermal activity during that time with the concomitant preservation of biochemically-derived organic matter. Both known biomarkers (i.e., as elucidated for early terrestrial samples and for primitive terrestrial microbiota) and novel, potentially unknown compounds should be characterized.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1023/A:1006508012904

    Articles: DFG German National Licenses
  18. 18
    Tao, G. -Q. ; Letham, D. S. ; Hocart, C. H. ; Summons, R. E.
    Springer
    Published 1991
    Staff View
    ISSN:
    1435-8107
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes:
    Summary Cytokinins are deactivated in radish cotyledons by conversion to 7- and 9-glucosides. In a search for inhibitors of this metabolism, the following compounds were found to be effective: (a) 6-benzylamino-2-(2-hydroxyethylamino)-9-methylpurine; (b) 3-isobutyl-1-methylxanthine; (c) papaverine; (d) theophylline; (e) caffeine; and (f) theobromine. The order of effectiveness was: (a)〉(b)=(c)〉(d)=(e)=(f). While the methylxanthines (b) and (d) inhibited formation of both 7- and 9-glucosides of 6-benzylaminopurine (BAP) approximately equally, compounds (a) and (c) preferentially inhibited formation of BAP 9-glucoside. Inhibition of BAP glucoside formation by (a) at 1.3 mM elevated the level of free BAP and BAP nucleotide 23- and 94-fold, respectively. While abscisic acid (ABA) suppressed conversion of zeatin riboside to zeatin 7-glucoside in radish cotyledons, it did not inhibit conversion of BAP to glucosides. Hence, ABA probably does not inhibit the glucosylating enzymes directly but rather reduces the availability of free zeatin when zeatin riboside is supplied. Auxins and nutrient supply did not affect conversion of zeatin riboside to zeatin 7-glucoside. Relative to cotyledons developed in light, those developed in darkness had a reduced capacity to convert zeatin riboside to zeatin 7-glucoside. The results presented have identified types of chemical structures which could be developed to provide more effective inhbitors of cytokininN-glucosylation.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF02279331

    Articles: DFG German National Licenses
  19. 19
    Staff View
    ISSN:
    1435-8107
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes:
    Abstract The endogenous cytokinins present in dryZea mays seed were determined using both radioimmunoassay and gas chromatography—mass spectrometry. Similar values for bases and ribosides were obtained by the two methods. The cytokinins present in embryo and endosperm were estimated separately using radioimmunoassay; similar levels of cytokinins were found in these two tissues. The major cytokinins detected on a whole-seed basis were dihydrozeatin riboside, O-glucosyldihydrozeatin riboside, zeatin 9-glucoside, zeatin, and the nucleotides of zeatin, dihydrozeatin, and isopentenyladenine. Cytokinin levels in the mature dry seed were considerably lower than cytokinin levels published in the literature for immature seed. Unexpected activity in the radioimmunoassays was detected in the wash from the DEAE cellulose column chromatography step. The compound(s) responsible for this activity did not have the solvent partitioning characteristics of a cytokinin base or riboside. They eluted as a single fraction following high-performance liquid chromatography on a Zorbax C8 column; this fraction showed no activity in theAmaranthus bioassay for cytokinins, but inhibited the activity of authentic zeatin riboside present at an optimal concentration.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF02024681

    Articles: DFG German National Licenses
  20. 20
    Badenoch-Jones, J. ; Summons, R. E. ; Entsch, B. ; Rolfe, B. G. ; Parker, C. W. ; Letham, D. S.

    Chichester : Wiley-Blackwell
    Published 1982
    Staff View
    ISSN:
    0306-042X
    Keywords:
    Chemistry ; Analytical Chemistry and Spectroscopy
    Source:
    Wiley InterScience Backfile Collection 1832-2000
    Topics:
    Chemistry and Pharmacology
    Notes:
    The following indole compounds have been unequivocally identified and semi-quantitated in culture supernatants of Rhizobium strains by gas chromatography mass spectrometry: indole-3-aldehyde, trytophol, indole-3-carboxylic acid, indole-3-glycollc acid, indole-3-actic acid, indole-3-glyoxylic acid, N-acethyl-L-tryptophan and indole-3-pyruvic acid, as well as indole-3-acetic acid. The strains included a number of chosen Rhizobium mutants defective in various stages of nodule formation, and the biological implications of the findings are discussed. Two alternative approaches to sample purification were taken, one based primarily on solvent partitioning and the other on high-performance liquid chromatography. The advantages of each method are discussed. Gas chromatographic retention times and mass spectra are given for the TMS derivatives of 17 authentic indole standards.
    Additional Material:
    2 Ill.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1002/bms.1200091005

    Articles: DFG German National Licenses