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  • 1
    ISSN: 1573-5044
    Keywords: adventitious organ formation ; in vitro culture ; Lycopersicon esculentum ; mannitol ; sodium chloride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The possible use of in vitro shoot morphogenesis and shoot apex culture to evaluate salt tolerance in cultivated tomato (Lycopersicon esculentum Mill.) has been analyzed, using two cultivars with similar salt tolerance, Pera and Hellfrucht frühstamm (HF). The effect of salt on shoot regeneration was studied by culturing leaf explants on media supplemented with 0, 43, 86, 129 and 172 mM NaCl. The presence of NaCl in the regeneration media at 86 mM strongly inhibited shoot regeneration in the cultivar HF, but not in Pera. However, the substitution of NaCl by mannitol, maintaining the same water potential in the culture media, decreased the regeneration percentage in Pera but did not affect HF. Shoot apices of both cultivars were also subcultured at 6-week intervals, for 4 subcultures, at the same NaCl concentrations as used in the previous experiment, and the shoot growth, leaf and root number, rooted shoot and shoot necrosis were recorded at the end of each subculture. Root formation was the parameter most affected by salt in both cultivars, Pera being more sensitive than HF. The substitution of NaCl by mannitol significantly increased the percentage of rooted shoots in Pera after four subcultures, and slightly decreased this percentage in HF. Shoot necrosis was only observed in the last subculture at NaCl higher than 86 mM, the percentage of necrotic shoots being higher in Pera than in HF (75% and 45%, respectively). The lack of agreement between the results obtained with the in vitro tests, e.g., adventitious shoot formation and growth of apical stem sections, suggests that this approach may not be a reliable tool to evaluate salt tolerance in cultivated tomato.
    Type of Medium: Electronic Resource
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  • 2
  • 3
  • 4
    Publication Date: 2004
    Keywords: Geochemistry ; Seismicity ; Borehole geophys. ; Volcanology ; PAG ; Fernandez ; Vinas ; Sanchez ; Martin ; Nuez ; Almazan
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  • 5
    Publication Date: 2009-12-22
    Description: The Rheic Ocean formed during the Late Cambrian-Early Ordovician when peri-Gondwanan terranes (e.g. Avalonia) drifted from the northern margin of Gondwana, and was consumed during the collision between Laurussia and Gondwana and the amalgamation of Pangaea. Several mafic complexes, from the Acatlan Complex in Mexico to the Bohemian Massif in eastern Europe, have been interpreted to represent vestiges of the Rheic Ocean. Most of these complexes are either Late Cambrian-Early Ordovician or Late Palaeozoic in age. Late Cambrian-Early Ordovician complexes are predominantly rift-related continental tholeiites, derived from an enriched c. 1.0 Ga subcontinental lithospheric mantle, and are associated with crustally-derived felsic volcanic rocks. These complexes are widespread and virtually coeval along the length of the Gondwanan margin. They reflect magmatism that accompanied the early stages of rifting and the formation of the Rheic Ocean, and they remained along the Gondwanan margin to form part of a passive margin succession as Avalonia and other peri-Gondwanan terranes drifted northward. True ophiolitic complexes of this age are rare, a notable exception occurring in NW Iberia where they display ensimatic arc geochemical affinities. These complexes were thrust over, or extruded into, the Gondwanan margin during the Late Devonian-Carboniferous collision between Gondwana and Laurussia (Variscan orogeny). The Late Palaeozoic mafic complexes (Devonian and Carboniferous) preserve many of the lithotectonic and/or chemical characteristics of ophiolites. They are characterized by derivation from an anomalous mantle which displays time-integrated depletion in Nd relative to Sm. Devonian ophiolites pre-date closure of the Rheic Ocean. Although their tectonic setting is controversial, there is a consensus that most of them reflect narrow tracts of oceanic crust that originated along the Laurussian margin, but were thrust over Gondwana during Variscan orogenesis. The relationship of the Carboniferous ophiolites to the Rheic Ocean sensu stricto is unclear, but some of them apparently formed in a strike-slip regimes within a collisional setting directly related to the final stages of the closure of the Rheic Ocean.
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  • 6
    Publication Date: 2008-05-29
    Description: Within the Appalachian-Variscan orogen of North America and southern Europe lie a collection of terranes that were distributed along the northern margin of West Gondwana in the late Neoproterozoic and early Palaeozoic. These peri-Gondwanan terranes are characterized by voluminous late Neoproterozoic (c. 640-570 Ma) arc magmatism and cogenetic basins, and their tectonothermal histories provide fundamental constraints on the palaeogeography of this margin and on palaeocontinental reconstructions for this important period in Earth history. Field and geochemical studies indicate that arc magmatism generally terminated diachronously with the formation of a transform margin, leading by the Early-Middle Cambrian to the development of a shallow-marine platform-passive margin characterized by Gondwanan fauna. However, important differences exist between these terranes that constrain their relative palaeogeography in the late Neoproterozoic and permit changes in the geometry of the margin from the late Neoproterozoic to the Early Cambrian to be reconstructed. On the basis of basement isotopic composition, the terranes can be subdivided into: (1) Avalonian-type (e.g. West Avalonia, East Avalonia, Meguma, Carolinia, Moravia-Silesia), which developed on juvenile, c. 1.3-1.0 Ga crust originating within the Panthalassa-like Mirovoi Ocean surrounding Rodinia, and which were accreted to the northern Gondwanan margin by c. 650 Ma; (2) Cadomian-type (e.g. North Armorican Massif, Ossa-Morena, Saxo-Thuringia, Moldanubia), which formed along the West African margin by recycling ancient (c. 2.0-2.2 Ga) West African crust; (3) Ganderian-type (e.g. Ganderia, Florida, the Maya terrane and possible the NW Iberian domain and South Armorican Massif), which formed along the Amazonian margin of Gondwana by recycling Avalonian and older Amazonian basement; and (4) cratonic terranes (e.g. Oaxaquia and the Chortis block), which represent displaced Amazonian portions of cratonic Gondwana. These contrasts imply the existence of fundamental sutures between these terranes prior to c. 650 Ma. Derivation of the Cadomian-type terranes from the West African craton is further supported by detrital zircon data from their Neoproterozoic-Ediacaran clastic rocks, which contrast with such data from the Avalonian- and Ganderian-type terranes that suggest derivation from the Amazonian craton. Differences in Neoproterozoic and Ediacaran palaeogeography are also matched in some terranes by contrasts in Cambrian faunal and sedimentary provenance data. Platformal assemblages in certain Avalonian-type terranes (e.g. West Avalonia and East Avalonia) have cool-water, high-latitude fauna and detrital zircon signatures consistent with proximity to the Amazonian craton. Conversely, platformal assemblages in certain Cadomian-type terranes (e.g. North Armorican Massif, Ossa-Morena) show a transition from tropical to temperate waters and detrital zircon signatures that suggest continuing proximity to the West African craton. Other terranes (e.g. NW Iberian domain, Meguma) show Avalonian-type basement and/or detrital zircon signatures in the Neoproterozoic, but develop Cadomian-type signatures in the Cambrian. This change suggests tectonic slivering and lateral transport of terranes along the northern margin of West Gondwana consistent with the transform termination of arc magmatism. In the early Palaeozoic, several peri-Gondwanan terranes (e.g. Avalonia, Carolinia, Ganderia, Meguma) separated from West Gondwana, either separately or together, and had accreted to Laurentia by the Silurian-Devonian. Others (e.g. Cadomian-type terranes, Florida, Maya terrane, Oaxaquia, Chortis block) remained attached to Gondwana and were transferred to Laurussia only with the closure of the Rheic Ocean in the late Palaeozoic.
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  • 7
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    U.S. Geol. Surv., Prof. Pap.
    In:  Professional Paper, The Guatemalan Earthquake of February 4, 1976, A Preliminary Report, Dordrecht, xvii+329 pp., U.S. Geol. Surv., Prof. Pap., vol. 1002, no. 231, pp. 52-66, (ISBN 1-4020-1729-4)
    Publication Date: 1976
    Keywords: Earthquake ; Source parameters ; Intensity
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  • 8
    ISSN: 1573-5176
    Keywords: acetylene reducing activity ; dinitrogen fixation ; N2-fixing cyanobacteria ; ricefields
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A device forin situ estimation of biological nitrogen fixation in shallow-water ricefields was developed using the acetylene-reducing assay. The device consists of a rigid transparent bottomless plastic bottle provided with an agitation system. Laboratory experiments using flooded pots inoculated withAnabaena UAM 202 indicated that agitation significantly reduced the time needed to detect the production of ethylene by eliminating the slow diffusion of acetylene and ethylene in water. A direct relationship between the abundance of cyanobacteria and the rate of acetylene reduction was observed in laboratory and field experiments. A negative correlation between the amount of combined nitrogen and the abundance of cyanobacteria was observed in the field.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1617-4623
    Keywords: Gene cluster ; Nitrate transport ; Regulatory mutant
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Three overlapping clones covering a Chlarnydomonas reinhardtii genomic region of about 32 kb appear to contain five genes potentially involved in nitrate assimilation in addition to the nitrate reductase structural locus nit-1. These new loci produced transcripts of 2.8, 2.2, 1.8 and 1.7 kb in nitrate-induced wild-type cells that, like the 3.4 kb transcript of nit-1, were undetectable in cells grown in ammonium. In addition, in a mutant defective at the regulatory locus, nit-2 for nitrate assimilation, which does not express the nit-1 gene transcript, accumulation of the four other transcripts was also blocked. They have been named nar (nitrate assimilation related) genes. The nar-1 and nar-2 loci are transcribed in the same orientation as nit-1. The nar-3 and nar-4 loci are transcribed divergently from nit-1. DNA and RNA sequences from both nar-3 and nar-4 cross-hybridized with each other indicating that they share similar sequences. Four nitrate assimilation-deficient mutants (C2, D2, F6 and G1) were characterized. These mutants lack nar transcripts and have major deletions and/or rearrangements in the nar gene cluster. In contrast to other nitrate reductase-deficient mutants and to wild type, deletion mutants and the regulatory mutant nit-2 were incapable of accumulating intracellular nitrate. Two of the mutants in which expression of all of the nar loci did not occur, C2 and D2, grew in nitrite medium and showed wild-type levels of both nitrite uptake and nitrite reductase activities. Thus the nar loci cannot be required for nitrite assimilation. Mutants F6 and G1 were unable to grow in either nitrite- or nitrate-containing medium, and lacked nitrate reductase, nitrite reductase, nitrate uptake and nitrite uptake activities. The inability to assimilate nitrite co-segregated with nit-1 in crosses between these mutants and wild type. These results indicate that a complex gene cluster responsible for the assimilation of nitrate has been identified in C. reinhardtii, and that, in addition, at least one locus necessary for nitrite assimilation is genetically linked to this cluster.
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  • 10
    ISSN: 1573-966X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Economics
    Type of Medium: Electronic Resource
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