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  • 1
    Electronic Resource
    Electronic Resource
    Adsorption and desorption of natural organic matter on iron oxide: mechanisms and models (1994)
    s.l. : American Chemical Society
    Environmental science & technology 28 (1994), S. 38-46 
    Details
    ISSN: 1520-5851
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/es00050a007
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  • 2
    Electronic Resource
    Electronic Resource
    Rosat X-ray light curves of early-type stars (1994)
    Springer
    Astrophysics and space science 221 (1994), S. 309-320 
    Details
    ISSN: 1572-946X
    Keywords: σ Ori,ζ Ori ; stars: early-type ; X-rays: stars
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have investigated ROSAT X-ray data of OB stars to search for evidence of time variability in the X-ray emission from early-type stars. As an example for such studies we present a detailed variability analysis for our two program starsσ Ori andζ Ori which have been multiply observed with ROSAT. The long-term analysis of both stars now covers a time range of 2.5 years and includes six pointed PSPC observations, an additional pointed HRI observation ofσ Ori and the ROSAT all-sky survey data of both stars. Over a long time range the X-ray light curves ofσ Ori andζ Ori show no evidence for variability. In the case ofζ Ori we detected a moderate increase in X-ray count rate during a period of 2 days which can be explained as a strong shock propagating in the wind of an O-type star.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01091162
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  • 3
    Electronic Resource
    Electronic Resource
    Absorption of X-ray emission of t tauri stars by circumstellar material (1995)
    Springer
    Astrophysics and space science 224 (1995), S. 93-96 
    Details
    ISSN: 1572-946X
    Keywords: T Tauri stars ; X-ray emission
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The study of star forming regions (SFR) allows us to observe many young stellar objects with both the same metallicities and distances but with different masses. Because of its close distance (∼ 140pc) Taurus-Auriga is one of the best studied SFR with more than 100 well-studied, low-mass, pre-main sequence stars, T Tauri stars (TTS). A motivation for studying X-ray emission of T associations is to understand the origin of X-rays and coronal activity. The large sample observed with the ROSAT All-Sky Survey (RASS) also enables us to compare different types of young stars. Other primary goals include star formation efficiency and the interaction of young stars with their intermediate environment (probed by absorption of X-rays). RASS detection rates are comparable withEinstein Observatory results: 43 out of 65 (66%) weak-lined TTS (WTTS) and 9 out of 79 (11%) classical TTS (CTTS) exhibit X-ray emission above RASS detection limit. A strong correlation between X-ray surface flux and stellar rotation indicates that WTTS are intrinsically more X-ray active than CTTS, because WTTS rotate faster. However, rotation is not the only parameter that determines X-ray activity. Also, we compare Taurus-Auriga TTS with TTS of southern SFR like ScoCen, Lupus, Chamaeleon, and CrA. A new result is that CTTS and WTTS can be discriminated reliably by their X-ray spectral hardness ratios. X-ray emission of CTTS appears to be harder, partly because of circumstellar absorption. Spectral fits give results consistent with Raymond-Smith spectra and emission temperatures of ∼ 1.0 keV for both WTTS and CTTS. However, we find that CTTS and WTTS have significantly different X-ray luminosity functions. Medians of absorption corrected X-ray luminosities (logL X in cgs units) are 29.701 ± 0.045 for WTTS and 29.091 ± 0.032 for CTTS. WTTS are intrinsically more luminous than CTTS, most likely because WTTS rotate on average faster than CTTS and are less absorbed. This paper concentrates on differences between CTTS and WTTS and indirect clues to be drawn from X-ray absorption and hardness ratios about circumstellar material around TTS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00667829
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  • 4
    Electronic Resource
    Electronic Resource
    Age-dependent induction of pyruvate, orthophosphate dikinase in Mesembryanthemum crystallinum L. (1995)
    Springer
    Planta 196 (1995), S. 492-500 
    Details
    ISSN: 1432-2048
    Keywords: Crassulacean acid metabolism ; Gene (expression, regulation) ; Mesembryanthemum ; Phosphoenol pyruvate carboxylase induction ; Pyruvate, orthophosphate dikinase induction ; Salt stress
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A full-length transcript for pyruvate, orthophosphate dikinase (PPDK; EC 2.7.9.1), has been characterized from Mesembryanthemum crystallinum. Under salt stress or with increasing age, this plant shows a transition from C3 to Crassulacean acid metabolism (CAM). The PPDK plays a central role in gluconeogenesis during the light phase of CAM. The transcript is 3165 bases in length with a single open reading frame of 2739 nucleotides specifying a protein of molecular mass 103098, including a transit peptide of mass 7902 for chloroplast import. The protein shares 44–77% sequence identity with PPDK from C4-plants and microorganisms. Known functional and regulatory amino acids are conserved. Southern-type hybridizations indicated one copy or very few closely related copies of the gene per haploid genome. We investigated the induction of PPDK at the mRNA and protein levels, using the well characterized induction of a CAM-form of phosphoenol pyruvate carboxylase (PEPCase) as internal standard. During wilting of excised leaves PEP-Case mRNA amounts increased strongly within 8 h. Under these conditions amounts of PPDK mRNA remained constant. Re-hydrating leaves from previously stressed plants led to a decrease in PEPCase and PPDK mRNA amounts. During salt stress, no correlation between PEPCase and PPDK was observed. Analysis of plants of different ages indicated that, even in well-watered plants, PPDK-specific protein and mRNA increased when the plants reached a certain age. In old plants, salt stress failed to further increase PPDK mRNA or protein levels. We conclude that PPDK and PEPCase, which are both required for CAM to be functional, are controlled by different regulatory mechanisms in the intact plant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203649
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  • 5
    Electronic Resource
    Electronic Resource
    The concentration of cryoprotective lectins in mistletoe (Viscum album L.) leaves is correlated with leaf frost hardiness (1997)
    Springer
    Planta 203 (1997), S. 140-144 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Cryoprotection ; Frost hardiness ; Lectin ; Spinacia ; Thylakoid ; Viscum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The leaves of mistletoe (Viscum album L.) contain three galactose- and N-acetylgalactosamine-specific isolectin groups (ML I, II, III). The groups ML I and ML III showed strong cryoprotective activity during freezing and thawing of isolated spinach (Spinacia oleracea L.) thylakoid membranes, while ML II showed no such activity. The cryoprotective efficiency of the proteins was correlated with their relative hydrophobicity, as determined by a fluorescence titration assay. We found that the frost hardiness of mistletoe leaves was seasonally regulated under natural conditions. While leaves harvested in winter were not damaged by freezing to −20 °C, leaves harvested in July had already suffered 70% electrolyte leakage after freezing to −5 °C. Likewise, the amount of ML I and ML III varied during the year, with the highest amounts of these cryoprotective lectins in winter and early spring and the lowest amounts during the summer months. There was no comparable change in the amount of ML II. These data suggest that some lectins may play a role in the stabilization of cellular membranes under environmental stress conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050175
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  • 6
    Electronic Resource
    Electronic Resource
    Expression of the CAM-form of phospho(enol)pyruvate carboxylase and nucleotide sequence of a full length cDNA from Mesembryanthemum crystallinum (1989)
    Springer
    Molecular genetics and genomics 215 (1989), S. 447-454 
    Details
    ISSN: 1617-4623
    Keywords: Ice plant ; Crassulacean acid metabolism (CAM) ; Mesembryanthemum crystallinum ; Salt stress ; Phospho(enol)pyruvate carboxylase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have determined the complete nucleotide sequence of a full length cDNA encoding the Crassulacean acid metabolism (CAM) isogene of phospho(enol)pyruvate carboxylase (PEPCase). The cDNA clone, 3348 bp in length, was obtained from mRNA isolated from Mesembryanthemum crystallinum (common ice plant) which had undergone salt stress and subsequent induction of CAM. The long open reading frame encodes PEPCase (EC 4.1.1.31) with a predicted molecular mass of 110533 daltons. The deduced amino acid sequence of the ice plant PEPCase is most similar to that from maize having an amino acid identity of 74.9%. Sequence identity in corresponding regions of the PEPCase proteins from Escherichia coli and the cyanobacterium Anacystis nidulans are 41.4% and 33.5%, respectively. A compilation of the four amino acid sequences permitted the identification of phylogenetically conserved regions within the proteins which may play a role in the function of this important enzyme in plant metabolism. Gene specific probes from 3′ coding and noncoding regions of the cDNA clone used to probe genomic Southern blots established that this PEPCase gene is present in one copy in the nuclear genome of M. crystallinum. Transcripts arising from this gene increase dramatically when M. crystallinum is irrigated with 0.5 M NaCl, a stress which induces this plant to switch the primary fixation of CO2 from C3 (Calvin cycle) to CAM mode. The salt-induced mRNA encodes a PEPCase isoform which is undetectable in plants in the C3 mode as demonstrated by Northern hybridization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00427042
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  • 7
    Electronic Resource
    Electronic Resource
    Direct screening of a small genome : Estimation of the magnitude of plant gene expression changes during adaptation to high salt (1990)
    Springer
    Molecular genetics and genomics 224 (1990), S. 347-356 
    Details
    ISSN: 1617-4623
    Keywords: Genome organization ; Environmental stress ; Changes in gene expression ; Mesembryanthemum crystallinum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mesembryanthemum crystallinum (common ice plant), a facultative halophyte with a genome size of 393 000 kb, was used to estimate the magnitude of changes in gene expression in response to environmental stress by excess salt. Such treatment induces a water-conserving pathway of carbon assimilation (CAM) which is, at least in part, transcriptionally controlled. From a genomic library, 200 phage containing approximately 3200 kb (0.8% of the genome) were randomly selected. The inserts in these clones could be divided into four classes ranging from highly repetitive DNA (class I clones) to single-copy DNA (class IV clones). The inserts of the 166 clones of classes II to IV were digested with various restriction enzymes and the fragments were analyzed by hybridization with radioactively labelled mRNA isolated from stressed and unstressed leaves. We found that a total of ∼ 140 DNA fragments hybridized with the RNA probe. Among those, several differentially regulated transcripts were observed. Stress-dependent fluctuation of mRNA abundance was verified by Northern analyses: one mRNA, not detectable in unstressed leaves, appeared in stressed leaves, while steady-state levels of three transcripts decreased during stress. All regulated signals are derived from low abundance mRNAs, which may be missed during screening of cDNA libraries. We conclude from these results that, for the entire genome, on the order of more than one hundred genes are differentially regulated in response to salt stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00262428
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  • 8
    Electronic Resource
    Electronic Resource
    Gene expression during CAM induction under salt stress in Mesembryanthemum: cDNA library and increased levels of mRNA for phosphoenolpyruvate carboxylase and pyruvate orthosphosphate dikinase (1988)
    Springer
    Photosynthesis research 17 (1988), S. 159-171 
    Details
    ISSN: 1573-5079
    Keywords: Crassulacean acid metabolism ; gene expression ; Mesembryanthemum crystallinum ; mRNA levels ; soil salinity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mesembryanthemum crystallinum responds to high salinity in the soil by shifting the mode of carbon assimilation from the C3 mode to Crassulacean acid metabolism (CAM). Several enzymes of carbon metabolism have increased apparent activities in the CAM mode, including phosphoenolpyruvate carboxylase (PEPcase) and pyruvate orthophosphate dikinase (PPDK). We have identified cDNA clones for PEPcase and PPDK by immunological screening of a cDNA library constructed in the protein expression vector lambda gt11. The clones were characterized by immunoblotting and RNA blotting techniques. RNA blotting showed that during CAM induction the steady-state level of mRNAs for both PEP case and PPDK increased.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00047687
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  • 9
    Electronic Resource
    Electronic Resource
    Peptide mit ungewöhnlichen seitenketten. Synthese und konformation von polyethylenglykol  -  polylysin-blöcken mit mesogenen seitengruppen (1981)
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Rapid Communications 2 (1981), S. 637-643 
    Details
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/marc.1981.030020919
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  • 10
    Electronic Resource
    Electronic Resource
    Poly(ethylene glycol)-bound peptides as single centre models for enzyme-like catalysis (1985)
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Rapid Communications 6 (1985), S. 785-789 
    Details
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/marc.1985.030061113
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