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  • 1
    Electronic Resource
    Electronic Resource
    Specific reduction of chloroplast carbonic anhydrase activity by antisense RNA in transgenic tobacco plants has a minor effect on photosynthetic CO2 assimilation (1994)
    Springer
    Planta 193 (1994), S. 331-340 
    Details
    ISSN: 1432-2048
    Keywords: Antisense RNA ; Carbon dioxide assimilation ; Carbonic anhydrase ; Nicotiana (transgenic plants)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract As an approach to understanding the physiological role of chloroplast carbonic anhydrase (CA), this study reports on the production and preliminary physiological characterisation of transgenic tobacco (Nicotiana tabacum L.) plants where chloroplast CA levels have been specifically suppressed with an antisense construct directed against chloroplast CA mRNA. Primary transformants with CA levels as low as 2% of wild-type levels were recovered, together with intermediate plants with CA activities of about 20–50% of wild-type levels. Plants with even the lowest CA levels were not morphologically distinct from the wild-type plants. Segregation analysis of the low-CA character in plants grown from T1 selfed seed indicated that at least one of the low-CA plants appears to have two active inserts and that at least two of the intermediate-CA plants have one active insert. Analysis of CO2 gas exchange of a group of low-CA plants with around 2% levels of CA indicated that this large reduction in chloroplastic CA did not appear to cause a measurable alteration in net CO2 fixation at 350 μbar CO2 and an irradiance of 1000 μmol quanta·m−2·s−1. In addition, no significant differences in Rubisco activity, chlorophyll content, dry weight per unit leaf area, stomatal conductance or the ratio of intercellular to ambient CO2 partial pressure could be detected. However, the carbon isotope compositions of leaf dry matter were significantly lower (0.85%o) for low-CA plants than for wildtype plants. This corresponds to a 15-μbar reduction in the CO2 partial pressure at the sites of carboxylation. The difference, which was confirmed by concurrent measurement of discrimination with gas exchange, would reduce the CO2 assimilation rate by 4.4%, a difference that could not be readily determined by gas-exchange techniques given the inherent variability found in tobacco. A 98% reduction in CA activity dramatically reduced the 18O discrimination in CO2 passing over the leaf, consistent with a marked reduction in the ratio of hydrations to carboxylations. We conclude that a reduction in chloroplastic CA activity of two orders of magnitude does not produce a major limitation on photosynthesis at atmospheric CO2 levels, but that normal activities of the enzyme appear to play a role in facilitated transfer of CO2 within the chloroplast, producing a marginal improvement in the efficiency of photosynthesis in C3 plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201810
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  • 2
    Electronic Resource
    Electronic Resource
    Specific reduction of chloroplast glyceraldehyde-3-phosphate dehydrogenase activity by antisense RNA reduces CO2 assimilation via a reduction in ribulose bisphosphate regeneration in transgenic tobacco plants (1995)
    Springer
    Planta 195 (1995), S. 369-378 
    Details
    ISSN: 1432-2048
    Keywords: Antisense RNA ; Glyceraldehyde-3-phos-phate dehydrogenase ; Metabolite pools Nicotiana(transgenic plants) ; Photosynthesis ; Stomate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The reduction of 3-phosphoglycerate (PGA) to triose phosphate is a key step in photosynthesis linking the photochemical events of the thylakoid membranes with the carbon metabolism of the photosynthetic carbon-reduction (PCR) cycle in the stroma. Glyceraldehyde-3-phosphate dehydrogenase: NADP oxidoreductase (GAPDH) is one of the two chloroplast enzymes which catalyse this reversible conversion. We report on the engineering of an antisense RNA construct directed against the tobacco (Nicotiana tabacum L.) chloroplastlocated GAPDH (A subunit). The construct was integrated into the tobacco genome by Agrobacterium-mediated transformation of leaf discs. Of the resulting transformants, five plants were recovered with reduced GAPDH activities ranging from 11 to 24% of wild-type (WT) activities. Segregation analysis of the kanamycin-resistance character in self-pollinated T1 seed from each of the five transformants revealed that one plant (GAP-R) had two active DNA inserts and the others had one insert. T1 progeny from GAP-R was used to generate plants with GAPDH activities ranging from WT levels to around 7% of WT levels. These were used to study the effect of variable GAPDH activities on metabolite pools for ribulose1,5-bisphosphate (RuBP) and PGA, and the accompanying effects on the rate of CO2 assimilation and other gasexchange parameters. The RuBP pool size was linearly related to GAPDH activity once GAPDH activity dropped below the range for WT plants, but the rate of CO2 assimilation was not affected until RuBP levels dropped to 30–40% of WT levels. That is, the CO2 assimilation rate fell when RuBP per ribulose-1,5-biphosphate carboxylase-oxygenase (Rubisco) site fell below 2 mol·(mol site)−1 while the ratio for WT plants was 4–5 mol·m(mol site)−1. Leaf conductance was not reduced in leaves with reduced GAPDH activities, resulting in an increase in the ratio of intercellular to ambient CO2 partial pressure. Conductance in plants with reduced GAPDH activities was still sensitive to CO2 and showed a normal decline with increases in CO2 partial pressure. Although PGA levels did not fluctuate greatly, the effect of reduced GAPDH activity on RuBP-pool size and assimilation rate can be interpreted as being due to a blockage in the regeneration of RuBP. Concomitant gas-ex change and chlorophyll a fluorescence measurements indicated that photosynthesis changed from being Rubisco-limited to being RuBP-regeneration-limited at a lower CO2 partial pressure in the antisense plants than in WT plants. Photosynthetic electron transport was down-regulated by the build-up of a large proton gradient and the electron-transport chain did not become over-reduced due to a shortage of NADP. Plants with severely reduced GAPDH activity were not photoinhibited despite the continuous presence of a large thylakoid proton gradient in the light. Along with plant size, Rubisco activity, leaf soluble protein and chlorophyll content were reduced in plants with the lowest GAPDH activities. We conclude that chloroplastic GAPDH activity does not appear to limit steady-state photosynthetic CO2 assimilation at ambient CO2. This is because WT leaves maintain the ratio of RuBP per Rubisco site about twofold higher than the level required to achieve a maximal rate of CO2 assimilation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202594
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  • 3
    Electronic Resource
    Electronic Resource
    Hydrosilylation of allyl carbamates by poly(methylhydrosiloxane) and related side-reactions (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 31 (1993), S. 2373-2381 
    Details
    ISSN: 0887-624X
    Keywords: hydrosilylation ; allyl carbamates ; poly(methylhydrosiloxane) ; side-reaction mechanism ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrosilylation of allyl carbamates by poly(methylhydrosiloxane) (PMHS) catalyzed by platinum- or rhodium-based complexes was investigated. About 10% of the carbamate molecules decompose during the hydrosilylation reaction through the cleavage of the carbamate bond. A redistribution process also takes place among the polysiloxane chains resulting in the formation of branched polymers but no crosslinking occurs. A mechanism for this side-reaction is proposed. © 1993 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1993.080310920
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  • 4
    Electronic Resource
    Electronic Resource
    Poly[glycidyl methacrylate(GMA)/methylmethacrylate(MMA)-b-butadiene(B)-b-GMA/MMA] reactive thermoplastic elastomers: Synthesis and characterization (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 3507-3515 
    Details
    ISSN: 0887-624X
    Keywords: thermoplastic elastomers ; polyglycidylmethacrylate ; polybutadiene ; block copolymers ; anionic polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: New block copolymers of the ABA type, where B stands for polybutadiene (PBD) and A for polyglycidylmethacrylate(PGMA), poly(methylmethacrylate(MMA)-co-GMA) and PMMA-b-PGMA, respectively, have been successfully synthesized by using the diadduct of tert-butyllithium (tert-BuLi) to meta-diisopropenylbenzene (m-DIB) as a difunctional initiator. The PBD midblock has been synthesized in a cyclohexane/diethylether (100/6, v/v) mixture at room temperature, whereas the methacrylate outer blocks have been synthesized in a cyclohexane/diethylether/THF (100/6/150, v/v/v) mixture at -78°C. Block copolymers of a very narrow molecular weight distribution (1.10) have been analyzed by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and tensile testing. These materials are phase separated and can exhibit tensile strength up to 22 MPa together with very high elongation at break (1500%). © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3507-3515, 1997
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 5
    Electronic Resource
    Electronic Resource
    Studies on the β-form of isotactic polypropylene, 1. Characterization of the β-form and study of the β-α transition during heating by wide angle X-ray diffraction (1986)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 187 (1986), S. 633-642 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The conditions for the formation of the β-form of isotactic polypropylene in the presence of a β-nucleator and the β-α transition during heating were studied by wide angle X-ray diffraction. A conditional crystallinity of the β-form, X′β, and a structural disorder parameter, S, deduced from WAXD data were defined for the characterization of the β-form in addition to the K value. The results show that X′β and S obviously depend on the content of β-nucleator, and that the β-α transition during heating essentially consists in the melting of the β-form and the successive recrystallization to the α-form.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1986.021870315
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  • 6
    Electronic Resource
    Electronic Resource
    Triblock copolymer based thermoplastic elastomeric gels of a large service temperature range: preparation and characterization (1997)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 198 (1997), S. 3719-3735 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Poly(methyl methacrylate)-block-polybutadiene-block-poly(methyl methacrylate) (MBM) triblock copolymers and their hydrogenated counterparts with poly(ethylene-co-1,2-butylene) midblock (MEBM) were swollen by an aliphatic oil of high boiling point which is a selective solvent for the central block. Thermoreversible gels are accordingly formed by both MBM and MEBM copolymers above a critical polymer content (Cr), which depends on the nature of the midblock and not on the copolymer molecular weight, at least in the investigated range. Cr has been found to be 5 wt.-% for an MBM block copolymer and 2 wt.-% for MEBM copolymers of various molecular weights. Gels of MEBM triblock copolymers exhibit interesting mechanical properties, such as high elongation at break (up to 870%) and high tensile strength (32 kPa). The most interesting feature of the MEBM gels is an upper service temperature as high as 170°C, thus more than 100°C higher than the value (47°C) reported for gels of an SEBS copolymer (S = polystyrene) of comparable molecular weight (100000) and composition (ca. 30 wt.-% hard block). The morphology of MEBM gels was studied by scanning electron microscopy (SEM) and found to be cocontinuous in case of a gel containing 20 wt.-% copolymer.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1997.021981132
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