Library

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    The primary processes of photosystem II in purified guard-cell protoplasts and mesophyll-cell protoplasts from Commelina communis L. (1983)
    Springer
    Planta 159 (1983), S. 554-560 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; Commelina ; Guard cell ; Oxygen evolution (guard cell) ; Photosystem II ; Protoplast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Guard-cell protoplasts were isolated by enzymic digestion of the epidermis peeled from the abaxial surface of leaves from Commelina communis L. The protoplasts were separated from mesophyll-cell protoplasts and other contaminants by density-gradient centrifugation, and the purity of the preparations carefully and quantitatively assessed by light microscopy. The preparations of guard-cell protoplasts were then compared with mesophyll-cell protoplasts in terms of the activity of photosystem II as assessed by a) the light-induced evolution of oxygen under both steady-state and flashing light and b) the characteristics of photosystem-II chlorophyll fluorescence. In all experiments, clear photosystem-II activity was found in guard-cell protoplasts, although some subtle distinctions between guard-cell and mesophyll-cell protoplasts were found. The contribution of any contaimination by mesophyll-cell chlorophyll to guard-cell-protoplast signals was estimated to be less than 3% in all cases. The results indicate that photosystem II is present and active in guard cells of Commelina.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00409145
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    CO2 and O2 dependence of PS II activity in C4 plants having genetically produced deficiencies in the C3 or C4 cycle (1998)
    Springer
    Photosynthesis research 58 (1998), S. 91-101 
    Details
    ISSN: 1573-5079
    Keywords: C4 photosynthesis ; PEP carboxylase mutants ; Photosystem II ; Rubisco transgenic plants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The CO2 dependence of rates of CO2 fixation (A) and photochemistry of PS II at 5, 15 and 30% O2 were analyzed in the C4 plant Amaranthus edulis having a C4 cycle deficiency [phosphoenolpyruvate carboxylase (PEPC) mutants], and in the C4 plant Flaveria bidentis having a C3 cycle deficiency [Rubisco small subunit antisense (αSSU)]. In the wild type (WT) A. edulis and its heterozygous mutant having less than 50% WT PEPC activity there was a similar dependence of A and PS II photochemistry on varying CO2, although the CO2 saturated rates were 25% lower in heterozygous plants. The homozygous plants having less than 2% PEPC of the WT had significant levels of photorespiration at ambient levels of CO2 and required about 30 times ambient levels for maximum rates of A. Despite variation in the capacity of the C4 cycle, more than 91% of PS II activity was linearly associated with A under varying CO2 at 5, 15 and 30% O2. However, the WT plant had a higher PS II activity per CO2 fixed under saturating CO2 than the homozygous mutant, which is suggested to be due to elimination of the C4 cycle and its associated requirement for ATP from a Mehler reaction. In the αSSU F. bidentis plants, a decreased rate of A (35%) and PS II activity (33%) accompanied a decrease in Rubisco capacity. There was some increase in alternative electron sinks at high CO2 when the C3 cycle was constrained, which may be due to increased flux through the C4 cycle via an ATP generating Mehler reaction. Nevertheless, even with constraints on the function of the C4 or C3 cycle by genetic modifications, analyses of CO2 response curves under varying levels of O2 indicate that CO2 assimilation is the main determinant of PS II activity in C4 plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006176713574
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Flash-induced redox changes in oxygen-evolving spinach Photosystem II core particles (1993)
    Springer
    Photosynthesis research 38 (1993), S. 169-176 
    Details
    ISSN: 1573-5079
    Keywords: Photosystem II ; PS II core ; oxygen-evolving complex ; UV asorbance changes ; EPR signal II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Flash-induced redox reactions in spinach PS II core particles were investigated with absorbance difference spectroscopy in the UV-region and EPR spectroscopy. In the absence of artificial electron acceptors, electron transport was limited to a single turnover. Addition of the electron acceptors DCBQ and ferricyanide restored the characteristic period-four oscillation in the UV absorbance associated with the S-state cycle, but not the period-two oscillation indicative of the alternating appearance and disappearance of a semiquinone at the QB-site. In contrast to PS II membranes, all active centers were in state S1 after dark adaptation. The absorbance increase associated with the S-state transitions on the first two flashes, attributed to the Z+S1→ZS2 and Z+S2→ZS3 transitions, respectively, had half-times of 95 and 380 μs, similar to those reported for PS II membrane fragments. The decrease due to the Z+S3→ZS0 transition on the third flash had a half-time of 4.5 ms, as in salt-washed PS II membrane fragments. On the fourth flash a small, unresolved, increase of less than 3 μs was observed, which might be due to the Z+S0→ZS1 transition. The deactivation of the higher S-states was unusually fast and occurred within a few seconds and so was the oxidation of S0 to S1 in the dark, which had a half-time of 2–3 min. The same lifetime was found for tyrosine D+, which appeared to be formed within milliseconds after the first flash in about 10% inactive centers and after the third and later flashes by active centers in Z+S3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00146416
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Absorbance difference spectra of the S-state transitions in Photosystem II core particles (1993)
    Springer
    Photosynthesis research 38 (1993), S. 323-330 
    Details
    ISSN: 1573-5079
    Keywords: Photosystem II ; PS II core ; oxygen evolving complex ; UV absorbance changes ; S-state spectra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Redox changes of the oxygen evolving complex in PS II core particles were investigated by absorbance difference spectroscopy in the UV-region. The oscillation of the absorbance changes induced by a series of saturating flashes could not be explained by the minimal Kok model (Kok et al. 1970) consisting of a 4-step redox cycle, S0 → S1 → S2 → S3 → S0, although the values of most of the relevant parameters had been determined experimentally. Additional assumptions which allow a consistent fit of all data are a slow equilibration of the S3 state with an inactive state, perhaps related to Ca2+-release, and a low quantum efficiency for the first turnover after dark-adaptation. Difference spectra of the successive S-state transitions were determined. At wavelengths above 370 nm, they were very different due to the different contribution of a Chl bandshift in each spectrum. At shorter wavelengths, the S1 → S2 transition showed a difference spectrum similar to that reported by Dekker et al. 1984b and attributed to an Mn(III) to Mn(IV) oxidation. The spectrum of absorbance changes associated with the S2 → S3 transition was similar to that reported by Lavergne 1991 for PS II membranes. The S0 → S1 transition was associated with a smaller but still substantial absorbance increase in the UV. Differences with the spectra reported by Lavergne 1991 are attributed to electrostatic effects on electron transfer at the acceptor side associated with the S-state dependence of proton release in PS II membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00046757
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Degradation of the Photosystem II D1 and D2 proteins in different strains of the cyanobacterium Synechocystis PCC 6803 varying with respect to the type and level of psbA transcript (2000)
    Springer
    Plant molecular biology 42 (2000), S. 635-645 
    Details
    ISSN: 1573-5028
    Keywords: cyanobacteria ; D1 ; D2 ; Photosystem II ; psbA ; Synechocystis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The turnover of the D1 and D2 proteins of Photosystem II (PSII) has been investigated by pulse-chase radiolabeling in several strains of the cyanobacterium Synechocystis PCC 6803 containing different types and levels of the psbA transcript. Strains lacking psbA1 and psbA3 gene and containing high levels of the psbA2 transcript showed the selective synthesis of D1 whose degradation could be slowed down by the protein synthesis inhibitor lincomycin. In contrast, in strains containing just the psbA3 gene, the intensity of the D1 protein labeling was lower and labeling of the D2 and CP43 proteins was stimulated in comparison to the psbA2-containing strains. In addition, the rate and selectivity of the D1 degradation and its dependence on the presence of lincomycin was proportional to the level of the psbA3 transcript in the particular strain. Consequently, there was parallel, lincomycin-independent and slowed-down breakdown of the D1 and D2 proteins in strains with the lowest level of psbA3 transcript. These results are discussed in terms of a model in which the rate of D1 and D2 degradation in cyanobacteria is affected not only by the rate of PSII photodamage, but also by the availability of newly synthesized D1 protein. Moreover, the comparison of the non-oxygen-evolving D1 mutants D170A** and Y161F*** differing by the presence of tyrosine Z has indicated a minor role of the oxidized form of this secondary PSII electron donor in the donor side mechanism of D1 and D2 protein breakdown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006305308196
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Hydrogen-bonding. Part 4. An analysis of solute hydrogen-bond basicity, in terms of complexation constants (log K), using F1 and F2 factors, the principal components of different kinds of basicityPart 3. M. H. Abraham, P. P. Duce, D. V. Prior, R. A. Schulz, J. J. Morris and P. J. Taylor, J. Chem. Soc. Faraday Trans. 1, 84, 865 (1988). (1989)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 243-254 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The principal components factors F1 and F2 in the equation \documentclass{article}\pagestyle{empty}\begin{document}$$ \log K = {\rm BDP}_0 + S_1 F_1 + S_2 F_2 $$\end{document} have been used to obtain S1 and S2 values for sets of hydrogen-bond bases against 32 reference acid/solvent systems. The constants S1 and S2 define an angle θ = tan-1 S2/S1 that is a measure of the electrostatic:covalent bonding ratio in the hydrogen-bond complex. It is shown that θ can vary from 53 (4-fluorophenol in CH2Cl2)to 86 degrees (Ph2NH in CCl4) depending on the reference acid and solvent. This variation in θ can lead to family dependent behaviour in plots of log K for bases against a given reference acid system vs log K for bases against another reference acid system, and precludes the construction of any general scale of hydrogen-bond basicity using log K values. Amongst a quite wide range of reference acid/solvent systems θ varies only from 64 to 73 degrees, and for bases against these reference systems a ‘reasonably general’ scale could be set up. Such a scale could be extended to bases against reference acid/solvent systems outside the 64-73 degree range provided that certain classes of base (e.g. pyridines, alkylamines) were excluded from the additional reference acid/solvent systems.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610020307
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Model solvent systems for QSAR. Part IV. The hydrogen bond acceptor behaviour of heterocycles (1994)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 7 (1994), S. 743-750 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An LSER analysis based on the partitioning of 15 proton acceptor heterocycles has succeeded in extracting Σβ values, but only at the cost of demonstrating solvent dependence for some of them. As noted by Abraham, the division lies between protic and aprotic organic phases. His observation that pyridine and quinoline are less effective acceptors when surrounded by solvent than in 1 : 1 association was confirmed, and possible reasons for this are discussed. Two other such cases are N-methylimidazole and pyridazine, both of which give lower Σβ values in octanol than in PGDP. For both, Σβ in PGDP is what would be expected on the basis of log Kβ. The value for pyridazine in octanol suggests that, here, the ‘α-effect’ is no longer operative; it is possible that this result can be generalized to other such heterocycles. Elsewhere, the most remarkable finding is that, where there are two proton acceptor sites in one heterocyclic ring, Σβ is the simple unattenuated sum of the separate βf values. If this result is general, it leads to a very simple way of estimating Σβ for heterocycles by calculation where data are unavailable. Evidence was also found, in certain cases, for hydrogen bonding to the π-donor heteroatom or the aromatic ring. The QSAR implications of these results are discussed.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610071213
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Electrochemical and photoelectronic spectral study of compounds with high ionization potentials: Anodic oxidation of vinyl triflates in aprotic solvents (1990)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 3 (1990), S. 670-676 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Microelectrodes can be used to measure redox half-wave potentials in aprotic solvents containing no purposely added supporting electrolyte. By employing an electrode of sufficiently small size, the accessible potential range in solution is considerably extended. The electrochemical oxidation of vinyl (enol) triflates, which are oxidized at high electrode potentials, can therefore be studied using an ultramicroelectrode. Oxidation and ionization potentials, determined by ultramicroelectrode voltammetry and He I photoelectron spectroscopy, respectively, of 2-methylprop-1-enyl, cyclohexenyl, cyclopentenyl, 1,1-diphenylethenyl and prop-2-enyl triflate are reported. The results from electrochemical measurements and photoelectron spectra were compared.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610031008
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Hydrogen-bonding 8.Part 7; M. H. Abraham, P. L. Grellier, D. V. Prior, P. P. Duce, J. J. Morris and P. J. Taylor. J. Chem Soc., Perkin Trans. 2, (in press). Possible equivalence of solute and solvent scales of hydrogen-bond basicity of non-associated compounds (1989)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 2 (1989), S. 540-552 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Using the solvatochromic indicator method, a scale of solvent hydrogen-bond basicity, β1 (General), has been set up using a series of double regression equations, \documentclass{article}\pagestyle{empty}\begin{document}$$ \nu = \nu _0 + s\pi _1^* + b\beta _1 $$\end{document} for 11 aniline-type indicators. A similar solvent scale, β1 (Special), has been constructed by the homomorphic comparison method using only results by Laurence et al. on the indicators 4-nitroaniline and 4-nitro-N,N-dimethylaniline. Results are available from our previous work on a general solute scale, β2H, and we have also obtained a special solute scale, β2 (pKHB) from available log K values for hydrogen-bond complexation of bases with 4-fluorophenol in CCl4. However, the two solute β2 scales are virtually identical.It is shown that there is a general connection between β1(General) and β2H, with r = 0·9775 and s.d. = 0·05 for 32 compounds, and between β1(Special) and β2H, with r = 0·9776 and s.d. = 0·06 for the same 32 compounds. The latter correlation over 60 compounds yields r = 0·9684 and s.d. = 0·07. However, there are so many compounds in these regressions for which the differences in the solvent and solute β values are larger than the total expected error of 0·07 units that the use of β1 to predict β2 or vice versa is a very hazardous procedure. About 70 new β1 values obtained by the double regression method are also reported.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610020706
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Thermodynamic and kinetic analysis of the dimerization of aqueous glyoxal (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 18 (1986), S. 775-789 
    Details
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Equilibria and rates of interconversion between monomeric and dimeric glyoxal were measured in aqueous solution. The equilibrium constant [G2]/[G1]2 was 0.56 M-1 at 25°C, and was hardly affected by changes of ionic strength and pH but increased rapidly with increase of temperature. The rate of depolymerization was first-order in dimer, with the pseudo first-order rate coefficient in the pH range 1.3-7.8being of the form b1[H3O+] + b2 + b3[OH-]/(1 + b4[OH-]) + b5[OH-]. Coefficients b1 and b2 were more strongly affected by changes of temperature, though [OH-] was much the more effective catalyst. This rate form has not previously been observed for monomer-dimer inter-conversion of α-hydroxycarbonyls and α-dicarbonyls or for related reactions such as mutarotations and hydrations. Equivalent rate forms arisefrom reactions where an intermediate at steady state and low concentration is produced.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/kin.550180705
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...