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  • oxygen evolution  (2)
  • Photosystems I and II  (1)
  • 1
    ISSN: 1573-5079
    Schlagwort(e): chlorophyll fluorescence ; photoacoustics ; Photosystems I and II ; photosynthetic induction ; reaction centers (active, inactive) ; quinone
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The amplitudes ratio of the fast and slow phases (Afast/Aslow) in the kinetics of the dark relaxation of variable chlorophyll fluorescence (FV) was studied after various periods of illumination of dark-adapted primary barley leaves. Simultaneously, photosynthetic activity was monitored using the photoacoustic technique and the photochemical and non-photochemical fluorescence quenching parameters. The ratio Afast/Aslow changed with the preceding illumination time in a two-step manner. During the first stage of photosynthetic induction (0–20 s of illumination), characterized by a drop in O2-dependent photoacoustic signal following an initial spike and by a relatively stable small value of photochemical FV quenching, the ratio Afast/Aslow remained practically unaltered. During the second stage (20–60 s of illumination), when both the rate of O2 evolution and the photochemical FV quenching were found to be sharply developed, a marked increase in the above ratio was also observed. A linear correlation was found between the value of the photochemical quenching and the ratio Afast/Aslow during the second phase of photosynthetic induction. It is concluded that the slow phase appearing in the kinetics of FV dark relaxation is not due to the existence of Photosystem II reaction centres lacking the ability to reduce P700+ with high rates, but is instead related to the limitation of electron release from Photosystem I during the initial stage of the induction period of photosynthesis. This limitation keeps the intersystem electron carriers in the reduced state and thus increases the probability of back electron transfer from QA − to the donor side of Photosystem II.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Photosynthesis research 30 (1991), S. 123-130 
    ISSN: 1573-5079
    Schlagwort(e): oxygen evolution ; calcium ; chloride ; electron transport ; photosynthetic inhibitors
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The inhibitory effect of Zn2+ on photosynthetic electron transport was investigated in native and CaCl2-treated (depleted in extrinsic polypeptides) Photosystem II (PS II) submembrane preparations. Inhibition of 2,6-dichlorophenolindophenol photoreduction by Zn2+ was much stronger in protein-depleted preparations in comparison to the native form. It was found that Ca2+ significantly reduced the inhibition in the native PS II preparations, as did Mn2+ in a combination with H2O2 in the protein-depleted counterparts. No other tested monovalent or divalent cations could replace Ca2+ or Mn2+ in the respective experiments. Diphenylcarbazide could partially relieve (40–45%) the inhibition in both types of preparations. The above indicates the presence of an active Zn2+ inhibitory site on the donor side of PS II. However, neither Ca2+ nor Mn2+ could completely prevent inhibition by high concentrations of Zn2+ (〉1 mM). We propose that elevated levels of Zn2+ strongly perturb the conformation of the PS II core complex and might also affect the acceptor side of the photosystem.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 44 (1994), S. 178-183 
    ISSN: 0006-3592
    Schlagwort(e): bioassay ; phytotoxicity ; photosynthesis ; immobilized membranes ; oxygen evolution ; Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The potential of thylakoid membranes immobilized in an albumin-glutaraldehyde crosslinked matrix in a fast bioassay for phytotoxicity measurements in aqueous samples is studied. Free and immobilized preparations are compared for their electron transport activity measured as the initial rate of oxygen evolution with 2,5-cichlorobenzoquinone as the artificial electron acceptor. Immobilized thylakoids were much stable under storage conditions; in the dark, at 4°C, they were fully stable in terms of photosynthetic activity for a period of 200 h. The immobilized membranes were as sensitive as the free thylakoids for the detection of most of the compounds tested (metal cations, sulfite, nitrite, and herbicides), all known as inhibitors of photosynthetic electron transport. In some instances, the immobilized preparations were even more sensitive than the free counterparts. The sensitivity could be further increased by lowering chlorophyll concentration in the assay. The short incubation period required (∼10 to 15 min) and the small volume of the assay (3 mL) suggest that this type of material should be useful in the detection of locations or effluents with phytotoxic character. © 1994 John Wiley & Sons, Inc.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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