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  • 2000-2004  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Photosystem II inhibition by moderate light under low temperature in intact leaves of chilling-sensitive and -tolerant plants (2004)
    Oxford, UK; Malden, USA : Munksgaard International Publishers
    Physiologia plantarum 121 (2004), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Photosystem II (PSII) activity was examsined in leaves of chilling-sensitive cucumber (Cucumis sativus L.), tomato (Lycopersicum esculentum L.), and maize (Zea mays L.), and in chilling-tolerant barley (Hordeum vulgare L.) illuminated with moderate white light (300 µmol m−2 s−1) at 4°C using chlorophyll a fluorescence measurements. PSII activity was inhibited in leaves of all the four plants as suggested by the decline in Fv/Fm, 1/Fo − 1/Fm, and Fv/Fo values. The changes in initial fluorescence level (Fo), Fv/Fm, 1/Fo − /1/Fm, and Fv/Fo ratios indicate a stronger PSII inhibition in cucumber, maize and tomato plants. The kinetics of chlorophyll a fluorescence rise showed complex changes in the magnitudes and rise of O-J, J-I, and I-P phases caused by photoinhibition. The selective suppression of the J-I phase of fluorescence rise kinetics provides evidence for weakened electron donation from the oxidizing side, whereas the accumulation of reduced QA suggests damage to the acceptor side of PSII. These findings imply that the process of chilling-induced photoinhibition involves damage to more than one site in the PSII complexes. Furthermore, comparative analyses of the decline in Fv/Fo and photooxidation of P700 explicitly show that the extent of photoinhibitory damage to PSII and photosystem I is similar in leaves of cucumber plants grown at a low irradiance level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.0031-9317.2004.00305.x
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Heterogeneity of photosystem II reaction centers as influenced by heat treatment of barley leaves (2000)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 110 (2000), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Three functionally distinct populations of PSII reaction centers differing in the ability to keep the primary acceptors in a reduced state and to transfer electrons to PSI were estimated using chlorophyll fluorescence measurements in primary barley leaves exposed to elevated temperatures in the range of 37–51°C. The capacity of the PSII reaction centers to perform at least one light-induced charge separation was not affected by a 5-min heat treatment at temperatures up to 51°C. The first population containing QB-non-reducing centers corresponded to 15–20% of the total PSII activity up to 45°C. In a second population, PSII reaction centers maintained QA reduction under light in the presence of oxygen, but not in the presence of a strong artificial PSI electron acceptor, methyl viologen. In a third population that gradually increases from zero at 37°C to about 60% at 45°C, the PSII centers were not able to keep QA in the reduced state even in the presence of oxygen as the sole electron acceptor. Three electron transport pathways, the pseudocyclic one involving both PSII and PSI, the NAD(P)H-dependent pathway mediated by PSI alone after the loss of activity in some PSII centers, and the PSI-driven ferredoxin-dependent route enhanced by weakly efficient PSII centers that are able to provide only catalytic amounts of electrons, are suggested to create a proton gradient in chloroplasts of heat-stressed leaves thus protecting PSII reaction centers from photodamage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.2000.110219.x
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    Paper (German National Licenses)
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