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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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  • 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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  • 3
    Electronic Resource
    Electronic Resource
    Control of Photosystem II in spinach leaves by continuous light and by light pulses given in the dark (1996)
    Springer
    Photosynthesis research 50 (1996), S. 181-191 
    Details
    ISSN: 1573-5079
    Keywords: chlorophyll fluorescence ; energy dissipation ; light scattering ; photosynthesis ; state transition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The light-induced induction of components of non-photochemical quenching of chlorophyll fluorescence which are distinguished by different rates of dark relaxation (qNf, rapidly relaxing and qNs, slowly relaxing or not relaxing at all in the presence brief saturating light pulses which interrupt darkness at low frequencies) was studied in leaves of spinach. After dark adaptation of the leaves, a fast relaxing component developed in low light only after a lag phase. Quenching increased towards a maximum with increasing photon flux density. This ‘fast’ component of quenching was identified as energy-dependent quenching qE. It required formation of an appreciable transthylakoid ΔpH and was insignificant when darkened spinach leaves received 1 s pulses of light every 30 s even though zeaxanthin was formed from violaxanthin under these conditions. Another quenching component termed qNs developed in low light without a lag phase. It was not dependent on a transthylakoid pH gradient, decayed exponentially with a long half time of relaxation and was about 20% of total quenching irrespective of light intensity. When darkened leaves were flashed at frequencies higher than 0.004 Hz with 1 s light pulses, this quenching also appeared. Its extent was very considerable, and it did not require formation of zeaxanthin. Relaxation was accelerated by far-red light, and this acceleration was abolished by NaF. We suggest that qNs is the result of a so-called state transition, in which LHC II moves after its phosphorylation from fluorescent PS II to nonfluorescent PS I. This state transition was capable of decreasing in darkened leaves the potential maximum quantum efficiency of electron flow through Photosystem II by about 20%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00014888
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  • 4
    Electronic Resource
    Electronic Resource
    Heat sensitivity of chloroplasts and leaves: Leakage of protons from thylakoids and reversible activation of cyclic electron transport (1999)
    Springer
    Photosynthesis research 59 (1999), S. 81-93 
    Details
    ISSN: 1573-5079
    Keywords: chlorophyll fluorescence ; cyclic electron flow ; high temperature ; light scattering ; photosynthesis ; Photosystems II and I
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In illuminated intact spinach chloroplasts, warming to and beyond 40 °C increased the proton permeability of thylakoids before linear electron transport through Photosystem II was inhibited. Simultaneously, antimycin A-sensitive cyclic electron transport around Photosystem II was activated with oxygen or CO2, but not with nitrite as electron acceptors. Between 40 to 42 °C, activation of cyclic electron transport balanced the loss of protons so that a sizeable transthylakoid proton gradient was maintained. When the temperature of darkened spinach leaves was slowly increased to 40°C, reduction of the quinone acceptor of Photosystem II, QA, increased particularly when respiratory CO2 production and autoxidation of plastoquinones was inhibited by decreasing the oxygen content of the atmosphere from 21 to 1%. Simultaneously, Photosystem II activity was partially lost. The enhanced dark QA reduction disappeared after the leaf temperature was decreased to 20 °C. No membrane energization was detected by light-scattering measurements during heating the leaf in the dark. In illuminated spinach leaves, light scattering and nonphotochemical quenching of chlorophyll fluorescence increased during warming to about 40 °C while Photosystem II activity was lost, suggesting extra energization of thylakoid membranes that is unrelated to Photosystem II functioning. After P700 was oxidized by far-red light, its reduction in the dark was biphasic. It was accelerated by factors of up to 10 (fast component) or even 25 (slow component) after short heat exposure of the leaves. Similar acceleration was observed at 20 °C when anaerobiosis or KCN were used to inhibit respiratory oxidation of reductants. Methyl viologen, which accepts electrons from reducing side of Photosystem II, completely abolished heat-induced acceleration of P700+ reduction after far-red light. The data show that increasing the temperature of isolated chloroplasts or intact spinach leaves to about 40 °C not only inhibits linear electron flow through Photosystem II but also activates Photosystem I-driven cyclic electron transport pathways capable of contributing to the transthylakoid proton gradient. Heterogeneity of the kinetics of P700+ reduction after far-red oxidation is discussed in terms of Photosystem I-dependent cyclic electron transport in stroma lamellae and grana margins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006149317411
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  • 5
    Electronic Resource
    Electronic Resource
    The efficiency of electron transfer from QA − to the donor side of Photosystem II decreases during induction of photosynthesis: Evidences from chlorophyll fluorescence and photoacoustic techniques (1996)
    Springer
    Photosynthesis research 47 (1996), S. 13-20 
    Details
    ISSN: 1573-5079
    Keywords: chlorophyll fluorescence ; photoacoustics ; Photosystems I and II ; photosynthetic induction ; reaction centers (active, inactive) ; quinone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00017749
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