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1.
Sándor Demeter  Imre Vass 《BBA》1984,764(1):24-32
In the glow curves of chloroplasts excited by a series of flashes at +1°C the intensity of the main thermoluminescence band appearing at +30°C (B band; B, secondary acceptor of Photosystem II) exhibits a period-4 oscillation with maxima on the 2nd and 6th flashes indicating the participation of the S3 state of the water-splitting system in the radiative charge recombination reaction. After long-term dark adaptation of chloroplasts (6 h), when the major part of the secondary acceptor pool (B pool) is oxidized, a period-2 contribution with maxima occurring at uneven flash numbers appears in the oscillation pattern. The B band can even be excited at ?160°C as well as by a single flash in which case the water-splitting system undergoes only one transition (S1 → S2). The experimental observations and computer simulation of the oscillatory patterns suggest that the B band originates from charge recombination of the S2B? and S3B? redox states. The half-time of charge recombination responsible for the B band is 48 s. When a major part of the plastoquinone pool is reduced due to prolonged excitation of the chloroplasts by continuous light, a second band (Q band; Q, primary acceptor of Photosystem II) appears in the glow curve at +10°C which overlaps with the B band. In chloroplasts excited by flashes prior to DCMU addition only the Q band can be observed showing maxima in the oscillation pattern at flash numbers 2, 6 and 10. The Q band can also be induced by flashes after DCMU addition which allows only one transition of the water-splitting system (S1 → S2). In the presence of DCMU, electrons accumulate on the primary acceptor Q, thus the Q band can be ascribed to the charge recombination of either the S2Q? or S3Q? states depending on whether the water-splitting system is in the S2 or the S3 state. The half-time of the back reaction of Q? with the donor side of PS II (S2 or S3 states) is 3 s. It was also observed that in a sequence of flashes the peak positions of the Q and B bands do not depend on the advancement of the water-splitting system from the S2 state to the S3 state. This result implies that the midpoint potential of the water-splitting system remains unmodified during the S2 → S3 transition.  相似文献   

2.
Thermoluminescence and delayed luminescence investigations of the autotrophically and photoheterotrophically cultivated green alga, Chlamydobotrys stellata, demonstrated that both the thermoluminescence and delayed luminescence yields are much lower in the photoheterotophic algae than in the autotrophic ones due to an efficient luminescence quenching of unknown mechanism. The relative contributions of the so called Q (S2Q?A charge recombination) and B (S2Q?B and S3Q?B charge recombinations) thermoluminescence bands to the glow curve as well as the QA(S2Q?B charge recombination) and QB (S2Q?B and S3Q?B charge recombinations) delayed luminescence components to the delayed luminescence decay of autotrophically and photoheterotrophically cultivated Chl. stellata were compared using a computer assisted curve resolution method. It was found that, while in the autotrophic cells the area of the B band was considerably larger than of the Q band, in photoheterotrophic cells the Q band was more effectively charged than the B band. In the delayed luminescence decay curves measured in the seconds to minutes time region the amplitude of the QA component relative to that of the QB component was larger in the photoheterotrophic cells than in the autotrophic ones. These observations demonstrate that, after light-induced charge separation in the photosystem II reaction centers of autotrophic cells, electrons are “quasipermanently” stored mainly in the secondary quinone acceptor pool, QB but in the nonquenched photosystem II reaction centers of photoheterotrophic cells the main reservoir of electrons is the primary quinone acceptor, QA. This behaviour indicates an inhibition of electron transport in the photoheterotrophic alga at the level of the secondary quinone acceptor, QB.  相似文献   

3.
H.Y. Nakatani  A.W. Rutherford  Y. Inoue 《BBA》1984,766(2):416-423
In this paper, we present the first measurements on thermoluminescence from isolated thylakoids to probe the recombination reactions of S2 (or possibly S3) with Q?B or Q?A, after bicarbonate depletion and its readdition. The effects of bicarbonate depletion on the S2Q?B (or S3O?B) thermoluminescence band was (1) a 6–10°C shift to a higher temperature; (2) a reduction in its intensity upon prolonged depletion; and (3) elimination after the first few flashes of the characteristic period four oscillations in its intensity as a function of the flash number. On the other hand, addition of diuron (3-(3′,4′-dichlorophenyl)-1,1-dimethylurea), which blocks electron flow from Q?A to QB, produced the same thermoluminescence band, at about + 20°C, assigned to S2Q?A recombination, in both depleted and reconstituted samples. These results suggest (1) the initial effect of bicarbonate depletion is to increase the activation energy for S2(S3)Q?B recombination; (2) with further depletion, the incidence of this recombination decreases and the cycling of the S2Q?B and S3Q?B recombination is inhibited through effects at the QB apoprotein; and (3) the depletion effects are fully reversible. It is suggested that a conformational change of the PS II complex in the region of the QB apoprotein is responsible for these effects.  相似文献   

4.
The influence of UV-B irradiation on photosynthetic oxygen evolution by isolated spinach thylakoids has been investigated using thermoluminescence measurements. The thermoluminescence bands arising from the S2QB - (B band) and S2QA (Q band) charge recombination disappeared with increasing UV-B irradiation time. In contrast, the C band at 50°C, arising from the recombination of QA - with an accessory donor of Photosystem II, was transiently enhanced by the UV-B irradiation. The efficiency of DCMU to block QA to QB electron transfer decreased after irradiation as detected by the incomplete suppression of the B band by DCMU. The flash-induced oscillatory pattern of the B band was modified in the UV-B irradiated samples, indicating a decrease in the number of centers with reduced QB. Based on the results of this study, UV-B irradiation is suggested to damage both the donor and acceptor sides of Photosystem II. The damage of the water-oxidizing complex does not affect a specific S-state transition. Instead, charge stabilization is enhanced on an accessory donor. The acceptor-side modifications decrease the affinity of DCMU binding. This effect is assumed to reflect a structural change in the QB/DCMU binding site. The preferential loss of dark stable QB - may be related to the same structural change or could be caused by the specific destruction of reduced quinones by the UV-B light.Abbreviations Chl chlorophyll - DCMU 3-(3,4,-dichlorophenyl)-1,1-dimethylurea - PS II Photosystem II - QA first quinone electron acceptor of PS II - QB second quinone electron acceptor of PS II - Tyr-D accessory electron donor of PS II - S0-S4 charge storage states of the water-oxidizing complex  相似文献   

5.
The effect of desiccation and rehydration on the function of Photosystem II has been studied in the desiccation tolerant lichen Cladonia convoluta by thermoluminescence. We have shown that in functional fully hydrated thalli thermoluminescence signals can be observed from the recombination of the S2(3)QB (B band), S2QA (Q band), Tyr-D+QA (C band) and Tyr-Z+(His+)QA (A band) charge stabilization states. These thermoluminescence signals are completely absent in desiccated thalli, but rapidly reappear on rehydration. Flash-induced oscillation in the amplitude of the thermoluminescence band from the S2(3)QB recombination shows the usual pattern with maxima after 2 and 6 flashes when rehydration takes place in light. However, after rehydration in complete darkness, there is no thermoluminescence emission after the 1 st flash, and the maxima of the subsequent oscillation are shifted to the 3rd and 7th flashes. It is concluded that desiccation of Cladonia convoluta converts PS II into a nonfunctional state. This state is characterized by the lack of stable charge separation and recombination, as well as by a one-electron reduction of the water-oxidizing complex. Restoration of PS II function during rehydration can proceed both in the light and in darkness. After rehydration in the dark, the first charge separation act is utilized in restoring the usual oxidation state of the water-oxidizing comples.Abbreviations Chl chlorophyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DT desiccation tolerant - PS II Photosystem II - TL thermoluminescence - P680 reaction center Chl of PS II - QA and QB puinone electron acceptors of PS II - S0,...,S4 the redox states of the water-oxidizing complex - Tyr-Z and Tyr-D redox-active tyrosine electron donors of PS II  相似文献   

6.
A.W. Rutherford  A.R. Crofts  Y. Inoue 《BBA》1982,682(3):457-465
A single flash given at − 15°C to chloroplasts results in charge separation in Photosystem II to form a stable state which, upon warming, recombines giving rise to luminescence. This recombination occurs at 25°C in untreated chloroplasts but is shifted to 0°C in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea or weak concentrations of a reducing agent. The luminescence at 0°C is attributed to recombination of the S2QA state while that at 25°C is attributed to recombination of S2QAQB (and S3QAQB upon further flash illumination). The identification of the thermoluminescence at 25°C is based upon the following experimental evidence: (1) illumination of chloroplasts in the presence of methyl viologen with 710 nm light before and after flash illumination has no effect on the extent or temperature of the thermoluminescence. This is taken as evidence that the plastoquinone pool is not involved in the recombination reaction. (2) Calculations of the extent of thermoluminescence expected after a number of flashes, assuming that S2QAQB and S3QAQB are the thermoluminescent reactants, give a good fit to the experimental results. (3) The effect of continuous illumination at 77 K (i.e., donation from cytochrome b-559 to QA and thence to QB or QB) results in predictable changes in the extent of flash-induced thermoluminescence.  相似文献   

7.
The nature of Cu2+ inhibition of photosystem II (PSII) photochemistry in pea (Pisum sativum L.) thylakoids was investigated monitoring Hill activity and light emission properties of photosystem II. In Cu2+-inhibited thylakoids, diphenyl carbazide addition does not relieve the loss of Hill activity. The maximum yield of fluorescence induction restored by hydroxylamine in Tris-inactivated thylakoids is markedly reduced by Cu2+. This suggests that Cu2+ does not act on the donor side of PSII but on the reaction center of PSII or on components beyond. Thermoluminescence and delayed luminescence studies show that charge recombination between the positively charged intermediate in water oxidation cycle (S2) and negatively charged primary quinone acceptor of pSII (QA) is largely unaffected by Cu2+. The S2QB charge recombination, however, is drastically inhibited which parallels the loss of Hill activity. This indicates that Cu2+ inhibits photosystem II photochemistry primarily affecting the function of the secondary quinone electron acceptor, QB. We suggest that Cu2+ does not block electron flow between the primary and secondary quinone acceptor but modifies the QB site in such a way that it becomes unsuitable for further photosystem II photochemistry.  相似文献   

8.
Luminescence decaying in the seconds to minutes time scale was studied in spinach chloroplasts and the following results were obtained: (1) After a series of flashes a slow phase which decays in the tens of seconds to minutes time scale was observed to oscillate with a pattern characteristic of S2Q?B and S3Q?B recombination. This phase was lost upon Tris-treatment or upon the addition of DCMU. (2) After every flash a small faster phase of luminescence decaying in the seconds time scale was also present. This phase progressively increased with increasing numbers of flashes but when methyl viologen was present no such progressive increase of this phase occurred. In the presence of DCMU this seconds time scale luminescence was greatly increased. This phase of luminescence is attributed to S2Q?A recombination. (3) Tris-treatment resulted in the appearance of an even faster phase of luminescence which may be due to Z+Q?B recombination. These results demonstrate a close correlation of the kinetics of luminescence decay with thermoluminescence emission temperature.  相似文献   

9.
《BBA》1987,892(2):224-235
The effects of Cl depletion and removal of the 33 kDa extrinsic protein on the charge stabilization in O2-evolving Photosystem II (PS II) particles were studied by curve fitting and deconvolution of thermoluminescence bands. The following results were obtained. (1) Cl depletion reversibly decreases the redox potential of the S2 state by 60–80 mV, and thereby elevates the recombination temperature of both S2QB and S2QA charge pairs. (2) Removal of the 33 kDa extrinsic protein specifically elevates the recombination temperature of the S2QA charge pair, with practically no effect on the S2QB pair. This was tentatively interpreted as showing that the protein removal decreases the redox potential of both S2 and QB, but not of QA, and, thus, the effects are mutually cancelled for the S2QB pair, but are manifested for the S2QA pair. (3) Deconvolution of glow curves demonstrated that S3 is not formed in Cl-depleted PS II, but is formed in 33 kDa protein-depleted PS II even at a low (20 mM) Cl concentration. Analysis of thermoluminescence oscillations confirmed that Cl depletion interrupts S2-S3 transition, whereas the protein removal interrupts S3-(S4)-S0 transition at mM Cl. (4) Cl depletion by SO2−4 replacement in the absence of 33 kDa protein affected thermoluminescence in a different way from that in the presence of the protein. Based on these findings, the properties of charge pairs in the Cl-depleted PS II particles were discussed in relation to the role of the 33 kDa extrinsic protein.  相似文献   

10.
Ruthenium red (RR) is known to be an inhibitor that binds to Ca2+ sites. It releases Ca2+ and Cl? together with the extrinsic polypeptide of 17 kDa associated with the oxygen evolving complex of photosystem II. In this work we used thermoluminescence to study S2/3QB? and S2QA? charge recombination. It is shown that RR produced a deeper inhibition of oxygen evolution compared with the effect of extrinsic polypeptide or Ca2+/Cl? depletion. Even though Mn is not released, the Mn cluster is disorganized by RR and the S1 → S2 transition is inhibited. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

11.
Formation of thermoluminescence signals is characteristics of energy- and charge storage in Photosystem II. In isolated D1/D2/cytochrome b-559 Photosystem II reaction centre preparation four thermoluminescence components were found. These appear at -180 (Z band), between -80 and -50 (Zv band), at -30 and at +35°C. The Z band arises from pigment molecules but not correlated with photosynthetic activity. The Zv and -30°C bands arise from the recombination of charge pairs stabilized in the Photosystem II reaction centre complex. The +35°C band probably corresponds to the artefact glow peak resulting from a pigment-protein-detergent interaction in subchloroplast preparations (Rózsa Zs, Droppa M and Horváth G (1989) Biochim Biophys Acta 973, 350–353).Abbreviations Chl chlorophyll - Cyt cytochrome - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - D1 psbA gene product - D2 psbD gene product - P680 primary electron donor of PS II - Pheo pheophytin - PS II Photosystem II - QA primary quinone acceptor of PS II - QB secondary quinone acceptor of PS II - RC reaction centre of PS II - TL thermoluminescence  相似文献   

12.
Photosystem II particles were exposed to 800 W m–2 white light at 20 °C under anoxic conditions. The Fo level of fluorescence was considerably enhanced indicating formation of stable-reduced forms of the primary quinone electron acceptor, QA. The Fm level of fluorescence declined only a little. The g=1.9 and g=1.82 EPR forms characteristic of the bicarbonate-bound and bicarbonate-depleted semiquinone-iron complex, QA Fe2+, respectively, exhibited differential sensitivity against photoinhibition. The large g=1.9 signal was rapidly diminished but the small g=1.82 signal decreased more slowly. The S2-state multiline signal, the oxygen evolution and photooxidation of the high potential form of cytochrome b-559 were inhibited approximately with the same kinetics as the g=1.9 signal. The low potential form of oxidized cytochrome b-559 and Signal IIslow arising from TyrD + decreased considerably slower than the g=1.9 semiquinone-iron signal. The high potential form of oxidized cytochrome b-559 was diminished faster than the low potential form. Photoinhibition of the g=1.9 and g=1.82 forms of QA was accompanied with the appearance and gradual saturation of the spin-polarized triplet signal of P 680. The amplitude of the radical signal from photoreducible pheophytin remained constant during the 3 hour illumination period. In the thermoluminescence glow curves of particles the Q band (S2QA charge recombination) was almost completely abolished. To the contrary, the C band (TyrD +QA charge recombination) increased a little upon illumination. The EPR and thermoluminescence observations suggest that the Photosystem II reaction centers can be classified into two groups with different susceptibility against photoinhibition.Abbreviations C band thermoluminescence band associated with Tyr-D+Q a charge recombination - Chl chlorophyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - EPR electron paramagnetic resonance - Fo initial fluorescence - Fm maximum fluorescence - Q band thermoluminescence band originating from S2Q a -charge recombination - Q a the primary quinone electron acceptor of PS II - P 680 the primary electron donor chlorophyll of PS II - S2 oxidation state of the water-splitting system - Phe pheophytin - TL thermoluminescence - Tyr d redox active tyrosine-160 of the D2 protein  相似文献   

13.
Photosystem II membranes were isolated from chloroplasts of pokeweed (Phytolacca americana) and rendered deficient in Ca2+, an inorganic cofactor of photosynthetic water oxidation. The thermoluminescence properties of such membranes were found to depend on the Ca2+-depleting method used. This feature was analyzed with respect to the thermoluminescence emission that accompanied the recombination reaction between the reduced acceptor QA and the oxidant of the S2 state. It was determined that the differences observed among various preparations of Ca2+-depleted membranes were attributable to the presence or absence of the extrinsic 23 kDa polypeptide on the membranes. The binding of this polypeptide to Ca2+-depleted membranes devoid of the 17 and 23 kDa extrinsic polypeptides caused the thermoluminescence to be emitted at a higher temperature due to a further stabilization of an already abnormally stable S2 state. Addition of the chelators EDTA or EGTA and of citrate brought about a similar response. The conditions required for the upshift of the emission temperature of thermoluminescence strongly resembled those identified by Boussac et al. (FEBS Lett. 277 (1990) 69–74) as responsible for modifying the EPR multiline signal from the S2 state of Ca2+-depleted PS II membranes. Consistent with the authors' interpretation of the reason for this modification, we conclude that the elevated emission temperature of the thermoluminescence emission reflects an abnormal ligand environment of the Mn-center in PS II that may be created by a direct ligation of the added agents to Mn. Evidence is also presented that the return to a normal S2 after an addition of Ca2+ occurs via yet another condition of S2 which, in terms of its thermoluminescence properties, resembles that of Ca2+-depleted membranes before addition of modifying agents, but is not identical to it.  相似文献   

14.
The photosystem Ⅱ (PSII) complex of photosynthetic membranes comprises a number of chlorophyll-binding proteins that are important to the electron flow. Here we report that the chlorophyll b-deficient mutant has decreased the amount of light-harvesting complexes with an increased amount of some core polypeptldes of PSII, including CP43 and CP47. By means of chlorophyll fluorescence and thermolumlnescence, we found that the ratio of Fv/Fm, qP and electron transport rate in the chlorophyll b-deficient mutant was higher compared to the wild type. In the chlorophyll lPdeflclent mutant, the decay of the primary electron acceptor quinones (QA-) reoxidation was decreased, measured by the fluorescence. Furthermore, the thermoluminescence studies in the chlorophyll bdeficient mutant showed that the B band (S2/S3QB-) decreased slightly and shifted up towards higher temperatures. In the presence of dlchlorophenyl-dlmethylurea, which is inhibited in the electron flow to the second electron acceptor quinines (QB) at the PSll acceptor side, the maximum of the Q band (S2QA-) was decreased slightly and shifted down to lower temperatures, compared to the wild type. Thus, the electron flow within PSll of the chlorophyⅡ b-deficient mutant was down-regulated and characterized by faster oxidation of the primary electron acceptor quinine QA-via forward electron flow and slower reduction of the oxidation S states.  相似文献   

15.
The action of the environmental toxic Pb2+ on photosynthetic electron transport was studied in thylakoid membranes isolated from spinach leaves. Fluorescence and thermoluminescence techniques were performed in order to determine the mode of Pb2+ action in photosystem II (PSII). The invariance of fluorescence characteristics of chlorophyll a (Chl a) and magnesium tetraphenylporphyrin (MgTPP), a molecule structurally analogous to Chl a, in the presence of Pb2+ confirms that Pb cation does not interact directly with chlorophyll molecules in PSII. The results show that Pb interacts with the water oxidation complex thus perturbing charge recombination between the quinone acceptors of PSII and the S2 state of the Mn4Ca cluster. Electron transfer between the quinone acceptors QA and QB is also greatly retarded in the presence of Pb2+. This is proposed to be owing to a transmembrane modification of the acceptor side of the photosystem.  相似文献   

16.
Misra  A.N.  Dilnawaz  F.  Misra  M.  Biswal  A.K. 《Photosynthetica》2001,39(1):1-9
Thermoluminescence (TL) in green plants arises from charge recombination of charged molecules in the reaction centre (RC) of photosystem 2 (PS2) in chloroplasts. The TL technique is used for detection of alterations in the architecture of PS2 RCs. The donor side 'S-states' and the acceptor side quinone molecules (QA and QB) are involved the charge recombination processes of PS2. High temperature (70–75 °C) glow peaks are also used to detect non-photosynthetic peroxidation processes in thylakoid membranes. The TL peaks with their characteristic charge recombination can be utilised for the study of chloroplast development, ageing, chemical, biotic, and abiotic stress induced alterations in the PS2 RC and for the study of the primary photochemical events of photosynthesis. The technique has been used successfully in the characterisation of transgenic plants in the study of genetically engineered organisms.  相似文献   

17.
The functional properties of a purified homogeneous spinach PS II-core complex with high oxygen evolution capacity (Haag et al. 1990a) were investigated in detail by measuring thermoluminescence and oscillation patterns of flash induced oxygen evolution and fluorescence quantum yield changes. The following results were obtained:
  1. Depending on the illumination conditions the PS II-core complexes exhibit several thermoluminescence bands corresponding to the A band, Q band and Zv band in PS II membrane fragments. The lifetime of the Q band (Tmax=10°C) was determined to be 8s at T=10°C. No B band corresponding to S2QB ? or S3QB ? recombination could be detected.
  2. The flash induced transient fluorescence quantum yield changes exhibit a multiphasi relaxation kinetics shich reflect the reoxidation of Q A ? . In control samples without exogenous acceptors this process is markedly slower than in PS II membrane fragments. The reaction becomes significantly retarded by addition of 10 μM DCMU. After dark incubation in the presence of K3[Fe(CN)6
  3. Excitation of dark-adapted samples with a train of short saturating flashes gives rise to a typical pattern dominated by a high O2 yield due to the third flash and a highly damped period four oscillation. The decay of redox states S2 and S3 are dominated by short life times of 4.3 s and 1.5 s, respectively, at 20°C.
The results of the present study reveal that in purified homogeneous PS II-core complexes with high oxygen evolution isolated from higher plants by β-dodecylmaltoside solubilization the thermodynamic properties and the kinetic parameters of the redox groups leading to electron transfer from water to QA are well preserved. The most obvious phenomenon is a severe modification of the QB binding site. The implications of this finding are discussed.  相似文献   

18.
Characteristics of thermoluminescence glow curves were compared in three types of Euglena cells: (i) strictly autotrophic, Cramer and Myers cells; (ii) photoheterotrophic cells sampled from an exponentially growing culture containing lactate as substrate repressing the photosynthetic activity; (iii) semiautotrophic cells, sampled when the lactate being totally exhausted, the photosynthesis was enhanced.In autotrophic and semiautotrophic cells, composite curves were observed after series of two or more actinic flashes fired at –10°C, which can be deconvoluted into a large band peaking in the range 12–22°C and a smaller one near 40°C, This second band presents the characteristics of a typical B band (due to S2/3QB - recombination), whereas the first one resembled the band, shifted by -15–20°C, which is observed in herbicide resistant plants. The amplitude of this major band, which was in all cases very low after one flash, exhibited oscillations of period four but rapidly damping, with maxima after two and six flashes. In contrast, photoheterotrophic Euglena displayed single, non-oscillating curves with maxima in the range 5–10°C.In autotrophic and semiautotrophic cells, oxidizing pretreatments by either a preillumination with one or more (up to twenty-five) flashes, or a far-red preillumination in the presence of methylviologen, followed by a short dark period, induced thermoluminescence bands almost single and shifted by +3–5°C, or +12°C, respectively. In autotrophic cells, far-red light plus methyl viologen treatment induced a band peaking at 31°C, as in isolated thylakoids from Euglena or higher plants, while it had barely any effect in photoheterotrophic cells.Due to metabolic activities in dark-adapted cells, a reduction of redox groups at the donor and acceptor sides of PS II dark-adapted cells is supposed to occur. Two different explanations can be proposed to explain such a shift in the position of the main band in dark-adapted autotrophic control. The first explanation would be that in these reducing conditions a decreasing value of the equilibrium constant for the reaction: SnQA -QBSnQAQB -, would determine the shift of the main TL band towards low temperatures, as observed in herbicide resistant material. The second explanation would be that the main band would correspond to peak III already observed in vivo and assigned to S2/3QB 2- recombinations.Abbreviations CM Cramer and Myers - D1 a 32 kDa protein component of the PS II reaction center, psbA.gene product - D2 a 34 kDa protein component of the PS II reaction center, psbD gene product - FR lar-red illumination - Lexpo and Lstat cells from lactate culture samples at exponential and stationary phase of growth - MV methylviologen - pBQ parabenzoquinone - PQ plastoquinone - PS II photosystem II - QA primary quinone electron acceptor - QB secondary quinone electron acceptor - TL thermoluminescence  相似文献   

19.
Thermoluminescence experiments have been carried out to study the effect of a transmembrane proton gradient on the recombination properties of the S2 and S3 states of the oxygen evolving complex with QA - and QB -, the reduced electron acceptors of Photosystem II. We first determined the properties of the S2QA - (Q band), S2QB - and S3QB - (B bands) recombinations in the pH range 5.5 to 9.0, using uncoupled thylakoids. The, a proton gradient was created in the dark, using the ATP-hydrolase function of ATPases, in coupled unfrozen thylakoids. A shift towards low temperature of both Q and B bands was observed to increase with the magnitude of the proton gradient measured by the fluorescence quenching of 9-aminoacridine. This downshift was larger for S3QB - than for S2QB - and it was suppressed by nigericin, but not by valinomycin. Similar results were obtained when a proton gradient was formed by photosystem I photochemistry. When Photosystem II electron transfer was induced by a flash sequence, the reduction of the plastoquinone pool also contributed to the downshift in the absence of an electron acceptor. In leaves submitted to a flash sequence above 0°C, a downshift was also observed, which was supressed by nigericin infiltration. Thus, thermoluminescence provides direct evidence on the enhancing effect of lumen acidification on the S3S2 and S2S1 reverse-transitions. Both reduction of the plastoquinone pool and lumen acidification induce a shift of the Q and B bands to lower temperature, with a predominance of lumen acidification in non-freezing, moderate light conditions.Abbreviations 9-AA 9-aminoacridine - EA activation energy - F0 constant fluorescence level - FM maximum fluorescence, when all PS-II centers are closed - FV variable fluorescence (FM–F0) - PS I, PS II Photosystem I, photosystem II - PQ plastoquinone - TL thermoluminescence  相似文献   

20.
The pH dependence of emission peak temperature and decay time of thermoluminescence arising from S2QB and S2QA recombinations demonstrates that a stabilization of S2QB occurs at low pH whereas stabilization of S2QA occurs at high pH. Based on comparative analysis of thermoluminescence parameters of the two types of recombination, we suggest that in the pH range between 5.3 and 7.5, Em(S2/S1) and Em(QA/QA ) are constant, but Em(QB/QB ) gradually increases with decreasing pH, while in the pH range between 7.5 and 8.5, an unusual change occurs on S2QA charge pair, which is interpreted as either a decrease in Em(S2/S1) or an increase in Em(QA/QA ).  相似文献   

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