共查询到20条相似文献,搜索用时 671 毫秒
1.
Alain Gauthier 《BBA》2006,1757(11):1547-1556
The flash-induced thermoluminescence (TL) technique was used to investigate the action of N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) on charge recombination in photosystem II (PSII). Addition of low concentrations (μM range) of TMPD to thylakoid samples strongly decreased the yield of TL emanating from S2QB− and S3QB− (B-band), S2QA− (Q-band), and YD+QA− (C-band) charge pairs. Further, the temperature-dependent decline in the amplitude of chlorophyll fluorescence after a flash of white light was strongly retarded by TMPD when measured in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Though the period-four oscillation of the B-band emission was conserved in samples treated with TMPD, the flash-dependent yields (Yn) were strongly declined. This coincided with an upshift in the maximum yield of the B-band in the period-four oscillation to the next flash. The above characteristics were similar to the action of the ADRY agent, carbonylcyanide m-chlorophenylhydrazone (CCCP). Simulation of the B-band oscillation pattern using the integrated Joliot-Kok model of the S-state transitions and binary oscillations of QB confirmed that TMPD decreased the initial population of PSII centers with an oxidized plastoquinone molecule in the QB niche. It was deduced that the action of TMPD was similar to CCCP, TMPD being able to compete with plastoquinone for binding at the QB-site and to reduce the higher S-states of the Mn cluster. 相似文献
2.
The functional state of the Photosystem (PS) II complex in Arabidopsis psbR T-DNA insertion mutant was studied. The ΔPsbR thylakoids showed about 34% less oxygen evolution than WT, which correlates with the amounts of PSII estimated from YDox radical EPR signal. The increased time constant of the slow phase of flash fluorescence (FF)-relaxation and upshift in the peak position of the main TL-bands, both in the presence and in the absence of DCMU, confirmed that the S2QA− and S2QB− charge recombinations were stabilized in ΔPsbR thylakoids. Furthermore, the higher amount of dark oxidized Cyt-b559 and the increased proportion of fluorescence, which did not decay during the 100s time span of the measurement thus indicating higher amount of YD+QA− recombination, pointed to the donor side modifications in ΔPsbR. EPR measurements revealed that S1-to-S2-transition and S2-state multiline signal were not affected by mutation. The fast phase of the FF-relaxation in the absence of DCMU was significantly slowed down with concomitant decrease in the relative amplitude of this phase, indicating a modification in QA to QB electron transfer in ΔPsbR thylakoids. It is concluded that the lack of the PsbR protein modifies both the donor and the acceptor side of the PSII complex. 相似文献
3.
Treatment with the herbicide acifluorfen-sodium (AF-Na), an inhibitor of protoporphyrinogen oxidase, caused an accumulation of protoporphyrin IX (Proto IX) , light-induced necrotic spots on the cucumber cotyledon within 12-24 h, and photobleaching after 48-72 h of light exposure. Proto IX-sensitized and singlet oxygen (1O2)-mediated oxidative stress caused by AF-Na treatment impaired photosystem I (PSI), photosystem II (PSII) and whole chain electron transport reactions. As compared to controls, the Fv/Fm (variable to maximal chlorophyll a fluorescence) ratio of treated samples was reduced. The PSII electron donor NH2OH failed to restore the Fv/Fm ratio suggesting that the reduction of Fv/Fm reflects the loss of reaction center functions. This explanation is further supported by the practically near-similar loss of PSI and PSII activities. As revealed from the light saturation curve (rate of oxygen evolution as a function of light intensity), the reduction of PSII activity was both due to the reduction in the quantum yield at limiting light intensities and impairment of light-saturated electron transport. In treated cotyledons both the Q (due to recombination of QA− with S2) and B (due to recombination of QB− with S2/S3) band of thermoluminescence decreased by 50% suggesting a loss of active PSII reaction centers. In both the control and treated samples, the thermoluminescence yield of B band exhibited a periodicity of 4 suggesting normal functioning of the S states in centers that were still active. The low temperature (77 K) fluorescence emission spectra revealed that the F695 band (that originates in CP-47) increased probably due to reduced energy transfer from the CP47 to the reaction center. These demonstrated an overall damage to the PSI and PSII reaction centers by 1O2 produced in response to photosensitization reaction of protoporphyrin IX in AF-Na-treated cucumber seedlings. 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.
6.
Krisztián Cser 《BBA》2007,1767(3):233-243
The mechanism of charge recombination was studied in Photosystem II by using flash induced chlorophyll fluorescence and thermoluminescence measurements. The experiments were performed in intact cells of the cyanobacterium Synechocystis 6803 in which the redox properties of the primary pheophytin electron acceptor, Phe, the primary electron donor, P680, and the first quinone electron acceptor, QA, were modified. In the D1Gln130Glu or D1His198Ala mutants, which shift the free energy of the primary radical pair to more positive values, charge recombination from the S2QA− and S2QB− states was accelerated relative to the wild type as shown by the faster decay of chlorophyll fluorescence yield, and the downshifted peak temperature of the thermoluminescence Q and B bands. The opposite effect, i.e. strong stabilization of charge recombination from both the S2QA− and S2QB− states was observed in the D1Gln130Leu or D1His198Lys mutants, which shift the free energy level of the primary radical pair to more negative values, as shown by the retarded decay of flash induced chlorophyll fluorescence and upshifted thermoluminescence peak temperatures. Importantly, these mutations caused a drastic change in the intensity of thermoluminescence, manifested by 8- and 22-fold increase in the D1Gln130Leu and D1His198Lys mutants, respectively, as well as by a 4- and 2.5-fold decrease in the D1Gln130Glu and D1His198Ala mutants, relative to the wild type, respectively. In the presence of the electron transport inhibitor bromoxynil, which decreases the redox potential of QA/QA− relative to that observed in the presence of DCMU, charge recombination from the S2QA− state was accelerated in the wild type and all mutant strains. Our data confirm that in PSII the dominant pathway of charge recombination goes through the P680+Phe− radical pair. This indirect recombination is branched into radiative and non-radiative pathways, which proceed via repopulation of P680* from 1[P680+Ph−] and direct recombination of the 3[P680+Ph−] and 1[P680+Ph−] radical states, respectively. An additional non-radiative pathway involves direct recombination of P680+QA−. The yield of these charge recombination pathways is affected by the free energy gaps between the Photosystem II electron transfer components in a complex way: Increase of ΔG(P680* ↔ P680+Phe−) decreases the yield of the indirect radiative pathway (in the 22-0.2% range). On the other hand, increase of ΔG(P680+Phe− ↔ P680+QA−) increases the yield of the direct pathway (in the 2-50% range) and decreases the yield of the indirect non-radiative pathway (in the 97-37% range). 相似文献
7.
Characterization of photosystem II in salt-stressed cyanobacterial Spirulina platensis cells 总被引:2,自引:0,他引:2
PSII activity was inhibited after Spirulina platensis cells were incubated with different salt concentrations (0-0.8 M NaCl) for 12 h. Flash-induced fluorescence kinetics showed that in the absence of DCMU, the half time of the fast and slow components decreased while that of the middle component increased considerably with increasing salt concentration. In the presence of DCMU, fluorescence relaxation was dominated by a 0.6s component in control cells. After salt stress, this was partially replaced by a faster new component with half time of 20-50 ms. Thermoluminescence measurements revealed that S(2)Q(A)(-) and S(2)Q(B)(-) recombinations were shifted to higher temperatures in parallel and the intensities of the thermoluminescence emissions were significantly reduced in salt-stressed cells. The period-four oscillation of the thermoluminescence B band was highly damped. There were no significant changes in contents of CP47, CP43, cytochrome c550, and D1 proteins. However, content of the PsbO protein in thylakoid fraction decreased but increased significantly in soluble fraction. The results suggest that salt stress leads to a modification of the Q(B) niche at the acceptor side and an increase in the stability of the S(2) state at the donor side, which is associated with a dissociation of the PsbO protein. 相似文献
8.
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
9.
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
10.
Hajnalka Laczkó-Dobos Bettina Ughy Szilvia Z. Tóth Ottó Zsiros Árpád Párducz Masayuki Komura Zoltán Gombos 《BBA》2008,1777(9):1184-1194
To analyze the role of phosphatidylglycerol (PG) in photosynthetic membranes of cyanobacteria we used two mutants of Synechocystis sp. PCC6803: the PAL mutant which has no phycobilisomes and shows a high PSII/PSI ratio, and a mutant derived from it by inactivating its cdsA gene encoding cytidine 5'-diphosphate diacylglycerol synthase, a key enzyme in PG synthesis. In a medium supplemented with PG the PAL/ΔcdsA mutant cells grew photoautotrophically. Depletion of PG in the medium resulted (a) in an arrest of cell growth and division, (b) in a slowdown of electron transfer from the acceptor QA to QB in PSII and (c) in a modification of chlorophyll fluorescence curve. The depletion of PG affected neither the redox levels of QA nor the S2 state of the oxygen-evolving manganese complex, as indicated by thermoluminescence studies. Two-dimensional PAGE showed that in the absence of PG (a) the PSII dimer was decomposed into monomers, and (b) the CP43 protein was detached from a major part of the PSII core complex. [35S]-methionine labeling confirmed that PG depletion did not block de novo synthesis of the PSII proteins. We conclude that PG is required for the binding of CP43 within the PSII core complex. 相似文献
11.
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
12.
Jun-Wei Guo Jin-Kui Guo Yun Zhao Lin-Fang Du 《植物学报(英文版)》2007,49(5):698-705
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
13.
Alberto Mezzetti Eliane NabedrykJacques Breton Melvin Y. OkamuraMark L. Paddock Giovanni GiacomettiWinfried Leibl 《BBA》2002,1553(3):320-330
Rapid-scan Fourier transform infrared (FTIR) difference spectroscopy was used to investigate the electron transfer reaction QA−QB→QAQB− (kAB(1)) in mutant reaction centers of Rhodobacter sphaeroides, where Asp-L210 and/or Asp-M17 have been replaced with Asn. Mutation of both residues decreases drastically kAB(1), attributed to slow proton transfer to Glu-L212, which becomes rate limiting for electron transfer to QB [M.L. Paddock et al., Biochemistry 40 (2001) 6893]. In the double mutant, the FTIR difference spectrum recorded during the time window 4-29 ms following a flash showed peaks at 1670 (−), 1601 (−) and 1467 (+) cm−1, characteristic of QA reduction. The time evolution of the spectra shows reoxidation of QA− and concomitant reduction of QB with a kinetics of about 40 ms. In native reaction centers and in both single mutants, formation of QB− occurs much faster than in the double mutant. Within the time resolution of the technique, protonation of Glu-L212, as characterized by an absorption increase at 1728 cm−1 [E. Nabedryk et al., Biochemistry 34 (1995) 14722], was found to proceed with the same kinetics as reduction of QB in all samples. These rapid-scan FTIR results support the model of proton uptake being rate limiting for the first electron transfer from QA− to QB and the identification of Glu-L212 as the main proton acceptor in the state QAQB−. 相似文献
14.
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 S2Q−A state while that at 25°C is attributed to recombination of S2QAQ−B (and S3QAQ−B 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 S2QAQ−B and S3QAQ−B 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 Q−B) results in predictable changes in the extent of flash-induced thermoluminescence. 相似文献
15.
The main cofactors involved in the function of Photosystem II (PSII) are borne by the D1 and D2 proteins. In some cyanobacteria, the D1 protein is encoded by different psbA genes. In Thermosynechococcus elongatus the amino acid sequence deduced from the psbA3 gene compared to that deduced from the psbA1 gene points a difference of 21 residues. In this work, PSII isolated from a wild type T. elongatus strain expressing PsbA1 or from a strain in which both the psbA1 and psbA2 genes have been deleted were studied by a range of spectroscopies in the absence or the presence of either a urea type herbicide, DCMU, or a phenolic type herbicide, bromoxynil. Spectro-electrochemical measurements show that the redox potential of PheoD1 is increased by 17 mV from −522 mV in PsbA1-PSII to −505 mV in PsbA3-PSII. This increase is about half that found upon the D1-Q130E single site directed mutagenesis in Synechocystis PCC 6803. This suggests that the effects of the D1-Q130E substitution are, at least partly, compensated for by some of the additional amino-acid changes associated with the PsbA3 for PsbA1 substitution. The thermoluminescence from the S2QA−• charge recombination and the C ≡ N vibrational modes of bromoxynil detected in the non-heme iron FTIR difference spectra support two binding sites (or one site with two conformations) for bromoxynil in PsbA3-PSII instead of one in PsbA1-PSII which suggests differences in the QB pocket. The temperature dependences of the S2QA−• charge recombination show that the strength of the H-bond to PheoD1 is not the only functionally relevant difference between the PsbA3-PSII and PsbA1-PSII and that the environment of QA (and, as a consequence, its redox potential) is modified as well. The electron transfer rate between P680+• and YZ is found faster in PsbA3 than in PsbA1 which suggests that the redox potential of the P680/P680+• couple (and hence that of 1P680*/P680+•) is tuned as well when shifting from PsbA1 to PsbA3. In addition to D1-Q130E, the non-conservative amongst the 21 amino acid substitutions, D1-S270A and D1-S153A, are proposed to be involved in some of the observed changes. 相似文献
16.
Taras K. Antal 《Biophysical journal》2009,96(11):4672-4680
The oxygen-evolving complex of Photosystem II cycles through five oxidation states (S0-S4), and dark incubation leads to 25% S0 and 75% S1. This distribution cannot be reached with charge recombination reactions between the higher S states and the electron acceptor QB−. We measured flash-induced oxygen evolution to understand how S3 and S2 are converted to lower S states when the electron required to reduce the manganese cluster does not come from QB−. Thylakoid samples preconditioned to make the concentration of the S1 state 100% and to oxidize tyrosine YD were illuminated by one or two laser preflashes, and flash-induced oxygen evolution sequences were recorded at various time intervals after the preflashes. The distribution of the S states was calculated from the flash-induced oxygen evolution pattern using an extended Kok model. The results suggest that S2 and S3 are converted to lower S states via recombination from S2QB− and S3QB− and by a slow change of the state of oxygen-evolving complex from S3 and S2 to S1 and S0 in reactions with unspecified electron donors. The slow pathway appears to contain two-electron routes, S2QB → S0QB, and S3QB → S1QB. The two-electron reactions dominate in intact thylakoid preparations in the absence of chemical additives. The two-electron reaction was replaced by a one-electron-per-step pathway, S3QB → S2QB → S1QB in PS II-enriched membrane fragments and in thylakoids measured in the presence of artificial electron acceptors. A catalase effect suggested that H2O2 acts as an electron donor for the reaction S2QB → S0QB but added H2O2 did not enhance this reaction. 相似文献
17.
18.
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
19.
Haijun Liu 《BBA》2009,1787(8):1029-1038
The Arabidopsis thaliana mutant psbo1 has recently been described and characterized. Loss of expression of the PsbO-1 protein leads to a variety of functional perturbations including elevated levels of the PsbO-2 protein and defects on both the oxidizing- and reducing-sides of Photosystem II. In this communication, two plant lines were produced using the psbo1 mutant as transgenic host, which contained an N-terminally histidine6-tagged PsbO-1 protein. This protein was expressed and correctly targeted into the thylakoid lumen. Immunological analysis indicated that different levels of expression of the modified PsbO-1 protein were obtained in different transgenic plant lines and that the level of expression in each line was stable over several generations. Examination of the Photosystem II closure kinetics demonstrated that the defective double reduction of QB and the delayed exchange of QBH2 with the plastoquinone pool which were observed during the characterization of the psbo1 mutant were effectively restored to wild-type levels by the His6-tagged PsbO-1 protein. Flash fluorescence induction and decay were also examined. Our results indicated that high expression of the modified PsbO-1 was required to increase the ratio of PS IIα/PS IIβ reaction centers to wild-type levels. Fluorescence decay kinetics in the absence of DCMU indicated that the expression of the His6-tagged PsbO-1 protein restored efficient electron transfer to QB, while in the presence of DCMU, charge recombination between QA− and the S2 state of the oxygen-evolving complex occurred at near wild-type rates. Our results indicate that high expression of the His6-tagged PsbO-1 protein efficiently complements nearly all of the photochemical defects observed in the psbo1 mutant. Additionally, this study establishes a platform on which the in vivo consequences of site-directed mutagenesis of the PsbO-1 protein can be examined. 相似文献
20.
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