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1.
In addition to the energy dissipation of excess light occurring in PSII antenna via the xanthophyll cycle, there is mounting
evidence of a zeaxanthin-independent pathway for non-photochemical quenching based within the PSII reaction centre (reaction
centre quenching) that may also play a significant role in photoprotection. It has been demonstrated that acclimation of higher
plants, green algae and cyanobacteria to low temperature or high light conditions which potentially induce an imbalance between
energy supply and energy utilization is accompanied by the development of higher reduction state of Q A and higher resistance to photoinhibition (Huner et al., 1998). Although this is a fundamental feature of all photoautotrophs,
and the acquisition of increased tolerance to photoinhibition has been ascribed to growth and development under high PSII
excitation pressure, the precise mechanism controlling the redox state of Q A and its physiological significance in developing higher resistance to photoinhibition has not been fully elucidated. In this
review we summarize recent data indicating that the increased resistance to high light in a broad spectrum of photosynthetic
organisms acclimated to high excitation pressure conditions is associated with an increase probability for alternative non-radiative
P680 +Q A
- radical pair recombination pathway for energy dissipation within the reaction centre of PSII. The various molecular mechanisms
that could account for non-photochemical quenching through PSII reaction centre are also discussed. 相似文献
2.
The inhibitory effect of Cr(VI) on the PSII of Synechocystis sp. was studied. Cr(VI) reduced O 2 evolution and inhibited the water‐splitting system in PSII. S‐states test and flash induction test showed that Cr(VI) exposure increased the proportion of inactivated PSII (PSII X) and PSII β reaction centers, which increased the fluxes of dissipated energy. JIP test and Q A? reoxidation test demonstrated that Cr(VI) treatment induces inhibition of electron transport from Q A? to Q B/Q B? and accumulation of P 680+. More Q A? had to be oxidized through S 2(Q AQ B) ? charge recombination and oxidation by PQ9 molecules in PSII under Cr(VI) stress. These changes finally decreased the index of photosynthesis performance. 相似文献
3.
Analysis of the partitioning of absorbed light energy within PSII into fractions utilized by PSII photochemistry (Ø PSII), thermally dissipated via ΔpH-and zeaxanthin-dependent energy quenching (Ø NPQ) and constitutive non-photochemical energy losses (Ø NO) was performed in wild type and F2 mutant of barley. The estimated energy partitioning of absorbed light to various pathways indicated that the fraction of Ø PSII was slightly higher, while the proportion of thermally dissipated energy through Ø NPQ was 38% lower in F2 mutant than in WT. In contrast, Ø NO, i.e. the fraction of absorbed light energy dissipated by additional quenching mechanism(s) was 34% higher in F2 mutant. The increased proportion of Ø NO correlated with narrowing the temperature gap (Δ TM) between S 2/3Q B− and S 2Q A− charge recombinations in F2 mutant as revealed by thermoluminescence measurements. We suggest that this would result in increased probability for an alternative non-radiative P680+Q A− radical pair recombination pathway for energy dissipation within the reaction centre of PSII (reaction center quenching) and that this additional quenching mechanism might play an important role in photoprotection when the capacity for the primary, zeaxanthin-dependent non-photochemical quenching (Ø NPQ) and state transitions pathways are restricted in the absence of LHCII polypeptides in F2 mutant.Key words: Energy partitioning, Non-photochemical quenching, Hordeum vulgare L., PSII photochemistry, QA, QB, Thermoluminescence 相似文献
4.
It has been demonstrated that antimony (Sb) at concentrations ranging from 1.0 to 10.0 mg L −1 inhibits O 2 evolution. Deeper insight into the influence of Sb on PSII was obtained with measurements of in vivo chlorophyll fluorescence.
The donor and the acceptor sides of PSII were shown to be the target of Sb. Sb treatment induces inhibition of electron transport
from Q A− to Q B/Q B− and accumulation of P 680+. S 2(Q AQ B) − charge recombination and oxidation by PQ9 molecules became more important in Q A− reoxidation as the electron transfer in PSII was inhibited. Sb exposure caused a steady increase in the proportion of PSII X and PSII β. These changes resulted in increased fluxes of dissipated energy and decreased index of photosynthesis performance, of maximum
quantum yield, and of the overall photosynthetic driving force of PSII. 相似文献
5.
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, P 680, and the first quinone electron acceptor, Q A, 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 S 2Q A− and S 2Q B− 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 S 2Q A− and S 2Q B− 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 Q A/Q A− relative to that observed in the presence of DCMU, charge recombination from the S 2Q A− 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 P 680+Phe − radical pair. This indirect recombination is branched into radiative and non-radiative pathways, which proceed via repopulation of P 680* from 1[P 680+Ph −] and direct recombination of the 3[P 680+Ph −] and 1[P 680+Ph −] radical states, respectively. An additional non-radiative pathway involves direct recombination of P 680+Q A−. 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 Δ G(P 680* ↔ P 680+Phe −) decreases the yield of the indirect radiative pathway (in the 22-0.2% range). On the other hand, increase of Δ G(P 680+Phe − ↔ P 680+Q A−) 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
6.
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
7.
The OJDIP rise in chlorophyll fluorescence during induction at different light intensities was mathematically modeled using 24 master equations describing electron transport through photosystem II (PSII) plus ordinary differential equations for electron budgets in plastoquinone, cytochrome f, plastocyanin, photosystem I, and ferredoxin. A novel feature of the model is consideration of electron in- and outflow budgets resulting in changes in redox states of Tyrosine Z, P680, and Q A as sole bases for changes in fluorescence yield during the transient. Ad hoc contributions by transmembrane electric fields, protein conformational changes, or other putative quenching species were unnecessary to account for primary features of the phenomenon, except a peculiar slowdown of intra-PSII electron transport during induction at low light intensities. The lower than F m post-flash fluorescence yield F f was related to oxidized tyrosine Z. The transient J peak was associated with equal rates of electron arrival to and departure from Q A and requires that electron transfer from Q A ? to Q B be slower than that from Q A ? to Q B ?. Strong quenching by oxidized P680 caused the dip D. Reduced plastoquinone, a competitive product inhibitor of PSII, blocked electron transport proportionally with its concentration. Electron transport rate indicated by fluorescence quenching was faster than the rate indicated by O 2 evolution, because oxidized donor side carriers quench fluorescence but do not transport electrons. The thermal phase of the fluorescence rise beyond the J phase was caused by a progressive increase in the fraction of PSII with reduced Q A and reduced donor side. 相似文献
8.
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 (S 2Q ?A charge recombination) and B (S 2Q ?B and S 3Q ?B charge recombinations) thermoluminescence bands to the glow curve as well as the Q A(S 2Q ?B charge recombination) and Q B (S 2Q ?B and S 3Q ?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 Q A component relative to that of the Q B 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, Q B but in the nonquenched photosystem II reaction centers of photoheterotrophic cells the main reservoir of electrons is the primary quinone acceptor, Q A. This behaviour indicates an inhibition of electron transport in the photoheterotrophic alga at the level of the secondary quinone acceptor, Q B. 相似文献
9.
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 S 2(3)Q B
– (B band), S 2Q A
– (Q band), Tyr-D +Q A
– (C band) and Tyr-Z +(His +)Q A
– (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 S 2(3)Q B
– 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
- P 680
reaction center Chl of PS II
- Q A and Q B
puinone electron acceptors of PS II
- S 0,...,S 4
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
10.
The temperature dependence of the electric field-induced chlorophyll luminescence in photosystem II was studied in Tris-washed, osmotically swollen spinach chloroplasts (blebs). The system II reaction centers were brought in the state Z +P +-Q A
-Q B
- by preillumination and the charge recombination to the state Z +PQ AQ B
- was measured at various temperatures and electrical field strengths. It was found that the activation enthalpy of this back reaction was 0.16 eV in the absence of an electrical field and diminished with increasing field strength. It is argued that this energy is the enthalpy difference between the states IQ A
- and I -Q A and accounts for about half of the free energy difference between these states. The redox state of Q B does not influence this free energy difference within 150 s after the photoreduction of Q A. The consequences for the interpretation of thermodynamic properties of Q A are discussed.Abbreviations DCMU
3(3,4-dichlorophenyl)-1,1-dimethylurea
- I
intermediary electron acceptor
- Mops
3-(N-morpholino)propanesulphonic acid
- P
(P 680) primary electron donor
- PS II
photosystem II
- Q A and Q B
first and second quinone electron acceptors
- Tricine
N-tris(hydroxymethyl)methylglycine
- Tris
tris-(hydroxymethyl)aminomethane
- Z
secondary electron donor
Dedicated to Professor L.N.M. Duysens on the occasion of his retirement 相似文献
11.
The protolytic reactions of PSII membrane fragments were analyzed by measurements of absorption changes of the water soluble indicator dye bromocresol purple induced by a train of 10 s flashes in dark-adapted samples. It was found that: a) in the first flash a rapid H +-release takes place followed by a slower H +-uptake. The deprotonation is insensitive to DCMU but is completely eliminated by linolenic acid treatment of the samples; b) the extent of the H +-uptake in the first flash depends on the redox potential of the suspension. In this time domain no H +-uptake is observed in the subsequent flashes; c) the extent of the H +-release as a function of the flash number in the sequence exhibits a characteristic oscillation pattern. Multiphasic release kinetics are observed. The oscillation pattern can be satisfactorily described by a 1, 0, 1, 2 stoichiometry for the redox transitions S i S i+1 (i=0, 1, 2, 3) in the water oxidizing enzyme system Y. The H +-uptake after the first flash is assumed to be a consequence of the very fast reduction of oxidized Q 400(Fe 3+) formed due to dark incubation with K 3[Fe(CN) 6]. The possible participation of component Z in the deprotonation reactions at the PSII donor side is discussed.Abbreviations A
protonizable group at the PSII acceptor side
- BCP
Bromocresol Purple
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- FWHM
Full Width at Half Maximum
- Q A, Q B
primary and secondary plastoquinone at PSII acceptor side
- Q 400
redox group at PSII-acceptor side (high spin Fe 2+)
- P680
Photoactive chlorophyll of PSII reaction center
- S i
redox states of the catalytic site of water oxidation
- Z
redox component connecting the catalytic site of water oxidation with the reaction center 相似文献
12.
The functional connection between redox component Y
z
identified as Tyr-161 of polypeptide D-1 (Debus et al. 1988) and P680 + was analyzed by measurements of laser flash induced absorption changes at 830 nm in PS II membrane fragments from spinach. It was found that neither DCMU nor the ADRY agent 2-(3-chloro-4-trifluoromethyl) anilino-3,5-dinitrothiophene (ANT 2p) affects the rate of P680 + reduction by Y
z
under conditions where the catalytic site of water oxidation stays in the redox state S 1. In contrast to that, a drastic retardation is observed after mild trypsin treatment at pH=6.0. This effect which is stimualted by flash illumination can be largely reversed by Ca 2+. The above mentioned data lead to the following conclusions: (a) the segment of polypeptide D-1 containing Tyr-161 and coordination sites of P680 is not allosterically affected by structural changes due to DCMU binding at the Q B-site which is also located in D-1. (b) ANT 2p as a strong protonophoric uncoupler and ADRY agent does not modify the reaction coordinate of P680 + reduction by Y
z
, and (c) Ca 2+ could play a functional role for the electronic and vibrational coupling between the redox groups Y
z
and P680. The electron transport from Y
z
to P680 + is discussed within the framework of a nonadiabatic process. Based on thermodynamic considerations the reorganization energy is estimated to be in the order of 0.5 V.Abbreviations ADRY
acceleration of the deactivation reactions of the water splitting enzyme system Y
- ANT 2p
2-(3-chloro-4-trifluoromethyl)anilino-3,5 dinitrothiophene
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- MES
2[N-Morpholino]ethanesulfonic acid
- PS II
photosystem II
- Q A, Q B
primary and secondary plastoquinone acceptor of photosystem II
- S
i
redox states of the catalytic site of water oxidation
- Y
z
redox active Tyr-161 of polypeptide D-1 相似文献
13.
Chl fluorescence induction (FI) was recorded in sunflower leaves pre-adapted to darkness or low preferentially PSI light, or inhibited by DCMU. For analysis the FI curves were plotted against the cumulative number of excitations quenched by PSII, n q, calculated as the cumulative complementary area above the FI curve. In the +DCMU leaves n q was <1 per PSII, suggesting pre-reduction of Q A during the dark pre-exposure. A strongly sigmoidal FI curve was constructed by complementing (shifting) the recorded FI curves to n q = 1 excitation per PSII. The full FI curve in +DCMU leaves was well fitted by a model assuming PSII antennae are excitonically connected in domains of four PSII. This result, obtained by gradually reducing Q A in PSII with pre-blocked Q B (by DCMU or PQH 2), differs from that obtained by gradually blocking the Q B site (by increasing DCMU or PQH 2 level) in leaves during (quasi)steady-state e ? transport (Oja and Laisk, Photosynth Res 114, 15–28, 2012). Explanations are discussed. Donor side quenching was characterized by comparison of the total n q in one and the same dark-adapted leaf, which apparently increased with increasing PFD during FI. An explanation for the donor side quenching is proposed, based on electron transfer from excited P680* to oxidized tyrosine Z (TyrZ ox). At high PFDs the donor side quenching at the J inflection of FI is due mainly to photochemical quenching by TyrZ ox. This quenching remains active for subsequent photons while TyrZ remains oxidized, following charge transfer to Q A. During further induction this quenching disappears as soon as PQ and Q A become reduced, charge separation becomes impossible and TyrZ is reduced by the water oxidizing complex. 相似文献
14.
An effect of desiccation (a decrease of relative water content from 97% to 10% within 35 h) on Photosystem II was studied
in barley leaf segments ( Hordeum vulgare L. cv. Akcent) using chlorophyll a fluorescence and thermoluminescence (TL). The O-J-I-P fluorescence induction curve revealed a decrease of F P and a slight shift of the J step to a shorter time with no change in its height. The analysis of the fluorescence decline
after a saturating light flash revealed an increased portion of slow exponential components with increasing desiccation. The
TL bands obtained after excitation by continuous light were situated at about –27°C (Z v band – recombination of P680 +Q A
−), –14 °C (A band – S 3Q A
−), +12 °C (B band – S 2/3Q B
−) and +45 °C (C band – TyrD +Q A
−). The bands related to the S-states of oxygen evolving complex (A and B) were reduced by desiccation and shifted to higher
and lower temperatures, respectively. In accordance with this, the band observed at about +27 °C (S 2Q B
−) after excitation by 1 flash fired at –10 °C and band at about +20 °C (S 2/3Q B
−) after 2 flashes decreased with increasing water deficit and shifted to lower temperatures. A new band around 5 °C appeared
in both regimes of TL excitation for a relative water content of under 42% and was attributed to the Q band (S 2Q A
−). It is suggested that under desiccation, an inhibition of the formation of S 2- and S 3-states in OEC occurred simultaneously with a lowering of electron transport on the acceptor side of PS II. The temperature
down-shift of the TL bands obtained after the flash excitation was induced at the initial phases of water stress, indicating
a decrease of the activation energy for the S 2/3Q B
−recombination.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
15.
Dallis grass ( Paspalum dilatatum Poir.) is a C 4/NADP‐ME gramineae, previously classified as semi‐tolerant to cold, although a complete study on this species acclimation process under a long‐term chilling and controlled environmental conditions has never been conducted. In the present work, plants of the variety Raki maintained at 25/18°C (day/night) (control) were compared with plants under a long‐term chilling at 10/8°C (day/night) (cold‐acclimated) in order to investigate how growth and carbon assimilation mechanisms are engaged in P. dilatatum chilling tolerance. Although whole plant mean relative growth rate (mean RGR) and leaf growth were significantly decreased by cold exposure, chilling did not impair plant development nor favour the investment in biomass below ground. Cold‐acclimated P. dilatatum cv. Raki had a lower leaf chlorophyll content, but a higher photosynthetic capacity at optimal temperatures, its range being shifted to lower values. Associated with this higher capacity to use the reducing power in CO 2 assimilation, cold‐acclimated plants further showed a higher capacity to oxidize the primary stable quinone electron acceptor of PSII, Q A. The activity and activation of phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) were not significantly affected by the long‐term chilling. Cold‐acclimated P. dilatatum cv. Raki apparently showed a lower transfer of excitation energy from the light‐harvesting complex of photosystem II to the respective reaction centre and enhancement of radiationless energy‐dissipating mechanisms at suboptimal temperatures. Overall, long‐term chilling resulted in several effects that comprise responses with an intermediate character of both chilling‐tolerant and –sensitive plants, which seem to play a significant role in the survival and acclimation of P. dilatatum cv. Raki at low temperature. 相似文献
16.
The nature of Cu 2+ 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 Cu 2+-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 Cu 2+. This suggests that Cu 2+ 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 (S 2) and negatively charged primary quinone acceptor of pSII (Q A−) is largely unaffected by Cu 2+. The S 2Q B− charge recombination, however, is drastically inhibited which parallels the loss of Hill activity. This indicates that Cu 2+ inhibits photosystem II photochemistry primarily affecting the function of the secondary quinone electron acceptor, Q B. We suggest that Cu 2+ does not block electron flow between the primary and secondary quinone acceptor but modifies the Q B site in such a way that it becomes unsuitable for further photosystem II photochemistry. 相似文献
17.
Necrotrophic fungal pathogens produce toxic compounds that induce cell death in infected plants. Often, the primary targets of these toxins and the way a plant responds to them are not known. In the present work, the effect of tenuazonic acid (TeA), a non–host‐specific toxin of Alternaria alternata, on Arabidopsis thaliana has been analysed. TeA blocks the Q B‐binding site at the acceptor side of photosystem II (PSII). As a result, charge recombination at the reaction centre (RC) of PSII is expected to enhance the formation of the excited triplet state of the RC chlorophyll that promotes generation of singlet oxygen ( 1O 2). 1O 2 activates a signalling pathway that depends on the two EXECUTER (EX) proteins EX1 and EX2 and triggers a programmed cell death response. In seedlings treated with TeA at half‐inhibition concentration 1O 2‐mediated and EX‐dependent signalling is activated as indicated by the rapid and transient up‐regulation of 1O 2‐responsive genes in wild type, and its suppression in ex1/ex2 mutants. Lesion formation occurs when seedlings are exposed to higher concentrations of TeA for a longer period of time. Under these conditions, the programmed cell death response triggered by 1O 2‐mediated and EX‐dependent signalling is superimposed by other events that also contribute to lesion formation. 相似文献
18.
Electric field-induced charge recombination in Photosystem II (PS II) was studied in osmotically swollen spinach chloroplasts (blebs) by measurement of the concomitant chlorophyll luminescence emission (electroluminescence). A pronounced dependence on the redox state of the two-electron gate Q B was observed and the earlier failure to detect it is explained. The influence of the Q B/Q B
– oscillation on electroluminescence was dependent on the redox state of the oxygen evolving complex; at times around one millisecond after flash illumination a large effect was observed in the states S 2 and S 3, but not in the state S 4 (actually Z +S 3). The presence of the oxidized secondary electron donor, tyrosine Z +, appeared to prevent expression of the Q B/Q B
– effect on electroluminescence, possibly because this effect is primarily due to a shift of the redox equilibrium between Z/Z + and the oxygen evolving complex.Abbreviations BSA
bovine serum albumin
- EDTA
ethylene-diaminetetraacetic acid
- EL
electroluminescence
- FCCP
carbonylcyanide p-trifluoromethyloxyphenyl-hydrazone
- HEPESI
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- I
primary electron acceptor
- MOPS
3-(N-morpholino) propane sulfonic acid
- P680
primary electron donor of Photosystem II
- P700
primary electron donor of Photosystem I
- Q A and Q B
secondary and tertiary electron acceptors of Photosystem II
- Z
secondary electron donor (D1 Tyr 161) 相似文献
19.
The light-induced oxidation of the accessory donor tyrosine-D (Y D) has been studied by measurements of the EPR Signal II slow at room temperature in the autotrophically and photoheterotrophically cultivated alga Chlamydobotrys stellata. After illumination and dark adaptation, Y D Signal II slow was observed only in autotrophic algae, i.e. under conditions of a linear photosynthetic electron transfer from water to NADP +. The addition of artificial electron acceptors phenyl-p-benzoquinone (PPQ) or dichloro-p-benzoquinone (DCQ) to the autotrophic cells caused an almost negligible increase of this signal. When photosynthetic electron flow and oxygen evolution were diminished by removal of the carbon source CO 2 and addition of acetate (photoheterotrophy), a pronounced Y D Signal II slow was seen only in presence of DCQ or PPQ. Several possibilities are discussed to explain the absence of Y D Signal II slow in photoheterotrophic Chl. stellata such as the existence of a cyclic PS II electron flow very effectively reducing P 680 and thereby preventing the possibility of Y D oxidation. Artificial electron acceptors withdraw electrons from this cycle thus keeping the primary quinone acceptor, Q A, oxidized and thereby diminishing the reduction of P 680
+ by cyclic PSII. This leads to the appearance of the Y D Signal II slow also in the photoheterotrophically grown algae.Abbreviations A-band-
thermoluminescence band associated with S 2Q A
- charge recombination
- DCQ-
2,5-dichlorobenzoquinone
- D 2-
structure protein of Photosystem II
- EPR-
electron paramagnetic resonance
- OEC-
oxygen evolving complex
- PPQ-
phenyl-p-benzoquinone
- PS II-
Photosystem II
- P 680-
reaction center of Photosystem II
- Q-band-
thermoluminescence band associated with S 2Q A
- charge recombination
- S i-
oxidation levels of the OEC
- Y D-
tyrosine-D accessory donor to P 680
- Y Z-
tyrosine-Z electron donor to P 680
Dedicated to Prof. Dr E. Schnepf/Heidelberg. 相似文献
20.
Deg1 protease functions in protease and chaperone of PSII complex components, but few works were performed to study the effects of Deg1 on electron transport activities on the donor and acceptor side of PSII and its correlation with the photoprotection of PSII during photoinhibition. Therefore, we performed systematic and comprehensive investigations of electron transfers on the donor and acceptor sides of photosystem II (PSII) in the Deg1-reduced transgenic lines deg1-2 and deg1-4. Both the maximal quantum efficiency of PSII photochemistry (Fv/Fm) and the actual PSII efficiency (ΦPSII) decreased significantly in the transgenic plants. Increases in nonphotochemical quenching (NPQ) and the dissipated energy flux per reaction center (DI0/RC) were also shown in the transgenic plants. Along with the decreased D1, CP47, and CP43 content, these results suggested photoinhibition under growth light conditions in transgenic plants. Decreased Deg1 caused inhibition of electron transfer on the PSII reducing side, leading to a decline in the number of QB-reducing centers and accumulation of QB-nonreducing centers. The Tm of the Q band shifted from 5.7 °C in the wild-type plant to 10.4 °C and 14.2 °C in the deg1-2 and deg1-4 plants, respectively, indicating an increase in the stability of S2QA¯ in transgenic plants. PSIIα in the transgenic plants largely reduced, while PSIIβ and PSIIγ increased with the decline in the Deg1 levels in transgenic plants suggesting PSIIα centers gradually converted into PSIIβ and PSIIγ centers in the transgenic plants. Besides, the connectivity of PSIIα and PSIIβ was downregulated in transgenic plants. Our results reveal that downregulation of Deg1 protein levels induced photoinhibition in transgenic plants, leading to loss of PSII activities on both the donor and acceptor sides in transgenic plants. These results give a new insight into the regulation role of Deg1 in PSII electron transport. 相似文献
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