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1.
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
2.
Sándor Demeter Jonathan H. A. Nugent László Kovács Gábor Bernát Michael C. W. Evans 《Photosynthesis research》1995,46(1-2):213-218
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
3.
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.
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
5.
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
6.
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
7.
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 FP 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 (Zv band – recombination of P680+QA
−), –14 °C (A band – S3QA
−), +12 °C (B band – S2/3QB
−) and +45 °C (C band – TyrD+QA
−). 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 (S2QB
−) after excitation by 1 flash fired at –10 °C and band at about +20 °C (S2/3QB
−) 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 (S2QA
−). It is suggested that under desiccation, an inhibition of the formation of S2- and S3-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 S2/3QB
−recombination.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
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
9.
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
10.
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
11.
《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 S2Q−B and S2Q−A charge pairs. (2) Removal of the 33 kDa extrinsic protein specifically elevates the recombination temperature of the S2Q−A charge pair, with practically no effect on the S2Q−B pair. This was tentatively interpreted as showing that the protein removal decreases the redox potential of both S2 and Q−B, but not of Q−A, and, thus, the effects are mutually cancelled for the S2Q−B pair, but are manifested for the S2Q−A 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
12.
The toxicity of heavy metals on photosystem 2 photochemistry, was investigated by monitoring Hill activity, fluorescence, and thermoluminescence properties of photosystem 2 (PS 2) in pea (Pisum sativum L. cv. Bombay) chloroplasts. In Co2+-, Ni2+- or Zn2+-treated chloroplasts 2,6-dichlorophenolindophenol-Hill activity was markedly inhibited. Addition of hydroxylamine which donates electrons close to PS 2 reaction center did not restore the PS 2 activity. Co2+-, Ni2+ or Zn2+ also inhibited PS 2 activity supported by hydroxylamine in tris (hydroxymethyl)aminomethane (Tris)-inactivated chloroplasts. These observations were confirmed by fluorescence transient measurements. This implies that the metal ions inhibit either the reaction center or the components of PS 2 acceptor side. Flash-induced thermoluminescence studies revealed that the S2Q?A charge recombination was insensitive to metal ion addition. The S2Q?B charge recombination, however, was inhibited with increase in the level of Co2+, Ni2+ or Zn2+. The observed sensitivity of S2?B charge recombination in comparison to the stability of S2Q?A recombination suggests that the metal ions inhibit at the level of secondary quinone electron acceptor. QB. We suggest that Co2+, Ni2+ or Zn2+ do not block the electron flow between the primary and secondary quinone electron acceptor, but possibly, directly modify QB site, leading to the loss of PS 2 activity. 相似文献
13.
We investigated the influence of CO2/HCO3
–-depletion and of the presence of acetate and formate on the in vivo photosynthetic electron transport in the two green algae Chlamydobotrys stellata and Chlamydomonas reinhardtii by means of thermoluminescence technique and mathematical glow curve analysis. The main effects of the removal of CO2 from the algal cultures was: (1) A shift of the glow curve peak position to lower temperatures resulting from a decrease of the B band and an increase of the Q band. (2) Treatment of CO2-deficient Chl. stellata with DCMU yielded two thermoluminescence bands in the Q band region peaking at around +12°C and +5°C; in case of Chl. reinhardtii DCMU treatment induced only one band with an emission maximum at +5°C. The presence of acetate or formate in CO2-depleted algal cultures lowered the intensities of all of the individual TL bands but that of a HT band (TL+37). The effects of CO2-depletion and of the presence of anions were fully reversible.Abbreviations DCMU
3-(3,4)-dichlorophenyl-1,1-dimethylurea
- HT band
high temperature TL band
- P680
reaction center chlorophyll of PS II
- QA and QB
primary and secondary quinone acceptors of PS II, respectively
- PS II
Photosystem II
- S2/3
redox states of the oxygen evolving complex of PS II
- TL
thermoluminescence 相似文献
14.
Inhibition of Photosystem II (PS II) activity by single turnover visible light flashes was studied in thylakoid membranes isolated form spinach. Flash illumination results in decreased oxygen evolving activity of PS II, which effect is most pronounced when the water-oxidizing complex is in the S2 and S3 states, and increases with increasing time delay between the subsequent flashes. By applying the fluorescent spin-trap DanePy, we detected the production of singlet oxygen, whose amount was increasing with increasing flash spacing. These findings were explained in the framework of a model, which assumes that recombination of the S2QB− and S3QB− states generate the triplet state of the reaction center chlorophyll and lead to the production of singlet oxygen. 相似文献
15.
Jack Farineau 《Photosynthesis research》1993,36(1):25-34
Characteristics of thermoluminescence (TL) glow curves were studied in thylakoids (isolated from pea leaves) or in intact pea leaves after an exposure to very high light for 2 min in the TL device. The inhibition of photosynthesis was detected as decreases of oxygen evolution rates and/or of variable fluorescence.In thylakoids exposed to high light, then dark adapted for 5 min, a flash regime induced TL glow curves which can be interpreted as corresponding to special B bands since: 1) they can be fitted by a single B band (leaving a residual band at –5°C) with a lower activation energy and a shift of the peak maximum by –5 to –6°C and, 2) the pattern of oscillation of their amplitudes was normal with a period of 4 and maxima on flashes 2 and 6. During a 1 h dark adaptation, no recovery of PS II activity occurred but the shift of the peak maximum was decreased to –1 to –2°C, while the activation energy of B bands increased. It is supposed that centers which remained active after the photoinhibitory treatment were subjected to reversible and probably conformational changes.Conversely, in intact leaves exposed to high light and kept only some minutes in the dark, TL bands induced by a flash regime were composite and could be deconvoluted into a special B band peaking near 30°C and a complex band with maximum at 2–5°C. In the case of charging bands by one flash, this low temperature band was largely decreased in size after a 10 min dark adaptation period; parallely, an increase of the B band type component appeared. Whatever was the flash number, bands at 2–5°C were suppressed by a short far red illumination given during the dark adaptation period and only remained a main band a 20°C; therefore, the origin of the low temperature band was tentatively ascribed to recombinations in centers blocked in state S2QA
–QB
2–. In vivo, the recovery of a moderately reduced state in the PQ pool, after an illumination, would be slow and under the dependence of a poising mechanism, probably involving an electron transfer between cytosol and chloroplasts or the so-called chlororespiration process.Abbreviations Ea-
activation energy
- FR-
far-red
- MV-
methylviologen
- pBQ-
p-benzoquinone
- PQ-
plastoquinone
- PS II-
Photosystem II
- QA-
primary quinone electron acceptor of PS II
- QB-
secondary quinone electron acceptor of PS II
- TL-
thermoluminescence 相似文献
16.
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:
- 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.
- 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
- 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.
17.
The filamentous cyanobacterium Microcoleus vaginatus, a major primary producer in desert biological sand crusts, is exposed to frequent hydration (by early morning dew) followed by desiccation during potentially damaging excess light conditions. Nevertheless, its photosynthetic machinery is hardly affected by high light, unlike “model” organisms whereby light-induced oxidative stress leads to photoinactivation of the oxygen-evolving photosystem II (PSII). Field experiments showed a dramatic decline in the fluorescence yield with rising light intensity in both drying and artificially maintained wet plots. Laboratory experiments showed that, contrary to “model” organisms, photosynthesis persists in Microcoleus sp. even at light intensities 2–3 times higher than required to saturate oxygen evolution. This is despite an extensive loss (85–90%) of variable fluorescence and thermoluminescence, representing radiative PSII charge recombination that promotes the generation of damaging singlet oxygen. Light induced loss of variable fluorescence is not inhibited by the electron transfer inhibitors 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), 2,5-dibromo-3-methyl-6-isopropylbenzoquinone (DBMIB), nor the uncoupler carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP), thus indicating that reduction of plastoquinone or O2, or lumen acidification essential for non-photochemical quenching (NPQ) are not involved. The rate of QA
− re-oxidation in the presence of DCMU is enhanced with time and intensity of illumination. The difference in temperatures required for maximal thermoluminescence emissions from S2/QA
− (Q band, 22°C) and S2,3/QB
− (B band, 25°C) charge recombinations is considerably smaller in Microcoleus as compared to “model” photosynthetic organisms, thus indicating a significant alteration of the S2/QA
− redox potential. We propose that enhancement of non-radiative charge recombination with rising light intensity may reduce harmful radiative recombination events thereby lowering 1O2 generation and oxidative photodamage under excess illumination. This effective photo-protective mechanism was apparently lost during the evolution from the ancestor cyanobacteria to the higher plant chloroplast. 相似文献
18.
Leaf discs of dark-adapted tobacco plants were excited by 2 flashes and kept in darkness at 20 °C for various time periods, then thermoluminescence emission was recorded without freezing the sample. The B band at 30 °C decreased with a half-time t1/2~1 min and the AG band at 45 °C with a t1/2~5 min. This corresponds to the decay kinetics of S2/3 in PS II centres in the state S2/3 QB- (B band) or S2/3 QB. Assuming that the 45 °C band is an ‘afterglow’ emission originating from those centres with an oxidized QB on which an electron is back-transferred from stroma reductants through a pathway induced by warming, the theoretical ratio of the B and AG band was compared to that measured experimentally. After 2 or 3 flashes producing mainly S3, the intensity of AG band encompassed several fold that of the B band, because recombining S3 recreated S2 QB AG-emitting centres. In order to confirm that the AG band is governed by the heat-induced activation of a dark QB-reducing pathway rather than by PS II charge recombination, the AG emission was characterized in triazine-resistant Chenopodium album weed biotypes. In these mutants where the QB pocket is altered, the B band is strongly downshifted to 18 °C, compared to 32 °C in the wild type, whereas the AG band is only downshifted by 3 or 4 °C, demonstrating that S2/3 QB- is not the limiting step of the AG emission. 相似文献
19.
Georgieva K Szigeti Z Sarvari E Gaspar L Maslenkova L Peeva V Peli E Tuba Z 《Planta》2007,225(4):955-964
The functional state of the photosynthetic apparatus of flowering homoiochlorophyllous desiccation tolerant plant Haberlea rhodopensis during dehydration and subsequent rehydration was investigated in order to characterize some of the mechanisms by which resurrection
plants survive drought stress. The changes in the CO2 assimilation rate, chlorophyll fluorescence parameters, thermoluminescence, fluorescence imaging and electrophoretic characteristics
of the chloroplast proteins were measured in control, moderately dehydrated (50% water content), desiccated (5% water content)
and rehydrated plants. During the first phase of desiccation the net CO2 assimilation decline was influenced by stomatal closure. Further lowering of net CO2 assimilation was caused by both the decrease in stomatal conductance and in the photochemical activity of photosystem II.
Severe dehydration caused inhibition of quantum yield of PSII electron transport, disappearance of thermoluminescence B band
and mainly charge recombination related to S2QA− takes place. The blue and green fluorescence emission in desiccated leaves strongly increased. It could be suggested that
unchanged chlorophyll content and amounts of chlorophyll–proteins, reversible modifications in PSII electron transport and
enhanced probability for non-radiative energy dissipation as well as increased polyphenolic synthesis during desiccation of
Haberlea contribute to drought resistance and fast recovery after rehydration. 相似文献
20.
Georgieva K Maslenkova L Peeva V Markovska Y Stefanov D Tuba Z 《Photosynthesis research》2005,85(2):191-203
The functional peculiarities and responses of the photosynthetic system in the flowering homoiochlorophyllous desiccation-tolerant (HDT) Haberlea rhodopensis and the non-desiccation-tolerant spinach were compared during desiccation and rehydration. Increasing rate of water loss clearly modifies the kinetic parameters of fluorescence induction, thermoluminescence emission, far-red induced P700 oxidation and oxygen evolution in the leaves of both species. The values of these parameters returned nearly to the control level after 24 h rehydration only of the leaves of HDT plant. PS II was converted in a non-functional state in desiccated spinach in accordance with the changes in membrane permeability, malondialdehyde, proline and H2O2 contents. Moreover, our data showed a strong reduction of the total number of PS II centers in Haberlea without any changes in the energetics of the charge recombination. We consider this observation, together with the previously reported unusually high temperature of B-band (S2QB-) emission of Haberlea to reflect some specific adaptive characteristics of the photosynthetic system. As far as we know this is the first time when such adaptive characteristics and mechanism of the photosynthetic system of a flowering HDT higher plant is described. These features of Haberlea can explain the fast recovery of its photosynthesis after desiccation, which enable this HDT plant to rapidly take advantage of frequent changes in water availability. 相似文献