共查询到20条相似文献,搜索用时 31 毫秒
1.
Jean-Marie Briantais Jean-Marc Ducruet Michael Hodges G. Heinrich Krause 《Photosynthesis research》1992,32(1):1-10
The effects of low temperature acclimation and photoinhibitory treatment on Photosystem 2 (PS 2) have been studied by thermoluminescence and chlorophyll fluorescence decay kinetics after a single turnover saturating flash. A comparison of unhardened and hardened leaves showed that, in the hardened case, a decrease in overall and B-band thermoluminescence emissions occurred, indicating the presence of fewer active PS 2 reaction centers. A modification in the form of the B-band emission was also observed and is attributed to a decrease in the apparent activation energy of recombination in the hardened leaves. The acclimated leaves also produced slower QA
– reoxidation kinetics as judged from the chlorophyll fluorescence decay kinetics. This change was mainly seen in an increased lifetime of the slow reoxidation component with only a small increase in its amplitude. Similar changes in both thermoluminescence and fluorescence decay kinetics were observed when unhardened leaves were given a high light photoinhibitory treatment at 4°C, whereas the hardened leaves were affected to a much lesser extent by a similar treatment. These results suggest that the acclimated plants undergo photoinhibition at 4°C even at low light intensities and that a subsequent high light treatment produces only a small additive photoinhibitory effect. Furthermore, it can be seen that photoinhibition eventually gives rise to PS 2 reaction centers which are no longer functional and which do not produce thermoluminescence or variable chlorophyll fluorescence.Abbreviations D1
The 32 kDa protein of Photosystem 2 reaction center
- Fm
maximum chlorophyll fluorescence yield
- F0
minimal chlorophyll fluorescence yield obtained when all PS 2 centers are open
- Fi
intermediate fluorescence level corresponding to PS 2 centers which are loosely or not connected to plastoquinone (non-B centers)
- Fv
maximum variable chlorophyll fluorescence yield (Fv=Fm–F0)
- PS 2
Photosystem 2
- QA and QB
respectively, primary and secondary quinonic acceptors of PS 2
- S1, S2 and S3
respectively, the one, two and three positively charged states of the oxygen evolving system
- Z
secondary donor of PS 2 相似文献
2.
Fifteen ancestral genotypes of United States soybean cultivars were screened for differences in photosynthetic electron transport capacity using isolated thylakoid membranes. Plants were grown in controlled environment chambers under high or low irradiance conditions. Thylakoid membranes were isolated from mature leaves. Photosynthetic electron transport was assayed as uncoupled Hill activity using 2,6-dichlorophenolindophenol (DCIP). Soybean electron transport activity was dependent on genotype and growth irradiance and ranged from 6 to 91 mmol DCIP reduced [mol chlorophyll]–1 s–1. Soybean plastocyanin pool size ranged from 0.1 to 1.3 mol plastocyanin [mol Photosystem I]–1. In contrast, barley and spinach electron transport activities were 140 and 170 mmol DCIP reduced [mol chlorophyll]–1 s–1, respectively, with plastocyanin pool sizes of 3 to 4 mol plastocyanin [mol Photosystem I]–1. No significant differences in the concentrations of Photosystem II, plastoquinone, cytochrome b6f complexes, or Photosystem I were observed. Thus, genetic differences in electron transport activity were correlated with plastocyanin pool size. The results suggested that plastocyanin pool size can vary significantly and may limit photosynthetic electron transport capacity in certain species such as soybean. Soybean plastocyanin consisted of two isoforms with apparent molecular masses of 14 and 11 kDa, whereas barley and spinach plastocyanins each consisted of single polypeptides of 8 and 12 kDa, respectively.Abbreviations DAP
days after planting
- DCIP
2,6-dichlorophenolindophenol
- LiDS
lithium dodecyl sulfate
- PPFD
photosynthetic photon flux density (mol photons m–2 s–1)
- PS I
Photosystem I
- PS II
Photosystem II
- P700
reaction center of Photosystem I
The US Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged. 相似文献
3.
Effects of photoinhibition on photosynthesis in pea (Pisum sativum L.) leaves were investigated by studying the relationship between the severity of a photoinhibitory treatment (measured as Fv/Fm) and several photoacoustic and chlorophyll a fluorescence parameters. Because of the observed linear relationship between the decline of Fv/Fm and the potential oxygen evolution rate determined by the photoacoustic method, the parameter Fv/Fm was used as an indicator for the severity of photoinhibition. Our analysis revealed that part of the Photosystem II (PS II) reaction centers is inactive in oxygen evolution and is also less sensitive to photoinhibition. Correcting the parameter qP (fraction of open PS II reaction centers) for inactive PS II centers unveiled a strong increase of qP in severely inhibited pea leaves, indicating that the inactivated active centers do no longer contribute to qP and that photoinhibition has an all or none effect on PS II centers. Analysis of qE (energy quenching) demonstrated its initial increase possibly associated with dephosphorylation of LHC II. Analysis of qI (photoinhibition dependent quenching) showed that the half-time of recovery of qI increases steeply below an Fv/Fm of 0.65. This increase of the relaxation half-time corresponds with a decrease of the electron transport rate J and tentatively indicates that the supply of ATP, needed for the recovery, starts to decrease. The data indicate the necessity of correcting for inactive centers in order to make valuable conclusions about effects of photoinhibition on photosynthetic parameters. 相似文献
4.
Summary
Selaginella lepidophylla, the resurrection plant, curls dramatically during desiccation and the hypothesis that curling may help limit bright light-induced damage during desiccation and rehydration was tested under laboratory conditions. Restraint of curling during desiccation at 25° C and a constant irradiance of 2000 mol m–2 s]t-1 significantly decreased PSII and whole-chain electron transport and the Fv/Fm fluorescence yield ratio following rehydration relative to unrestrained plants. Normal curling during desiccation at 37.5°C and 200 mol m–2 s–1 irradiance did not fully protect against photoinhibition or chlorophyll photooxidation indicating that some light-induced damage occurred early in the desiccation process before substantial curling. Photosystem I electron transport was less inhibited by high-temperature, high-irradiance desiccation than either PSII or whole-chain electron transport and PSI was not significantly affected by restraint of curling during desiccation at 25°C and high irradiance. Previous curling also helped prevent photoinhibition of PSII electron transport and loss of whole-plant photosynthetic capacity as the plants uncurled during rehydration at high light. These results demonstrate that high-temperature desiccation exacerbated photoinhibition, PSI was less photoinhibited than PSII or whole-chain electron transport, and stem curling ameliorated bright light-induced damage helping to make rapid recovery of photosynthetic competence possible when the plants are next wetted. 相似文献
5.
Constant Signarbieux 《Environmental and Experimental Botany》2011,71(2):192-197
As drought stress is expected to occur more frequently in future climate in central Europe, survival and productivity of grassland species are an important issue. Non-stomatal limitation processes related to the drought-stress inhibition of photosynthesis of selected grassland species were analysed at three locations using leaf gas exchange and chlorophyll fluorescence. The effect of an artificial drought on the non-stomatal limitations differed considerably between species present in the same grassland plot. The maximum efficiency of photosystem II (Fv/Fm), indicator for the intactness of the photosynthetic electron transport, showed only small differences under drought. On the other hand, more pronounced effects were observed for the carboxylation velocity of Rubisco (Vc,max). Vc,max was in Phleum pratense about 20% lower under drought than in control plants, while other species in the same plot were far less affected. The carboxylation velocity of Rubisco is highly sensitive to water deficit and might represent a tool to evaluate the drought response of various species in order to address the performance of grasslands. 相似文献
6.
Suleyman I. Allakhverdiev Hidenori Hayashi Yoko Fujimura Vyacheslav V. Klimov Norio Murata 《Photosynthesis research》1993,35(3):345-349
We examined the effects of o-phenanthroline and LiClO4 on oxygen evolution and electron transport in the Photosystem 2 complex of the pea. Treatment of Photosystem 2 particles with a combination of 3.0 mM o-phenanthroline and 1.0 M LiClO4 for 30–40 min at 0°C decreased the oxygen-evolving activity with the electron acceptor (either phenyl-p-benzoquinone or 2,6-dichlorophenol indophenol) to less than 5% of the original level. However with the same treatment, the electron-transport activity from an artificial electron donor, 1,5-diphenylcarbohydrazide, to 2,6-dichlorophenol indophenol remained at 60% of the original activity. The amount of manganese in the Photosystem 2 complex decreased in parallel with the loss of oxygen evolution following treatment. These observations suggest that the treatment of the Photosystem 2 complex with o-phenanthroline and LiClO4 inhibits electron transport on the oxygen-evolving side much more significantly than on the electron-acceptor side.Abbreviations Chl
chlorophyll
- DCPIP
2,6-dichlorophenol indophenol
- DPC
1,5-diphenylcarbo hydrazide
- EDTA
ethylenediaminetetraacetic acid
- Hepes
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- Mes
4-morpholineethanesulfonic acid
- PBQ
phenyl-p-benzoquinone
- PS 2
Photosystem 2 相似文献
7.
Germlings of Phytophthora palmivora possess at least two systems for the uptake of inorganic phosphate (Pi). The first is synthesized on germination in medium containing 50 M Pi and has a Km of approx. 30 M (Vmax=7–9 nmol Pi/h·106 cells). The second is synthesized under conditions of Pi-deprivation and has a higher affinity for Pi (Km=1–2 M), but a lower Vmax (0.5–2 nmol Pi/h·106 cells). The fungicide phosphite likewise enters the germlings via two different transport systems, the synthesis of which also depends on the concentration of Pi in the medium. The Km of the lower affinity system is 3 mM (Vmax=20 nmol phosphite/h·106 cells) and that of the higher affinity system is 0.6 mM (Vmax=12 nmol/h·106 cells). Pi and phosphite are competitive inhibitors for each other's transport in both systems. However, whereas mM concentrations of phosphite are necessary to inhibit Pi transport, only M concentrations of Pi are required to inhibit phosphite transport. A third system of uptake for Pi also exists, since when phosphate-deprived cells are presented with mM concentrations of Pi, they transport the anion at a very high rate (around 100 nmol/h·106 cells). High rates of transport of phosphite are also observed when these cells are presented with mM concentrations of this anion. 相似文献
8.
The amplitudes ratio of the fast and slow phases (Afast/Aslow) in the kinetics of the dark relaxation of variable chlorophyll fluorescence (FV) was studied after various periods of illumination of dark-adapted primary barley leaves. Simultaneously, photosynthetic activity was monitored using the photoacoustic technique and the photochemical and non-photochemical fluorescence quenching parameters. The ratio Afast/Aslow changed with the preceding illumination time in a two-step manner. During the first stage of photosynthetic induction (0–20 s of illumination), characterized by a drop in O2-dependent photoacoustic signal following an initial spike and by a relatively stable small value of photochemical FV quenching, the ratio Afast/Aslow remained practically unaltered. During the second stage (20–60 s of illumination), when both the rate of O2 evolution and the photochemical FV quenching were found to be sharply developed, a marked increase in the above ratio was also observed. A linear correlation was found between the value of the photochemical quenching and the ratio Afast/Aslow during the second phase of photosynthetic induction. It is concluded that the slow phase appearing in the kinetics of FV dark relaxation is not due to the existence of Photosystem II reaction centres lacking the ability to reduce P700+ with high rates, but is instead related to the limitation of electron release from Photosystem I during the initial stage of the induction period of photosynthesis. This limitation keeps the intersystem electron carriers in the reduced state and thus increases the probability of back electron transfer from QA
– to the donor side of Photosystem II.Abbreviations Afast/Aslow
the ratio of magnitudes between the fast and slow phases of dark relaxation of variable fluorescence
- FO
initial level of chlorophyll fluorescence
- FV
variable chlorophyll fluorescence (F-FO)
- (FV)S
the yield of variable chlorophyll fluorescence under saturating pulse in illuminated leaves
- (FV)M
the yield of variable chlorophyll fluorescence under saturating pulse in dark-adapted leaves
- PA
photoacoustic
- PSI
Photosystem I
- PS II
Photosystem II
- qN
non-photochemical quenching
- qQ
photochemical quenching 相似文献
9.
Transpiration, xylem water potential and water channel activity were studied in developing stolons and leaves of strawberry (Fragaria × ananassa Duch.) subjected to drought or flooding, together with morphological studies of their stomata and other surface structures. Stolons had 0.12 stomata mm–2 and a transpiration rate of 0.6 mmol H2O m–2 s–1, while the leaves had 300 stomata mm–2 and a transpiration rate of 5.6 mmol H2O m–2 s–1. Midday water potentials of stolons were always less negative than in leaves enabling nutrient ion and water transport via or to the strawberry stolons. Drought stress, but not flooding, decreased stolon and leaf water potential from –0.7 to –1 MPa and from –1 to –2 MPa, respectively, with a concomitant reduction in stomatal conductance from 75 to 30 mmol H2O m–2 s–1. However, leaf water potentials remained unchanged after flooding. Similarly, membrane vesicles derived from stolons of flooded strawberry plants showed no change in water channel activity. In these stolons, turgor may be preserved by maintaining root pressure, an electrochemical and ion gradient and xylem differentiation, assuming water channels remain open. By contrast, water channel activity was reduced in stolons of drought stressed strawberry plants. In every case, the effect of flooding on water relations of strawberry stolons and leaves was less pronounced than that of drought which cannot be explained by increased ABA. Stomatal closure under drought could be attributed to increased delivery of ABA from roots to the leaves. However, stomata closed more rapidly in leaves of flooded strawberry despite ABA delivery from the roots in the xylem to the leaves being strongly depressed. This stomatal closure under flooding may be due to release of stress ethylene. In the relative absence of stomata from the stolons, cellular (apoplastic) water transport in strawberry stolons was primarily driven by water channel activity with a gradient from the tip of the stolon to the base, concomitant with xylem differentiation and decreased water transport potential from the stolon tip to its base. Reduced water potential in the stolons under drought are discussed with respect to reduced putative water channel activity. 相似文献
10.
Tanya G. Falbel L. Andrew Staehelin William W. Adams III 《Photosynthesis research》1994,42(3):191-202
Three light intensity-dependent Chl b-deficient mutants, two in wheat and one in barley, were analyzed for their xanthophyll cycle carotenoids and Chl fluorescence characteristics under two different growth PFDs (30 versus 600 mol photons·m–2 s–1 incident light). Mutants grown under low light possessed lower levels of total Chls and carotenoids per unit leaf area compared to wild type plants, but the relative proportions of the two did not vary markedly between strains. In contrast, mutants grown under high light had much lower levels of Chl, leading to markedly greater carotenoid to Chl ratios in the mutants when compared to wild type. Under low light conditions the carotenoids of the xanthophyll cycle comprised approximately 15% of the total carotenoids in all strains; under high light the xanthophyll cycle pool increased to over 30% of the total carotenoids in wild type plants and to over 50% of the total carotenoids in the three mutant strains. Whereas the xanthophyll cycle remained fairly epoxidized in all plants grown under low light, plants grown under high light exhibited a considerable degree of conversion of the xanthophyll cycle into antheraxanthin and zeaxanthin during the diurnal cycle, with almost complete conversion (over 90%) occurring only in the mutants. 50 to 95% of the xanthophyll cycle was retained as antheraxanthin and zeaxanthin overnight in these mutants which also exhibited sustained depressions in PS II photochemical efficiency (Fv/Fm), which may have resulted from a sustained high level of photoprotective energy dissipation activity. The relatively larger xanthophyll cycle pool in the Chl b-deficient mutant could result in part from the reported concentration of the xanthophyll cycle in the inner antenna complexes, given that the Chl b-deficient mutants are deficient in the peripheral LHC-II complexes.Abbreviations A
antheraxanthin
- Chl
chlorophyll
- Fo and Fm
minimal yield (at open PS II reaction centers) and maximal yield (at closed centers) of chlorophyll fluorescence in darkness
- F
level of fluorescence during illumination with photosynthetically active radiation
- Fm
maximal yield (at closed centers) of chlorophyll fluorescence during illumination with photosynthetically active radiation
- (Fm–F)/Fm
actual efficiency of PS II during illumination with photosynthetically active radiation
- Fv/Fm+(Fm–Fo)/Fm
intrinsic efficiency of PS II in darkness
- LHC_II
light-harvesting chlorophyll-protein complex of Photosystem II
- PFD
photon flux density (between 400 and 700 nm)
- PS I
Photosystem I
- PS II
Photosystem II
- V
violaxanthin
- Z
zeaxanthin 相似文献
11.
The role of electron transport to O2 in mitigating against photoinactivation of Photosystem (PS) II was investigated in leaves of pea (Pisum sativum L.) grown in moderate light (250 mol m–2 s–1). During short-term illumination, the electron flux at PS II and non-radiative dissipation of absorbed quanta, calculated from chlorophyll fluorescence quenching, increased with increasing O2 concentration at each light regime tested. The photoinactivation of PS II in pea leaves was monitored by the oxygen yield per repetitive flash as a function of photon exposure (mol photons m–2). The number of functional PS II complexes decreased nonlinearly with increasing photon exposure, with greater photoinactivation of PS II at a lower O2 concentration. The results suggest that electron transport to O2, via the twin processes of oxygenase photorespiration and the Mehler reaction, mitigates against the photoinactivation of PS II in vivo, through both utilization of photons in electron transport and increased nonradiative dissipation of excitation. Photoprotection via electron transport to O2
in vivo is a useful addition to the large extent of photoprotection mediated by carbon-assimilatory electron transport in 1.1% CO2 alone.Abbreviations Fm, Fo, Fv-
maximal, initial (corresponding to open PS II traps) and variable chlorophyll fluorescence yield, respectively
- NPQ-
non-photochemical quenching
- PS-
photosystem
- QA-
primary quinone acceptor
- qP-
photochemical quenching coefficient 相似文献
12.
Summary
Geotrichum candidum (isolate 1–9) pathogenic on citrus fruits, appears to lack siderophore production. Iron uptake byG. candidum is mediated by two distinct iron-regulated, energy-and temperature-dependent transport systems that require sulfhydryl groups. One system exhibits specificity for either ferric or ferrous iron, whereas the other exhibits specificity for ferrioxamine-B-mediated iron uptake and presumably other hydroxamate siderophores. Radioactive iron uptake from59FeCl3 showed an optimum at pH 6 and 35° C, and Michaelis-Menten kinetics (apparentK
m = 3 m,V
max = 0.054 nmol · mg–1 · min–1). The maximal rate of Fe2+ uptake was higher than Fe3+ (V
max = 0.25 nmol · mg–1 · min–1) but theK
m was identical. Reduction of ferric to ferrous iron prior to transport could not be detected. The ferrioxamine B system exhibits an optimum at pH 6 and 40° C and saturation kinetics (K
m = 2 M,V
max = 0.22 nmol · mg–1 · min–1). The two systems were distinguished as two separate entities by negative reciprocal competition, and on the basis of differential response to temperature and phenazine methosulfate. Mössbauer studies revealed that cells fed with either57FeCl3 or57FeCl2 accumulated unknown ferric and ferrous binding metabolites. 相似文献
13.
Chlorella was used to study the effects of dehydration on photosynthetic activities. The use of unicellular green algae assured that the extent of dehydration was uniform throughout the whole cell population during the course of desiccation. Changes in the activities of the cells were monitored by measurements of fluorescence induction kinetics. It was found that inhibition of most of the photosynthetic activities started at a similar level of cellular water content. They included CO2 fixation, photochemical activity of Photosystem II and electron transport through Photosystem I. The blockage of electron flow through Photosystem I was complete and the whole transition occurred within a relative short time of dehydration. On the other hand, the suppression of Photosystem II activity was incomplete and the transition took a longer time of dehydration. Upon rehydration, the inhibition of Photosystem II activity was fully reversible when samples were in the middle of the transition, but was not thereafter. The electron transport through Photosystem I was also reversible during the transition, but was only partially afterward.Abbreviations DCMU
3-(3,4-dichlorophenyl)-1,1-dimethyl urea
- Fm
maximum fluorescence yield
- F0
non-variable fluorescence level emitted when all PS II centers are open
- Fv
variable part of fluorescence
- PS
photosystem
- QA
primary quinone acceptor of Photosystem II 相似文献
14.
Elevated atmospheric CO2 concentration [CO2] and the change of water distribution in arid and semiarid areas affect plant physiology and ecosystem processes. The interaction of elevated [CO2] and drought results in the complex response such as changes in the energy flux of photosynthesis. The performance of photosystem (PS) II and the electron transport were evaluated by using OJIP induction curves of chlorophyll a fluorescence and the P N-C i curves in the two-factor controlled experiment with [CO2] of 380 (AC) or 750 (EC) [μmol mol?1] and water stress by 10% polyethylene glycol 6000. Compared to water-stressed maize (Zea mays L.) under AC, the EC treatment combined with water stress decreased the number of active reaction centers but it increased the antenna size and the energy flux (absorbed photon flux, trapping flux, and electron transport flux) of each reaction center in PSII. Thus, the electron transport rate was enhanced, despite the indistinctively changed quantum yield of the electron transport and energy dissipation. The combination of EC and the water-stress treatment resulted in the robust carboxylation rate without elevating the saturated photosynthetic rate (P max). This study demonstrated that maize was capable of transporting more electrons into the carboxylation reaction, but this could not be used to increase P max under EC. 相似文献
15.
JEAN‐MARC LIMOUSIN LAURENT MISSON ANNE‐VIOLETTE LAVOIR NICOLAS K. MARTIN SERGE RAMBAL 《Plant, cell & environment》2010,33(5):863-875
Seasonal drought can severely impact leaf photosynthetic capacity. This is particularly important for Mediterranean forests, where precipitation is expected to decrease as a consequence of climate change. Impacts of increased drought on the photosynthetic capacity of the evergreen Quercus ilex were studied for two years in a mature forest submitted to long‐term throughfall exclusion. Gas exchange and chlorophyll fluorescence were measured on two successive leaf cohorts in a control and a dry plot. Exclusion significantly reduced leaf water potential in the dry treatment. In both treatments, light‐saturated net assimilation rate (Amax), stomatal conductance (gs), maximum carboxylation rate (Vcmax), maximum rate of electron transport (Jmax), mesophyll conductance to CO2 (gm) and nitrogen investment in photosynthesis decreased markedly with soil water limitation during summer. The relationships between leaf photosynthetic parameters and leaf water potential remained identical in the two treatments. Leaf and canopy acclimation to progressive, long‐term drought occurred through changes in leaf area index, leaf mass per area and leaf chemical composition, but not through modifications of physiological parameters. 相似文献
16.
A model is presented describing the relationship between chlorophyll fluorescence quenching and photoinhibition of Photosystem (PS) II-dependent electron transport in chloroplasts. The model is based on the hypothesis that excess light creates a population of inhibited PS II units in the thylakoids. Those units are supposed to posses photochemically inactive reaction centers which convert excitation energy to heat and thereby quench variable fluorescence. If predominant photoinhibition of PS II and cooperativity in energy transfer between inhibited and active units are presumed, a quasi-linear correlation between PS II activity and the ratio of variable to maximum fluorescence, FVFM, is obtained. However, the simulation does not result in an inherent linearity of the relationship between quantum yield of PS II and FVFM ratio. The model is used to fit experimental data on photoinhibited isolated chloroplasts. Results are discussed in view of current hypotheses of photoinhibition.Abbreviations FM
maximum total fluorescence
- F0
initial fluorescence
- FV
maximum variable fluorescence
- PS
Photosystem
- QA, QB
primary and secondary electron acceptors of Photosystem II 相似文献
17.
Changes in plant growth, photosynthetic gas exchange, chlorophyll fluorescence and stem diameter of soybean [Glycine max (L.) Merr.] plants under drought stress were studied. Total plant dry mass was reduced by 30 % compared to well-watered control
plants. Leaf water potential was slightly decreased by water stress. Water stress induced daytime shrinkage and reduced night-time
expansion of stem. Photosynthetic rate, stomatal conductance and transpiration rate were significantly declined by water stress,
while the intercellular CO2 concentration was changed only slightly at the initiation of stress treatment. The maximum photochemical efficiency of photosystem
2 and apparent photosynthetic electron transport rate were not changed by water stress. 相似文献
18.
Regulation of electron transport rate through Photosystem I (PS I) was investigated in intact sunflower leaves. The rate constant of electron donation via the cytochrome b
6
f complex (kq, s–1) was obtained from the postillumination P700+ reduction rate, measured as the exponential decay of the light-dark difference (D830) of the 830 nm transmission signal. D830 corresponding to maximum oxidisable P700 (D830m) was obtained by applying white light flashes of different intensity and extrapolating the plot of the quantum yield Y vs. D830 to the axis of abscissae (Y->0). Maximum quantum yield of PS I at completely reduced P700 (Ym) was obtained by extrapolating the same plot to the axis of ordinates (D830->0). Regulation of kq, D830m and Ym under rate-limiting CO2 and O2 concentrations applied after air (21% O2, 310 ppm CO2) was investigated. The amplitude of the downregulation of kq (photosynthetic control) was maximal when electron transport rate (ETR) was limited to about 3 nmol cm–2 s–1 and decreased when ETR was higher or lower. Downregulation did not occur in the absence of CO2 and O2. These gases acted only as substrates of ribulosebisphosphate carboxylase-oxygenase, no high-affinity reaction of O2 leading to enhanced photosynthetic control (e.g. Mehler reaction) was detected. After the transition, D830m at first decreased and then increased again, showing that the reduction of the PS I acceptor side disappeared as a result of the downregulation of kq. The variation of Ym had two reasons, PS I acceptor side reduction and variable excitation capture efficiency by P700. It is concluded that electron transport through PS I is coregulated by the rate of plastoquinol oxidation at Cyt b
6
f, excitation capture efficiency by P700, and by acceptor side reduction.Abbreviations Cyt b
6
f
cytochrome b
6
f complex
- D830
difference of the 830 nm signal from the dark level
- ETR
electron transport rate
- PAD
photon absorption density nmol cm–2 s–1
- PFD
incident photon flux density, nmol cm–2 s–1
- PS I
Photosystem I
- PS II
Photosystem II
- PQH2
plastoquinol
- P700
Photosystem I donor pigment
- Y
quantum yield of PS I electron transport, rel. un. 相似文献
19.
David B. Knaff 《BBA》1973,325(2):284-296
1. Cytochrome f (λmax = 554 nm, Em = +0.35 V) and cytochrome b558 (λmax = 558 nm, Em = +0.35 V) were photooxidized by Photosystem I and photoreduced by Photosystem II in a cell-free preparation from the blue-green alga Nostoc muscorum. The steady-state oxidation levels of both cytochromes were affected by noncyclic electron acceptors and by inhibitors of noncyclic electron transport. These results are consistent with the hypothesis that the mechanism of NADP reduction by water involves a Photosystem II and a Photosystem I light reaction operating in series and linked by a chain of electron carriers that includes cytochrome f and cytochrome b558.2. Phosphorylation cofactors shifted the steady-state of cytochrome f to a more reduced level under conditions of noncyclic electron transport but had no effect on cytochrome b558. These observations suggest that the noncyclic phosphorylation site lies before cytochrome f (on the Photosystem II side) and that cytochrome f is closer to this site than is cytochrome b558.3. A Photosystem II photoreduction of C550 at 77 °K was observed, suggesting that in blue-green algae, as in other plants, C550 is closely associated with the primary electron acceptor for Photosystem II. A Photosystem I photooxidation of P700 at 77 °K was observed, consistent with P700 serving as the primary electron donor of Photosystem I. 相似文献
20.
Photochemical efficiencies of photosystem I (PSI) and photosystem II (PSII) were studied in dry thalli of the lichen Hypogymnia physodes and during their re-hydration. In dry thalli, PSII reaction centers are photochemically inactive, as evidenced by the absence of variable chlorophyll (Chl) fluorescence, whereas the primary electron donor of PSI, P700, exhibits irreversible oxidation under continuous light. Upon application of multiple- and, particularly, single-turnover pulses in dry lichen, P700 oxidation partially reversed, which indicated recombination between P700+ and the reduced acceptor FX of PSI. Re-wetting of air-dried H. physodes initiated the gradual restoration of reversible light-induced redox reactions in both PSII and PSI, but the recovery was faster in PSI. Two slow components of P700+ reduction occurred after irradiation of partially and completely hydrated thalli with strong white light. In contrast, no slow component was found in the kinetics of re-oxidation of QA–, the reduced primary acceptor of PSII, after exposure of such thalli to white light. This finding indicated the inability of PSII in H. physodes to provide the reduction of the plastoquinone pool to significant levels. It is concluded that slow alternative electron transport routes may contribute to the energetics of photosynthesis to a larger extent in H. physodes than in higher plants.Abbreviations A0 and A1 Primary acceptor chlorophyll and secondary electron acceptor phylloquinone - Chl a Chlorophyll a - Fm Maximal level of chlorophyll fluorescence when all PSII centers are closed - Fo Minimal level of fluorescence when all PSII centers are open after dark adaptation - FR Far-red - Fv Variable fluorescence (=Fm–Fo) - FX, FA, and FB Iron–sulfur centers - MT pulse Multiple-turnover pulse - PS Photosystem - P700 Reaction center chlorophyll of PSI - QA Primary quinone acceptor of PSII - QB Secondary quinone acceptor of PSII - ST pulse Single-turnover pulse 相似文献