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1.
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
2.
Chlorophyll a fluorescence induction (FI) is widely used as a probe for studying photosynthesis. On illumination, fluorescence emission rises from an initial level O to a maximum P through transient steps, termed J and I. FI kinetics reflect the overall performance of photosystem II (PSII). Although FI kinetics are commonly and easily measured, there is a lack of consensus as to what controls the characteristic series of transients, partially because most of the current models of FI focus on subsets of reactions of PSII, but not the whole. Here we present a model of fluorescence induction, which includes all discrete energy and electron transfer steps in and around PSII, avoiding any assumptions about what is critical to obtaining O J I P kinetics. This model successfully simulates the observed kinetics of fluorescence induction including O J I P transients. The fluorescence emission in this model was calculated directly from the amount of excited singlet-state chlorophyll in the core and peripheral antennae of PSII. Electron and energy transfer were simulated by a series of linked differential equations. A variable step numerical integration procedure ( ode15s) from MATLAB provided a computationally efficient method of solving these linked equations. This in silico representation of the complete molecular system provides an experimental workbench for testing hypotheses as to the underlying mechanism controlling the O J I P kinetics and fluorescence emission at these points. Simulations based on this model showed that J corresponds to the peak concentrations of Q
A
−
Q B (Q A and Q B are the first and second quinone electron acceptor of PSII respectively) and Q
A
−
Q
B
−
and I to the first shoulder in the increase in concentration of Q
A
−
Q
B
2−
. The P peak coincides with maximum concentrations of both Q
A
−
Q
B
2−
and PQH 2. In addition, simulations using this model suggest that different ratios of the peripheral antenna and core antenna lead to differences in fluorescence emission at O without affecting fluorescence emission at J, I and P. An increase in the concentration of Q B-nonreducing PSII centers leads to higher fluorescence emission at O and correspondingly decreases the variable to maximum fluorescence ratio ( F
v/ F
m). 相似文献
3.
Oxygen evolution per single-turnover flash (STF) or multiple-turnover pulse (MTP) was measured with a zirconium O 2 analyzer from sunflower leaves at 22°C. STF were generated by Xe arc lamp, MTP by red LED light of up to 18000 μmol quanta m −2 s −1. Ambient O 2 concentration was 10–30 ppm, STF and MTP were superimposed on far-red background light in order to oxidize plastoquinone
(PQ) and randomize S-states. Electron (e −) flow was calculated as 4 times O 2 evolution. Q
A → Q
B electron transport was investigated firing double STF with a delay of 0 to 2 ms between the two. Total O 2 evolution per two flashes equaled to that from a single flash when the delay was zero and doubled when the delay exceeded
2 ms. This trend was fitted with two exponentials with time constants of 0.25 and 0.95 ms, equal amplitudes. Illumination
with MTP of increasing length resulted in increasing O 2 evolution per pulse, which was differentiated with an aim to find the time course of O 2 evolution with sub-millisecond resolution. At the highest pulse intensity of 2.9 photons ms −1 per PSII, 3 e − initially accumulated inside PSII and the catalytic rate of PQ reduction was determined from the throughput rate of the fourth
and fifth e −. A light response curve for the reduction of completely oxidized PQ was a rectangular hyperbola with the initial slope of
1.2 PSII quanta per e − and V
m of 0.6 e − ms −1 per PSII. When PQ was gradually reduced during longer MTP, V
m decreased proportionally with the fraction of oxidized PQ. It is suggested that the linear kinetics with respect to PQ are
apparent, caused by strong product inhibition due to about equal binding constants of PQ and PQH 2 to the Q
B site. The strong product inhibition is an appropriate mechanism for down-regulation of PSII electron transport in accordance
with rate of PQH 2 oxidation by cytochrome b 6f. 相似文献
4.
Mutants of Rhodobacter (Rba.) sphaeroides are described which were designed to study electron transfer along the so-called B-branch of reaction center (RC) cofactors.
Combining the mutation L(M214)H, which results in the incorporation of a bacteriochlorophyll, β, for H A [Kirmaier et al. (1991) Science 251: 922–927] with two mutations, G(M203)D and Y(M210)W, near B A, we have created a double and a triple mutant with long lifetimes of the excited state P * of the primary donor P, viz. 80 and 160 ps at room temperature, respectively. The yield of P +Q A
− formation in these mutants is reduced to 50 and 30%, respectively, of that in wildtype RCs. For both mutants, the quantum
yield of P +H B
− formation was less than 10%, in contrast to the 15% B-branch electron transfer demonstrated in RCs of a similar mutant of
Rba. capsulatus with a P * lifetime of 15 ps [Heller et al. (1995) Science 269: 940–945]. We conclude that the lifetime of P * is not a governing factor in switching to B-branch electron transfer. The direct photoreduction of the secondary quinone,
Q B, was studied with a triple mutant combining the G(M203)D, L(M214)H and A(M260)W mutations. In this triple mutant Q A does not bind to the reaction center [Ridge et al. (1999) Photosynth Res 59: 9–26]. It is shown that B-branch electron transfer
leading to P +Q B
− formation occurs to a minor extent at both room temperature and at cryogenic temperatures (about 3% following a saturating
laser flash at 20 K). In contrast, in wildtype RCs P +Q B
− formation involves the A-branch and does not occur at all at cryogenic temperatures. Attempts to accumulate the P +Q B
− state under continuous illumination were not successful. Charge recombination of P +Q B
− formed by B-branch electron transfer in the new mutant is much faster (seconds) than has been previously reported for charge
recombination of P +Q B
− trapped in wildtype RCs (10 5 s) [Kleinfeld et al. (1984b) Biochemistry 23: 5780–5786]. This difference is discussed in light of the different binding
sites for Q B and Q B
− that recently have been found by X-ray crystallography at cryogenic temperatures [Stowell et al. (1997) Science 276: 812–816].
We present the first low-temperature absorption difference spectrum due to P +Q B
−.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
5.
The recent crystallographic structure at 3.0 Å resolution of PSII from Thermosynechococcus elongatus has revealed a cavity in the protein which connects the membrane phase to the binding pocket of the secondary plastoquinone Q B. The cavity may serve as a quinone diffusion pathway. By fluorescence methods, electron transfer at the donor and acceptor sides was investigated in the same membrane-free PSII core particle preparation from T. elongatus prior to and after crystallization; PSII membrane fragments from spinach were studied as a reference. The data suggest selective enrichment of those PSII centers in the crystal that are intact with respect to O 2 evolution at the manganese-calcium complex of water oxidation and with respect to the integrity of the quinone binding site. One and more functional quinone molecules (per PSII monomer) besides of Q A and Q B were found in the crystallized PSII. We propose that the extra quinones are located in the Q B cavity and serve as a PSII intrinsic pool of electron acceptors. 相似文献
6.
Lumenal extrinsic proteins PsbO, PsbP, and PsbQ of photosystem II (PSII) protect the catalytic cluster Mn 4CaO 5 of oxygen-evolving complex (OEC) from the bulk solution and from soluble compounds in the surrounding medium. Extraction of PsbP and PsbQ proteins by NaCl-washing together with chelator EGTA is followed also by the depletion of Ca 2+ cation from OEC. In this study, the effects of PsbP and PsbQ proteins, as well as Ca 2+ extraction from OEC on the kinetics of the reduced primary electron acceptor (Q A ?) oxidation, have been studied by fluorescence decay kinetics measurements in PSII membrane fragments. We found that in addition to the impairment of OEC, removal of PsbP and PsbQ significantly slows the rate of electron transfer from Q A ? to the secondary quinone acceptor Q B. Electron transfer from Q A ? to Q B in photosystem II membranes with an occupied Q B site was slowed down by a factor of 8. However, addition of EGTA or CaCl 2 to NaCl-washed PSII did not change the kinetics of fluorescence decay. Moreover, the kinetics of Q A ? oxidation by Q B in Ca-depleted PSII membranes obtained by treatment with citrate buffer at pH 3.0 (such treatment keeps all extrinsic proteins in PSII but extracts Ca 2+ from OEC) was not changed. The results obtained indicate that the effect of NaCl-washing on the Q A ? to Q B electron transport is due to PsbP and PsbQ extrinsic proteins extraction, but not due to Ca 2+ depletion. 相似文献
7.
The effect of cumulative over-saturating pulses (OSP) of white light (1 s, >10 000 μmol photons m −2 s −1), applied every 20 min on pea leaves, was investigated during a complete diurnal cycle of 24 h. In dark-adapted leaves, this
treatment leads to a progressive decline of the optimum Photosystem II (PS II) quantum yield. Continuous low background light
(except far-red light) had a protective effect against this OSP-induced photoinactivation. The lack of far-red effect could
be due to its absorption mainly in PS I and not in PS II, but could be also due to the general low absorption in this wavelength
region. The photoinactivation was enhanced in leaves that had been previously infiltrated with chloramphenicol. The quantum
yield of CO 2 assimilation, but not its maximal capacity, was inhibited by the OSP treatment. The most spectacular effects observed, in
addition to an irreversible quenching of Fm, was a strong inhibition of Q A
− reoxidation revealed by a large increase in the Fs level and consequently by a decrease of ΔF/Fm′. Under such conditions,
we observed that the electron flow deduced from ΔF/Fm′ underestimated the real electron flow to CO 2. Time-resolved Chlorophyll a fluorescence measurements showed that the reduced capacity of Q A
− reoxidation in OSP treated leaves was accompanied by the appearance of a 4.7 ns component attributed to PS II charge recombination.
We suggest that a modification at the Q B site may influence the redox potential of Q A/Q A
−, facilitating the reversion of the primary charge separation. In addition, a 1.2 ns fluorescence component accumulated, which
appeared to be responsible for the underestimation of PS II electron flow. The observed photoinactivation seemed to be different
from the photoinhibition often described in the literature, which occurs under continuous light.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
Filtrates from crushed Moringa oleifera seeds were tested for their effects on growth and Photosystem II efficiency of the common bloom-forming cyanobacterium Microcystis aeruginosa. M. aeruginosa populations exhibited good growth in controls and treatments with 4- and 8-mg crushed Moringa seeds per liter, having similar growth rates of 0.50 (±0.01) per day. In exposures of 20- to 160-mg crushed Moringa seeds L −1, growth rates were negative and on average −0.23 (±0.05) .day −1. Presumably, in the higher doses of 20- to 160-mg crushed seeds per liter, the cyanobacteria died, which was supported by
a rapid drop in the Photosystem II efficiency (Φ PSII), while the Φ PSII was high and unaffected in 0, 4, and 8 mg L −1. High-density populations of M. aeruginosa (chlorophyll- a concentrations of ∼270 μg L −1) were reduced to very low levels within 2 weeks of exposure to ≥80-mg crushed seeds per liter. At the highest dosage of 160 mg L −1, the Φ PSII dropped to zero rapidly and remained nil during the course of the experiment (14 days). Hence, under laboratory conditions,
a complete wipeout of the bloom could be achieved. This is the first study that yielded evidence for cyanobactericidal activity
of filtrate from crushed Moringa seeds, suggesting that Moringa seed extracts might have a potential as an effect-oriented measure lessening cyanobacterial nuisance. 相似文献
9.
Detached leaves of tomato ( Lycopersicon esculentum Mill.) experienced photoinhibition associated with sharp reductions in net photosynthetic rate (Pn), quantum efficiency of
PSII (Φ PSII) and photochemical quenching (qP) even though they were exposed to mild light intensity (400 μmol m −2 s −1 PPFD) at 28°C. Photoinhibition and the reduction in Pn, Φ PSII and qP, however, were significantly alleviated by 1 mg l −1 ABA, 0.1 mg l −1
N-(2-chloro-4-pyridyl)- N′-phenylurea (CPPU) and 0.01 mg l −1 24-epibrassinolide (EBR). Higher concentrations, however, reduced the effects or even exacerbated the occurrence of photoinhibition.
Superoxide dismutase and ascorbate peroxidase activity in leaves increased with the increases in ABA concentration within
1–100 mg l −1, CPPU concentration within 0.1–10 mg l −1 and EBR concentration within 0.01–1.0 mg l −1. Catalase and guaiacol peroxidase activity also increased with the increase in EBR concentration but CPPU and ABA treatments
at higher concentrations caused a decrease. Malondialdehyde (MDA) content decreased with the increase in CPPU concentration.
ABA and EBR, however, decreased MDA concentration only at 1 and 0.01 mg l −1, respectively. In conclusion, detached leaves had increased sensitivity to PSII photoinhibition. Photoinhibition-induced
decrease in photosynthesis, however, was significantly alleviated by EBR, CPPU and ABA at a proper concentration. 相似文献
10.
We investigated the effects of limiting (1.96 × 10 −9 mol l −1 total Cu, corresponding to pCu 14.8; where pCu = −log [Cu 2+]) and toxic Cu concentrations up to 8.0 × 10 −5 mol l −1 total Cu (equivalent to pCu 9.5) on growth rates and photosynthetic activity of exponentially grown Phaeocystis cordata, using batch and semi-continuous cultures. With pulse amplitude modulated (PAM) fluorometry, we determined the photochemical
response of P. cordata to the various Cu levels, and showed contrasting results for the batch and semi-continuous cultures. Although maximum photosystem
II (PSII) quantum yield (Φ M) was optimal and constant in the semi-continuous P. cordata, the batch cultures showed a significant decrease in Φ M with culture age (0–72 h). The EC50 for the batch cultures was higher (2.0 × 10 −10 mol l −1, pCu9.7), than that for the semi-continuous cultures (6.3 × 10 −11 mol l −1, pCu10.2). The semi-continuous cultures exhibited a systematic and linear decrease in Φ M as Cu levels increased (for [Cu 2+] < 1.0 × 10 −12 mol l −1, pCu12.0), however, no effect of high Cu was observed on their operational PSII quantum yield (Φ′ M). Similarly, semi-continuous cultures exhibited a significant decrease in Φ M, but not in Φ′ M, because of low-Cu levels. Thus, Cu toxicity and Cu limitation damage the PSII reaction centers, but not the processes downstream
of PSII. Quenching mechanisms (NPQ and Q
n) were lower under high Cu relative to the controls, suggesting that toxic Cu impairs photo-protective mechanisms. PAM fluorometry
is a sensitive tool for detecting minor physiological variations. However, culturing techniques (batch vs. semi-continuous)
and sampling time might account for literature discrepancies on the effects of Cu on PSII. Semi-continuous culturing might
be the most adequate technique to investigate Cu effects on PSII photochemistry. 相似文献
11.
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
12.
Phosphatidylglycerol (PG), containing the unique fatty acid Δ3, trans-16:1-hexadecenoic acid, is a minor but ubiquitous lipid component of thylakoid membranes of chloroplasts and cyanobacteria.
We investigated its role in electron transfers and structural organization of Photosystem II (PSII) by treating Arabidopsis thaliana thylakoids with phospholipase A 2 to decrease the PG content. Phospholipase A 2 treatment of thylakoids (a) inhibited electron transfer from the primary quinone acceptor Q A to the secondary quinone acceptor Q B, (b) retarded electron transfer from the manganese cluster to the redox-active tyrosine Z, (c) decreased the extent of flash-induced
oxidation of tyrosine Z and dark-stable tyrosine D in parallel, and (d) inhibited PSII reaction centres such that electron
flow to silicomolybdate in continuous light was inhibited. In addition, phospholipase A 2 treatment of thylakoids caused the partial dissociation of (a) PSII supercomplexes into PSII dimers that do not have the
complete light-harvesting complex of PSII (LHCII); (b) PSII dimers into monomers; and (c) trimers of LHCII into monomers.
Thus, removal of PG by phospholipase A 2 brings about profound structural changes in PSII, leading to inhibition/retardation of electron transfer on the donor side,
in the reaction centre, and on the acceptor side. Our results broaden the simple view of the predominant effect being on the
Q B-binding site. 相似文献
13.
By simultaneously analyzing the chlorophyll a fluorescence transient and light absorbance at 820 nm as well as chlorophyll fluorescence quenching, we investigated the
effects of different photon flux densities (0, 15, 200 μmol m −2 s −1) with or without 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on the repair process of cucumber ( Cucumis sativus L.) leaves after treatment with low temperature (6°C) combined with moderate photon flux density (200 μmol m −2 s −1) for 6 h. Both the maximal photochemical efficiency of Photosystem II (PSII) ( F
v/ F
m) and the content of active P700 (Δ I/ I
o) significantly decreased after chilling treatment under 200 μmol m −2 s −1 light. After the leaves were transferred to 25°C, F
v/ F
m recovered quickly under both 200 and 15 μmol m −2 s −1 light. Δ I/ I
o recovered quickly under 15 μmol m −2 s −1 light, but the recovery rate of Δ I/ I
o was slower than that of F
v/ F
m. The cyclic electron transport was inhibited by chilling-light treatment obviously. The recovery of Δ I/ I
o was severely suppressed by 200 μmol m −2 s −1 light, whereas a pretreatment with DCMU effectively relieved this suppression. The cyclic electron transport around PSI recovered
in a similar way as the active P700 content did, and the recovery of them was both accelerated by pretreatment with DCMU.
The results indicate that limiting electron transport from PSII to PSI protected PSI from further photoinhibition, accelerating
the recovery of PSI. Under a given photon flux density, faster recovery of PSII compared to PSI was detrimental to the recovery
of PSI or even to the whole photosystem. 相似文献
14.
In this study, effects of antimony Sb(V) on growth, pigments content, oxygen evolution, and photosystem II (PSII) activity of Microcystis aeruginosa were investigated. JIP-test, Q A ? reoxidation kinetic test and S-state test were used in this study to study the energy distribution and electron transport in PSII. Treatment with Sb(V) at various concentrations ranging from 5 to 100?mg/l had long-term effects on growth, pigments content, and oxygen evolution of M. aeruginosa. Low concentration of Sb(V) had no significant inhibition of the biomass production and PSII activity but inhibited the pigment synthesis. Growth, pigments content, oxygen evolution, and PSII activity were seriously inhibited when treated by high concentration of Sb(V) (100?mg/l). The target sites of Sb(V) toxic effect on the PSII of M. aeruginosa were mainly on the donor side and the apparatus in the light-dependent reaction. The quantum yield for photochemistry, density of reaction centers and photosynthesis performance index decreased, whereas the dissipated energy increased. PSII activity of M. aeruginosa was promoted when exposure to 50?mg/l Sb(V) by increasing the density of active reaction centers and electron transport after Q A ? . 相似文献
15.
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
16.
Difference femtosecond absorption spectroscopy with 20-fsec temporal resolution was applied to study a primary stage of charge
separation and transfer processes in reaction centers of YM210L and YM210L/FM197Y site-directed mutants of the purple bacterium
Rhodobacter sphaeroides at 90 K. Photoexcitation was tuned to the absorption band of the primary electron donor P at 880 nm. Coherent oscillations
in the kinetics of stimulated emission of P* excited state at 940 nm and of anion absorption of monomeric bacteriochlorophyll
B A− at 1020 nm were monitored. The absence of tyrosine YM210 in RCs of both mutants leads to strong slowing of the primary reaction
P* → P +B A− and to the absence of stabilization of separated charges in the state P +B A−. Mutation FM197Y increases effective mass of an acetyl group of pyrrole ring I in the bacteriochlorophyll molecule P B of the double mutant YM210L/FM197Y by a hydrogen bond with OH-TyrM197 group that leads to a decrease in the frequency of
coherent nuclear motions from 150 cm −1 in the single mutant YM210L to ∼100 cm −1 in the double mutant. Oscillations with 100–150 cm −1 frequencies in the dynamics of the P* stimulated emission and in the kinetics of the reversible formation of P +B A− state of both mutants reflect a motion of the P B molecule relatively to P A in the area of mutual overlapping of their pyrrole rings I. In the double mutant YM210L/FM197Y the oscillations in the P*
emission band and the B A− absorption band are conserved within a shorter time ∼0.5 psec (1.5 psec in the YM210L mutant), which may be a consequence
of an increase in the number of nuclei forming a wave packet by adding a supplementary mass to the dimer P. 相似文献
17.
This work aims to: (1) correlate photochemical activity and productivity, (2) characterize the flow pattern of culture layers
and (3) determine a range of biomass densities for high productivity of the freshwater microalga Chlorella spp., grown outdoors in thin-layer cascade units. Biomass density, irradiance inside culture, pigment content and productivity
were measured in the microalgae cultures. Chlorophyll-fluorescence quenching was monitored in situ (using saturation-pulse
method) to estimate photochemical activities. Photobiochemical activities and growth parameters were studied in cultures of
biomass density between 1 and 47 g L −1. Fluorescence measurements showed that diluted cultures (1–2 g DW L −1) experienced significant photostress due to inhibition of electron transport in the PSII complex. The highest photochemical
activities were achieved in cultures of 6.5–12.5 g DW L −1, which gave a maximum daylight productivity of up to 55 g dry biomass m −2 day −1. A midday depression of maximum PSII photochemical yield ( F
v/ F
m) of 20–30% compared with morning values in these cultures proved to be compatible with well-performing cultures. Lower or
higher depression of F
v/ F
m indicated low-light acclimated or photoinhibited cultures, respectively. A hydrodynamic model of the culture demonstrated
highly turbulent flow allowing rapid light/dark cycles (with frequency of 0.5 s −1) which possibly match the turnover of the photosynthetic apparatus. These results are important from a biotechnological point
of view for optimisation of growth of outdoor microalgae mass cultures under various climatic conditions. 相似文献
18.
The role of tyrosine M210 in charge separation and stabilization of separated charges was studied by analyzing of the femtosecond
oscillations in the kinetics of decay of stimulated emission from P* and of a population of the primary charge separated state
P +B A− in YM210L and YM210L/HL168L mutant reaction centers (RCs) of Rhodobacter sphaeroides in comparison with those in native Rba. sphaeroides RCs. In the mutant RCs, TyrM210 was replaced by Leu. The HL168L mutation placed the redox potential of the P +/P pair 123 mV below that of native RCs, thus creating a theoretical possibility of P +B A− stabilization. Kinetics of P* decay at 940 nm of both mutants show a significant slowing of the primary charge separation
reaction in comparison with native RCs. Distinct damped oscillations in these kinetics with main frequency bands in the range
of 90–150 cm −1 reflect mostly nuclear motions inside the dimer P. Formation of a very small absorption band of B A− at 1020 nm is registered in RCs of both mutants. The formation of the B A− band is accompanied by damped oscillations with main frequencies from ∼10 to ∼150 cm −1. Only a partial stabilization of the P +B A− state is seen in the YM210L/HL168L mutant in the form of a small non-oscillating background of the 1020-nm kinetics. A similar
charge stabilization is absent in the YM210L mutant. A model of oscillatory reorientation of the OH-group of TyrM210 in the
electric fields of P + and B A− is proposed to explain rapid stabilization of the P +B A− state in native RCs. Small oscillatory components at ∼330–380 cm −1 in the 1020-nm kinetics of native RCs are assumed to reflect this reorientation. We conclude that the absence of TyrM210
probably cannot be compensated by lowering of the P +B A− free energy that is expected for the double YM210L/HL168L mutant. An oscillatory motion of the HOH55 water molecule under
the influence of P + and B A− is assumed to be another potential contributor to the mechanism of P +B A− stabilization. 相似文献
19.
Tenuazonic acid (TeA) is a putative phytotoxin obtained from Alternaria alternata, the organism that can cause brown leaf spot disease of Crofton weed ( Eupatorium adenophorum). It is demonstrated here that the tenuazonic acid inhibits the activity of photosystem II (PSII); the I50-value is 48 μg mL ?1. Evidences from chlorophyll fluorescence show that tenuazonic acid interrupts electron transport between Q A and Q B on the acceptor side of PSII. It does not have an effect on the antenna pigments, the oxygen-evolving complex (OEC) at the donor side of PSII. On the basis of the fluorescence induction kinetics and competition experiments with [ 14C]atrazine, it is shown that tenuazonic acid does not share the same binding environment with atrazine despite their common action target: the Q B-site. It is concluded that tenuazonic acid is a member of a novel class of PSII inhibitors. 相似文献
20.
We review the factors that control the efficiency of carotenoid-chlorophyll excitation transfer in photosynthetic light harvesting.
For this we summarize first the recently developed theory that describes electronic couplings between carotenoids and chlorophylls
and we outline in particular the influence of length of conjugated system and of symmetry breaking on the couplings. We focus
hereby on the structurally solved lycopene-BChl system of LH 2 from Rhodospirillum molischianum and the peridinin-Chl a system of PCP from Amphidinium carterae. In addition, we review recent spectroscopic data for neurosporene, spheroidene and lycopene, three carotenoids with different
lengths of conjugated systems. On the basis of the measured energies, emission lineshapes, solution and protein environment
lifetimes for their 2A −
g and 1B u
+ states as well as of the theoretically determined couplings, we conclude that the transfer efficiencies from the 2A g
− state are controlled by the Car(2A g
−)–BChl(Q g) electronic couplings and the 2A g
− → 1A g
− internal conversion rates. We suggest that symmetry breaking and geometry rather than length of conjugated system dominate
couplings involving the 2A g
− state. Differences in transfer efficiencies from the 1B u
+ state in LH 2 and PCP are found to be dominated by the differences in spectral overlap. The role of the 1B u
+ state is likely to be influenced by a lower-lying (in longer polyenes), optically forbidden 1B u
− state.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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