| 1. |
- Borodich, A, et al.
(författare)
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Segregation of the photosystems in higher plant thylakoids and short- and long-term regulation by a mesoscopic approach
- 2003
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Ingår i: Journal of Theoretical Biology. - 0022-5193 .- 1095-8541. ; 225:4, s. 431-441
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we consider the relationship between the lateral segregation of photosystems I and II in the grana and characteristics of the short- and long-term regulation in thylakoids following the mesoscopic approach. Our study is thermodynamic; it is based on the Flory-Huggins theory for binary mixtures and the McMillan-Mayer theory of heterogeneous solutions. We demonstrate that state transitions promote rearrangement of photosystems by either favoring their mixing after LHCII phosphorylation or enhancing their segregation after LHCII dephosphorylation. This regulation influences the entire system properties locally. We also demonstrate that the variations of the photosystem ratio promote rearrangement of the photosystems preserving their segregation. This regulation influences the entire system properties globally. The studies presented are another indication of the importance of the segregation of the photosystems in the grana thylakoids of higher plants. Segregation of PSIs and PSIIs is a signature of the spinodal decomposition, which is a fine regulatory mechanism, related to both the short- and long-term adaptations of the photosynthetic apparatus in higher plant thylakoids. (C) 2003 Elsevier Ltd. All rights reserved.
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| 2. |
- Borodich, A, et al.
(författare)
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Segregation of the photosystems in thylakoids depends on their size
- 2003
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728 .- 1879-2650. ; 1606:1-3, s. 73-82
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Tidskriftsartikel (refereegranskat)abstract
- Lateral segregation of two types of photosystems in thylakoid membranes of green plants is one of the key factors that provide the stability and fine-tuning of the light quanta supply by pigment proteins and non-cyclic electron transport. Due to this specific feature of the membrane structural organization, the photosynthetic units function in the green plants with optimal performance. In this report a mesoscopic theory is outlined to address the physical aspects of segregation phenomenon. Results of theoretical studies and computer simulations suggest that charge mismatch and the size difference between two photosystems in grana are most responsible for their lateral segregation, which is driven by the screened electrostatic and lipid-induced interactions. Comparative simulations of photosystems of different sizes show the crucial dependence of their ordering on a geometrical parameter. It seems that the size effect alone may prevent photosystems from segregated arrangement in cyanobacterial thylakoids. (C) 2003 Elsevier B.V. All rights reserved.
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| 3. |
- Ivanov, A G, et al.
(författare)
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Iron stress restricts photosynthetic intersystem electron transport in Synechococcus sp, PCC 7942
- 2000
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Ingår i: FEBS Letters. - 0014-5793 .- 1873-3468. ; 485:2-3, s. 173-177
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Tidskriftsartikel (refereegranskat)abstract
- Although exposure of Synechococcus sp. PCC 7942 to iron stress induced the accumulation of the isiA gene product (CP43') compared with non-stressed controls, immunodetection of the N-terminus of cytochrome (Cyt) f indicated that iron stress not only reduced the content of the 40 kDa, heme-binding, Cyt f polypeptide by 32% but it also specifically induced the accumulation of a new, 23 kDa, non-heme-binding, putative Cyt f polypeptide, Concomitantly, iron stress restricted intersystem electron transport based on the in vivo reduction of P700(+), monitored as DeltaA(820)/A(820) in the presence and absence of electron transport inhibitors, as well as the inhibition of the Emerson enhancement effect on O-2 evolution. However, iron stress appeared to be associated with enhanced rates of PS I cyclic electron transport, low rates of PS I-driven photoreduction of NADP(+) but comparable rates for PS II+PS I photoreduction of NADP(+) relative to controls. We hypothesize that Synechococcus sp, PCC 7942 exhibits a dynamic capacity to uncouple PS II and PS I electron transport, which may allow for the higher than expected growth rates observed during iron stress. (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.
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| 4. |
- Ivanov, A G, et al.
(författare)
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Low-temperature modulation of the redox properties of the acceptor side of photosystem II : photoprotection through reaction centre quenching of excess energy
- 2003
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Ingår i: Physiologia Plantarum. - 0031-9317 .- 1399-3054. ; 119:3, s. 376-383
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Tidskriftsartikel (refereegranskat)abstract
- Although it has been well established that acclimation to low growth temperatures is strongly correlated with an increased proportion of reduced Q(A) in all photosynthetic groups, the precise mechanism controlling the redox state of Q(A) and its physiological significance in developing cold tolerance in photoautotrophs has not been fully elucidated. Our recent thermoluminescence (TL) measurements of the acceptor site of PSII have revealed that short-term exposure of the cyanobacterium Synechococcus sp. PCC 7942 to cold stress, overwintering of Scots pine (Pinus sylvestris L.), and acclimation of Arabidopsis plants to low growth temperatures, all caused a substantial shift in the characteristic T-M of S(2)Q(B)(-) recombination to lower temperatures. These changes were accompanied by much lower overall TL emission, restricted electron transfer between Q(A) and Q(B), and in Arabidopsis by a shift of the S(2)Q(A)(-)-related peak to higher temperatures. The shifts in recombination temperatures are indicative of a lower activation energy for the S(2)Q(B)(-) redox pair and a higher activation energy for the S(2)Q(A)(-) redox pair. This results in an increase in the free-energy gap between P680(+)Q(A)(-) and P680(+)Pheo(-) and a narrowing of the free energy gap between Q(A) and Q(B) electron acceptors. We propose that these effects result in an increased population of reduced Q(A) (Q(A)(-)), facilitating non-radiative P680(+)Q(A)(-) radical pair recombination within the PSII reaction centre. The proposed reaction centre quenching could be an important protective mechanism in cyanobacteria in which antenna and zeaxanthin cycle-dependent quenching are not present. In herbaceous plants, the enhanced capacity for dissipation of excess light energy via PSII reaction centre quenching following cold acclimation may complement their capacity for increased utilization of absorbed light through CO2 assimilation and carbon metabolism. During overwintering of evergreens, when photosynthesis is inhibited, PSII reaction centre quenching may complement non-photochemical quenching within the light-harvesting antenna when zeaxanthin cycle-dependent energy quenching is thermodynamically restricted by low temperatures. We suggest that PSII reaction centre quenching is a significant mechanism enabling cold-acclimated organisms to acquire increased resistance to high light.
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| 5. |
- Ivanov, A G, et al.
(författare)
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Photosynthetic electron transport adjustments in overwintering Scots pine (Pinus sylvestris L.)
- 2001
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Ingår i: Planta. - 0032-0935 .- 1432-2048. ; 213:4, s. 575-585
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Tidskriftsartikel (refereegranskat)abstract
- As shown before [C. Ottander et al. (1995) Planta 197:176-183], there is a severe inhibition of the photosystem (PS) II photochemical efficiency of Scots pine (Pinus sylvestris L.) during the winter. In contrast, the in vivo PSI photochemistry is less inhibited during winter as shown by in vivo measurements of DeltaA(820)/Delta (820) (P700(+)). There was also an enhanced cyclic electron transfer around PSI in winter-stressed needles as indicated by 4-fold faster reduction kinetics of P700(+). The differential functional stability of PSII and PSI was accompanied by a 3.7-fold higher intersystem electron pool size, and a 5-fold increase in the stromal electron pool available for P700(+) reduction. There was also a strong reduction of the QB band in the thermoluminescence glow curve and markedly slower Q-A re-oxidation in needles of winter pine, indicating an inhibition of electron transfer between QA and QB. The data presented indicate that the plastoquinone pool is largely reduced in winter pine, and that this reduced state is likely to be of metabolic rather than photochemical origin. The retention of PSI photochemistry, and the suggested metabolic reduction of the plastoquinone pool in winter stressed needles of Scots pine are discussed in terms of the need for enhanced photoprotection of the needles during the winter and the role of metabolically supplied energy for the recovery of photosynthesis from winter stress in evergreens.
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| 6. |
- Ivanov, A G, et al.
(författare)
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Seasonal responses of photosynthetic electron transport in Scots pine (Pinus sylvestris L.) studied by thermoluminescence
- 2002
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Ingår i: Planta. - : Springer Science and Business Media LLC. - 0032-0935 .- 1432-2048. ; 215:3, s. 457-465
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Tidskriftsartikel (refereegranskat)abstract
- The potential of photosynthesis to recover from winter stress was studied by following the thermoluminescence (TL) and chlorophyll fluorescence changes of winter pine needles during the exposure to room temperature (20 degreesC) and an irradiance of 100 mumol m(-2) s(-1). TL measurements of photosystem 11 (PSII) revealed that the S(2)Q(B)(-) charge recombinations (the B-band) were shifted to lower temperatures in winter pine needles, while the S(2)Q(A)(-) recombinations (the Q-band) remained close to 0 degreesC. This was accompanied by a drastically reduced (65%) PSII photochemical efficiency measured as F-v/F-m and a 20-fold faster rate of the fluorescence transient from F-o to F, as compared to summer pine. A strong positive correlation between the increase in the photochemical efficiency of PSII and the increase in the relative contribution of the B-band was found during the time course of the recovery process. The seasonal dynamics of TL in Scots pine needles studied under field conditions revealed that between November and April, the contribution of the Q- and B-bands to the overall TL emission was very low (less than 5%). During spring, the relative contribution of the Q- and B-bands, corresponding to charge recombination events between the acceptor and donor sides of PSII, rapidly increased, reaching maximal values in late July. A sharp decline of the B-band was observed in late summer, followed by a gradual decrease, reaching minimal values in November. Possible mechanisms of the seasonally induced changes in the redox properties Of S-2/S(3)Q(B)(-) recombinations are discussed. It is proposed that the lowered redox potential Of Q(B) in winter needles increases the population Of Q(A)(-). thus enhancing the probability for non-radiative P680(+) Q(A)(-) recombination. This is suggested to enhance the radiationless dissipation of excess light within the PSII reaction center during cold acclimation and during cold winter periods.
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| 7. |
- Leonardos, E D, et al.
(författare)
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Daily photosynthetic and C-export patterns in winter wheat leaves during cold stress and acclimation
- 2003
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Ingår i: Physiologia Plantarum. - 0031-9317 .- 1399-3054. ; 117:4, s. 521-531
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Tidskriftsartikel (refereegranskat)abstract
- Diurnal patterns of whole-plant and leaf gas exchange and (14) C-export of winter wheat acclimated at 20 and 5degreesC were determined. The 5degreesC-acclimated plants had lower relative growth rates, smaller biomass and leaf area, but larger specific leaf weight than 20degreesC plants. Photosynthetic rates in 20degreesC and 5degreesC-acclimated leaves were similar; however, daytime export from 5degreesC-acclimated leaves was 45% lower. Photosynthesis and export remained steady in 20degreesC and 5degreesC-acclimated leaves during the daytime. By comparison, photosynthesis in 5degreesC-stressed leaves (20degreesC-acclimated plants exposed to 5degreesC 12 h before and during measurements) declined from 70 to 50% of the 20degreesC-acclimated leaves during the daytime, while export remained constant at 35% of the 20degreesC-acclimated and 60% of the 5degreesC-acclimated leaves. At high light and CO2 , photosynthesis and export increased in both 20degreesC and 5degreesC-acclimated leaves, but rates in 5degreesC-stressed leaves remained unchanged. At all conditions daytime export was greater than nighttime export. Taken together, during cold acclimation photosynthesis was upregulated, whereas export was only partially increased. We suggest that this reflects a requirement of cold-acclimated plants to both sustain an increased leaf metabolic demand while concomitantly supporting translocation of photoassimilates to overwintering sinks.
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| 8. |
- Rojdestvenski, I, et al.
(författare)
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A carbonic anhydrase catalyzed CO2 pump in Chlamydomonas reinhardtii : In vivo experiments, computer modelling, and theory
- 2000
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Ingår i: Russian journal of plant physiology. - 1021-4437 .- 1608-3407. ; 47:5, s. 613-621
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Tidskriftsartikel (refereegranskat)abstract
- We studied the bicarbonate depletion effects on photosynthesis in high-CO2 grown-cell wall-less mutants of Chlamydomonas reinhardtii with (cw92) and without (cia3/cw15) active carbonic anhydrase (CA) associated with photosystem II (PSII). The mutants were grown in a high-CO2 medium and then washed with a CO2-free buffer. We discuss the shutdown of oxygen evolution in cw92 as a consequence of CO2 depletion of the Calvin cycle. It is suggested that CA acts as part of a PSII-driven pump delivering CO2 from the lumen into the stroma, where it becomes available to the Calvin cycle. Our model is supported by computer simulation data and accommodates the results of in vivo experiments as well as the differences between cw92 and cia3 mutants. We also present a simple theory of the phenomena discussed, based on a time-scale hierarchy approach, which describes the CO2 depletion in cw92 using only two rate constants-V-max and K-m of the Calvin cycle.
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| 9. |
- Rojdestvenski, I, et al.
(författare)
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A two-dimensional many-body system with competing interactions as a model for segregation of photosystems in thylakoids of green plants
- 2000
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Ingår i: European Biophysics Journal. - 0175-7571 .- 1432-1017. ; 29:3, s. 214-220
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Tidskriftsartikel (refereegranskat)abstract
- We address the segregation of photosystems I (PSI) and II (PSII) in thylakoid membranes by means of a molecular dynamics method. We assume a two-dimensional (in-plane) problem with PSI and PSII being represented by particles with different values of negative charge. The pair interactions between particles include a screened Coulomb repulsive part and am exponentially decaying attractive part. Our modeling results suggest that the system may have a complicated phase behavior, including a quasi-crystalline phase at low ionic screenmg, a disordered phase and: in addition, a possible "clotting" agglomerate phase at high screening where the photosystems tend to clot together. The relevance of the observed phenomena to the stacking of thylakoid membranes is discussed.
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| 10. |
- Rojdestvenski, I, et al.
(författare)
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Segregation of photosystems in thylakoid membranes as a critical phenomenon
- 2002
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Ingår i: Biophysical Journal. - 0006-3495 .- 1542-0086. ; 82:4, s. 1719-1730
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of the two photosystems, PSI and PSII, in grana and stroma lamellae of the chloroplast membranes is not uniform. PSII are mainly concentrated in grana and PSI in stroma thylakoids. The dynamics and factors controlling the spatial segregation of PSI and PSII are generally not well understood, and here we address the segregation of photosystems in thylakoid membranes by means of a molecular dynamics method. The lateral segregation of photosystems was studied assuming a model comprising a two-dimensional (in-plane), two-component, many-body system with periodic boundary conditions and competing interactions between the photosystems in the thylakoid membrane. PSI and PSII are represented by particles with different values of negative charge. The pair interactions between particles include a screened Coulomb repulsive part and an exponentially decaying attractive part. The modeling results suggest a complicated phase behavior of the system, including quasi-crystalline phase of randomly distributed complexes of PSII and PSI at low ionic screening, well defined clustered state of segregated complexes at high screening, and in addition, an intermediate agglomerate phase where the photosystems tend to aggregate together without segregation. The calculations demonstrated that the ordering of photosystems within the membrane was the result of interplay between electrostatic and lipid-mediated interactions. At some values of the model parameters the segregation can be represented visually as well as by analyzing the correlation functions of the configuration.
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