| 1. |
- Bossmann, B, et al.
(författare)
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Screening of chlorina mutants of barley (Hordeum vulgare L.) with antibodies against light-harvesting proteins of PS I and PS II : Absence of specific antenna proteins
- 1997
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Ingår i: Photosynthesis Research. - 0166-8595 .- 1573-5079. ; 52:2, s. 127-136
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Tidskriftsartikel (refereegranskat)abstract
- Twenty-three chlorina (clo) mutants from the barley mutant collection of the Carlsberg Laboratory, Copenhagen, were tested for the presence of the four light-harvesting chlorophyll (Chl) a/b-binding proteins (LHC) of Photosystem I (Lhcal-4) and the PS II antenna proteins Lhcb1-3 (LHC II), Lhcb4-6 (CP29, CP26, CP24) and PsbS (CP22) using monospecific and monoclonal antibodies. Mutants allelic to barley mutant clo-f2, impaired in Chi b synthesis, provided evidence that Lhca4, Lhcb1 and Lhcb6 are unstable in the absence of Chi b, and the accumulation of Lhcb2, Lhcb3 and Lhcb4 is also impaired. Mutants at the locus chlorina-a (clo-a(117), clo-a(126) and clo-a(134)) lack or have only trace amounts of Lhca1, Lhca4, Lhcb1 and Lhcb3, whereas a mutant at the locus chlorina-b (clo-b(125)) had reduced amounts of all Lhca proteins. These two mutations could have an effect in protein import or assembly. Evidence is presented that Lhcb5 is the innermost LHC protein of PS II, and that Lhca1 and Lhca4, which have been supposed to be intimately associated in the LHCI-730 complex, can accumulate independently of each other. 77 K fluorescence emission spectra taken from leaves of clo-f2(101), clo-a(126) and clo-b(125) indicate that chlorophyll(s) emitting at 742 nm are coupled to the presence of Lhca4 that is bound to the reaction centre, and those emitting around 730 nm are located on Lhca1.
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| 2. |
- Campbell, D, et al.
(författare)
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Two forms of the photosystem II D1 protein alter energy dissipation and state transitions in the cyanobacterium Synechococcus sp PCC 7942
- 1996
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Ingår i: Photosynthesis Research. - 0166-8595 .- 1573-5079. ; 47:2, s. 131-144
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Tidskriftsartikel (refereegranskat)abstract
- Synechococcus sp. PCC 7942 (Anacystis nidulans R2) contains two forms of the Photosystem II reaction centre protein D1, which differ in 25 of 360 amino acids. D1:1 predominates under low light hut is transiently replaced by D1:2 upon shifts to higher light. Mutant cells containing only D1:1 have lower photochemical energy capture efficiency and decreased resistance to photoinhibition, compared to cells containing D1:2. We show that when dark-adapted or under low to moderate light, cells with D1:1 have higher non-photochemical quenching of PS II fluorescence (higher q(N)) than do cells with D1:2. This is reflected in the 77 K chlorophyll emission spectra, with lower Photosystem II fluorescence at 697-698 nm in cells containing D1:1 than in cells with D1:2. This difference in quenching of Photosystem II fluorescence occurs upon excitation of both chlorophyll at 435 nm and phycobilisomes at 570 nm. Measurement of time-resolved room temperature fluorescence shows that Photosystem II fluorescence related to charge stabilization is quenched more rapidly in cells containing D1:1 than in those with D1:2. Cells containing D1:1 appear generally shifted towards State II, with PS II down-regulated, while cells with D1:2 tend towards State I. In these cyanobacteria electron transport away from PS II remains non-saturated even under photoinhibitory levels of light. Therefore, the higher activity of D1:2 Photosystem II centres may allow more rapid photochemical dissipation of excess energy into the electron transport chain. D1:1 confers capacity for extreme State II which may be of benefit under low and variable light.
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| 3. |
- Oquist, Gunnar, 1941-, et al.
(författare)
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The cyanobacterium Synechococcus modulates Photosystem II function in response to excitation stress through D1 exchange
- 1995
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Ingår i: Photosynthesis Research. - 0166-8595 .- 1573-5079. ; 46:1-2, s. 151-158
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Tidskriftsartikel (refereegranskat)abstract
- In this minireview we discuss effects of excitation stress on the molecular organization and function of PS II as induced by high light or low temperature in the cyanobacterium Synechococcus sp. PCC 7942. Synechococcus displays PS II plasticity by transiently replacing the constitutive D1 form (D1:1) with another form (D1:2) upon exposure to excitation stress. The cells thereby counteract photoinhibition by increasing D1 turn over and modulating PS II function. A comparison between the cyanobacterium Synechococcus and plants shows that in cyanobacteria, with their large phycobilisomes, resistance to photoinhibition is mainly through the dynamic properties ( D1 turnover and quenching) of the reaction centre. In contrast, plants use antenna quenching in the light-harvesting complex as an important means to protect the reaction center from excessive excitation.
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| 4. |
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| 5. |
- Arvidsson, Per-Ola, et al.
(författare)
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Purification and identification of the violaxanthin de-epoxidase as a 43 kDa protein
- 1996
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Ingår i: Photosynthesis Research. - 0166-8595. ; 49:2, s. 119-129
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Tidskriftsartikel (refereegranskat)abstract
- Violaxanthin deepoxidase (VDE) has been purified from spinach (Spinacia oleracea) leaves. The purification included differential sonication of thylakoid membranes, differential (NH4)2SO4 fractionation, gel filtration chromatography and finally either hydrophobic interaction chromatography or anion exchange chromatography. A total purification of more than 5000-fold compared to the original thylakoids enabled the identification of a 43 kDa protein as the VDE, in contrast to earlier reported molecular weight of 54–60 kDa. A detailed comparison was made for the VDE activity and polypeptide pattern for the different fractions throughout the purification and the best correlation was always found for the 43 kDa protein. The highest specific activity obtained was 256 mol g–1 s–1 protein, which is at least 10-fold higher than reported earlier. We estimate that there is 1 VDE molecule per 20–100 electron transport chains. The 43 kDa protein was N-terminally sequenced, after protection of cysteine residues with -mercaptoethanol and iodoacetamid, and a unique sequence of 20 amino acids was obtained. The amino acid composition of the protein revealed a high abundance of charged and polar amino acids and remarkably, 11 cysteine residues. Two other proteins (39.5 kDa and 40 kDa) copurifying with VDE were also N-terminally sequenced. The N-terminal part of the 39.5 kDa protein showed complete sequence identity both with the N-terminal part of cyt b 6 and an internal sequence of polyphenol oxidase.
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| 6. |
- Arvidsson, Per-Ola, et al.
(författare)
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Violaxanthin accessibility and temperature dependency for de-epoxidation in spinach thylakoid membranes
- 1997
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Ingår i: Photosynthesis Research. - 0166-8595. ; 52:1, s. 39-48
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Tidskriftsartikel (refereegranskat)abstract
- Using DTT and iodoacetamide as a novel irreversible method to inhibit endogenous violaxanthin de-epoxidase, we found that violaxanthin could be converted into zeaxanthin from both sides of the thylakoid membrane provided that purified violaxanthin de-epoxidase was added. The maximum conversion was the same from both sides of the membrane. Temperature was found to have a strong influence both on the rate and degree of maximal violaxanthin to zeaxanthin conversion. Thus only 50% conversion of violaxanthin was detected at 4 degreesC, whereas at 25 degreesC and 37 degreesC the degree of conversion was 70% and 80%, respectively. These results were obtained with isolated thylakoids from non-cold acclimated leafs. Pigment analysis of sub-thylakoid membrane domains showed that violaxanthin was evenly distributed between stroma lamellae and grana partitions. This was in contrast to chlorophyll a and beta-carotene which were enriched in stroma lamellae fractions while chlorophyll b, lutein and neoxanthin were enriched in the grana membranes. In combination with added violaxanthin de-epoxidase we found almost the same degree of conversion of violaxanthin to zeaxanthin (73-78%) for different domains of the thylakoid membrane. We conclude that violaxanthin de-epoxidase converts violaxanthin in the lipid matrix and not at the proteins, that violaxanthin does not prefer one particular membrane region or one particular chlorophyll protein complex, and that the xanthophyll cycle pigments are oriented in a vertical manner in order to be accessible from both sides of the membrane when located in the lipid matrix.
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| 7. |
- Björn, Lars Olof
(författare)
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Effect of back reactions in the S-cycle on photosynthesis in very weak light
- 1995
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Ingår i: Photosynthesis Research. - 0166-8595. ; 46:1-2, s. 203-206
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Tidskriftsartikel (refereegranskat)abstract
- Photosynthesis in light which is so weak that excitation rates are comparable to the decay rates of S-states is modelled. It is found that oxygen evolution rate varies in a non-linear way with Photosystem II excitation rate in this region, but asymptotically approaches a linear relationship (with a slope of one oxygen molecule per four excitations) as excitation rate increases. The asymptote gives an intercept (zero oxygen evolution rate) on the excitation rate axis. The question is raised, whether this model is compatible with photoautotrophy in a red alga found at 268 m depth and able to carry out photosynthesis in extremely weak light. It is found that no unorthodox mechanisms for the S-cycle in this alga have to be assumed to explain its performance.
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| 8. |
- Bratt, Charlotte Eva, et al.
(författare)
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Regulation of violaxanthin de-epoxidase activity by pH and ascorbate concentration
- 1995
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Ingår i: Photosynthesis Research. - 0166-8595. ; 45:2, s. 169-175
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Tidskriftsartikel (refereegranskat)abstract
- The activity of violaxanthin de-epoxidase has been studied both in isolated thylakoids and after partial purification, as a function of pH and ascorbate concentration. We demonstrate that violaxanthin de-epoxidase has a Km for ascorbate that is strongly dependent on pH, with values of 10, 2.5, 1.0 and 0.3 mM at pH 6.0, 5.5, 5.0 and 4.5, respectively. These values can be expressed as a single Km±0.1±0.02 mM for the acid form of ascorbate. Release of the protein from the thylakoids by sonication was also found to be strongly pH dependent with a cooperativity of 4 with respect to protons and with an inflexion point at pH 6.7. These results can explain some of the discrepancies reported in the literature and provide a more consistent view of zeaxanthin formation in vivo.
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| 9. |
- Eskling, Marie, et al.
(författare)
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Changes in the quantities of violaxanthin de-epoxidase, xanthophylls and ascorbate in spinach upon shift from low to high light
- 1998
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Ingår i: Photosynthesis Research. - 0166-8595. ; 57:1, s. 41-50
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Tidskriftsartikel (refereegranskat)abstract
- Zeaxanthin, a carotenoid in the xanthophyll cycle, has been suggested to play a role in the protection against photodestruction. We have studied the importance of the parameters involved in zeaxanthin formation by comparing spinach plants grown in low light (100 to 250 mol m-2 s-1) to plants transferred to high light (950 mol m-2 s-1). Different parameters were followed for a total of 11 days. Our experiments show that violaxanthin de-epoxidase decreased between 15 and 30%, the quantity of xanthophyll cycle pigments doubled to 100 mmol (mol Chl)-1, corresponding to 27 mol m-2, and the rate of violaxanthin to zeaxanthin conversion was doubled. Lutein and neoxanthin increased from 50 to 71 mol m-2 and from 16 to 23 mol m-2, respectively. On a leaf area basis, chlorophyll and -carotene levels first decreased and then after 4 days increased. The chlorophyll a/b ratio was unchanged. The quantity of ascorbate was doubled to 2 mmol m-2, corresponding to an estimated increase in the chloroplasts from 25 to 50 mM. In view of our data, we propose that the increase in xanthophyll cycle pigments and ascorbate only partly explain the increased rate of conversion of violaxanthin to zeaxanthin, but the most probable explanation of the faster conversion is an increased accessibility of violaxanthin in the membrane.
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| 10. |
- Geijer, Paulina, et al.
(författare)
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Simultaneous detection of spin-coupled and decoupled QA- EPR-signals in Photosystem II complexes isolated with isoelectric focusing
- 1998
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Ingår i: Photosynthesis Research. - 0166-8595. ; 58:3, s. 231-243
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Tidskriftsartikel (refereegranskat)abstract
- The Photosystem II multisubunit protein complex can be extracted from thylakoid membranes with non-ionic detergents and subjected to various spectroscopical and biochemical investigations. This paper shows that after extraction with dodecyl-beta-D-maltoside, several Photosystem II complexes could be resolved by isoelectric focusing. Structurally, the various Photosystem II complexes differed from each other in polypeptide composition, especially with regard to the chlorophyll a/b-binding proteins, which gave rise to differing isoelectric points. Functionally, the various Photosystem II complexes differed from each other on the acceptor side, as judged by acceptor side-dependent electron transfer and electron paramagnetic resonance (EPR). The Q_{A}^- Fe2+-signal (g = 1.84), arising from Q_{A}^- spin-coupled to the acceptor-side iron, and a radical signal arising from decoupled Q_{A}^- (g = 2.0045) could be detected simultaneously in some of the Photosystem II complexes, and the amount of each of the two signals were inversely related. The results are discussed in relation to previously known heterogeneities in Photosystem II.
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