| 1. |
- Huner, Norman P A, et al.
(författare)
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Photoprotection of Photosystem II: Reaction center quenching versus antenna quenching
- 2006
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Ingår i: Photoprotection, Photoinhibition, Gene Regulation and Environment. - : Springer. - 9781402035647 ; , s. 155-174
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Photoprotection, Photoinhibition, Gene Regulation, and Environment examines the processes whereby plants monitor environmental conditions and orchestrate their response to change, an ability paramount to the life of all plants. "Excess light", absorbed by the light-harvesting systems of photosynthetic organisms, is an integrative indicator of the environment, communicating the presence of intense light and any conditions unfavorable for growth and photosynthesis. Key plant responses are photoprotection and photoinhibition. In this volume, the dual role of photoprotective responses in the preservation of leaf integrity and in redox signaling networks modulating stress acclimation, growth, and development is addressed. In addition, the still unresolved impact of photoinhibition on plant survival and productivity is discussed. Specific topics include dissipation of excess energy via thermal and other pathways, scavenging of reactive oxygen by antioxidants, proteins key to photoprotection and photoinhibition, peroxidation of lipids, as well as signaling by reactive oxygen, lipid-derived messengers, and other messengers that modulate gene expression. Approaches include biochemical, physiological, genetic, molecular, and field studies, addressing intense visible and ultraviolet light, winter conditions, nutrient deficiency, drought, and salinity. This book is directed toward advanced undergraduate students, graduate students, and researchers interested in Plant Ecology, Stress Physiology, Plant Biochemistry, Integrative Biology, and Photobiology.
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| 2. |
- Ivanov, Alexander G, et al.
(författare)
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Acclimation to temperature and irradiance modulates PSII charge recombination.
- 2006
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Ingår i: FEBS Letters. - : Wiley. - 0014-5793. ; 580:11, s. 2797-802
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Tidskriftsartikel (refereegranskat)abstract
- Acclimation of wild type and the chlorina F2 mutant of barley to either high light or low temperature results in a 2- to 3-fold increase in non-photochemical quenching which occurred independently of either energy-dependent quenching (qE), xanthophyll cycle-mediated antenna quenching or state transitions. Results of in vivo thermoluminescence measurements used to address this conundrum indicated that excitation pressure regulates the temperature gap for Click to view the MathML source and Click to view the MathML source charge recombinations within photosystem II reaction centers. This is discussed in terms of photoprotection through non-radiative charge recombination.
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| 3. |
- Ivanov, Alexander G, et al.
(författare)
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Characterization of the photosynthetic apparatus in cortical bark chlorenchyma of Scots pine.
- 2006
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Ingår i: Planta. - : Springer Science and Business Media LLC. - 0032-0935 .- 1432-2048. ; 223:6, s. 1165-77
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Tidskriftsartikel (refereegranskat)abstract
- Winter-induced inhibition of photosynthesis in Scots pine (Pinus sylvestris L.) needles is accompanied by a 65% reduction of the maximum photochemical efficiency of photosystem II (PSII), measured as F v/F m, but relatively stable photosystem I (PSI) activity. In contrast, the photochemical efficiency of PSII in bark chlorenchyma of Scots pine twigs was shown to be well preserved, while PSI capacity was severely decreased. Low-temperature (77 K) chlorophyll fluorescence measurements also revealed lower relative fluorescence intensity emitted from PSI in bark chlorenchyma compared to needles regardless of the growing season. Nondenaturating SDS-PAGE analysis of the chlorophyll–protein complexes also revealed much lower abundance of LHCI and the CPI band related to light harvesting and the core complex of PSI, respectively, in bark chlorenchyma. These changes were associated with a 38% reduction in the total amount of chlorophyll in the bark chlorenchyma relative to winter needles, but the Chl a/b ratio and carotenoid composition were similar in the two tissues. As distinct from winter pine needles exhibiting ATP/ADP ratio of 11.3, the total adenylate content in winter bark chlorenchyma was 2.5-fold higher and the estimated ATP/ADP ratio was 20.7. The photochemical efficiency of PSII in needles attached to the twig recovered significantly faster (28–30 h) then in detached needles. Fluorescence quenching analysis revealed a high reduction state of Q A and the PQ-pool in the green bark tissue. The role of bark chlorenchyma and its photochemical performance during the recovery of photosynthesis from winter stress in Scots pine is discussed.
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| 4. |
- Ivanov, Alexander G, et al.
(författare)
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Digalactosyl-diacylglycerol deficiency impairs the capacity for photosynthetic intersystem electron transport and state transitions in Arabidopsis thaliana due to photosystem I acceptor-side limitations.
- 2006
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Ingår i: Plant Cell Physiology. - : Oxford University Press (OUP). - 0032-0781 .- 1471-9053. ; 47:8, s. 1146-57
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Tidskriftsartikel (refereegranskat)abstract
- Compared with wild type, the dgd1 mutant of Arabidopsis thaliana exhibited a lower amount of PSI-related Chl–protein complexes and lower abundance of the PSI-associated polypeptides, PsaA, PsaB, PsaC, PsaL and PsaH, with no changes in the levels of Lhca1–4. Functionally, the dgd1 mutant exhibited a significantly lower light-dependent, steady-state oxidation level of P700 (P700+) in vivo, a higher intersystem electron pool size, restricted linear electron transport and a higher rate of reduction of P700+ in the dark, indicating an increased capacity for PSI cyclic electron transfer compared with the wild type. Concomitantly, the dgd1 mutant exhibited a higher sensitivity to and incomplete recovery of photoinhibition of PSI. Furthermore, dgd1 exhibited a lower capacity to undergo state transitions compared with the wild type, which was associated with a higher reduction state of the plastoquinone (PQ) pool. We conclude that digalactosyl-diacylglycerol (DGDG) deficiency results in PSI acceptor-side limitations that alter the flux of electrons through the photosynthetic electron chain and impair the regulation of distribution of excitation energy between the photosystems. These results are discussed in terms of thylakoid membrane domain reorganization in response to DGDG deficiency in A. thaliana.
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| 5. |
- Ivanov, Alexander G, et al.
(författare)
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Iron deficiency in cyanobacteria causes monomerization of photosystem I trimers and reduces the capacity for state transitions and the effective absorption cross section of photosystem I in vivo.
- 2006
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 141:4, s. 1436-45
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Tidskriftsartikel (refereegranskat)abstract
- The induction of the isiA (CP43') protein in iron-stressed cyanobacteria is accompanied by the formation of a ring of 18 CP43' proteins around the photosystem I (PSI) trimer and is thought to increase the absorption cross section of PSI within the CP43'-PSI supercomplex. In contrast to these in vitro studies, our in vivo measurements failed to demonstrate any increase of the PSI absorption cross section in two strains (Synechococcus sp. PCC 7942 and Synechocystis sp. PCC 6803) of iron-stressed cells. We report that iron-stressed cells exhibited a reduced capacity for state transitions and limited dark reduction of the plastoquinone pool, which accounts for the increase in PSII-related 685 nm chlorophyll fluorescence under iron deficiency. This was accompanied by lower abundance of the NADP-dehydrogenase complex and the PSI-associated subunit PsaL, as well as a reduced amount of phosphatidylglycerol. Nondenaturating polyacrylamide gel electrophoresis separation of the chlorophyll-protein complexes indicated that the monomeric form of PSI is favored over the trimeric form of PSI under iron stress. Thus, we demonstrate that the induction of CP43' does not increase the PSI functional absorption cross section of whole cells in vivo, but rather, induces monomerization of PSI trimers and reduces the capacity for state transitions. We discuss the role of CP43' as an effective energy quencher to photoprotect PSII and PSI under unfavorable environmental conditions in cyanobacteria in vivo.
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| 6. |
- Ivanov, Alexander G., et al.
(författare)
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The decreased PG content of pgp1 inhibits PSI photochemistry and limits reaction center and light-harvesting polypeptide accumulation in response to cold acclimation
- 2022
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Ingår i: Planta. - : Springer. - 0032-0935 .- 1432-2048. ; 255:2
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Tidskriftsartikel (refereegranskat)abstract
- Main conclusion: Decreased PG constrains PSI activity due to inhibition of transcript and polypeptide abundance of light-harvesting and reaction center polypeptides generating a reversible, yellow phenotype during cold acclimation of pgp1.Cold acclimation of the Arabidopsis pgp1 mutant at 5 °C resulted in a pale-yellow phenotype with abnormal chloroplast ultrastructure compared to its green phenotype upon growth at 20 °C despite a normal cold-acclimation response at the transcript level. In contrast, wild type maintained its normal green phenotype and chloroplast ultrastructure irrespective of growth temperature. In contrast to cold acclimation of WT, growth of pgp1 at 5 °C limited the accumulation of Lhcbs and Lhcas assessed by immunoblotting. However, a novel 43 kD polypeptide of Lhcb1 as well as a 29 kD polypeptide of Lhcb3 accumulated in the soluble fraction which was absent in the thylakoid membrane fraction of cold-acclimated pgp1 which was not observed in WT. Cold acclimation of pgp1 destabilized the Chl–protein complexes associated with PSI and predisposed energy distribution in favor of PSII rather than PSI compared to the WT. Functionally, in vivo PSI versus PSII photochemistry was inhibited in cold-acclimated pgp1 to a greater extent than in WT relative to controls. Greening of the pale-yellow pgp1 was induced when cold-acclimated pgp1 was shifted from 5 to 20 °C which resulted in a marked decrease in excitation pressure to a level comparable to WT. Concomitantly, Lhcbs and Lhcas accumulated with a simultaneous decrease in the novel 43 and 29kD polypeptides. We conclude that the reduced levels of phosphatidyldiacylglycerol in the pgp1 limit the capacity of the mutant to maintain the structure and function of its photosynthetic apparatus during cold acclimation. Thus, maintenance of normal thylakoid phosphatidyldiacylglycerol levels is essential to stabilize the photosynthetic apparatus during cold acclimation.
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| 7. |
- Ivanov, Alexander G, et al.
(författare)
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The induction of CP43' by iron-stress in Synechococcus sp. PCC 7942 is associated with carotenoid accumulation and enhanced fatty acid unsaturation.
- 2007
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Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002 .- 0005-2728. ; 1767:6, s. 807-13
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Tidskriftsartikel (refereegranskat)abstract
- Comparative lipid analysis demonstrated reduced amount of PG (50%) and lower ratio of MGDG/DGDG in iron-stressed Synechococcus sp. PCC 7942 cells compared to cells grown under iron sufficient conditions. In parallel, the monoenoic (C:1) fatty acids in MGDG, DGDG and PG increased from 46.8%, 43.7% and 45.6%, respectively in control cells to 51.6%, 48.8% and 48.7%, respectively in iron-stressed cells. This suggests increased membrane dynamics, which may facilitate the diffusion of PQ and keep the PQ pool in relatively more oxidized state in iron-stressed compared to control cells. This was confirmed by chlorophyll fluorescence and thermoluminescence measurements. Analysis of carotenoid composition demonstrated that the induction of isiA (CP43′) protein in response to iron stress is accompanied by significant increase of the relative abundance of all carotenoids. The quantity of carotenoids calculated on a Chl basis increased differentially with nostoxanthin, cryptoxanthin, zeaxanthin and β-carotene showing 2.6-, 3.1-, 1.9- and 1.9-fold increases, respectively, while the relative amount of caloxanthin was increased only by 30%. HPLC analyses of the pigment composition of Chl–protein complexes separated by non-denaturating SDS-PAGE demonstrated even higher relative carotenoids content, especially of cryptoxanthin, in trimer and monomer PSI Chl–protein complexes co-migrating with CP43′ from iron-stressed cells than in PSI complexes from control cells where CP43′ is not present. This implies a carotenoid-binding role for the CP43′ protein which supports our previous suggestion for effective energy quenching and photoprotective role of CP43′ protein in cyanobacteria under iron stress.
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| 8. |
- Rosso, Dominic, et al.
(författare)
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IMMUTANS does not act as a stress-induced safety valve in the protection of the photosynthetic apparatus of Arabidopsis during steady-state photosynthesis.
- 2006
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 142:2, s. 574-85
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Tidskriftsartikel (refereegranskat)abstract
- IMMUTANS (IM) encodes a thylakoid membrane protein that has been hypothesized to act as a terminal oxidase that couples the reduction of O2 to the oxidation of the plastoquinone (PQ) pool of the photosynthetic electron transport chain. Because IM shares sequence similarity to the stress-induced mitochondrial alternative oxidase (AOX), it has been suggested that the protein encoded by IM acts as a safety valve during the generation of excess photosynthetically generated electrons. We combined in vivo chlorophyll fluorescence quenching analyses with measurements of the redox state of P700 to assess the capacity of IM to compete with photosystem I for intersystem electrons during steady-state photosynthesis in Arabidopsis (Arabidopsis thaliana). Comparisons were made between wild-type plants, im mutant plants, as well as transgenics in which IM protein levels had been overexpressed six (OE-6x) and 16 (OE-16x) times. Immunoblots indicated that IM abundance was the only major variant that we could detect between these genotypes. Overexpression of IM did not result in increased capacity to keep the PQ pool oxidized compared to either the wild type or im grown under control conditions (25°C and photosynthetic photon flux density of 150 µmol photons m–2 s–1). Similar results were observed either after 3-d cold stress at 5°C or after full-leaf expansion at 5°C and photosynthetic photon flux density of 150 µmol photons m–2 s–1. Furthermore, IM abundance did not enhance protection of either photosystem II or photosystem I from photoinhibition at either 25°C or 5°C. Our in vivo data indicate that modulation of IM expression and polypeptide accumulation does not alter the flux of intersystem electrons to P700+ during steady-state photosynthesis and does not provide any significant photoprotection. In contrast to AOX1a, meta-analyses of published Arabidopsis microarray data indicated that IM expression exhibited minimal modulation in response to myriad abiotic stresses, which is consistent with our functional data. However, IM exhibited significant modulation in response to development in concert with changes in AOX1a expression. Thus, neither our functional analyses of the IM knockout and overexpression lines nor meta-analyses of gene expression support the model that IM acts as a safety valve to regulate the redox state of the PQ pool during stress and acclimation. Rather, IM appears to be strongly regulated by developmental stage of Arabidopsis.
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| 9. |
- Savitch, Leonid V., et al.
(författare)
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Regulation of energy partitioning and alternative electron transport pathways during cold acclimation of lodgepole pine is oxygen dependent
- 2010
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Ingår i: Plant and Cell Physiology. - : Oxford University Press (OUP). - 0032-0781 .- 1471-9053. ; 51:9, s. 1555-1570
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Tidskriftsartikel (refereegranskat)abstract
- Second year needles of Lodgepole pine (Pinus contorta L.) were exposed for 6 weeks to either simulated control summer [summer; 25C/250 photon flux denisty (PFD)], autumn (autumn; 15C/250 PFD) or winter conditions (winter; 5C/250 PFD). We report that the proportion of linear electron transport utilized in carbon assimilation (ETRCO2) was 40 lower in both autumn and winter pine when compared with the summer pine. In contrast, the proportion of excess photosynthetic linear electron transport (ETRexcess) not used for carbon assimilation within the total ETRJf increased by 30 in both autumn and winter pine. In autumn pine acclimated to 15C, the increased amounts of excess electrons were directed equally to 21kPa O-2-dependent and 2kPa O-2-dependent alternative electron transport pathways and the fractions of excitation light energy utilized by PSII photochemistry ((PSII)), thermally dissipated through (NPQ) and dissipated by additional quenching mechanism(s) ((f,D)) were similar to those in summer pine. In contrast, in winter needles acclimated to 5C, 60 of photosynthetically generated excess electrons were utilized through the 2kPa O-2-dependent electron sink and only 15 by the photorespiratory (21kPa O-2) electron pathway. Needles exposed to winter conditions led to a 3-fold lower (PSII), only a marginal increase in (NPQ) and a 2-fold higher (f,D), which was O-2 dependent compared with the summer and autumn pine. Our results demonstrate that the employment of a variety of alternative pathways for utilization of photosynthetically generated electrons by Lodgepole pine depends on the acclimation temperature. Furthermore, dissipation of excess light energy through constitutive non-photochemical quenching mechanisms is O-2 dependent.
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