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Öquist, Gunnar
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Publications (10 of 134) Show all publications
Kurepin, L. V., Stangl, Z. R., Ivanov, A. G., Bui, V., Mema, M., Huner, N. P. A., . . . Hurry, V. (2018). Contrasting acclimation abilities of two dominant boreal conifers to elevated CO2 and temperature. Plant, Cell and Environment, 41(6), 1331-1345
Open this publication in new window or tab >>Contrasting acclimation abilities of two dominant boreal conifers to elevated CO2 and temperature
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2018 (English)In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 41, no 6, p. 1331-1345Article in journal (Refereed) Published
Abstract [en]

High latitude forests will experience large changes in temperature and CO2 concentrations this century. We evaluated the effects of future climate conditions on 2 dominant boreal tree species, Pinus sylvestris L. and Picea abies (L.) H. Karst, exposing seedlings to 3 seasons of ambient (430 ppm) or elevated CO2 (750 ppm) and ambient temperatures, a + 4 degrees C warming or a + 8 degrees C warming. Pinus sylvestris responded positively to warming: seedlings developed a larger canopy, maintained high net CO2 assimilation rates (Anet), and acclimated dark respiration (Rdark). In contrast, carbon fluxes in Picea abies were negatively impacted by warming: maximum rates of Anet decreased, electron transport was redirected to alternative electron acceptors, and thermal acclimation of Rdark was weak. Elevated CO2 tended to exacerbate these effects in warm-grown Picea abies, and by the end of the experiment Picea abies from the +8 degrees C, high CO2 treatment produced fewer buds than they had 3 years earlier. Treatments had little effect on leaf and wood anatomy. Our results highlight that species within the same plant functional type may show opposite responses to warming and imply that Picea abies may be particularly vulnerable to warming due to low plasticity in photosynthetic and respiratory metabolism.

Keywords
boreal forest, chlorophyll fluorescence, photosynthesis, stomatal conductance, temperature-CO2 interactions, thermal acclimation
National Category
Forest Science Botany
Identifiers
urn:nbn:se:umu:diva-150886 (URN)10.1111/pce.13158 (DOI)000434162400009 ()29411877 (PubMedID)2-s2.0-85044520215 (Scopus ID)
Available from: 2018-08-31 Created: 2018-08-31 Last updated: 2018-08-31Bibliographically approved
Öquist, G. & Benner, M. (2015). Why are some nations more successful than others in research impact?: a comparison between Denmark and Sweden. In: Isabell M. Welpe, Jutta Wollersheim, Stefanie Ringelhan, Margit Osterloh (Ed.), Incentives and Performance: Governance of Research Organizations (pp. 241-257). Springer
Open this publication in new window or tab >>Why are some nations more successful than others in research impact?: a comparison between Denmark and Sweden
2015 (English)In: Incentives and Performance: Governance of Research Organizations / [ed] Isabell M. Welpe, Jutta Wollersheim, Stefanie Ringelhan, Margit Osterloh, Springer, 2015, p. 241-257Chapter in book (Other academic)
Abstract [en]

Bibliometric impact analyses show that Swedish research has less international visibility than Danish research. When taking a global view on all subject fields and selecting publications cited higher than the 90th percentile, i.e., the Top 10 %—publications, the Swedish Research Council shows that although Sweden ranks 15 % above world average, Denmark, the Netherlands and Switzerland rank 35–40 % above. To explain these different performances, The Royal Swedish Academy of Sciences asked us to compare the national research systems on three levels: priority setting at national level, governance of universities and direction and funding of research. There are of course many similarities between the Danish and Swedish research systems but there are still subtle differences that have developed over time, which may explain the different international visibility. First of all, it does not depend on different levels of public spending on research and development. However, the core funding of universities relative external funding is higher in Denmark than in Sweden. The academic leadership of Danish universities in terms of board, vice-chancellor, faculty dean and department chair is also more coherent and focused on priority setting, recruitment, organization and deployment of resources to establish research environments that operate at the forefront of international research. On all these points we see a weaker leadership in Sweden. Furthermore, over the last 20 years, public funding of research in Sweden has become more and more unpredictable and program oriented with many new actors, while the Danish funding system, although it also has developed over time, shows more consistency with strong actors to fund individuals with novel ideas. The research policy in Sweden has also developed multiple, sometimes even conflicting goals, which have undermined conditions for high-impact research, while in Denmark a policy to support excellence in research has been more coherent.

Place, publisher, year, edition, pages
Springer, 2015
National Category
Sociology Information Studies
Identifiers
urn:nbn:se:umu:diva-111739 (URN)10.1007/978-3-319-09785-5_15 (DOI)2-s2.0-84944611681 (Scopus ID)978-3-319-09785-5 (ISBN)978-3-319-09784-8 (ISBN)
Available from: 2015-11-20 Created: 2015-11-20 Last updated: 2018-06-07Bibliographically approved
Ivanov, A. G., Rosso, D., Savitch, L. V., Stachula, P., Rosembert, M., Öquist, G., . . . Huener, N. P. (2012). Implications of alternative electron sinks in increased resistance of PSII and PSI photochemistry to high light stress in cold-acclimated Arabidopsis thaliana. Photosynthesis Research, 113(1-3), 191-206
Open this publication in new window or tab >>Implications of alternative electron sinks in increased resistance of PSII and PSI photochemistry to high light stress in cold-acclimated Arabidopsis thaliana
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2012 (English)In: Photosynthesis Research, ISSN 0166-8595, E-ISSN 1573-5079, Vol. 113, no 1-3, p. 191-206Article in journal (Refereed) Published
Abstract [en]

Exposure of control (non-hardened) Arabidopsis leaves to high light stress at 5 A degrees C resulted in a decrease of both photosystem II (PSII) (45 %) and Photosystem I (PSI) (35 %) photochemical efficiencies compared to non-treated plants. In contrast, cold-acclimated (CA) leaves exhibited only 35 and 22 % decrease of PSII and PSI photochemistry, respectively, under the same conditions. This was accompanied by an accelerated rate of P700(+) re-reduction, indicating an up-regulation of PSI-dependent cyclic electron transport (CET). Interestingly, the expression of the NDH-H gene and the relative abundance of the Ndh-H polypeptide, representing the NDH-complex, decreased as a result of exposure to low temperatures. This indicates that the NDH-dependent CET pathway cannot be involved and the overall stimulation of CET in CA plants is due to up-regulation of the ferredoxin-plastoquinone reductase, antimycin A-sensitive CET pathway. The lower abundance of NDH complex also implies lower activity of the chlororespiratory pathway in CA plants, although the expression level and overall abundance of the other well-characterized component involved in chlororespiration, the plastid terminal oxidase (PTOX), was up-regulated at low temperatures. This suggests increased PTOX-mediated alternative electron flow to oxygen in plants exposed to low temperatures. Indeed, the estimated proportion of O-2-dependent linear electron transport not utilized in carbon assimilation and not directed to photorespiration was twofold higher in CA Arabidopsis. The possible involvement of alternative electron transport pathways in inducing greater resistance of both PSII and PSI to high light stress in CA plants is discussed.

Place, publisher, year, edition, pages
Dordrecht: , 2012
Keywords
Alternative electron flows, Cold acclimation, Photoprotection, Photosystem II, Photosystem I, PTOX
National Category
Botany
Identifiers
urn:nbn:se:umu:diva-60326 (URN)10.1007/s11120-012-9769-y (DOI)000308188800014 ()
Available from: 2012-11-09 Created: 2012-10-09 Last updated: 2018-06-08Bibliographically approved
Chow, W. S., Fan, D.-Y., Oguchi, R., Jia, H., Losciale, P., Park, Y.-I., . . . Anderson, J. M. (2012). Quantifying and monitoring functional photosystem II and the stoichiometry of the two photosystems in leaf segments: approaches and approximations. Photosynthesis Research, 113(1-3), 63-74
Open this publication in new window or tab >>Quantifying and monitoring functional photosystem II and the stoichiometry of the two photosystems in leaf segments: approaches and approximations
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2012 (English)In: Photosynthesis Research, ISSN 0166-8595, E-ISSN 1573-5079, Vol. 113, no 1-3, p. 63-74Article, review/survey (Refereed) Published
Abstract [en]

Given its unique function in light-induced water oxidation and its susceptibility to photoinactivation during photosynthesis, photosystem II (PS II) is often the focus of studies of photosynthetic structure and function, particularly in environmental stress conditions. Here we review four approaches for quantifying or monitoring PS II functionality or the stoichiometry of the two photosystems in leaf segments, scrutinizing the approximations in each approach. (1) Chlorophyll fluorescence parameters are convenient to derive, but the information-rich signal suffers from the localized nature of its detection in leaf tissue. (2) The gross O-2 yield per single-turnover flash in CO2-enriched air is a more direct measurement of the functional content, assuming that each functional PS II evolves one O-2 molecule after four flashes. However, the gross O-2 yield per single-turnover flash (multiplied by four) could over-estimate the content of functional PS II if mitochondrial respiration is lower in flash illumination than in darkness. (3) The cumulative delivery of electrons from PS II to P700(+) (oxidized primary donor in PS I) after a flash is added to steady background far-red light is a whole-tissue measurement, such that a single linear correlation with functional PS II applies to leaves of all plant species investigated so far. However, the magnitude obtained in a simple analysis (with the signal normalized to the maximum photo-oxidizable P700 signal), which should equal the ratio of PS II to PS I centers, was too small to match the independently-obtained photosystem stoichiometry. Further, an under-estimation of functional PS II content could occur if some electrons were intercepted before reaching PS I. (4) The electrochromic signal from leaf segments appears to reliably quantify the photosystem stoichiometry, either by progressively photoinactivating PS II or suppressing PS I via photo-oxidation of a known fraction of the P700 with steady far-red light. Together, these approaches have the potential for quantitatively probing PS II in vivo in leaf segments, with prospects for application of the latter two approaches in the field.

Place, publisher, year, edition, pages
Dordrecht: Springer, 2012
Keywords
Chlorophyll fluorescence, Electrochromic signal, Oxygen evolution, P700, Photosystem II, PS II/PS I stoichiometry
National Category
Botany
Identifiers
urn:nbn:se:umu:diva-60325 (URN)10.1007/s11120-012-9740-y (DOI)000308188800005 ()
Available from: 2012-11-09 Created: 2012-10-09 Last updated: 2018-06-08Bibliographically approved
Ivanov, A., Sane, P., Simidjiev, I., Park, Y.-I., Huner, N. & Öquist, G. (2012). Restricted capacity for PSI-dependent cyclic electron flow in Delta petE mutant compromises the ability for acclimation to iron stress in Synechococcus sp PCC 7942 cells. Biochimica et Biophysica Acta - Bioenergetics, 1817(8), 1277-1284
Open this publication in new window or tab >>Restricted capacity for PSI-dependent cyclic electron flow in Delta petE mutant compromises the ability for acclimation to iron stress in Synechococcus sp PCC 7942 cells
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2012 (English)In: Biochimica et Biophysica Acta - Bioenergetics, ISSN 0005-2728, E-ISSN 1879-2650, Vol. 1817, no 8, p. 1277-1284Article in journal (Refereed) Published
Abstract [en]

Exposure of wild type (WT) and plastocyanin coding petE gene deficient mutant (Delta petE) of Synechococcus cells to low iron growth conditions was accompanied by similar iron-stress induced blue-shift of the main red Chl a absorption peak and a gradual decrease of the Phc/Chl ratio, although Delta petE mutant was more sensitive when exposed to iron deficient conditions. Despite comparable iron stress induced phenotypic changes, the inactivation of petE gene expression was accompanied with a significant reduction of the growth rates compared to WT cells. To examine the photosynthetic electron fluxes in vivo, far-red light induced P700 redox state transients at 820 nm of WT and Delta petE mutant cells grown under iron sufficient and iron deficient conditions were compared. The extent of the absorbance change (Delta A(820)/A(820)) used for quantitative estimation of photooxidizable P700(+) indicated a 2-fold lower level of P700(+) in Delta petE compared to WT cells under control conditions. This was accompanied by a 2-fold slower re-reduction rate of P700(+) in the Delta petE indicating a lower capacity for cyclic electron flow around PSI in the cells lacking plastocyanin. Thermoluminescence (TL) measurements did not reveal significant differences in PSII photochemistry between control WT and Delta petE cells. However, exposure to iron stress induced a 4.5 times lower level of P700(+), 2-fold faster re-reduction rate of P700(+) and a temperature shift of the TL peak corresponding to S-2/S(3)Q(B)(-) charge recombination in WT cells. In contrast, the iron-stressed Delta petE mutant exhibited only a 40% decrease of P700(+) and no significant temperature shift in S-2/S(3)Q(B)(-) charge recombination. The role of mobile electron carriers in modulating the photosynthetic electron fluxes and physiological acclimation of cyanobacteria to low iron conditions is discussed. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial. (C) 2012 Elsevier B.V. All rights reserved.

Keywords
Electron transport, Iron stress, Photosystem I, P700, Plastocyanin, Synechococcus sp PCC 7942
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-57739 (URN)10.1016/j.bbabio.2012.03.014 (DOI)000306202700020 ()
Available from: 2012-08-20 Created: 2012-08-14 Last updated: 2018-06-08Bibliographically approved
Sane, P. V., Ivanov, A. G., Öquist, G. & Huener, N. P. A. (2012). Thermoluminescence. In: Julian J. Eaton-Rye,Baishnab C. Tripathy, Thomas D. Sharkey (Ed.), Photosynthesis: Plastid Biology, Energy Conversion and Carbon Assimilation (pp. 445-474). Springer Netherlands
Open this publication in new window or tab >>Thermoluminescence
2012 (English)In: Photosynthesis: Plastid Biology, Energy Conversion and Carbon Assimilation / [ed] Julian J. Eaton-Rye,Baishnab C. Tripathy, Thomas D. Sharkey, Springer Netherlands, 2012, p. 445-474Chapter in book (Refereed)
Abstract [en]

Thermo luminescence (TL) of photosynthetic membranes was discovered by William Arnold and Helen Sherwood in 1957. In the last half century, several studies have elucidated the mechanism of TL emission, which showed that the recombination of different charge pairs generated and trapped during pre-illumination are responsible for the observed light emission. Since most of the TL bands originate within Photosystem II (PS II), the technique of TL has become a useful complementary tool to chlorophyll a fluorescence to probe subtle changes in PS II photochemistry. The technique is simple and non-invasive; it has been successfully used to study leaf, cells, thylakoids and even reaction center preparations. The TL technique provides quick information about the redox potential changes of the bound primary quinone (Q(A)) and the secondary quinone (Q(B)) acceptors of PS II; TL has been extensively used to study the effects of photoinhibition, mutations, stresses and myriad responses of the photosynthetic apparatus during acclimation and adaptation. This chapter reviews crucial evidence for the identification of charge pairs responsible for the generation of different TL bands; the relationship of these bands to the components of delayed light emission; responses to excitation pressure arising out of environmental factors; methodology, and instrumentation. A model based on the detailed analysis of the redox shifts of the PS II electron acceptors Q(A) and Q(B), explaining the possibility of non-radiative dissipation of excess light energy within the reaction center of PS II (reaction center quenching) and its physiological significance in photoprotection of the photosynthetic membranes has been suggested. Developments in the analysis of biophysical parameters and the non-adherence of photosynthetic TL to the analysis by the 1945 theory of J.T. Randall and M.H.F. Wilkins have been briefly reviewed.

Place, publisher, year, edition, pages
Springer Netherlands, 2012
Series
Advances in Photosynthesis and Respiration, ISSN 1572-0233 ; 34
National Category
Botany Organic Chemistry
Identifiers
urn:nbn:se:umu:diva-74384 (URN)10.1007/978-94-007-1579-0_19 (DOI)000304125200019 ()978-94-007-1578-3 (ISBN)978-94-007-1579-0 (ISBN)
Available from: 2013-06-28 Created: 2013-06-27 Last updated: 2018-06-08Bibliographically approved
Savitch, L. V., Ivanov, A. G., Krol, M., Sprott, D. P., Öquist, G. & Huner, N. P. A. (2010). Regulation of energy partitioning and alternative electron transport pathways during cold acclimation of lodgepole pine is oxygen dependent. Plant and Cell Physiology, 51(9), 1555-1570
Open this publication in new window or tab >>Regulation of energy partitioning and alternative electron transport pathways during cold acclimation of lodgepole pine is oxygen dependent
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2010 (English)In: Plant and Cell Physiology, ISSN 0032-0781, E-ISSN 1471-9053, Vol. 51, no 9, p. 1555-1570Article in journal (Refereed) Published
Abstract [en]

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.

Identifiers
urn:nbn:se:umu:diva-37353 (URN)10.1093/pcp/pcq101 (DOI)000281952800018 ()
Available from: 2010-10-28 Created: 2010-10-28 Last updated: 2018-06-08Bibliographically approved
Ivanov, A. G., Sane, P. V., Hurry, V., Oquist, G. & Huner, N. P. (2008). Photosystem II reaction centre quenching: mechanisms and physiological role.. Photosynthesis Research, 98(1-3), 565-74
Open this publication in new window or tab >>Photosystem II reaction centre quenching: mechanisms and physiological role.
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2008 (English)In: Photosynthesis Research, ISSN 0166-8595, Vol. 98, no 1-3, p. 565-74Article in journal (Refereed) Published
Abstract [en]

Dissipation of excess absorbed light energy in eukaryotic photoautotrophs through zeaxanthin- and DpHdependent photosystem II antenna quenching is considered the major mechanism for non-photochemical quenching and photoprotection. However, there is mounting evidence of a zeaxanthin-independent pathway for dissipation of excess light energy based within the PSII reaction centre that may also play a significant role in photoprotection. We summarize recent reports which indicate that this enigma can be explained, in part, by the fact that PSII reaction centres can be reversibly interconverted from photochemical energy transducers that convert light into ATP

and NADPH to efficient, non-photochemical energy quenchers that protect the photosynthetic apparatus from photodamage. In our opinion, reaction centre quenching complements photoprotection through antenna quenching, and dynamic regulation of photosystem II reaction centre represents a general response to any environmental condition that predisposes the accumulation of reduced QA in the photosystem II reaction centres of prokaryotic and eukaryotic photoautotrophs. Since the evolution of reaction centres preceded the evolution of light harvesting systems, reaction centre quenching may represent the oldest photoprotective mechanism.10.1007/s1120-00

Identifiers
urn:nbn:se:umu:diva-11507 (URN)doi:10.1007/s1120-008-9365-3 (DOI)18821028 (PubMedID)
Available from: 2009-01-13 Created: 2009-01-13 Last updated: 2018-06-09Bibliographically approved
Ivanov, A. G., Hurry, V., Sane, P. V., Oquist, G. & Huner, N. P. (2008). Reaction centre quenching of excess light energy and photoprotection of photosystem II. Journal of Plant Biology, 51(2), 85-96
Open this publication in new window or tab >>Reaction centre quenching of excess light energy and photoprotection of photosystem II
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2008 (English)In: Journal of Plant Biology, Vol. 51, no 2, p. 85-96Article in journal (Refereed) Published
Abstract [en]

In addition to the energy dissipation of excess light occurring in PSII antenna via the xanthophyll cycle, there is mounting evidence of a zeaxanthin-independent pathway for non-photochemical quenching based within the PSII reaction centre (reaction centre quenching) that may also play a significant role in photoprotection. It has been demonstrated that acclimation of higher plants, green algae and cyanobacteria to low temperature or high light conditions which potentially induce an imbalance between energy supply and energy utilization is accompanied by the development of higher reduction state of QA and higher resistance to photoinhibition (Huner et al., 1998). Although this is a fundamental feature of all photoautotrophs, and the acquisition of increased tolerance to photoinhibition has been ascribed to growth and development under high PSII excitation pressure, the precise mechanism controlling the redox state of QA and its physiological significance in developing higher resistance to photoinhibition has not been fully elucidated. In this review we summarize recent data indicating that the increased resistance to high light in a broad spectrum of photosynthetic organisms acclimated to high excitation pressure conditions is associated with an increase probability for alternative non-radiative P680+QA − radical pair recombination pathway for energy dissipation within the reaction centre of PSII. The various molecular mechanisms that could account for nonphotochemical quenching through PSII reaction centre are also discussed.

Identifiers
urn:nbn:se:umu:diva-10447 (URN)
Available from: 2008-09-11 Created: 2008-09-11 Last updated: 2018-06-09Bibliographically approved
Björn, L. O., Sundqvist, C. & Öquist, G. (2007). A tribute to Per Halldal (1922-1986), a Norwegian photobiologist in Sweden.. Photosynthesis Research, 92(1), 7-11
Open this publication in new window or tab >>A tribute to Per Halldal (1922-1986), a Norwegian photobiologist in Sweden.
2007 (English)In: Photosynthesis Research, ISSN 0166-8595, Vol. 92, no 1, p. 7-11Article in journal (Other academic) Published
Identifiers
urn:nbn:se:umu:diva-15864 (URN)doi:10.1007/s11120-006-9072-x (DOI)17342447 (PubMedID)
Available from: 2007-08-03 Created: 2007-08-03 Last updated: 2018-06-09Bibliographically approved
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