| 1. |
- Damkjær, Jakob T, 1976-, et al.
(author)
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The photosystem II light-harvesting protein Lhcb3 affects the macrostructure of photosystem II and the rate of state transitions in Arabidopsis
- 2009
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In: The Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 21, s. 3245-3256
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Journal article (peer-reviewed)abstract
- The main trimeric light-harvesting complex of higher plants (LHCII) consists of three different Lhcb proteins (Lhcb1-3). We show that Arabidopsis thaliana T-DNA knockout plants lacking Lhcb3 (koLhcb3) compensate for the lack of Lhcb3 by producing increased amounts of Lhcb1 and Lhcb2. As in wild-type plants, LHCII-photosystem II (PSII) supercomplexes were present in Lhcb3 knockout plants (koLhcb3), and preservation of the LHCII trimers (M trimers) indicates that the Lhcb3 in M trimers has been replaced by Lhcb1 and/or Lhcb2. However, the rotational position of the M LHCII trimer was altered, suggesting that the Lhcb3 subunit affects the macrostructural arrangement of the LHCII antenna. The absence of Lhcb3 did not result in any significant alteration in PSII efficiency or qE type of nonphotochemical quenching, but the rate of transition from State 1 to State 2 was increased in koLhcb3, although the final extent of state transition was unchanged. The level of phosphorylation of LHCII was increased in the koLhcb3 plants compared with wild-type plants in both State 1 and State 2. The relative increase in phosphorylation upon transition from State 1 to State 2 was also significantly higher in koLhcb3. It is suggested that the main function of Lhcb3 is to modulate the rate of state transitions.
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| 2. |
- Eiler, Alexander, 1976-
(author)
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The Niches of Bacterial Populations in Productive Waters : Examples from Coastal Waters and Four Eutrophic Lakes
- 2006
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Doctoral thesis (other academic/artistic)abstract
- Recent research in microbial ecology has focused on how aquatic bacterial communities are assembled. Only a few of these studies follow a “Gleasonian” approach where the roles of single bacterial populations are in focus. In this thesis, novel molecular tools were used to describe the distribution and evolutionary relationships of microbes in productive aquatic environments. Many new phylogenetic groups of bacteria were identified, likely representing bacterial populations restricted to productive freshwaters. I also addressed the dynamics and functional role of individual bacterial populations in eutrophic lakes and brackish environments with a focus on either biogeochemically significant or potentially pathogenic representatives. Flavobacteria blooms were observed, on occasions characterized by high heterotrophic production. In addition to high temporal dynamics microbial community composition and function differed on the spatial scale, as exemplified by free-living and Cyanobacteria-associated habitats. At the community scale, microbial processes, such as biomass production and substrate uptake could be predicted from the presence and absence of individual bacterial populations. I also studied the niches of potentially pathogenic Vibrio populations in various coastal waters. Using a novel culture-independent method, a V. cholerae population was detected along the entire Swedish coastline. Results from an environmental survey and a laboratory mesocosm experiment reveal that phytoplankton-derived dissolved organic matter enhance the growth of V. cholerae and other Vibrio spp. and hence create a largely overlooked niche for these heterotrophic bacteria. This thesis and future work on the role of individual bacterial populations will facilitate predictions of biogeochemical cycles and the distribution of bacteria in the context of global climate change and local eutrophication.
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| 3. |
- Fredin, Maria Fritsch, 1970, et al.
(author)
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The application and relevance of ex vivo culture systems for assessment of IBD treatment in murine models of colitis
- 2008
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In: Pharmacological Research. - : Elsevier BV. - 1043-6618 .- 1096-1186. ; 58:3-4, s. 222-231
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Journal article (peer-reviewed)abstract
- The aim of this study was to investigate the relevance of mouse ex vivo cultures as a first screening model for new therapeutic agents of Inflammatory Bowel Disease (IBD). Two murine models (dextran sodium sulphate (DSS)-induced colitis and Gαi2-deficient mice) and two anti-inflammatory agents (methyl-prednisolone and the proteasome inhibitor MG132) were evaluated. The in vivo effects of methyl-prednisolone were assessed in both models. Ex vivo colonic tissue from both mouse models were cultured in the presence or absence of the drugs and TaqMan Low-Density arrays were used to assess the regulation of inflammatory genes before and after drug treatment. Colitis induced a similar inflammatory gene profile in both mouse models in in vivo studies and in ex vivo cultures. The differences encountered reflected the different phases of colitis in the models, e.g. innate cytokine/chemokine profile in the DSS model and T cell related markers in Gαi2-deficient mice. After steroid treatment, a similar pattern of genes was suppressed in the two mouse models. We confirmed the suppression of inflammatory gene expression for IL-1β, IL-6 and iNOS in ex vivo and in vivo colons from both mouse models by quantitative RT-PCR. Importantly, the inflammatory responses in the murine ex vivo culture system reflected the in vivo response in the inflamed colonic tissue as assessed by changes in inflammatory gene expression, suggesting that the murine culture system can be used for validation of future IBD therapies.
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| 4. |
- Kovács, Laszlo, et al.
(author)
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Lack of the light-harvesting complex CP24 affects the structure and function of the grana membranes of higher plant chloroplasts.
- 2006
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In: The Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 18:11, s. 3106-20
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Journal article (peer-reviewed)abstract
- The photosystem II (PSII) light-harvesting antenna in higher plants contains a number of highly conserved gene products whose function is unknown. Arabidopsis thaliana plants depleted of one of these, the CP24 light-harvesting complex, have been analyzed. CP24-deficient plants showed a decrease in light-limited photosynthetic rate and growth, but the pigment and protein content of the thylakoid membranes were otherwise almost unchanged. However, there was a major change in the macroorganization of PSII within these membranes; electron microscopy and image analysis revealed the complete absence of the C2S2M2 light-harvesting complex II (LHCII)/PSII supercomplex predominant in wild-type plants. Instead, only C2S2 supercomplexes, which are deficient in the LHCIIb M-trimers, were found. Spectroscopic analysis confirmed the disruption of the wild-type macroorganization of PSII. It was found that the functions of the PSII antenna were disturbed: connectivity between PSII centers was reduced, and maximum photochemical yield was lowered; rapidly reversible nonphotochemical quenching was inhibited; and the state transitions were altered kinetically. CP24 is therefore an important factor in determining the structure and function of the PSII light-harvesting antenna, providing the linker for association of the M-trimer into the PSII complex, allowing a specific macroorganization that is necessary both for maximum quantum efficiency and for photoprotective dissipation of excess excitation energy.
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| 5. |
- Ruban, Alexander V, et al.
(author)
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Plasticity in the composition of the light harvesting antenna of higher plants preserves structural integrity and biological function.
- 2006
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In: Journal of Biological Chemistry. - 0021-9258. ; 281:21, s. 14981-90
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Journal article (peer-reviewed)abstract
- Arabidopsis plants in which the major trimeric light harvesting complex (LHCIIb) is eliminated by antisense expression still exhibit the typical macrostructure of photosystem II in the granal membranes. Here the detailed analysis of the composition and the functional state of the light harvesting antennae of both photosystem I and II of these plants is presented. Two new populations of trimers were found, both functional in energy transfer to the PSII reaction center, a homotrimer of CP26 and a heterotrimer of CP26 and Lhcb3. These trimers possess characteristic features thought to be specific for the native LHCIIb trimers they are replacing: the long wavelength form of lutein and at least one extra chlorophyll b, but they were less stable. A new population of loosely bound LHCI was also found, contributing to an increased antenna size for photosystem I, which may in part compensate for the loss of the phosphorylated LHCIIb that can associate with this photosystem. Thus, the loss of LHCIIb has triggered concerted compensatory responses in the composition of antennae of both photosystems. These responses clearly show the importance of LHCIIb in the structure and assembly of the photosynthetic membrane and illustrate the extreme plasticity at the level of the composition of the light harvesting system.
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