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41.
42.
Vincent EJ Jassey Geneviève Chiapusio Philippe Binet Alexandre Buttler Fatima Laggoun‐Défarge Frédéric Delarue Nadine Bernard Edward AD Mitchell Marie‐Laure Toussaint André‐Jean Francez Daniel Gilbert 《Global Change Biology》2013,19(3):811-823
Peatlands contain approximately one third of all soil organic carbon (SOC). Warming can alter above‐ and belowground linkages that regulate soil organic carbon dynamics and C‐balance in peatlands. Here we examine the multiyear impact of in situ experimental warming on the microbial food web, vegetation, and their feedbacks with soil chemistry. We provide evidence of both positive and negative impacts of warming on specific microbial functional groups, leading to destabilization of the microbial food web. We observed a strong reduction (70%) in the biomass of top‐predators (testate amoebae) in warmed plots. Such a loss caused a shortening of microbial food chains, which in turn stimulated microbial activity, leading to slight increases in levels of nutrients and labile C in water. We further show that warming altered the regulatory role of Sphagnum‐polyphenols on microbial community structure with a potential inhibition of top predators. In addition, warming caused a decrease in Sphagnum cover and an increase in vascular plant cover. Using structural equation modelling, we show that changes in the microbial food web affected the relationships between plants, soil water chemistry, and microbial communities. These results suggest that warming will destabilize C and nutrient recycling of peatlands via changes in above‐ and belowground linkages, and therefore, the microbial food web associated with mosses will feedback positively to global warming by destabilizing the carbon cycle. This study confirms that microbial food webs thus constitute a key element in the functioning of peatland ecosystems. Their study can help understand how mosses, as ecosystem engineers, tightly regulate biogeochemical cycling and climate feedback in peatlands 相似文献
43.
Tomasz Krupnik Eva Kotabová Laura S. van Bezouwen Rados?aw Mazur Maciej Garstka Peter J. Nixon James Barber Radek Kaňa Egbert J. Boekema Joanna Kargul 《The Journal of biological chemistry》2013,288(32):23529-23542
Members of the rhodophytan order Cyanidiales are unique among phototrophs in their ability to live in extremely low pH levels and moderately high temperatures. The photosynthetic apparatus of the red alga Cyanidioschyzon merolae represents an intermediate type between cyanobacteria and higher plants, suggesting that this alga may provide the evolutionary link between prokaryotic and eukaryotic phototrophs. Although we now have a detailed structural model of photosystem II (PSII) from cyanobacteria at an atomic resolution, no corresponding structure of the eukaryotic PSII complex has been published to date. Here we report the isolation and characterization of a highly active and robust dimeric PSII complex from C. merolae. We show that this complex is highly stable across a range of extreme light, temperature, and pH conditions. By measuring fluorescence quenching properties of the isolated C. merolae PSII complex, we provide the first direct evidence of pH-dependent non-photochemical quenching in the red algal PSII reaction center. This type of quenching, together with high zeaxanthin content, appears to underlie photoprotection mechanisms that are efficiently employed by this robust natural water-splitting complex under excess irradiance. In order to provide structural details of this eukaryotic form of PSII, we have employed electron microscopy and single particle analyses to obtain a 17 Å map of the C. merolae PSII dimer in which we locate the position of the protein mass corresponding to the additional extrinsic protein stabilizing the oxygen-evolving complex, PsbQ′. We conclude that this lumenal subunit is present in the vicinity of the CP43 protein, close to the membrane plane. 相似文献
44.
ADRIAN KIN MICHAŁ GRUSZCZYŃSKI DAVID MARTILL JIM D. MARSHALL BŁAŻEJ BŁAŻEJOWSKI 《Lethaia: An International Journal of Palaeontology and Stratigraphy》2013,46(1):71-81
A rich assemblage of exceptionally preserved marine and terrestrial fossils occurs in fine‐grained limestones in the upper part of the Late Tithonian (Middle Volgian) shallowing upward carbonate sequence in Central Poland. The richest horizon, a deposit known locally as the Corbulomima horizon, is named after the shallow burrowing suspension feeding bivalve Corbulomima obscura, moulds of which occur in densities of up to 500 per square metre on some bedding planes. The fauna in this bed also includes organic and phosphatic remains of a wide range of other creatures including the exuviae of limulids and decapods, disarticulated fish skeletons and rare isolated pterosaur bones and teeth. There are also perfectly preserved dragonfly wings and beetle exoskeletons. The average stable carbon and oxygen isotope values for ostracod shells and fine‐grained sediment from this horizon suggest precipitation of the calcium carbonate from warm seawater of normal marine salinity. The carbonate sediments overlying the fossiliferous horizon have been interpreted as nearshore to shoreface facies. These pass abruptly into coarse reworked intraclastic sediments interpreted as possible tsunami or storm surge over‐wash deposits. The clasts in this deposit have more positive oxygen isotope values than those in the underlying limestone, which may indicate that they were lithified in a slightly more evaporative, perhaps intertidal, setting. The succession terminates with silicified fine‐grained limestones likely to have formed in extremely shallow lagoonal environments. In contrast with the Solnhofen limestones of Lower Tithonian age in south‐central Germany the Corbulomima horizon is interpreted as a transitional deposit formed in a shallow marine setting by rapid burial with elements of both Konservat‐ and Konzentrat‐Lagerstätte preservation. □Konzentrat and Konservat‐Lagerstätte, Taphonomy, Palaeoenvironment, Paleogeography, Late Jurassic, Poland. 相似文献
45.
Chauhan D Folea IM Jolley CC Kouril R Lubner CE Lin S Kolber D Wolfe-Simon F Golbeck JH Boekema EJ Fromme P 《Biochemistry》2011,50(5):686-692
Iron (Fe) availability is a major limiting factor for primary production in aquatic environments. Cyanobacteria respond to Fe deficiency by derepressing the isiAB operon, which encodes the antenna protein IsiA and flavodoxin. At nanomolar Fe concentrations, a PSI-IsiA supercomplex forms, comprising a PSI trimer encircled by two complete IsiA rings. This PSI-IsiA supercomplex is the largest photosynthetic membrane protein complex yet isolated. This study presents a detailed characterization of this complex using transmission electron microscopy and ultrafast fluorescence spectroscopy. Excitation trapping and electron transfer are highly efficient, allowing cyanobacteria to avoid oxidative stress. This mechanism may be a major factor used by cyanobacteria to successfully adapt to modern low-Fe environments. 相似文献
46.
The PsbW protein stabilizes the supramolecular organization of photosystem II in higher plants 总被引:1,自引:0,他引:1
García-Cerdán JG Kovács L Tóth T Kereïche S Aseeva E Boekema EJ Mamedov F Funk C Schröder WP 《The Plant journal : for cell and molecular biology》2011,65(3):368-381
PsbW, a 6.1-kDa low-molecular-weight protein, is exclusive to photosynthetic eukaryotes, and associates with the photosystem II (PSII) protein complex. In vivo and in vitro comparison of Arabidopsis thaliana wild-type plants with T-DNA insertion knock-out mutants completely lacking the PsbW protein, or with antisense inhibition plants exhibiting decreased levels of PsbW, demonstrated that the loss of PsbW destabilizes the supramolecular organization of PSII. No PSII-LHCII supercomplexes could be detected or isolated in the absence of the PsbW protein. These changes in macro-organization were accompanied by a minor decrease in the chlorophyll fluorescence parameter F(V) /F(M) , a strongly decreased PSII core protein phosphorylation and a modification of the redox state of the plastoquinone (PQ) pool in dark-adapted leaves. In addition, the absence of PsbW protein led to faster redox changes in the PQ pool, i.e. transitions from state 1 to state 2, as measured by changes in stationary fluorescence (F(S) ) kinetics, compared with the wild type. Despite these dramatic effects on macromolecular structure, the transgenic plants exhibited no significant phenotype under normal growth conditions. We suggest that the PsbW protein is located close to the minor antenna of the PSII complex, and is important for the contact and stability between several PSII-LHCII supercomplexes. 相似文献
47.
Long-range organization of bacteriochlorophyll in chlorosomes of Chlorobium tepidum investigated by cryo-electron microscopy 总被引:1,自引:0,他引:1
Oostergetel GT Reus M Gomez Maqueo Chew A Bryant DA Boekema EJ Holzwarth AR 《FEBS letters》2007,581(28):5435-5439
Intact chlorosomes of Chlorobium tepidum were embedded in amorphous ice layers and examined by cryo-electron microscopy to study the long-range organization of bacteriochlorophyll (BChl) layers. End-on views reveal that chlorosomes are composed of several multi-layer tubules of variable diameter (20-30 nm) with some locally undulating non-tubular lamellae in between. The multi-layered tubular structures are more regular and larger in a C. tepidum mutant that only synthesizes [8-ethyl, 12-methyl]-BChl d. Our data show that wild-type C. tepidum chlorosomes do not have a highly regular, long-range BChl c layer organization and that they contain several multi-layered tubules rather than single-layer tubules or exclusively undulating lamellae as previously proposed. 相似文献
48.
49.
Kereïche S Bourinet L Keegstra W Arteni AA Verbavatz JM Boekema EJ Robert B Gall A 《FEBS letters》2008,582(25-26):3650-3656
The integral membrane light-harvesting (LH) proteins from purple photosynthetic bacteria form circular oligomers of an elementary unit that is composed of two very hydrophobic polypeptides, termed alpha and beta. These apoprotein dimers are known to associate into closed circular arrays of 8, 9 and 16 alpha/beta-mers. We report the existence of peripheral LH proteins purified from Allochromatium vinosum with two intermediate ring sizes and postulate that one is a 13 alpha/beta-mer. This shows that LH proteins are able to form membrane rings of continuously increasing diameter from 68 to 115A. The presence of these new ring sizes warrants further study, as it will help to further validate the structure-function models of LH proteins currently found in the literature. 相似文献
50.
Paul R Bessell Darren J Shaw Nicholas J Savill Mark EJ Woolhouse 《BMC veterinary research》2008,4(1):40