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  • 1
    ISSN: 1432-2048
    Keywords: Key words: Diatom ; Envelope membranes ; Photosynthetic activity ; Plastid isolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. A protocol for the isolation of intact plastids from two marine centric diatoms, Odontella sinensis (Greville) Grunow and Coscinodiscus granii Gough, has been worked out. The cells were broken in a Yeda Press, and the intact plastids were purified by centrifugation in Percoll gradients. Electron microscopy indicates that at least one of the four envelope membranes is present in the isolated plastids. The plastids are photosynthetically active as proven by CO2 fixation which was measured by light-dependent oxygen evolution. Rates up to 50 μmol O2 · (mg Chl)−1 · h−1, i.e. about 40% of the in vivo rate of photosynthesis were obtained. The inhibition of CO2 fixation by external phosphate and the ability of the plastids to reduce added 3-phosphoglycerate photosynthetically indicate the presence of a phosphate translocator in the envelope of the diatom plastids. Light-dependent O2 evolution upon addition of nitrite indicates the presence of nitrite reductase in these plastids. Purified envelope membranes of Odontella plastids analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis contain polypeptides similar to those of the envelope of higher-plant chloroplasts. However, there are additional bands present, which in part may be constituents of the two additional envelope membranes (“chloroplast endoplasmic reticulum”) and in part may represent additional components of the inner membranes.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2017-02-16
    Description: Sea ice is a large environment controlled by a number of abiotic factors (i.e. low temperatures and high salinities). Despite these harsh conditions, it is inhabited by a diverse community and significantly contributing to primary production in ice-covered regions. While this biodiversity has been investigated in the past by classical methods, little is known about its functional biodiversity, i.e. which species are actively contributing with which functions to the community. By sequencing 18S rRNA and rDNA amplicons, we were able to compare the “total” biodiversity (rDNA-based) with the “active” biodiversity (rRNA-based) and found an over-representation of certain groups (i.e. Bacillariophyceae and Ciliophora) in the active part of the community. Furthermore, we were able to isolate an abundant naviculoid sea ice diatom member (CCMP2297) of the Arctic sea ice community and conducted temperature stress experiments (10 °C, 5 °C, -2 °C, -5 °C) and analyzed not only physiological responses to high and cold temperature stress, but also the molecular responses to thermal stress by sequencing the transcriptome. We found that based on physiological parameters this diatom has a broad thermal range (5 °C to -5 °C) but significantly changes its gene expression pattern at higher temperatures.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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  • 3
    Publication Date: 2019-03-08
    Description: The Southern Ocean houses a diverse and productive community of organisms. Unicellular eukaryotic diatoms are the main primary producers in this environment, where photosynthesis is limited by low concentrations of dissolved iron and large seasonal fluctuations in light, temperature and the extent of sea ice. How diatoms have adapted to this extreme environment is largely unknown. Here we present insights into the genome evolution of a cold-adapted diatom from the Southern Ocean, Fragilariopsis cylindrus based on a comparison with temperate diatoms. We find that approximately 24.7 per cent of the diploid F. cylindrus genome consists of genetic loci with alleles that are highly divergent from those of temperate diatoms (15.1 megabases of the total genome size of 61.1 megabases). These divergent alleles were differentially expressed across environmental conditions, including darkness, low iron, freezing, elevated temperature and increased CO2. Alleles with the largest ratio of non-synonymous to synonymous nucleotide substitutions also show the most pronounced condition-dependent expression, suggesting a correlation between diversifying selection and allelic differentiation. Divergent alleles may be involved in adaptation to environmental fluctuations in the Southern Ocean.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
    Publication Date: 2017-02-16
    Description: Sea ice is a large and diverse ecosystem inhabited by bacteria and protists contributing significantly to primary production in ice-covered regions. In the Arctic Ocean, sea ice consists of mixed multi-year ice (MYI) and thinner first-year ice (FYI). Due to global warming we experience a shift from MYI towards FYI. Despite the great importance of the sea ice ecosystem, little is known about its functional biodiversity, i.e. which species are actively contributing with which functions to the community. We investigated the eukaryotic biodiversity in MYI and FYI from the central Arctic Ocean using 18S rRNA and rDNA amplicons and compared the “total” biodiversity (rDNA-based) with the “active” biodiversity (rRNA-based). Groups like Ciliophora, Bicosoecida and Bacillariophyceae were over-represented in the active part of the community and grazers appear most active in one FYI station due to the advanced stage of melt compared to the other stations. Furthermore, preliminary results of transcriptomic stress experiments with an abundant naviculoid sea ice diatom show that based on physiological parameters this diatom has a broad thermal range (5 °C to -5 °C) but significantly changes its gene expression pattern at higher temperatures.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , notRev
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