40 research outputs found

    Ultrastructure of calcareous dinophytes (Thoracosphaeraceae, Peridiniales) with a focus on vacuolar crystal-like particles.

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    Biomineralization in calcareous dinophytes (Thoracosphaeracaea, Peridiniales) takes place in coccoid cells and is presently poorly understood. Vacuolar crystal-like particles as well as collection sites within the prospective calcareous shell may play a crucial role during this process at the ultrastructural level. Using transmission electron microscopy, we investigated the ultrastructure of coccoid cells at an early developmental stage in fourteen calcareous dinophyte strains (corresponding to at least ten species of Calciodinellum, Calcigonellum, Leonella, Pernambugia, Scrippsiella, and Thoracosphaera). The shell of the coccoid cells consisted either of one (Leonella, Thoracosphaera) or two matrices (Scrippsiella and its relatives) of unknown element composition, whereas calcite is deposited in the only or the outer layer, respectively. We observed crystal-like particles in cytoplasmic vacuoles in cells of nine of the strains investigated and assume that they are widespread among calcareous dinophytes. However, similar structures are also found outside the Thoracosphaeraceae, and we postulate an evolutionarily old physiological pathway (possibly involved in detoxification) that later was specialized for calcification. We aim to contribute to a deeper knowledge of the biomineralization process in calcareous dinophytes

    Nitrogen deficiency in Arabidopsis affects galactolipid composition and gene expression and results in accumulation of fatty acid phytyl esters

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    Nitrogen is an essential nutrient for plants because it represents a major constituent of numerous cellular compounds, including proteins, amino acids, nucleic acids and lipids. While N deprivation is known to have severe consequences for primary carbon metabolism, the effect on chloroplast lipid metabolism has not been analysed in higher plants. Nitrogen limitation in Arabidopsis led to a decrease in the chloroplast galactolipid monogalactosyldiacylglycerol (MGDG) and a concomitant increase in digalactosyldiacylglycerol (DGDG), which correlated with an elevated expression of the DGDG synthase genes DGD1 and DGD2. The amounts of triacylglycerol and free fatty acids increased during N deprivation. Furthermore, phytyl esters accumulated containing medium-chain fatty acids (12:0, 14:0) and a large amount of hexadecatrienoic acid (16:3). Fatty acid phytyl esters were localized to chloroplasts, in particular to thylakoids and plastoglobules. Different polyunsaturated acyl groups were found in phytyl esters accumulating in Arabidopsis lipid mutants and in other plants, including 16:3 and 18:3 species. Therefore N deficiency in higher plants results in a co-ordinated breakdown of galactolipids and chlorophyll with deposition of specific fatty acid phytyl esters in thylakoids and plastoglobules of chloroplasts

    The paramutated SULFUREA locus of tomato is involved in auxin biosynthesis

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    The tomato (Solanum lycopersicum) sulfurea mutation displays trans-inactivation of wild-type alleles in heterozygous plants, a phenomenon referred to as paramutation. Homozygous mutant plants and paramutated leaf tissue of heterozygous plants show a pigment-deficient phenotype. The molecular basis of this phenotype and the function of the SULFUREA gene (SULF) are unknown. Here, a comprehensive physiological analysis of the sulfurea mutant is reported which suggests a molecular function for the SULFUREA locus. It is found that the sulf mutant is auxin-deficient and that the pigment-deficient phenotype is likely to represent only a secondary consequence of the auxin deficiency. This is most strongly supported by the isolation of a suppressor mutant which shows an auxin overaccumulation phenotype and contains elevated levels of indole-3-acetic acid (IAA). Several lines of evidence point to a role of the SULF gene in tryptophan-independent auxin biosynthesis, a pathway whose biochemistry and enzymology is still completely unknown. Thus, the sulfurea mutant may provide a promising entry point into elucidating the tryptophan-independent pathway of IAA synthesis

    Long-term bio-cultural heritage: exploring the intermediate disturbance hypothesis in agro-ecological landscapes (Mallorca, c. 1850–2012)

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    Cellular fine structures and histochemical reactions in the tissue of a cypress twig preserved in Baltic amber

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    A twig of a cypress plant preserved for ca. 45Myr in Baltic amber was analysed by light and electron microscopy. Cross-sections of the whole plant showed an almost intact tissue of the entire stem and leaves, revealing, to our knowledge, the oldest and most highly preserved tissue from an amber inclusion reported so far. The preparations are based on a new technique of internal imbedding, whereby the hollow spaces within the inclusion are filled with synthetic resin which stabilizes the cellular structures during the sectioning procedure. Cytological stains applied to the sections reacted with cell walls and nuclei. A strong green auto-fluorescence of the cuticle and the resin canals in the leaves was observed. Transmission electron micrographs revealed highly preserved fine structures of cell walls, membranes and organelles. The results were compared with taxonomically related recent Glyptostrobus and Juniperus plants

    Functions of Chloroplastic Adenylate Kinases in Arabidopsis1[W][OA]

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    Adenosine monophosphate kinase (AMK; adenylate kinase) catalyses the reversible formation of ADP by the transfer of one phosphate group from ATP to AMP, thus equilibrating adenylates. The Arabidopsis (Arabidopsis thaliana) genome contains 10 genes with an adenylate/cytidylate kinase signature; seven of these are identified as putative adenylate kinases. Encoded proteins of at least two members of this Arabidopsis adenylate kinase gene family are targeted to plastids. However, when the individual genes are disrupted, the phenotypes of both mutants are strikingly different. Although absence of AMK2 causes only 30% reduction of total adenylate kinase activity in leaves, there is loss of chloroplast integrity leading to small, pale-looking plantlets from embryo to seedling development. In contrast, no phenotype for disruption of the second plastid adenylate kinase was found. From this analysis, we conclude that AMK2 is the major activity for equilibration of adenylates and de novo synthesis of ADP in the plastid stroma

    Ultrastructural traits in detail.

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    <p>(TEM). A. Multiply-stalked pyrenoid covered by a starch shed of <i>Calciodinellum</i> aff. <i>operosum</i> (GeoB 34, note the large, vacuolar crystal-like particles). B. Different chloroplast types of <i>Scrippsiella bicarinata</i> (GeoB 411, note that chloroplasts could be connected to multiply-stalked pyrenoids covered by a starch shed, or have interlamellar pyrenoids, with thylakoid lamellae leading through the pyrenoid. C. Two to four thylakoid lamellae (arrows) of <i>Scrippsiella bicarinata</i> (GeoB 411). D. Mitochondria with tubular cristae of <i>Scrippsiella</i> aff. <i>trochoidea</i> (GeoB 283). Abbreviations: ch, chloroplast; cb, crystal-like particle; me, membrane; mt, mitochondrion; py, pyrenoid; st, starch grain; tr, trichocyst. Scale bars: A and B 1 µm, C and D 0.1 µm.</p
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