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  • 1
    ISSN: 1550-7408
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Calreticulin is the major high capacity, low affinity Ca2+ binding protein localized within the endoplasmic reticulum. It functions as a reservoir for triggered release of Ca2+ by the endoplasmic reticulum and is thus integral to eukaryotic signal transduction pathways involving Ca2+ as a second messenger. The early branching photosynthetic protist Euglena gracilis is shown to possess calreticulin as its major high capacity Ca2+ binding protein. The protein was purified, microsequenced and cloned. Like its homologues from higher eukaryotes, calreticulin from Euglena possesses a short signal peptide for endoplasmic reticulum import and the C-terminal retention signal KDEL, indicating that these components of the eukaryotic protein routing apparatus were functional in their present form prior to divergence of the euglenozoan lineage. A gene phytogeny for calreticulin and calnexin sequences in the context of eukaryotic homologues indicates i) that these Ca2+ binding endoplasmic reticulum proteins descend from a gene duplication that occurred in the earliest stages of eukaryotic evolution and furthermore iii that Euglenozoa express the calreticulin protein of the kinetoplastid (trypanosomes and their relatives) lineage, rather than that of the eukaryotic chlorophyte which gave rise to Euglena's plastids. Evidence for conservation of endoplasmic reticulum routing and Ca2+ binding function of calreticulin from Euglena traces the functional history of Ca2+ second messenger signal transduction pathways deep into eukaryotic evolution.
    Materialart: Digitale Medien
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  • 2
    ISSN: 1432-1211
    Schlagwort(e): Key words Interferon regulatory factor 1 ; IRF1 ; Chicken ; Polymorphism ; Microchromosome
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Materialart: Digitale Medien
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  • 3
    ISSN: 1432-1211
    Schlagwort(e): Key words Interleukin-2 ; Chicken ; Chromosomal location ; Cytokine ; Synteny
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract  The gene encoding a chicken cytokine with T-cell proliferative activity was cloned, sequenced, and mapped. The results show that this cytokine is chicken IL2 and not IL15. The exon:intron structure of chicken IL2 corresponds almost exactly to those of mammalian IL2s with the exceptions of exon 2 and introns 2 and 3 which are shorter. Chicken IL2 contains five repeats of the "instability" motif ATTTA in the 3′untranslated region in exon 4. It is a single-copy gene, with neither structural (amino acid) nor promoter sequence polymorphisms identified. Analysis of the predicted amino acid sequence suggests that overall protein structure is conserved, but the receptor binding sites are not. A number of potential regulatory sequences similar to those found in mammals have been identified in the promoter. These include (5′–3′) a composite NF-AT/ "AP-1" element, a CD28 response element, an AP-1 element, an NF-AT element, and the AP-1 part of an AP-1/octamer composite element. The mammalian NF-κB and octamer binding sites seem to be absent, although there are alternative potential NF-κB and octamer-binding elements in the chicken IL2 promoter, in close proximity to their mammalian homologues. Sequence comparisons also predict other potential transcription factor binding sites as yet undescribed in mammalian IL2 promoters. A Taq I polymorphism was identified which enabled chicken IL2 to be mapped to chromosome 4, linked to ANX5, with synteny with mouse chromosome 3 and human chromosome 4. This is the first non-mammalian cytokine gene to be mapped.
    Materialart: Digitale Medien
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  • 4
    ISSN: 1432-2048
    Schlagwort(e): Aquatic angiosperm (photosynthesis) ; Bicarbonate utilization ; Egeria (photosynthesis, ultrastructure) ; Photosynthesis (leaf, stem)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Photosynthetic mechanisms have been compared in leaves and, separately, in stems of Egeria densa Planch. In order to correlate the structural and functional characteristics of the two organs (1) the ultrastructural features of leaves and stems have been studied and (2) their photosynthetic activity has been evaluated by measuring in vivo both oxygen evolution and the kinetics of chlorophyll fluorescence. The results confirm the aquatic behaviour of the leaf which is able to utilize inorganic C supplied both as CO2 and HCO 3 − . In this respect, the different wall organization found in the two cell layers of the leaf is particularly interesting, since it could be related to the known polar mechanism of inorganic-C uptake. The stem, by contrast, behaves rather as an aerial organ, needing very high CO2 concentrations in the aquatic environment in order to carry out photosynthesis. In the stem, the aerenchyma plays a role in supplying the green cells with gaseous respiratory CO2, thus facilitating the photosynthetic activity of the submerged stems.
    Materialart: Digitale Medien
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  • 5
    ISSN: 1432-2048
    Schlagwort(e): Key words: Brefeldin A ; Daucus ; Endomembrane syst-em ; Protein secretion ; Somatic embryogenesis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract. Brefeldin A, an inhibitor of protein secretion, caused typical alterations to the endomembrane system with limited effects on viability when given to unorganized carrot cells growing in suspension. When given to the same cells during particular stages of embryogenesis, it caused similar endomembrane lesions and an almost complete arrest of the embryogenic process. Addition of conditioned medium containing extracellular secreted proteins to the embryos during treatment with Brefeldin A allowed acquisition of polarity and the continuation of a quasi-normal embryogenic process.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1432-2048
    Schlagwort(e): Key words: Chitinase ; Daucus ; Plant development ; Secretion ; Somatic embryogenesis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract. The carrot cell variant ts11 is unable to form somatic embryos at the non-permissive temperature of 32 °C, but the block can be overcome by the addition of a 32-kDa acidic endochitinase to the medium. In this work we conducted a cyto-histological analysis of the blocked embryo forms. The morphology of the endomembrane system is altered; in particular, the ER is dilated and may show electron-dense precipitates and continuity with the plasma membrane. These morphological alterations do not occur in the presence of externally-added endochitinase. We also noticed modifications of the culture medium that are probably related to the morphological observations: the total amount of secreted proteins is reduced and pulse-chase experiments revealed that, compared with wild-type cells, the secretion of major polypeptides is reduced while new minor polypeptides are secreted. Western blot analysis revealed the presence of the binding protein BiP, a resident of the ER and of glutamine synthase, a cytosolic protein, in the medium of ts11 but not wild-type cells. These results indicate that ts11 is altered in the secretory pathway but do not clarify the role of endochitinase.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Protoplasma 128 (1985), S. 208-217 
    ISSN: 1615-6102
    Schlagwort(e): Cation exchange ; Cell wall ; Fucus virsoides ; Intertidal seaweeds ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The ultrastructure of the cell wall and the distribution of alginate, cellulose and fucoidans were studied in the intertidal algaFucus virsoides. Microanalysis and precipitation with KPA revealed a cation localization in the wall, mainly corresponding with sulphated polysaccharide distribution. Thus, the adaptive resistance to changes in ionic environment seems to take place through a cation binding to the cell wall polysaccharides, principally at the thallus surface, employing an avoidance mechanism.
    Materialart: Digitale Medien
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  • 8
    ISSN: 1615-6102
    Schlagwort(e): Zea mays L. ; Etioplasts ; Etioplast differentiation ; Etioplast senescence ; Optical diffraction ; Prolamellar body arrangement ; Prothylakoids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The entire life-cycle of maize leaf etioplasts has been followed. Prolamellar bodies with different types of tubular membrane arrangement can be found in the juvenile stages of the organelles, while in mature etioplasts nearly all the prolamellar bodies exhibit an “hexagonal ring” arrangement, which, by optical diffraction, appears to be the most regular and compact possible. The prothylakoid membranes also undergo changes during organelle differentiation, and their different organization and arrangement produce a clear dimorphism between the etioplasts of mesophyll and bundle sheath cells. In senescent etioplasts the prothylakoids are more affected, while the prolamellar bodies appear rather stable, also in situations where protochlorophyll(ide) content is very low. The formation of clusters of osmiophilic globules is coupled with the breakdown of the etioplast membranes.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Protoplasma 119 (1984), S. 110-120 
    ISSN: 1615-6102
    Schlagwort(e): Plastid greening ; Zea mays ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The effects of light intensity and cell age on the greening of etioplasts were studied in seedlings of maize. We could see that in the youngest tissues examined by us the etioplast greening is very fast and occurs according to a particular pattern which is characterized by the contemporary presence of grana and large non crystalline prolamellar bodies. On the contrary, in the oldest examined tissues the etioplast greening is slow and the formation of grana appears to be delayed and subsequent to the using up of the prolamellar bodies. In the young tissues the intensity of the light mainly affects the duration of the lag-phase preceding the chlorophyll accumulation, while in the old tissues it also affects the total amount of chlorophyllous pigments, the restraining effect of the light appearing amplified by a concomitant restraining effect of cell age.
    Materialart: Digitale Medien
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  • 10
    ISSN: 1615-6102
    Schlagwort(e): Carrot hypocotyl explant ; Flow cytometry ; Somatic embryogenesis ; Ultrastructure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary The cellular events occurring in carrot hypocotyl explants during long-term and pulse treatment with 2,4-D were followed using different techniques (light and transmission electron microscopy, flow cytometry, PCNA staining). Different morphogenetic pathways were induced under the various experimental conditions. Nevertheless, in the explants the activated cells were the same (provascular cells) and they showed very similar structural and ultrastructural changes. The long-term treatment with 2,4-D induced rapid re-activation of the cell cycle.
    Materialart: Digitale Medien
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