1,721,055 research outputs found
Digalactosyl-diacylglycerol-deficiency lowers the thermal stability of thylakoid membranes
Get PDFWe investigated the effects of digalactosyl-diacylglycerol (DGDG) on the organization and thermal stability of thylakoid membranes, using wild-type Arabidopsis thaliana and the DGDG-deficient mutant, dgd1. Circular-dichroism measurements reveal that DGDG-deficiency hampers the formation of the chirally organized macrodomains containing the main chlorophyll a/b light-harvesting complexes. The mutation also brings about changes in the overall chlorophyll fluorescence lifetimes, measured in whole leaves as well as in isolated thylakoids. As shown by time-resolved measurements, using the lipophylic fluorescence probe Merocyanine 540 (MC540), the altered lipid composition affects the packing of lipids in the thylakoid membranes but, as revealed by flash-induced electrochromic absorbance changes, the membranes retain their ability for energization. Thermal stability measurements revealed more significant differences. The disassembly of the chiral macrodomains around 55°C, the thermal destabilization of photosystem I complex at 61°C as detected by green gel electrophoresis, as well as the sharp drop in the overall chlorophyll fluorescence lifetime above 45°C (values for the wild type—WT) occur at 4–7°C lower temperatures in dgd1. Similar differences are revealed in the temperature dependence of the lipid packing and the membrane permeability: at elevated temperatures MC540 appears to be extruded from the dgd1 membrane bilayer around 35°C, whereas in WT, it remains lipid-bound up to 45°C and dgd1 and WT membranes become leaky around 35 and 45°C, respectively. It is concluded that DGDG plays important roles in the overall organization of thylakoid membranes especially at elevated temperatures
Influence of Nitrogen Availability on Sulfate Assimilation Pathway in Arabidopsis thaliana
No full textSulfate and nitrate, which contain sulfur and nitrogen in their most highly oxidized form, are the dominant species available to many plants for covering their needs for these elements (1–3). In amino acids, including sulfur containing amino acids cysteine and methionine, both sulfur and nitrogen are present in reduced form, therefore, sulfate and nitrate have to be reduced for their synthesis. The dominant portion of amino acids is used for protein synthesis hence the SIN ratio in plants remains quite stable. Plants appear to possess a mechanism to coordinate assimilatory sulfate and nitrate reduction so that the appropriate proportions of both sulfur containing and other amino acids are available for protein synthesis (4–7). These reports also indicate that the second enzyme of assimilatory sulfate reduction APS reductase is highly regulated by different nutritional conditions. In this study we were particularly interested in the regulation of APS reductase activity, mRNA expression, and protein accumulation under different conditions of nitrogen availability in Arabidopsis thaliana plants
Effects of CO2, light and temperature on rubisco activase protein in wheat leaf segments
No full textRubisco activase catalyzes the ATP-dependent activation of rubisco. At moderately
elevated temperature (for wheat above 30°C), rubisco activase becomes reversibly
inactivated in leaf segments (2). A further increase of the temperature (for wheat above
40°C) causes partial insolubilization and the formation of aggregates in less than 30
minutes.
Senescence in wheat leaf segments depends on the availability of CO2, the illumination
and the incubation temperature. In general, net protein degradation is delayed under
CO2 depletion. At higher light (PAR: 150 μmol m-2 s- 1), several stromal proteins are less
rapidly degraded than at low light (PAR: 50 μmol m-2 s- 1). In absence of CO2 and at the
higher PAR, chloroplast enzymes are maintained in wheat leaf segments over days even
at 35°C indicating that senescence and net degradation of chloroplast proteins are not
necessarily accelerated by such unfavorable conditions for photosynthesis. The fate of
rubisco activase protein under such conditions is of special interest, since its activity is
temperature-sensitive and this enzyme plays an important role in the regulation of
rubisco activity and as a consequence of the Calvin-cycle
Application of light-emitting diodes (LED's) in algal culture: In culture light harvesting efficiency of the green alga chlorella and the cyanobacterium calothrix
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Light induced reversible structural changes in chirally organized macroaggregates of purified chlorophyll a/b protein complexes
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