1,721,052 research outputs found
Gas exchanges, metabolism, and morphology of Dunaliella salina in response to the CO2 concentration and nitrogen source used for growth.
No full textThe halotolerant alga Dunaliella salina was cultured on 10 mM NH4+ or NO3- with air CO2 or 5% (v/v) CO2. Cells grown on NH4+ rather than NO3- were up to 17% larger in volume but had similar division rates. The photosynthetic K0.5 of dissolved inorganic C per cell was reduced, but the light- and CO2-saturated photosynthesis, dark respiration, and light-independent fixation rates were increased. The cells exhibited 2- to 5-fold greater activities of ribulose-1,5-bisphosphate carboxylase/oxygenase, phosphoenolpyruvate carboxylase and carboxykinase, and carbonic anhydrase and more soluble and ribulose-1,5-bisphosphate carboxylase/oxygenase protein. Chlorophyll and [beta]-carotene also increased by 30 to 70%. However, starch and glycerol decreased, indicating that C was reallocated from carbohydrates into protein and pigments by growth on NH4+. Algae cultured on air-CO2 rather than a high CO2 concentration were 44% smaller with 55 to 67% lower cell division rates and thus appeared C-limited, despite the operation of a CO2-concentrating mechanism. Cells cultured on air-CO2 had less protein and starch and 28% more glycerol, but the pigment content was unchanged. In only one growth regime was the cell glycerol concentration sufficient to maintain osmotic equilibrium with the external medium, indicating that an additional osmoticum was required. It appears that the N source, as well as the growth [CO2], substantially modifies photosynthetic and growth characteristics, light-independent C metabolism, and C-allocation patterns of D. salina cells
Changes in cell size induced by growth conditions affect the photosynthetic characteristics of Dunaliella salina
No full textOrganic carbon release by Dunaliella salina (Chlorophyta) under different growth conditions of CO2, nitrogen, and salinity
No full textTwo strains of Dunaliella salina (Dunal) Teod., UTEX 1644 and UTEX 200, were cultured under different growth regimes, including 10 mM NO3− or NH4+, 1.5 or 3.0 M NaCl, and low (0.035%) or high (5%) CO2 in air. The release of 14C-labeled dissolved organic carbon (DOC), expressed as a rate and as a percentage of photosynthetic 14CO2 assimilation, was subsequently determined. The percentage of DOC released was inversely related to cell density in the assay medium, but photosynthesis on a per-cell basis was not. Release of DOC was low, in the range of 1–5% of photosynthesis, but during acclimation to growth on NH4+, it rose to 11%. The presence of NH4+ rather than NO3− in the growth medium increased the rate of release by both strains, but the percentage release was stimulated only in UTEX 200 cells, because their photosynthetic rate was depressed by NH4+. For UTEX 1644, high, as compared to low, CO2-grown cells, had somewhat higher rates and percentages of DOC release, but release from UTEX 200 cells was unaffected by the growth-CO2. The rate of DOC release by high CO2-grown cells was not enhanced at a low concentration of dissolved inorganic carbon, indicating that the released material did not originate from the photorespiratory pathway. The effects of NaCl on DOC release varied with strain and growth conditions. For UTEX 200, the cells in NO3−, but not NH4+, exhibited a doubling or more in percentage of release with a doubling in NaCl concentration, irrespective of growth-CO2. With UTEX 1644 the low CO2-grown cells showed the greatest enhancement in 3.0 M NaCl. Organic matter accumulated on the external surface of the cell membrane and constituted a well-defined cell-coat, which was more dense in NH4+ than in NO3−-grown cells. Microtubules, which may play a role in maintaining cell shape, were observed just below the plasma membrane.
From a practical viewpoint, the presence of organic material in the hypersaline ponds of salt-works is detrimental to salt production. When D. salina cells become abundant in such ponds, the attendant, continuous release of DOC may make a significant contribution to the problem
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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