1,721,089 research outputs found
Mineral nutrition in photolithotrophs: cellular mechanisms controlling growth in terrestrial and aquatic habitats
No full textStrategies for the allocation of resources under sulfur limitation in the green alga Dunaliella salina
Full text linkThe effect of sulfur limitation on the partitioning of carbon, nitrogen, and sulfur was investigated in Dunaliella salina. D. salina was able to adapt to 6 microM sulfate; under these conditions, the cells showed reduced growth and photosynthetic rates. Whereas intracellular sulfate was depleted, phosphate, nitrate, and ammonium increased. Amino acids showed a general increase, and alanine became the most abundant amino acid. The activities of four key enzymes of carbon, sulfur, and nitrogen metabolism were differentially regulated: Adenosine 5' triphosphate sulfurylase activity increased 4-fold, nitrate reductase and phosphoenolpyruvate (PEP) carboxylase activities decreased 4- and 11-fold, respectively, whereas carbonic anhydrase activity remained unchanged. Sulfur limitation elicited specific increase or decrease of the abundance of several proteins, such us Rubisco, PEP carboxylase, and a light harvesting complex protein. The accumulation of potentially toxic ammonium indicates an insufficient availability of carbon skeletons. Sulfur deficiency thus induces an imbalance between carbon and nitrogen. The dramatic reduction in PEP carboxylase activity suggests that carbon was diverted away from anaplerosis and possibly channeled into C3 metabolism. These results indicate that it is the coordination of key steps and components of carbon, nitrogen, and sulfur metabolism that allows D. salina to adapt to prolonged sulfur limitation
Sulfur and primary production in aquatic environments: an ecological perspective
No full textSulfur is one of the critical elements in living matter, as it participates in several structural, metabolic and
catalytic activities. Photosynthesis is an important process that entails the use of sulfur during both the light
and carbon reactions. Nearly half of global photosynthetic carbon fixation is carried out by phytoplankton
in the aquatic environment. Aquatic environments are very different from one another with respect to
sulfur content: while in the oceans sulfate concentration is constantly high, freshwaters are characterized by
daily and seasonal variations and by a wide range of sulfur concentration. The strategies that algal cells
adopt for energy and resource allocation often reflect these differences. In the oceans, the amount and
chemical form of sulfur has changed substantially during the course of the Earth’s history; it is possible that
sulfur availability played a role in the evolution of marine phytoplankton communities and it may continue
to have appreciable effects on global biogeochemistry and ecology. Phytoplankton is also the main biogenic
source of sulfur; sulfur can be released into the atmosphere by algal cells as dimethylsulfide, with possibly
important repercussions on global climate. These and related matters are discussed in this review
Sulfur and phytoplankton: acquisition, metabolism and impact on the environment
No full textSulfur emission from marine phytoplankton has been recognized as an important
factor for global climate and as an entry into the biogeochemical S cycle. Despite
this significance, little is known about the cellular S metabolism in algae that forms
the basis of this emission. Some biochemical and genetic evidence for regulation of S
uptake and assimilation is available for the freshwater model alga
Chlamydomonas
.
However, the marine environment is substantially different from most freshwaters,
containing up to 50 times higher free sulfate concentrations and challenging the
adaptive mechanisms of primary and secondary S metabolism in marine algae. This
review intends to integrate ecological and physiological data to provide a comprehensive
view of the role of S in the oceans
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Regulation of nitrate and sulfate uptake in maize genotypes in response to the availability of nitrate
No full textSulfur assimilation in photosynthetic organisms: molecular functions and regulations of transporters and assimilatory enzymes
No full textSulfur is required for growth of all organisms and is present in a wide variety
of metabolites having distinctive biological functions. Sulfur is cycled
in ecosystems in nature where conversion of sulfate to organic sulfur
compounds is primarily dependent on sulfate uptake and reduction
pathways in photosynthetic organisms and microorganisms. In vascular
plant species, transport proteins and enzymes in this pathway are functionally
diversified to have distinct biochemical properties in specific
cellular and subcellular compartments. Recent findings indicate regulatory
processes of sulfate transport and metabolism are tightly connected
through several modes of transcriptional and posttranscriptional mechanisms.
This review provides up-to-date knowledge in functions and
regulations of sulfur assimilation in plants and algae, focusing on sulfate
transport systems andmetabolic pathways for sulfate reduction and
synthesis of downstream metabolites with diverse biological functions
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