1,721,172 research outputs found
Interactions between C and N metabolism in Dunaliella salina cells cultured at elevated CO2 and high N concentrations
No full textThe green algaDunaliella salina UTEX 200 was cultured at high (5 percnt;) [CO2] in a medium containing 10 mmol/L of either NO3− or NH4+ as the sole N source. Specific growth rate was 50 percnt; higher for NH4+-grown cells than for their counterparts cultured in the presence of NO3−. Cell size, protein content, Rubisco protein, phosphoenolpyruvate carboxylase (PEPC) activity, and light independent carbon fixation were enhanced by growth in the presence of NH4+. On the other hand, maximal photosynthetic rate and cell glycerol concentration were lower when N was supplied as NH4+. The activity of glutamine synthetase was affected very little by the N-source.D. salina UTEX 200 showed some peculiarities in its mechanism of adaptation to high [N] in comparison to other strains previously used for similar studies. This allowed dissection of the underlying mechanism of the growth response to high [N], highlighting the potential role of PEPC, the main anaplerotic enzyme, as a pivotal player in the adaptation of cells to these conditions
Homeostasis: an underestimated focal point of ecology and evolution.
No full textBackground - The concept of homeostasis is often ill-defined, in the scientific literature. The word “homeostasis”, literally, indicates the absence of changes and an absolute maintenance of the status quo. The multiplicity of possible examples of homeostasis suggests that it is essentially impossible that all aspects of the composition of the organism and the rate of processes carried out by the organism are simultaneously held constant, when the environment changes are in the non-lethal range.
Scope - In attempting to clarify the usage of the term homeostasis, I emphasise the probable contributions to evolutionary fitness of homeostasis main attributes: rate processes and compositions. I also attempted to identify the aspects of homeostasis that are most likely to be subject to natural selection.
Conclusions - The tendency to retain the status quo derives from the interplay of functions (among which growth), metabolic pools and elemental stoichiometry. The set points around which oscillations occur in biological system and their control mechanisms are determined by evolutionary processes; consequently, also the tendency of a cell to be homeostatic with respect to a given set point is selectable. A homeostatic response to external perturbations may be selectively favoured when the potential reproductive advantage offered by a reorganization of cell resources cannot be exploited. This is most likely to occur in the case of environmental perturbations of moderate intensity and short duration relative to the growth rate. Under these circumstances, homeostasis may be an energetically and competitively preferable option, because it requires no alteration of the expressed proteome and eliminates the requirement for reverse acclimation, upon cessation of the perturbation.
This review also intends to be a stimulus to “ad hoc” experiments to assess the ecological and evolutionary relevance of homeostasis
Effetti di differenti condizioni di coltura sulla biologia della microalga verde alotollerante Dunaliella salina
No full textThe physiological responses of te green alga Dunaliella salina to pCO2 and differenti chemcial sources of nitrogen are described in details. Le risposte della fisiologia della alga verde Dunaleilla salina a variazioni di pCO2 e delle forma chimica di N son descritte in dettaglio
Morfologia e strutture riproduttive di Gracilaria sp., entità critica della flora algale mediterranea
No full textThe reproductive structure of an allegedly new species of the genus Gracilaria are describe
Adaptation of Dunaliella salina (Volvocales, Chlorophyta) to growth on NH4+ as the sole N source
No full textThe green, wall-less microalga Dunaliella salina.(Dunal) Teodoresco (Volvocales, Chlorophyceae) UTEX 200 was cultured at air-equilibrium CO2 concentration, at 1.5 M NaCl, in the presence of either 10 mM NO3− or 10 mM NH4+ as the sole N source. The N source strongly influenced photosynthesis and C metabolism, and it altered the cell size. Growth on NH4+ caused a 20% increase of the cell volume. Chlorophyll, β-carotene, and protein content were higher by 49%, 75%, and 104%, respectively, in NH4+-grown cells compared to their NO3−-grown counterparts. By contrast, glycerol decreased by about 20% when N was supplied as NH4+ rather than as NO3−. Cells adapted to growth on NH4+ were more efficient at using light and inorganic C for photosynthesis and showed a greater affinity for photons and CO2 than cells cultured in medium containing NO3−. Ribulose bisphosphate carboxylase/oxygenase (Rubisco) protein and activity were present at about the same level in both NO3−- and NH4+-grown cells, but in vivo Rubisco activity was about three times higher in algae cultured on NH4+. Phosphoenolpyruvate (PEP) carboxylase, PEP carboxykinase, and carbonic anhydrase activities were stimulated by growth on NH4+. The mechanisms of adaptation to growth at high NH4+ concentrations are discussed
Biomineralisation by photosynthetic organisms: evidence of co-evolution of the organisms and their environment?
No full textBiomineralization is widespread among photosynthetic organisms in the ocean, in inland waters and on land.
The most quantitatively important biogeochemical role of land plants today in biomineralization is silica
deposition in vascular plants, especially grasses. Terrestrial plants also increase the rate of weathering, providing
the soluble substrates for biomineralization on land and in water bodies, a role that has had global biogeochemical
impacts since the Devonian. The dominant photosynthetic biomineralizers in today’s ocean are diatoms and
radiolarians depositing silica and coccolithophores and foraminifera depositing calcium carbonate. Abiotic
precipitation of silica from supersaturated seawater in the Precambrian preceded intracellular silicification
dominated by sponges, then radiolarians and finally diatoms, with successive declines in the silicic acid concentration
in the surface ocean, resulting in some decreases in the extent of silicification and, probably, increases in
the silicic acid affinity of the active influx mechanisms. Calcium and bicarbonate concentrations in the surface
ocean have generally been supersaturating with respect to the three common calcium carbonate biominerals
through geological time, allowing external calcification as well as calcification in compartments within cells or
organisms. The forms of calcium carbonate in biominerals, and presumably the evolution of the organisms that
produce them, have been influenced by abiotic variations in calcium and magnesium concentrations in seawater,
and calcium carbonate deposition has probably also been influenced by carbon dioxide concentration whose
variations are in part biologically determined. Overall, there has been less biological feedback on the availability
of substrates for calcification than is the case for silicification
Compositional homeostasis of the dinoflagellate Protoceratium reticulatum grown at three different pCO2
No full textIn the CO2-richer world that awaits us, the impact of elevated pCO2 on the allocation of resources in
phytoplankton may have profound repercussions on the physiology of the microalgae and on the
ecology of the ecosystems of which they are part. We studied the overall physiology and cell
composition of the potentially toxic dinoflagellate Protoceratium reticulatum subjected to a mediumterm
increase of CO2.
The physiological responses investigated were growth rates, cell size, photosynthetic and respiratory
rates, and key enzyme activities. Cell composition was assessed by conventional analytical methods and
FTIR spectroscopy.
After 3 generations of incubation at current atmospheric, high and very high pCO2 (380, 1000,
5000ppm CO2), growth, photosynthesis, and dark respiration rates increased significantly, but the
internal composition was only slightly affected.
We propose the homeostasis of cell composition as a strategy that organisms can use to tackle
environmental perturbations, especially when they are of relatively short duratio
Ecological implications of algal CCMs and their regulation
No full textThe capacity of algae to express CO2 concentrating mechanisms (CCMs) is regulated by environmental factors. Some of these factors, especially photon flux, can influence the instantaneous activity of a CCM without necessarily affecting gene expression or the capacity of the cell to transport inorganic carbon. Other environmental parameters, especially those causing changes in the availability of CO2 dissolved in the surrounding medium, act at a transcriptional level. In this review, the complex interactions between environmental factors in controlling CCM activity will be discussed, as will the ecological consequences of CCMs as they relate to the growth and ecological performance of algal cells in nature. We also consider the consequences of global climate change for the performance of algae with and without CCMs
Impact of environmental conditions on photosynthesis, growth and carbon allocation strategies of hypersaline species of Dunaliella.
No full textHypersaline environments pose a number of ecological and metabolic challenges to the
organisms that live in them. Primary producers, such as halotolerant species of the green
microalgal genus Dunaliella, are no exception. In this paper we focus on the problems posed
to the acquisition and metabolism of inorganic nutrients and on the consequences of
exposure to high light and UV radiation. We show that not only does growth in high salinity
environments have repercussions on the flow of carbon into osmolytes such as glycerol, it
also affects speciation of inorganic carbon and the uptake of inorganic ions by the cells. The
strategies that Dunaliella adopt to optimize resource utilization and the interactions among
metabolic pathways are also discussed
Direct and indirect influence of sulfur availability on phytoplankton evolutionary trajectories
No full textThe sulfate facilitation hypothesis suggests that changes in ocean sulfate concentration influenced the rise to dominance of phytoplankton species of the red lineage. The mechanistic reasons for this phenomenon are not yet understood. We started to address this question by investigating the differences in S utilization by algae of the green and red lineages and in cyanobacteria cultured in the presence of either 5 mmol L-1 (approximately equivalent to Paleozoic ocean concentrations) or 30 mmol L- 1 (corresponding to post-Mesozoic/ extant concentrations) sulfate. The activities of the main enzymes involved in SO42-- assimilation changed in response to changes in growth sulfate
concentration. ATP sulfurylase showed different kinetics in the various taxa, with an especially odd behavior for the dinoflagellate. Sulfate availability had a modest effect on cell organic composition.
Species-specific differences in the use of some elements were instead obvious in algae grown in the presence of different sulfate concentrations, overall confirming that algae of the red lineage do better at high sulfate than algae of the green lineage. The increase in sulfate concentration may thus have had an impact on phytoplankton radiation both through changes in their enzymatic machinery and through indirect repercussion on elemental usage
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