1,721,072 research outputs found
Algae
No full textAlgae frequently get a bad press. Pond slime is a problem in garden pools, algal blooms can produce toxins that incapacitate or kill animals and humans and even the term seaweed is pejorative — a weed being a plant growing in what humans consider to be the wrong place. Positive aspects of algae are generally less newsworthy — they are the basis of marine food webs, supporting fisheries and charismatic marine megafauna from albatrosses to whales, as well as consuming carbon dioxide and producing oxygen. Here we consider what algae are, their diversity in terms of evolutionary origin, size, shape and life cycles, and their role in the natural environment and in human affairs
Nitrogen and sulfur assimilation in plants and algae
No full textNitrogen and Sulfur are abundant constituent of plant and algal cells that are assimilated at the lowest oxidation number, as NH4+ and S2-, although they can be acquired with their highest oxidation number, as NO3- and SO42-. Some occasional differences and variants exists for transport and assimilation systems; the greatest differences in the way vascular plants and algae use N and S, however, most probably resides in regulation. For instance, nitrate assimilation in plants is strongly regulated by phosphorylation. In algae, redox regulation appears to be more important. Similarly, sulfate reduction has its main control step at the level of APS reductase in higher plants, whereas in algae a redox regulation has been recently been hypothesized for ATP sulfurylase, the first step in sulfate assimilation. Unfortunately, the information on the regulation of N and S acquisition and assimilation is limited to very few species (e.g. Chlamydomonas reinhardtii) this is especially true in the case of sulfur. This review attempts to highlight the points of divergence in N and S utilization by plants and algae, leaving aside the biochemical details and the features that do not show any obvious difference
Growth rate affects the responses of the green alga Tetraselmis suecica to external perturbations
No full textAcclimation to environmental changes involves a modification of the expressed proteome and metabolome. The reproductive advantage associated with the higher fitness that acclimation provides to the new conditions more than compensates for the costs of acclimation. To exploit such an advantage, however, the duration of the perturbation must be sufficiently long relative to the growth rate. Otherwise, a selective pressure may exist in favour of responses that minimize changes in carbon allocation and resource use and do not require reversal of the acclimation after the perturbation ceases (compositional homeostasis). We hypothesize that the choice between acclimation and homeostasis depends on the duration of the perturbation relative to the length of the cell cycle. To test this hypothesis, we cultured the green alga Tetraselmis suecica at two growth rates and subjected the cultures to three environmental perturbations. Carbon allocation was studied with Fourier transform infrared (FTIR) spectroscopy; elemental stoichiometry was investigated by Total Reflection X-Ray Fluorescence (TXRF) spectroscopy. Our data confirmed that growth rate is a crucial factor for C allocation in response to external changes, with a higher degree of compositional homeostasis in cells with lower growth rate
Impact of taxonomy, geography and depth on δ13C and δ15N variation in a large collection of macroalgae.
No full textThe natural abundance of carbon stable isotopes (delta13C) of marine macrophytes has been measured in previous studies and used to analyze differences in Ci assimilation among the three macroalgal phyla, Chlorophyta, Ochrophyta, and Rhodophyta, and seagrasses, distinguishing diffusive CO2 entry from the operation of a CO2-concentrating mechanisms (CCM). The work reported here further resolves the patterns of delta13C variation in aquatic macrophytes related to their taxonomy, geographic location (and consequently climatic conditions), and vertical zonation. Analyses of delta13C for 87 species are reported, including eight that have not been previously examined, belonging to taxa in the three macroalgal phyla, plus two species of seagrasses, collected at different latitudes. For one species of each phylum, analyses were also conducted through a vertical depth gradient. Representative species were used in a pH drift experiment, in order to compare the mechanism of Ci acquisition for photosynthesis with the delta13C subsequently determined on the same specimen. Our results suggest that the delta13C values were mostly determined by taxonomy. Depth effects on C stable isotope composition differed among taxa. The parallel measurements of delta15N are more difficult to interpret mechanistically; + there are no robust phylogenetic and large-scale biogeographic correlations; local factors of natural (e.g., upwellings) and anthropogenic (e.g., sewage outfall) inputs predominate in determining the macrophyte delta15N
Insights into the evolution of CCMs from comparisons with other resource acquisition and assimilation processes.
No full textRegarding inorganic carbon as ‘just another’ chemical resource used in the
growth of aquatic photolithotrophs, we ask three questions and then attempt to
answer them. (1) How common are catalysed chemical changes of the resource
outside the cell, and accumulation of the resource inside the cell prior to
assimilation, for the diverse chemical resources used? (2) Do acquisition and
assimilationmeet evolutionary optimality criteriawith respect to the use of other
resources? (3) Are there clues to the evolutionary origin of inorganic carbon
concentrating mechanism (CCMs) in the mechanisms of acquisition of other
resources and vice versa? Evidence considered includes molecular genetic
similarities between CCM components and components of other resource
acquisition mechanisms, and palaeogeochemical evidence on the timing of
restrictions on the availability of the resources such that extracellular transformation
ofmaterials, and their accumulationwithin cells prior to assimilation,
are needed. Provisional answers to the questions are as follows: (1) Many
common chemical resources other than inorganic carbon are subject to
extracellular chemical conversion and/or accumulation prior to assimilation,
e.g. ammonium, nitrate, urea, amino acids, organic and inorganic phosphate
and iron; (2) There is some evidence for optimality of CCMs and of less complex
resource acquisition processes, exemplified by NH4 1 entry and assimilation,
though many more data are needed and (3) There are molecular genetic
similarities between CCM components and transporters for other solutes and
components of respiratory NADH dehydrogenases that are consistent with their
use in CCMs representing a derived evolutionary state. Palaeogeochemical
evidence suggests that CCMs evolved later than did at least some of the
extracellular chemical transformation and/or accumulation mechanisms for
other resources
Combined Nitrogen
No full textAlgae can use a wide range of combined N sources. All of them can use NH4+, and probably also use urea and one of more amino acids; most of them can also use NO2- and NO3-, and some can use betaines and/or purines. Transport of combined N into cells very often uses H+ or Na+ symport. Two cations transported per anionic N species, and one cation transported per neutral N species, enables the electrical potential difference across the membrane generated by active cation efflux to be used to increase the accumulation ratio inside:outside of the combined N species. Cationic N forms, e.g. NH4+, sometimes occur at very low concentrations in the natural environment, and cation symport can increase the steady-state NH4+ concentration. The transporters have been to some extent characterised at the molecular level, especially for the plasmalemma. Assimilation of inorganic N species into organic N within the cell use well-established pathways, i.e. NO3- reductase, NO2- reductase, and glutamine synthetase – glutamine-oxoglutarate aminotransferase enzymes. N assimilation, and especially the initial step (NO3- reductase), are under more direct redox control in microalgae than in vascular plants. Combined N species which as NO and NO3- are involved in signalling within the cell, but extent to which they modulate metabolism in response to internal and external cues needs clarification. It is important to bear in mind that the conclusions drawn here generally come from work on relatively few microalgal species, and generalisations should be viewed with caution
Energy costs of carbon dioxide concentrating mechanisms in aquatic organisms
No full textMinimum energy (as photon) costs are predicted for core reactions of photosynthesis, for photorespiratory metabolism in algae lacking CO2 concentrating mechanisms (CCMs) and for various types of CCMs; in algae, with CCMs; allowance was made for leakage of CO2 from the internal pool. These predicted values are just compatible with the minimum measured photon costs of photosynthesis in microalgae and macroalgae lacking or expressing CCMs. More energy-expensive photorespiration, for example for organisms using Rubiscos with lower CO2-O2 selectivity coefficients, would be less readily accommodated within the lowest measured photon costs of photosynthesis by algae lacking CCMs. The same applies to the cases of CCMs with higher energy costs of active transport of protons or inorganic carbon species, or greater allowance for significant leakage from the accumulated intracellular pool of CO2. High energetic efficiency can involve a higher concentration of catalyst to achieve a given rate of reaction, adding to the resource costs of growth. There are no obvious mechanistic interpretations of the occurrence of CCMs algae adapted to low light and low temperatures using the rationales adopted for the occurrence of C4 photosynthesis in terrestrial flowering plants. There is an exception for cyanobacteria with low-selectivity Form IA or IB Rubiscos, and those dinoflagellates with low-selectivity Form II Rubiscos, for which very few natural environments have high enough CO2:O2 ratios to allow photosynthesis in the absence of CCMs
Acquisition and metabolism of carbon in the Ochrophyta other than diatoms
Full text linkThe acquisition and assimilation of inorganic C have been investigated in several of the 15 clades of the Ochrophyta other than diatoms, with biochemical, physiological and genomic data indicating significant mechanistic variation. Form ID Rubiscos in the Ochrophyta are characterized by a broad range of kinetics values. In spite of relatively high K0.5CO2 and low CO2 : O2 selectivity, diffusive entry of CO2 occurs in the Chrysophyceae and Synurophyceae. Eustigmatophyceae and Phaeophyceae, on the contrary, have CO2 concentrating mechanisms, usually involving the direct or indirect use of [Formula: see text] This variability is possibly due to the ecological contexts of the organism. In brown algae, C fixation generally takes place through a classical C3 metabolism, but there are some hints of the occurrence of C4 metabolism and low amplitude CAM in a few members of the Fucales. Genomic data show the presence of a number of potential C4 and CAM genes in Ochrophyta other than diatoms, but the other core functions of many of these genes give a very limited diagnostic value to their presence and are insufficient to conclude that C4 photosynthesis is present in these algae.This article is part of the themed issue 'The peculiar carbon metabolism in diatoms'.</p
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
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