507 research outputs found
Adsorption studies of Mo and V onto ferrihydrite
No full textIn this paper, the kinetics of Mo and V (100 ?M) uptake on ferrihydrite (FHY) were evaluated in batch, mono-sorbate systems at pH between 4 and 9, and in bi-sorbate systems in the presence of P (100 ?M) at pH 7. In the Mo and V single-sorbate experiments, 100% adsorption was observed at pH values below 6 and 8, respectively. Above the point of zero charge (PZC = 7.97) of FHY, the adsorption efficiency for Mo dropped dramatically (20% at pH 8) while V showed high uptake efficiencies even at pH 9 (60% efficiency). The results from the bi-sorbate experiments (Mo-P and V-P) showed that at pH 7, P out-competed (97%) Mo for binding sites on FHY, while in the V-P binary system only ?44% of the binding sites are occupied by P with the remaining sites being occupied by V. <br/
Identification of black sturgeon caviar pigment as eumelanin
No full textReported herein is the purification of the pigment of black sturgeon caviar and its unambiguous identification as a typical eumelanin by means of chemical degradation coupled with electron paramagnetic resonance (EPR) evidence. HPLC and LC-MS analysis of oxidative degradation mixtures revealed the formation of pyrrole-2,3,5-tricarboxylic acid (PTCA), a specific marker of eumelanin pigments, in yields compatible with a 6.5% w/w pigment content. EPR spectral features and parameters were in close agreement with those reported for a typical natural eumelanin such as Sepia melanin from squid ink. The identification for the first time of eumelanin in a fish roe is expected to provide a novel molecular basis for the valorization of black caviar and production wastes thereof in food chemistry and diet
Ice sheets as a significant source of highly reactive nanoparticulate iron to the oceans
No full textThe Greenland and Antarctic Ice Sheets cover ~\n10% of global land surface, but are rarely considered as active components of the global iron cycle. The ocean waters around both ice sheets harbour highly productive coastal ecosystems, many of which are iron limited. Measurements of iron concentrations in subglacial runoff from a large Greenland Ice Sheet catchment reveal the potential for globally significant export of labile iron fractions to the near-coastal euphotic zone. We estimate that the flux of bioavailable iron associated with glacial runoff is 0.40–2.54?Tg per year in Greenland and 0.06–0.17?Tg per year in Antarctica. Iron fluxes are dominated by a highly reactive and potentially bioavailable nanoparticulate suspended sediment fraction, similar to that identified in Antarctic icebergs. Estimates of labile iron fluxes in meltwater are comparable with aeolian dust fluxes to the oceans surrounding Greenland and Antarctica, and are similarly expected to increase in a warming climate with enhanced melting
The Chemical Composition of Rainfall and Throughfall in Five Forest Communities: A Case Study in Fort Benning, Georgia
No full textIn order to investigate the effects of canopy-dependent processes on throughfall chemistry, comparative studies on the chemical composition of throughfall were carried out in five characteristic forest types of the southeastern United States within Fort Benning Military Installation from January 2002 to August 2003. The concentrations and fluxes of and total organic carbon (TOC), total Kjeldahl nitrogen (TKN), and total phosphorus (TP) were determined in rainfall and throughfall. Seasonal variations in chemical fluxes were also evaluated. Throughfall concentrations of TOC, TKN, and TP in matured pine stand were higher than in rainfall and other forest stands. Throughfall nutrient concentrations in wetland were lowest as compared to rainfall as well as hardwood, mixed, plantation, and pine stands. The average TOC, TKN, and TP concentrations in the matured pine stand were 17.2, 0.74, and 0.057 mg/L, respectively. In wetland stands, average concentrations of TOC, TKN, and TP were 4.0, 0.54, and 0.034 mg/L, respectively. Hardwood stand had the lowest TKN concentration of 0.53 mg/L. Nutrient fluxes were generally higher during the dormant season (November–April) as compared to the growing season (May–October). The highest and lowest TOC fluxes during dormant season were contributed from pine stand (801.7 g/ha) and wetland stand (186.2 g/ha), respectively. Rainfall was the major contributor of TKN fluxes in growing season (32.3 g/ha) as well as in dormant season (34.1 g/ha). Similarly, highest TP flux was produced in mixed stand (2.7 g/ha) during the dormant season. Enrichment ratios of nutrients reveal that, in general, forest stands used up nutrients during growing season and washed off during the dormant season
Federal Land Management, Carbon Sequestration, and Climate Change in the Southeastern U.S.: A Case Study with Fort Benning
No full textLand use activities can have a major impact on the temporal trends and spatial patterns of regional land−atmosphere exchange of carbon. Federal lands generally have substantially different land management strategies from surrounding areas, and the carbon consequences have rarely been quantified and assessed. Using the Fort Benning Installation as a case study, we used the General Ensemble biogeochemical Modeling System (GEMS) to simulate and compare ecosystem carbon sequestration between the U.S. Army’s Fort Benning and surrounding areas from 1992 to 2050. Our results indicate that the military installation sequestered more carbon than surrounding areas from 1992 to 2007 (76.7 vs 18.5 g C m−2 yr−1), and is projected to continue sequestering more carbon from 2008 to 2050 (75.7 vs 25.6 g C m−2 yr−1), mostly because of the proactive management approaches adopted on military training lands. Our results suggest that federal lands might play a positive and important role in sequestering and conserving atmospheric carbon because some anthropogenic disturbances (e.g., urbanization, forest harvesting, and agriculture) can be minimized or prevented on federal lands
Dynamics of protein and polar lipid recruitment during lipid droplet assembly in Chlamydomonas reinhardtii
No full textTsai C-H, Zienkiewicz K, Amstutz CL, et al. Dynamics of protein and polar lipid recruitment during lipid droplet assembly in Chlamydomonas reinhardtii. The Plant Journal. 2015;83(4):650-660.In plants, neutral lipids are frequently synthesized and stored in seed tissues, where the assembly of lipid droplets (LDs) coincides with the accumulation of triacylglycerols (TAGs). In addition, photosynthetic, vegetative cells can form cytosolic LDs and much less information is known about the makeup and biogenesis of these LDs. Here we focus on Chlamydomonas reinhardtii as a reference model for LDs in a photosynthetic cell, because in this unicellular green alga LD dynamics can be readily manipulated by nitrogen availability. Nitrogen deprivation leads to cellular quiescence during which cell divisions cease and TAGs accumulate. The major lipid droplet protein (MLDP) forms a proteinaceous coat surrounding mature LDs. Reducing the amount of MLDP affects LD size and number, TAG breakdown and timely progression out of cellular quiescence following nitrogen resupply. Depending on nitrogen availability, MLDP recruits different proteins to LDs, tubulins in particular. Conversely, depolymerization of microtubules drastically alters the association of MLDP with LDs. LDs also contain select chloroplast envelope membrane proteins hinting at an origin of LDs, at least in part, from chloroplast membranes. Moreover, LD surface lipids are rich in de novo synthesized fatty acids, and are mainly composed of galactolipids which are typical components of chloroplast membranes. The composition of the LD membrane is altered in the absence of MLDP. Collectively, our results suggest a mechanism for LD formation in C.reinhardtii involving chloroplast envelope membranes by which specific proteins are recruited to LDs and a specialized polar lipid monolayer surrounding the LD is formed. Significance Statement Lipid droplets (LDs) are dynamic organelles of virtually every cell type and are involved in numerous metabolic and physiological processes. Many aspects of LD biology, particularly in photosynthetic cells remain obscure. Using Chlamydomonas reinhardtii as a model, we uncovered an interaction of microtubules with the major lipid droplet protein affecting protein targeting to LDs. We also provide evidence for a specialized polar lipid composition of LDs suggesting an origin of LDs from chloroplast envelope membranes
The metagenomics of biosilicification: causes and effects
No full textIn order to determine the links between geochemical parameters controlling the formation of silica sinter in hot springs and their associated microbial diversity, a detailed characterisation of the waters and of in situ-grown silica sinters was combined with molecular phylogenetic analyses of the bacterial communities in Icelandic geothermal environments. At all but one site, the microorganisms clearly affected, and in part controlled, the formation of the macroscopic textures and structures of silica sinter edifices. In addition, the class and genera level phylogenetic diversity and distribution appeared to be closely linked to variations in temperature, salinity and pH regimes
fsn1995/topography-control-of-ice-albedo: Geo-topographic and Phenological Analysis of the Darkening of the Greenland Ice Sheet
No full text<p>Feng, S., Cook, J. M., Naegeli, K., Anesio, A. M., Benning, L. G., & Tranter, M. (2024). The Impact of Bare Ice Duration and Geo‐Topographical Factors on the Darkening of the Greenland Ice Sheet. Geophysical Research Letters, 51(1), e2023GL104894. https://doi.org/10.1029/2023GL104894</p>
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Using genomic DNA-based probe-selection to improve the sensitivity of high-density oligonucleotide arrays when applied to heterologous species
No full textHigh-density oligonucleotide (oligo) arrays are a powerful tool for transcript profiling. Arrays based on GeneChip® technology are amongst the most widely used, although GeneChip® arrays are currently available for only a small number of plant and animal species. Thus, we have developed a method to improve the sensitivity of high-density oligonucleotide arrays when applied to heterologous species and tested the method by analysing the transcriptome of Brassica oleracea L., a species for which no GeneChip® array is available, using a GeneChip® array designed for Arabidopsis thaliana (L.) Heynh. Genomic DNA from B. oleracea was labelled and hybridised to the ATH1-121501 GeneChip® array. Arabidopsis thaliana probe-pairs that hybridised to the B. oleracea genomic DNA on the basis of the perfect-match (PM) probe signal were then selected for subsequent B. oleracea transcriptome analysis using a .cel file parser script to generate probe mask files. The transcriptional response of B. oleracea to a mineral nutrient (phosphorus; P) stress was quantified using probe mask files generated for a wide range of gDNA hybridisation intensity thresholds. An example probe mask file generated with a gDNA hybridisation intensity threshold of 400 removed > 68 % of the available PM probes from the analysis but retained >96 % of available A. thaliana probe-sets. Ninety-nine of these genes were then identified as significantly regulated under P stress in B. oleracea, including the homologues of P stress responsive genes in A. thaliana. Increasing the gDNA hybridisation intensity thresholds up to 500 for probe-selection increased the sensitivity of the GeneChip® array to detect regulation of gene expression in B. oleracea under P stress by up to 13-fold. Our open-source software to create probe mask files is freely available http://affymetrix.arabidopsis.info/xspecies/ webcite and may be used to facilitate transcriptomic analyses of a wide range of plant and animal species in the absence of custom arrays
Synthesis and transfer of galactolipids in the chloroplast envelope membranes of Arabidopsis thaliana
No full textGalactolipids [monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG)] are the hallmark lipids of photosynthetic membranes. The galactolipid synthases MGD1 and DGD1 catalyze consecutive galactosyltransfer reactions but localize to the inner and outer chloroplast envelopes, respectively, necessitating intermembrane lipid transfer. Here we show that the N-terminal sequence of DGD1 (NDGD1) is required for galactolipid transfer between the envelopes. Different diglycosyllipid synthases (DGD1, DGD2, and Chloroflexus glucosyltransferase) were introduced into the dgd1-1 mutant of Arabidopsis in fusion with N-terminal extensions (NDGD1 and NDGD2) targeting to the outer envelope. Reconstruction of DGDG synthesis in the outer envelope membrane was observed only with diglycosyllipid synthase fusion proteins carrying NDGD1, indicating that NDGD1 enables galactolipid translocation between envelopes. NDGD1 binds to phosphatidic acid (PA) in membranes and mediates PA-dependent membrane fusion in vitro. These findings provide a mechanism for the sorting and selective channeling of lipid precursors between the galactolipid pools of the two envelope membranes
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