1,351 research outputs found
Far Ultraviolet Spectroscopic Explorer Spectroscopy of the O VI Resonance Doublet in Sand 2 (WO)
We present Far Ultraviolet Spectroscopic Explorer spectroscopy of Sand 2, an LMC WO-type Wolf-Rayet star, revealing the O VI resonance P Cygni doublet at 1032-1038 Å. These data are combined with Hubble Space Telescope Faint Object Spectrograph ultraviolet and Mount Stromlo 2.3 m optical spectroscopy and analyzed using a spherical, non-LTE, line-blanketed code. Our study reveals exceptional stellar parameters: T* ~ 150,000 K, v∞ = 4100 km s-1, log(L/L☉) = 5.3, andimg1.gif = 1 × 10-5 M☉ yr-1, if we adopt a volume filling factor of 10%. Elemental abundances of C/He ~ 0.7 ± 0.2 and O/He ~ 0.15img2.gif by number qualitatively support previous recombination line studies. We confirm that Sand 2 is more chemically enriched in carbon than LMC WC stars and that it is expected to undergo a supernova explosion within the next 5 × 104 yr
A viscoelastic deadly fluid in carnivorous pitcher plants
Background : The carnivorous plants of the genus Nepenthes, widely
distributed in the Asian tropics, rely mostly on nutrients derived from
arthropods trapped in their pitcher-shaped leaves and digested by their
enzymatic fluid. The genus exhibits a great diversity of prey and pitcher forms
and its mechanism of trapping has long intrigued scientists. The slippery inner
surfaces of the pitchers, which can be waxy or highly wettable, have so far
been considered as the key trapping devices. However, the occurrence of species
lacking such epidermal specializations but still effective at trapping insects
suggests the possible implication of other mechanisms. Methodology/Principal
Findings : Using a combination of insect bioassays, high-speed video and
rheological measurements, we show that the digestive fluid of Nepenthes
rafflesiana is highly viscoelastic and that this physical property is crucial
for the retention of insects in its traps. Trapping efficiency is shown to
remain strong even when the fluid is highly diluted by water, as long as the
elastic relaxation time of the fluid is higher than the typical time scale of
insect movements. Conclusions/Significance : This finding challenges the common
classification of Nepenthes pitchers as simple passive traps and is of great
adaptive significance for these tropical plants, which are often submitted to
high rainfalls and variations in fluid concentration. The viscoelastic trap
constitutes a cryptic but potentially widespread adaptation of Nepenthes
species and could be a homologous trait shared through common ancestry with the
sundew (Drosera) flypaper plants. Such large production of a highly
viscoelastic biopolymer fluid in permanent pools is nevertheless unique in the
plant kingdom and suggests novel applications for pest control
Revealing natural relationships among arbuscular mycorrhizal fungi: culture line BEG47 represents Diversispora epigaea, not Glomus versiforme
Background: Understanding the mechanisms underlying biological phenomena, such as evolutionarily conservative trait inheritance, is predicated on knowledge of the natural relationships among organisms. However, despite their enormous ecological significance, many of the ubiquitous soil inhabiting and plant symbiotic arbuscular mycorrhizal fungi (AMF, phylum Glomeromycota) are incorrectly classified.
Methodology/Principal Findings:
Here, we focused on a frequently used model AMF registered as culture BEG47. This fungus is a descendent of the ex-type culture-lineage of Glomus epigaeum, which in 1983 was synonymised with Glomus versiforme. It has since then been used as ‘G. versiforme BEG47’. We show by morphological comparisons, based on type material, collected 1860–61, of G. versiforme and on type material and living ex-type cultures of G. epigaeum, that these two AMF species cannot be conspecific, and by molecular phylogenetics that BEG47 is a member of the genus Diversispora.
Conclusions: This study highlights that experimental works published during the last >25 years on an AMF named ‘G. versiforme’ or ‘BEG47’ refer to D. epigaea, a species that is actually evolutionarily separated by hundreds of millions of years from all members of the genera in the Glomerales and thus from most other commonly used AMF ‘laboratory strains’. Detailed redescriptions substantiate the renaming of G. epigaeum (BEG47) as D. epigaea, positioning it systematically in the order Diversisporales, thus enabling an evolutionary understanding of genetical, physiological, and ecological traits, relative to those of other AMF. Diversispora epigaea is widely cultured as a laboratory strain of AMF, whereas G. versiforme appears not to have been cultured nor found in the field since its original description
Interleukin-1 regulates multiple atherogenic mechanisms in response to fat feeding
Background: Atherosclerosis is an inflammatory process that develops in individuals with known risk factors that include hypertension and hyperlipidaemia, influenced by diet. However, the interplay between diet, inflammatory mechanisms and vascular risk factors requires further research. We hypothesised that interleukin-1 (IL-1) signaling in the vessel wall would raise arterial blood pressure and promote atheroma.
Methodology/Principal Findings: Apoe(-/-) and Apoe(-/-)/IL-1R1(-/-) mice were fed high fat diets for 8 weeks, and their blood pressure and atherosclerosis development measured. Apoe(-/-)/IL-R1(-/-) mice had a reduced blood pressure and significantly less atheroma than Apoe(-/-) mice. Selective loss of IL-1 signaling in the vessel wall by bone marrow transplantation also reduced plaque burden (p<0.05). This was associated with an IL-1 mediated loss of endothelium-dependent relaxation and an increase in vessel wall Nox 4. Inhibition of IL-1 restored endothelium-dependent vasodilatation and reduced levels of arterial oxidative stress.
Conclusions/Significance: The IL-1 cytokine system links atherogenic environmental stimuli with arterial inflammation, oxidative stress, increased blood pressure and atherosclerosis. This is the first demonstration that inhibition of a single cytokine can block the rise in blood pressure in response to an environmental stimulus. IL-1 inhibition may have profound beneficial effects on atherogenesis in man
Does Speaking Two Dialects in Daily Life Affect Executive Functions? An Event-Related Potential Study
Whether using two languages enhances executive functions is a matter of debate. Here, we
take a novel perspective to examine the bilingual advantage hypothesis by comparing bidialect
with mono-dialect speakers’ performance on a non-linguistic task that requires executive
control. Two groups of native Chinese speakers, one speaking only the standard Chinese
Mandarin and the other also speaking the Southern-Min dialect, which differs from the
standard Chinese Mandarin primarily in phonology, performed a classic Flanker task. Behavioural
results showed no difference between the two groups, but event-related potentials
recorded simultaneously revealed a number of differences, including an earlier P2 effect in
the bi-dialect as compared to the mono-dialect group, suggesting that the two groups
engage different underlying neural processes. Despite differences in the early ERP component,
no between-group differences in the magnitude of the Flanker effects, which is an
index of conflict resolution, were observed in the N2 component. Therefore, these findings
suggest that speaking two dialects of one language does not enhance executive functions.
Implications of the current findings for the bilingual advantage hypothesis are discussed
Graded reductions in pre-exercise muscle glycogen impair exercise capacity but do not augment cell skeletal muscle signalling: implication for CHO periodisation
We examined the effects of graded muscle glycogen on exercise capacity and modulation of skeletal muscle signalling pathways associated with the regulation of mitochondrial biogenesis. In a repeated measures design, eight males completed a sleep-low, train-low model comprising an evening glycogen depleting cycling protocol followed by an exhaustive exercise capacity test (8 x 3 min at 80% PPO, followed by 1 min efforts at 80% PPO until exhaustion) the subsequent morning. Following glycogen depleting exercise, subjects ingested a total of 0 g kg-1 (L-CHO), 3.6 g kg-1 (M-CHO) or 7.6 g kg-1 (H-CHO) of carbohydrate during a 6 h period prior to sleeping, such that exercise was commenced the next morning with graded (P < 0.05) muscle glycogen concentrations (Mean ± SD) (L-CHO: 88 ± 43, M-CHO: 185 ± 62, H-CHO: 278 ± 47 mmol kg-1 dw). Despite differences (P < 0.05) in exercise capacity at 80% PPO between trials (L-CHO: 18 ± 7, M-CHO: 36 ± 3, H-CHO: 44 ± 9 min) exercise induced comparable AMPKThr172 phosphorylation (~4 fold) and PGC-1α mRNA expression (~5 fold) post- and 3 h post-exercise, respectively. In contrast, exercise nor CHO availability affected the phosphorylation of p38MAPKThr180/Tyr182, CaMKIIThr268 or mRNA expression of p53, Tfam, CPT-1, CD36 or PDK4. Data demonstrate that when exercise is commenced with muscle glycogen below 300 mmol kg-1 dw, further graded reductions of 100 mmol kg-1 dw impair exercise capacity but do not augment skeletal muscle cell signaling
A [4Fe-4S]-Fe(CO)(CN)-L-cysteine intermediate is the first organometallic precursor in [FeFe] hydrogenase H-cluster bioassembly.
Biosynthesis of the [FeFe] hydrogenase active site (the 'H-cluster') requires the interplay of multiple proteins and small molecules. Among them, the radical S-adenosylmethionine enzyme HydG, a tyrosine lyase, has been proposed to generate a complex that contains an Fe(CO)2(CN) moiety that is eventually incorporated into the H-cluster. Here we describe the characterization of an intermediate in the HydG reaction: a [4Fe-4S][(Cys)Fe(CO)(CN)] species, 'Complex A', in which a CO, a CN- and a cysteine (Cys) molecule bind to the unique 'dangler' Fe site of the auxiliary [5Fe-4S] cluster of HydG. The identification of this intermediate-the first organometallic precursor to the H-cluster-validates the previously hypothesized HydG reaction cycle and provides a basis for elucidating the biosynthetic origin of other moieties of the H-cluster
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