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971.
972.
Lucas Anjos de Souza Sara Adrián López de Andrade Sarah Caroline Ribeiro de Souza Marlene Aparecida Schiavinato 《Acta Physiologiae Plantarum》2012,34(2):523-531
Heavy metals (HMs) are environmental pollutants of great concern to humans because of their high potential toxicity. Lead
is a HM that is present in the soil in very small amounts, but anthropogenic activities have increased its content in some
locations, which can make these areas unproductive or inappropriate for crop production. However, there are some plants that
can grow in contaminated soils and, thus, can be useful for the removal or stabilisation of such contaminants. In addition,
plants that are not able to tolerate high concentrations of HMs in the soil can become tolerant or increase their performance
when associated with arbuscular mycorrhizal (AM) fungi. Accordingly, this study was carried out to verify whether the inoculation
of Glomus etunicatum, an AM fungus species, in Calopogonium mucunoides would influence plant tolerance to increasing concentrations of Pb in the soil. The experimental design was completely randomised,
in a 2 × 4 factorial design, and the treatments consisted of inoculation (or not) with the AM fungus, G. etunicatum, and the addition of four Pb concentrations (0, 250, 500 or 1,000 mg kg−1) to the soil. The results showed that the association of C. mucunoides with G. etunicatum promoted biomass production, and nutrient uptake (P, S and Fe) was also positively influenced by mycorrhization. The malondialdehyde
content was higher in non-mycorrhizal leaves, suggesting a reduction in the damage to membranes by lipid peroxidation in plants
associated with mycorrhizae. However, the Pb concentration in the shoots did not differ between the mycorrhizal and non-mycorrhizal
plants. The results of our study suggest that the AM symbiosis can be considered very effective in contributing to the tolerance
of C. mucunoides to Pb. 相似文献
973.
Oliveira AV Gaspar AR Francisco SC Quintela DA 《International journal of biometeorology》2012,56(2):319-332
The present experimental work is dedicated to the analysis of the effect of walking on the thermal insulation of the air layer
(I
a
) and on the convective heat transfer coefficients (h
conv
) of the human body. Beyond the standing static posture, three step rates were considered: 20, 30 and 45 steps/min. This corresponds
to walking speeds of approximately 0.23, 0.34 and 0.51 m/s, respectively. The experiments took place in a climate chamber
with an articulated thermal manikin with 16 independent parts. The indoor environment was controlled through the inner wall
temperatures since the objective of the tests was restricted to the influence of the walking movements under calm conditions.
Five set points were selected: 10, 15, 20, 25 and 30°C, and the operative temperature within the test chamber varied between
11.9 and 29.6°C. The highest and lowest I
a
values obtained were equal to 0.87 and 0.71 clo, respectively, and the reduction in insulation due to walking ranged between
9.8 and 11.5%. The convective coefficients (h
conv
) for the whole body and for the different body segments were also determined for each step rate. In the case of the whole
body, for the standing static reference posture, the mean value of h
conv
was equal to 3.3 W/m2°C and a correlation [Nu = Nu(Gr)] for natural convection is also presented in good agreement with previous results. For the other postures, the values of
h
conv
were equal to 3.7, 3.9 and 4.2 W/m2°C, respectively for 20, 30 and 45 steps/min. 相似文献
974.
Martin SL Cakmak S Hebbern CA Avramescu ML Tremblay N 《International journal of biometeorology》2012,56(4):605-619
The environmental changes caused by climate change represent a significant challenge to human societies. One part of this
challenge will be greater heat-related mortality. Populations in the northern hemisphere will experience temperature increases
exceeding the global average, but whether this will increase or decrease total temperature-related mortality burdens is debated.
Here, we use distributed lag modeling to characterize temperature-mortality relationships in 15 Canadian cities. Further,
we examine historical trends in temperature variation across Canada. We then develop city-specific general linear models to
estimate change in high- and low-temperature-related mortality using dynamically downscaled climate projections for four future
periods centred on 2040, 2060 and 2080. We find that the minimum mortality temperature is frequently located at approximately
the 75th percentile of the city’s temperature distribution, and that Canadians currently experience greater and longer lasting
risk from cold-related than heat-related mortality. Additionally, we find no evidence that temperature variation is increasing
in Canada. However, the projected increased temperatures are sufficient to change the relative levels of heat- and cold-related
mortality in some cities. While most temperature-related mortality will continue to be cold-related, our models predict that
higher temperatures will increase the burden of annual temperature-related mortality in Hamilton, London, Montreal and Regina,
but result in slight to moderate decreases in the burden of mortality in the other 11 cities investigated. 相似文献
975.
We have investigated the inhibition by SulA of the assembly of Escherichia coli FtsZ. Using quantitative GTPase and fluorescence assays, we found that SulA inhibition resulted in an increase in the apparent critical concentration for FtsZ assembly. The increase in apparent critical concentration was always less than the total amount of SulA added, suggesting that the association of SulA and FtsZ was of modest affinity. Isothermal titration calorimetry gave a value of 0.78 μM for the dissociation constant of the FtsZ-SulA complex, similar in magnitude to the 0.72 μM critical concentration of FtsZ protofilament assembly at steady state. We modeled the reaction as an equilibrium competition between (a) FtsZ subunits assembling onto protofilaments or (b) binding SulA. When FtsZ was assembled in GMPCPP or in EDTA, the inhibition by SulA was reduced. The reduced inhibition could be explained by a 3- and 10-fold weaker binding of SulA to FtsZ. The mutant D212G, which has no GTPase activity and therefore minimal subunit cycling, was shown here to assemble one-stranded protofilaments, and the assembly was blocked by SulA. We also assayed the SulA and FtsZ proteins from Pseudomonas. The SulA inhibition was stronger than with the E. coli proteins, and the model indicated a 5-fold higher affinity of Pseudomonas SulA for FtsZ. 相似文献
976.
The increase in multidrug resistant bacteria has sparked an interest in the development of novel antibiotics. Antimicrobial peptides that operate by crossing the cell membrane may also have the potential to deliver drugs to intracellular targets. Buforin 2 (BF2) is an antimicrobial peptide that shares sequence identity with a fragment of histone subunit H2A and whose bactericidal mechanism depends on membrane translocation and DNA binding. Previously, novel histone-derived antimicrobial peptides (HDAPs) were designed based on properties of BF2, and DesHDAP1 and DesHDAP3 showed significant antibacterial activity. In this study, their DNA binding, permeabilization, and translocation abilities were assessed independently and compared to antibacterial activity to determine whether they share a mechanism with BF2. To investigate the importance of proline in determining the peptides' mechanisms of action, proline to alanine mutants of the novel peptides were generated. DesHDAP1, which shows significant similarities to BF2 in terms of secondary structure, translocates effectively across lipid vesicle and bacterial membranes, while the DesHDAP1 proline mutant shows reduced translocation abilities and antimicrobial potency. In contrast, both DesHDAP3 and its proline mutant translocate poorly, though the DesHDAP3 proline mutant is more potent. Our findings suggest that a proline hinge can promote membrane translocation in some peptides, but that the extent of its effect on permeabilization depends on the peptide's amphipathic properties. Our results also highlight the different antimicrobial mechanisms exhibited by histone-derived peptides and suggest that histones may serve as a source of novel antimicrobial peptides with varied properties. 相似文献
977.
Romi H Cohen I Landau D Alkrinawi S Yerushalmi B Hershkovitz R Newman-Heiman N Cutting GR Ofir R Sivan S Birk OS 《American journal of human genetics》2012,90(5):893-899
Meconium ileus, intestinal obstruction in the newborn, is caused in most cases by CFTR mutations modulated by yet-unidentified modifier genes. We now show that in two unrelated consanguineous Bedouin kindreds, an autosomal-recessive phenotype of meconium ileus that is not associated with cystic fibrosis (CF) is caused by different homozygous mutations in GUCY2C, leading to a dramatic reduction or fully abrogating the enzymatic activity of the encoded guanlyl cyclase 2C. GUCY2C is a transmembrane receptor whose extracellular domain is activated by either the endogenous ligands, guanylin and related peptide uroguanylin, or by an external ligand, Escherichia coli (E. coli) heat-stable enterotoxin STa. GUCY2C is expressed in the human intestine, and the encoded protein activates the CFTR protein through local generation of cGMP. Thus, GUCY2C is a likely candidate modifier of the meconium ileus phenotype in CF. Because GUCY2C heterozygous and homozygous mutant mice are resistant to E. coli STa enterotoxin-induced diarrhea, it is plausible that GUCY2C mutations in the desert-dwelling Bedouin kindred are of selective advantage. 相似文献
978.
979.
Goehring I Gerencser AA Schmidt S Brand MD Mulder H Nicholls DG 《The Journal of biological chemistry》2012,287(19):15706-15717
Oscillations in plasma membrane potential play a central role in glucose-induced insulin secretion from pancreatic β-cells and related insulinoma cell lines. We have employed a novel fluorescent plasma membrane potential (Δψ(p)) indicator in combination with indicators of cytoplasmic free Ca(2+) ([Ca(2+)](c)), mitochondrial membrane potential (Δψ(m)), matrix ATP concentration, and NAD(P)H fluorescence to investigate the role of mitochondria in the generation of plasma membrane potential oscillations in clonal INS-1 832/13 β-cells. Elevated glucose caused oscillations in plasma membrane potential and cytoplasmic free Ca(2+) concentration over the same concentration range required for insulin release, although considerable cell-to-cell heterogeneity was observed. Exogenous pyruvate was as effective as glucose in inducing oscillations, both in the presence and absence of 2.8 mM glucose. Increased glucose and pyruvate each produced a concentration-dependent mitochondrial hyperpolarization. The causal relationships between pairs of parameters (Δψ(p) and [Ca(2+)](c), Δψ(p) and NAD(P)H, matrix ATP and [Ca(2+)](c), and Δψ(m) and [Ca(2+)](c)) were investigated at single cell level. It is concluded that, in these β-cells, depolarizing oscillations in Δψ(p) are not initiated by mitochondrial bioenergetic changes. Instead, regardless of substrate, it appears that the mitochondria may simply be required to exceed a critical bioenergetic threshold to allow release of insulin. Once this threshold is exceeded, an autonomous Δψ(p) oscillatory mechanism is initiated. 相似文献
980.
The recent discovery of a model compounds of [NiFe] hydrogenase that catalyzes the heterolytic cleavage of the H2 molecule into a proton and a stable hydride in water solution under room conditions opened up the possibility to understand
the mechanism of H2 uptake by this peculiar class of enzymes. The simplest model compound belongs to the class of NiRu bimetallic cationic complexes
mimicking, in water solution and at room conditions, the hydrogenase active site. By using first-principles molecular dynamics
computer simulations, in the Car–Parrinello scheme, we investigated models including the water solvent and nitrate counterions.
Several simulations, starting from different initial configurations, provided information on the first step of the H2 cleavage: (1) the pathway of H2 approach towards the active site; (2) the role of the ruthenium-bonded water molecule in providing a base that extracts the
proton from the activated H2 molecule; (3) the minor role of Ni in activating the H2 molecule and its role in stabilizing the hydride produced. 相似文献