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At least 739 records · Page 41Linked to original sources
PubMed2005

A second pathway for gas out of the pressure chamber--what is being squeezed?

We report a qualitative description of the flows of gas that occur through a leaf when its balance pressure is measured in the pressure chamber. There are two distinct pathways: (a) a bulk flow of gas through the intercellular air spaces, and (b) a diffusion-driven pathway where gas is dissolved into solution under high pressure and comes out of solution at the liquid/atmosphere surface of the cut end where the pressure is atmospheric. The intercellular space flow is well known. It is argued that this flow shows to a reasonable approximation, that the externally supplied gas is squeezing the non-gaseous part of the leaf, and the outer boundary of the non-gaseous material is the boundary of the system that is being manipulated. The second pathway, the diffusion-driven flow, has not (we believe) been described before, and is analogous to a diver getting the bends. The diffusion-based flow demonstrates that gas spaces can and do form inside the outer boundary of the non-gaseous part of the leaf when a balance pressure is measured. These interior gas spaces alter the value recorded for the balance pressure, and complicate any interpretation of what this measurement tells us about the water status of the plant. A hypothesis is proposed that the diffusion-based flow from the xylem comes from vessels that are embolized, and that percentage embolisms might be measured by the proportion of vessels showing the diffusion-driven flow.

Acacia↗
PubMed2004

Nitrogen nutrition and isotopic discrimination in tropical ectomycorrhizal fungi.

It is known that many ectomycorrhizal (EcM) fungi are able to utilise complex organic sources of nitrogen. Two hypotheses were tested using isolates of tropical EcM fungi grown in vitro: (i) EcM fungi isolated from mineral soils of tropical rain forests are less able to utilise organic sources of nitrogen than mineral sources; and (ii) nitrogen isotope discrimination patterns follow those of the nitrogen source utilised. Pisolithus albus and Tomentella sp. represented tropical EcM fungi and they were grown along with Thelephora terrestris. All three species were able to utilise bovine serum albumen as a nitrogen source and P. albus produced the greatest biomass on this source of nitrogen. Nitrate was generally less well utilised than ammonium although all three species were able to grow on this nitrogen source. The nitrogen source which led to the greatest biomass also led to the highest fungal nitrogen concentration in P. albus and Tomentella sp., but not T. terrestris. All three species discriminated against (15)N when grown on BSA and NO(3) but there were interspecific differences in isotope discrimination when grown on NH(4). From a limited number of isolates, it was found that EcM fungi from tropical soils utilise protein nitrogen as well as mineral nitrogen and there can be considerable nitrogen isotope discrimination during the utilisation of all these nitrogen sources.

Acacia↗
PubMed2000

Preparation and evaluation of the in vitro drug release properties and mucoadhesion of novel microspheres of hyaluronic acid and chitosan.

Rapid mucociliary clearance of intranasally administered drugs is often a key factor in determining the bioavailability of such therapeutic agents. The use of mucoadhesive microparticles provide a potential strategy for improving retention of drugs within the nasal cavity, and thereby improve the resultant pharmacokinetic profile. This study describes the comparison of a number of novel, potentially mucoadhesive microspheres, prepared by solvent evaporation, composed of hyaluronic acid (HA), chitosan glutamate (CH) and a combination of the two with microcapsules of HA and gelatin prepared by complex coacervation. The microspheres had a mean particle size of 19.91+/-1.57 microm (HA), 28.60+/-1.34 microm (HA/CH), 29.47+/-3.58 microm (CH). The incorporation of a model drug, gentamicin sulphate (%) was 46.90+/-0.53 (HA), 28.04+/-1.21 (HA/CH) and 13.32+/-1.04 (CH). The in vitro release profiles of microsphere formulations prepared by solvent evaporation were determined. The release of gentamicin from HA and HA/CH was 50% longer than CH and was best modelled as a release from a matrix. The degree of mucoadhesion of each formulation was investigated by determining the mucociliary transport rate (MTR) of the microparticles across an isolated frog palate. Acacia/gelatin microcapsules were used as a positive control. The rank order of mucoadhesion for the microspheres and the microparticles was HA=HA/CH>CH>HA/gelatin>CHins. The entrapment of gentamicin did not affect the mucoadhesive properties (P>0.05, Mann--Whitney U-test). The combination of HA with chitosan may afford additional advantages in combining the mucoadhesive potential of HA with the penetration enhancing effect of chitosan.

Acacia↗
PubMed2000

AFLP fingerprint analysis of Bradyrhizobium strains isolated from Faidherbia albida and Aeschynomene species.

The diversity of Bradyrhizobium isolates from Faidherbia albida and Aeschynomenee species was assessed using AFLP analysis, a high-resolution genomic fingerprinting technique. Reference strains from Bradyrhizobium japonicum, Bradyrhizobium elkanii and Bradyrhizobium liaoningense were included for comparison. At a similarity level of 50%, a total of 34 different groups were obtained by cluster analysis of the genomic fingerprints. Four of these clusters correspond to the three reference species, demonstrating the large diversity of the isolates studied. Comparison with other data demonstrates that AFLP has a higher resolution than restriction analysis of 16S rRNA genes, SDS-PAGE analysis of proteins and phenotypic analysis. Results of the latter two methods showed little correspondence with the genotypic data.

Acacia↗
PubMed2003

High-performance thin-layer chromatography-bioautography for multiple antibiotic residues in cow's milk.

An analytical method to identify and quantify multiple antibiotic residues (chloramphenicol, ampicillin, benzylpenicillin, dicloxacillin and erythromycin) in cow's milk by high-performance thin-layer chromatography (HPTLC) combined with bioautography was developed. The test microorganism used for bioautography was Bacillus subtilis ATCC 6633. Antibiotic residues were extracted with acetonitrile, fat eliminated with petroleum ether and residues isolated with dichloromethane The sensitivity of the method guarantees the detection of the above-mentioned antibiotics at levels below maximum residue limits (MRL) allowed for milk. Percentage recoveries ranged between 90 and 100%, with coefficients of variation between 7.2 and 21.3%. Some advantages of this methodology over thin-layer chromatography (TLC)/bioautography are also discussed.

Animals↗
PubMed2006

C6-oxidation and c5-epimerization of locust bean galactomannan studied by high field NMR and circular dichroism.

Galactose depleted locust bean gum was selectively oxidized in C(6) position and epimerized with mannuronan C(5)-epimerases to obtain the corresponding artificial uronanes. These new pseudo-alginates were characterized by NMR spectroscopy and circular dichroism (CD). Specifically, 1D and 2D NMR techniques allowed the degree of epimerization, the distribution of mannuronic and guluronic acid residues in the polysaccharidic chain, and the average G block length to be determined. In addition, NMR diffusion experiments showed that the epimerization reaction did not significantly degrade the polysaccharidic chains. Circular dichroism was used to investigate the kinetics of the epimerization reaction and to evidence the specific interaction between the epimerized locust bean samples with Ca(II) ions in dilute solution. All of the samples considered in this study form wall to wall gels in concentrated polymer solutions.

Acacia↗
PubMed2006

Positive psychotherapy.

Positive psychotherapy (PPT) contrasts with standard interventions for depression by increasing positive emotion, engagement, and meaning rather than directly targeting depressive symptoms. The authors have tested the effects of these interventions in a variety of settings. In informal student and clinical settings, people not uncommonly reported them to be "life-changing." Delivered on the Web, positive psychology exercises relieved depressive symptoms for at least 6 months compared with placebo interventions, the effects of which lasted less than a week. In severe depression, the effects of these Web exercises were particularly striking. This address reports two preliminary studies: In the first, PPT delivered to groups significantly decreased levels of mild-to-moderate depression through 1-year follow-up. In the second, PPT delivered to individuals produced higher remission rates than did treatment as usual and treatment as usual plus medication among outpatients with major depressive disorder. Together, these studies suggest that treatments for depression may usefully be supplemented by exercises that explicitly increase positive emotion, engagement, and meaning. ((c) 2006 APA, all rights reserved).

Affect↗
PubMed2026

A prolonged hydrothermal past at Santorini Caldera revealed by sedimentary trace metal and microbial signatures.

Hydrothermal systems in volcanic calderas are critical in signalling volcanic unrest, forming ore deposits, and sustaining chemosynthetic microorganisms. Analysis of a ~3500-year sequence of sediments collected from the Santorini caldera, Greece, during International Ocean Discovery Program (IODP) Expedition 398 reveals the behaviour of a prolonged paleo-hydrothermal system. Sediment geochemical and metagenomic data record vigorous hydrothermal activity and metal fluxes for ~1100 years, within a 2270-year window between two major eruptions. Sediment hydrothermally-derived trace metals are significantly enriched over background (~200-fold for As and Hg, and 10-50-fold for Mn, Sb, Mo, and V), with long-term metal fluxes (9 t yr-1 As, 2.5 t yr-1 Cu, 7 kg yr-1 Ag) comparable to fluxes from present-day geothermal fields in the Taupo Volcanic Zone. Metagenomic analysis identifies elevated metal resistance genes-signals of microbial adaptation to heightened hydrothermal stressors. Here we integrate geological and genomic evidence to decipher the paleoenvironmental and biogeochemical history of the past hydrothermal system at Santorini caldera.

Geologic Sediments↗
PubMed1976

The metabolism in vivo and in vitro of plasma low-density lipoprotein from a subject with inherited hypercholesterolaemia.

1. The metabolism in vivo and in vitro of an abnormal low-density lipoprotein (LDL) obtained from a patient with an inherited form of hypercholesterolaemia was compared with that of LDL obtained from a normal subject. 2. The rates of turnover of the apoprotein of the two types of LDL in a normal subject, and their uptake and catabolism by normal lymphocytes in vitro, were similar. 3. It is concluded that the abnormal behaviour of the patient's LDL may not be due to an abnormality in the apoprotein component.

Acacia↗
PubMed2000

High relatedness and inbreeding at the origin of eusociality in gall-inducing thrips.

Within the haplodiploid eusocial gall-inducing thrips, a species-level phylogeny combined with genetic data for five eusocial species enables an inference of levels of relatedness and inbreeding values for lineages at the origin of eusociality. Character optimization using data from five eusocial species indicates that the lineage or lineages where eusociality is inferred to have originated exhibit relatedness of 0.64-0.92, and F(IS) of 0.33-0.64. The high inbreeding coefficients found in these eusocial thrips have increased relatedness among and within both sexes and have reduced the haplodiploidy-induced relatedness asymmetries [Hamilton, W. D. (1964) J. Theor. Biol. 7, 1-52]. These results indicate that unusually high relatedness is associated with the origin of eusociality, and they suggest a role for inbreeding in the evolution of bisexual helping.

Acacia↗
PubMed2006

PKB and megalin determine the survival or death of renal proximal tubule cells.

Renal proximal tubule cells have a remarkable ability to reabsorb large quantities of albumin through megalin-mediated endocytosis. This is an essential process for overall body homeostasis. Overstressing this endocytic system with a prolonged excess of albumin is injurious to proximal tubule cells. How these cells function and protect themselves from injury is unknown. Here, we show that megalin is the sensor that determines whether cells will be protected or injured by albumin. Megalin, through a novel mechanism, binds PKB in a D-3-phosphorylated phospholipid-insensitive manner, anchoring PKB in the luminal plasma membrane. Whereas low doses of albumin are protective, an overload of albumin decreases megalin expression followed by a reduction of plasma membrane PKB, PKB activity, and Bad phosphorylation induced by PKB. The result is albumin-induced apoptosis. These results reveal a model for PKB distribution in the plasma membrane and elucidate mechanisms involved in both the protective and toxic effects of albumin on proximal tubule cells. In addition, our findings suggest a mechanism for the progression of chronic kidney disease to end-stage renal disease.

Albumins↗