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1.
Arbuscular mycorrhizal (AM) fungi play a prominent role in plant nutrition by supplying mineral nutrients, particularly inorganic phosphate (Pi), and also constitute an important carbon sink. AM stimulates plant growth and development, but the underlying mechanisms are not well understood. In this study, Medicago truncatula plants were grown with Rhizophagus irregularis BEG141 inoculum (AM), mock inoculum (control) or with Pi fertilization. We hypothesized that AM stimulates plant growth through either modifications of leaf anatomy or photosynthetic activity per leaf area. We investigated whether these effects are shared with Pi fertilization, and also assessed the relationship between levels of AM colonization and these effects. We found that increased Pi supply by either mycorrhization or fertilization led to improved shoot growth associated with increased nitrogen uptake and carbon assimilation. Both mycorrhized and Pi-fertilized plants had more and longer branches with larger and thicker leaves than the control plants, resulting in an increased photosynthetically active area. AM-specific effects were earlier appearance of the first growth axes and increased number of chloroplasts per cell section, since they were not induced by Pi fertilization. Photosynthetic activity per leaf area remained the same regardless of type of treatment. In conclusion, the increase in growth of mycorrhized and Pi-fertilized Medicago truncatula plants is linked to an increase in the surface for sunlight capture, hence increasing their photosynthetic production, rather than to an increase in the photosynthetic activity per leaf area.  相似文献   
2.
Recent investigations have demonstrated that taurine and phosphoethanolamine (PEA) are the amino acids most sensitive to microdialysis-perfusion with reduced concentrations of NaCl. The aim of the present work was to assess the importance of Na+ deficiency in evoking this response. Further, the previously described selectivity of replacement of Cl- with acetate with respect to amino acid release was reinvestigated. The hippocampus of urethane-anesthetized rats was dialyzed with Krebs-Ringer bicarbonate buffer, and amino acid concentrations of the perfusate were determined. Choline chloride was then stepwise substituted for NaCl, and, in some cases, mannitol (122 mM) was included in low sodium-containing media. In other experiments, NaCl was replaced with sodium acetate. The dialysate levels of taurine increased selectively in response to Na+ substitution. The elevation of taurine was linearly related to the increase in choline chloride, and maximal levels amounted to 335% of basal levels. The increase in extracellular taurine was not inhibited by perfusion with medium made hyperosmotic with mannitol. Replacement of Cl- with acetate stimulated the release of taurine to 652% of resting levels. In addition, PEA levels increased to 250% of control concentration. Other amino acids were unaffected by Cl- substitution. The results show that taurine transport is considerably more sensitive to Na+ depletion than glutamate transport, which also is known to be Na+ dependent. The taurine increase evoked by low Na+ is not caused by cellular swelling as it was unaffected by hyperosmolar medium. Finally, substitution of acetate for Cl- causes a specific elevation of extracellular taurine and PEA, possibly as a result of cytotoxic edema.  相似文献   
3.
Streptococcus pyogenes is a significant bacterial pathogen in the human population. The importance of virulence factors for the survival and colonization of S. pyogenes is well established, and many of these factors are exposed to the extracellular environment, enabling bacterial interactions with the host. In the present study, we quantitatively analyzed and compared S. pyogenes proteins in the growth medium of a strain that is virulent to mice with a non-virulent strain. Particularly, one of these proteins was present at significantly higher levels in stationary growth medium from the virulent strain. We determined the three-dimensional structure of the protein that showed a unique tetrameric organization composed of four helix-loop-helix motifs. Affinity pull-down mass spectrometry analysis in human plasma demonstrated that the protein interacts with histidine-rich glycoprotein (HRG), and the name sHIP (streptococcal histidine-rich glycoprotein-interacting protein) is therefore proposed. HRG has antibacterial activity, and when challenged by HRG, sHIP was found to rescue S. pyogenes bacteria. This and the finding that patients with invasive S. pyogenes infection respond with antibody production against sHIP suggest a role for the protein in S. pyogenes pathogenesis.  相似文献   
4.
Summary Semigranular cells from the crayfish, Pacifastacus leniusculus, were separated by Percoll gradient centrifugation and were used to study the encapsulation of foreign particles. The semigranular cells were found strongly to encapsulate glass beads coated with haemocyte lysate in which the prophenoloxidase-activating system had been activated with laminarin or with a low concentration of calcium ions. The granular cells only weakly encapsulated these particles. The encapsulationpromoting factor was purified from haemocyte lysates and found to be a 76 kD protein which was recognized by an antiserum to the previously described 76 kD cell-adhesion factor. After the last step in purification (Con A-Sepharose chromatography), the flowthrough consisted of several proteins, which had some, but less, encapsulation-promoting activity and contained a 30 kD band that was also recognized by the antiserum to the 76 kD cell-adhesion factor. If the haemocyte lysate prepared in low [Ca2+] was incubated with a -1,3-glucan prior to purification, no 76 kD protein could be isolated but only a 30 kD protein. The 30 kD protein thus seems to be a degradation product of the 76 kD cell-adhesion factor. We conclude that the 76 kD protein which is released from degranulating haemocytes, and to a lesser extent its 30 kD fragment, can promote encapsulation. Phenoloxidase did not have any encapsulation-promoting activity.  相似文献   
5.
Hydroperoxide lyases (HPLs) of the CYP74 family (P450 superfamily) are widely distributed enzymes in higher plants and are responsible for the stress-initiated accumulation of short-chain aldehydes. Fatty acid hydroperoxides serve as substrates for HPLs; however, details of the HPL-promoted conversion are still incompletely understood. In the present work, we report first time the micropreparative isolation and the NMR structural studies of fatty acid hemiacetal (TMS/TMS), the short-lived HPL product. With this aim, linoleic acid 9(S)?hydroperoxide (9(S)?HPOD) was incubated with recombinant melon hydroperoxide lyase (CmHPL, CYP74C2) in a biphasic system of water/hexane for 60?s at 0?°C, pH?4.0. The hexane layer was immediately decanted and vortexed with a trimethylsilylating mixture. Analysis by GC–MS revealed a major product, i.e. the bis-TMS derivative of a hemiacetal which was conclusively identified as 9?hydroxy?9?[(1′E,3′Z)?nonadienyloxy]?nonanoic acid by NMR-spectroscopy. Further support for the hemiacetal structure was provided by detailed NMR-spectroscopic analysis of the bis-TMS hemiacetal generated from [13C18]9(S)?HPOD in the presence of CmHPL. The results obtained provide incontrovertible evidence that the true products of the HPL group of enzymes are hemiacetals, and that the short-chain aldehydes are produced by their rapid secondary chain breakdown. Therefore, we suggest replacing the name “hydroperoxide lyase”, which does not reflect the factual isomerase (intramolecular oxidoreductase) activity, with “hemiacetal synthase” (HAS).  相似文献   
6.
To prevent the global spread of tuberculosis (TB) infection, a novel vaccine that triggers potent and long-lived immunity is urgently required. A plasmid-based vaccine has been developed to enhance activation of major histocompatibility complex (MHC) class I–restricted CD8+ cytolytic T cells using a recombinant Bacille Calmette-Guérin (rBCG) expressing a pore-forming toxin and the Mycobacterium tuberculosis (Mtb) antigens Ag85A, 85B and TB10.4 followed by a booster with a nonreplicating adenovirus 35 (rAd35) vaccine vector encoding the same Mtb antigens. Here, the capacity of the rBCG/rAd35 vaccine to induce protective and biologically relevant CD8+ T-cell responses in a nonhuman primate model of TB was investigated. After prime/boost immunizations and challenge with virulent Mtb in rhesus macaques, quantification of immune responses at the single-cell level in cryopreserved tissue specimen from infected organs was performed using in situ computerized image analysis as a technological platform. Significantly elevated levels of CD3+ and CD8+ T cells as well as cells expressing interleukin (IL)-7, perforin and granulysin were found in TB lung lesions and spleen from rBCG/rAd35-vaccinated animals compared with BCG/rAd35-vaccinated or unvaccinated animals. The local increase in CD8+ cytolytic T cells correlated with reduced expression of the Mtb antigen MPT64 and also with prolonged survival after the challenge. Our observations suggest that a protective immune response in rBCG/rAd35-vaccinated nonhuman primates was associated with enhanced MHC class I antigen presentation and activation of CD8+ effector T-cell responses at the local site of infection in Mtb-challenged animals.  相似文献   
7.
At a given level of serum cholesterol, patients with T2D have an increased risk of developing atherosclerosis compared with nondiabetic subjects. We hypothesized that T2D patients have an increased interstitial fluid (IF)-to-serum gradient ratio for LDL, due to leakage over the vascular wall. Therefore, lipoprotein profiles in serum and IF from 35 T2D patients and 35 healthy controls were assayed using fast performance liquid chromatography. The IF-to-serum gradients for VLDL and LDL cholesterol, as well as for apoB, were clearly reduced in T2D patients compared with healthy controls. No such differences were observed for HDL cholesterol. Contrary to our hypothesis, the atherogenic VLDL and LDL particles were not increased in IF from diabetic patients. Instead, they were relatively sparser than in healthy controls. The most probable explanation to our unexpected finding is that these lipoproteins are more susceptible to retainment in the extravascular space of these patients, reflecting a more active uptake by, or adhesion to, tissue cells, including macrophages in the vascular wall. Further studies are warranted to further characterize the mechanisms underlying these observations, which may be highly relevant for the understanding of why the propensity to develop atherosclerosis is increased in T2D.  相似文献   
8.
When groups of individuals differ in activities that may influence the production of reactive molecules, such as superoxide, we expect selection to result in congruent upregulation of antioxidant production in the group(s) most at risk of suffering concomitant erosion of essential tissue and biomolecules, such as DNA. We investigate this in a (near) annual lizard species, the Australian painted dragon (Ctenophorus pictus), in which males and females have fundamentally different lifestyles, with males being overtly conspicuous and aggressive, whereas females are placid and camouflaged. When kept in identical conditions to females in captivity, males had higher levels of superoxide dismutase (SOD) through the activity season, which is consistent with selection for a higher capacity of superoxide antioxidation and a lower level of DNA damage than females. Males, however, lacked the clear negative, linear relationship between SOD and DNA erosion observed in females, suggesting that female upregulation of SOD results in a more predictable antioxidation and a more immediate target for selection. Lastly, we analysed aspects of female reproduction from a DNA erosion perspective. Females closer to ovulation, hence with less remaining, circulating vitellogenin, had higher superoxide levels. Furthermore, a multiple regression analysis showed that females that produced more clutches over time suffered more DNA erosion, whereas females with higher SOD levels suffered less DNA erosion.  相似文献   
9.
There has been a long-term decline in spring and fall numbers of Clethrionomys rufocanus in boreal Sweden in 1971–2005. Previous studies on permanent sampling plots in the centre of 2.5 × 2.5 km landscapes suggested that habitat fragmentation (sensu destruction) could have contributed to the decline. Therefore, we tested these findings in a field study and compared trapping results on the central sampling plots of landscapes with a low degree of fragmentation (LDF) and of “hot spot” type with trapping results in managed forest landscapes with a high degree of fragmentation (HDF). We predicted that C. rufocanus would be more common on the LDF plots. We used our permanent plots supplemented with a new sample of plots, mainly of the rare LDF type, inside or just outside the long-term study area. Very few voles were trapped on both plot types, and no difference was found. However, a subsequent pilot study with trapping in a national park with large areas of pristine, unfragmented forest yielded more voles than in the managed, more fragmented, areas. Consequently, the initial field study data and some other recent data were also re-analysed from a “local patch quality” perspective. This alternative approach revealed the positive importance of large focal patches of forest >60 years old and their content of old-growth (pine) forest (>100 years). Interestingly, at the landscape level, the frequency distribution of patches of forest >60 years old, old-growth (>100 years), and especially of old-growth pine forest (>100 years), relative to the properties of plots with C. rufocanus, suggested that there are few forest patches left that are suitable for C. rufocanus. Our current results suggest that habitat fragmentation cannot be excluded as a contributing cause to the long-term decline of C. rufocanus in boreal Sweden.  相似文献   
10.
The mammalian tick-borne flavivirus group (MTBFG) contains viruses associated with important human and animal diseases such as encephalitis and hemorrhagic fever. In contrast to mosquito-borne flaviviruses where recombination events are frequent, the evolutionary dynamic within the MTBFG was believed to be essentially clonal. This assumption was challenged with the recent report of several homologous recombinations within the Tick-borne encephalitis virus (TBEV). We performed a thorough analysis of publicly available genomes in this group and found no compelling evidence for the previously identified recombinations. However, our results show for the first time that demonstrable recombination (i.e., with large statistical support and strong phylogenetic evidences) has occurred in the MTBFG, more specifically within the Louping ill virus lineage. Putative parents, recombinant strains and breakpoints were further tested for statistical significance using phylogenetic methods. We investigated the time of divergence between the recombinant and parental strains in a Bayesian framework. The recombination was estimated to have occurred during a window of 282 to 76 years before the present. By unravelling the temporal setting of the event, we adduce hypotheses about the ecological conditions that could account for the observed recombination.  相似文献   
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