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991.
Morten S. Frederiksen Marta Pérez Juan Manuel Ruiz 《Journal of experimental marine biology and ecology》2008,358(1):98-109
The effect of increased sediment sulfide concentrations on the sulfur isotopic composition (δ34S), total sulfur (TS) and elemental sulfur (S0) concentrations in plant tissues was studied for the two seagrasses Zostera marina (3 weeks in laboratory) and Posidonia oceanica (4 months in situ). Porewater sulfide concentrations were experimentally regulated and plants exposed to high sediment sulfide concentrations had δ34S signals closer to the δ34S of sulfide, whereas plants exposed to no / low sulfide concentrations had δ34S signals closer to the δ34S of seawater sulfate, indicating a higher sulfide invasion in plants exposed to high sulfide concentrations. The δ34S varied between the plant tissues in both species with the leaves having more positive δ34S signals than roots and rhizomes, indicating that sulfide was invading into the roots and moved to the other tissues through the lacunae. TS and S0 concentrations were higher in plants exposed to sulfide in both experiments suggesting that sulfur derived from sediment sulfide accumulated in the plants. The δ34S signal in S0 was similar to sediment sulfide verifying that S0 found in the seagrasses originated from sediment sulfide. Direct comparisons of δ34S in the two different seagrasses and across the treatments were not possible due to large differences in δ34S of the sulfur sources. Fsulfide adjusted for these differences and may be a useful alternative, when δ34S of the sulfur sources varies between study sites. There were no significant effects of sulfide exposure on plant growth and mortality in Z. marina and P. oceanica after 3 weeks and 8 weeks exposure, respectively, but P. oceanica showed indications of reduced growth and higher mortality after 16 weeks of sulfide exposure probably due to sulfide invasion/toxicity. 相似文献
992.
The effect that an increase in the activity of an enzyme has on its flux normally decreases with activity increase. To achieve a large increase in flux by manipulating a single step would therefore require a high initial effect that maintains or increases when the activity is increased, what has been called sustained or paradoxical control. Using metabolic control analysis for large responses, we derive conditions for sustained or paradoxical control in terms of elasticity coefficients. These are used to characterise types of rate laws contributing to this behaviour. The result that simple pathways, with normal kinetics, subject to large activity changes can lead to paradoxical control behaviour suggests that this type of pattern may be much more ubiquitous than could have, in principle, been suspected. 相似文献
993.
Pellizzari EH Barontini M Figuerola Mde L Cigorraga SB Levin G 《Life sciences》2008,83(11-12):413-420
AIMS: Pheochromocytomas are catecholamine-secreting tumors that also synthesize and secrete several neuropeptides, including opioids. A negative regulation of catecholamine secretion by opioids has been postulated in chromaffin cells. However, results obtained so far are contradictory when referred to human pheochromocytomas. The aim of this study was to define the role of locally produced enkephalins on catecholamine release in human pheochromocytoma cells. MAIN METHODS: Cells obtained from eleven human pheochromocytomas of different genetic origins were cultured for 5 days. Cultures were maintained under basal condition or under enkephalin, dexamethasone and naloxone alone or in combination with enkephalin or dexamethasone-stimulated conditions. Catecholamine and enkephalin levels in the culture medium were measured by HPLC-ED and RIA respectively. KEY FINDINGS: Enkephalin induced a decrease in norepinephrine levels in all tumor cultures. Dexamethasone treatment, which increased enkephalin levels, also decreased catecholamine levels. On the other hand, the addition of naloxone to the cultures reverted to normal the inhibitory action exerted by enkephalin and dexamethasone treatments. SIGNIFICANCE: These results suggest the existence of an autocrine negative regulatory loop exerted by enkephalin on norepinephrine release in human pheochromocytoma cells. 相似文献
994.
Costa PM Lobo J Caeiro S Martins M Ferreira AM Caetano M Vale C Delvalls TA Costa MH 《Mutation research》2008,654(1):29-37
Juvenile Solea senegalensis (Senegalese sole) were exposed to freshly collected sediments from three sites of the Sado Estuary (West-Portuguese coast) in 28-day laboratory assays in order to assess the ecological risk from sediment contaminants, by measuring two genotoxicity biomarkers in peripheral blood: the percentage of Erythrocyte Nuclear Abnormalities (ENA) by use of an adaptation of the micronucleus test, and the percentage of DNA strand-breakage (DNA-SB) with the Comet assay. Sediments were surveyed for metallic (Cr, Ni, Cu, Zn, As, Cd and Pb) and organic (PAHs (polycyclic aromatic hydrocarbons), PCBs (polychlorinated biphenyls) and DDTs (dichloro-diphenyl-trichloroethane)) contaminants. Sediments from site A (farthest from hotspots of contamination) were found to be the least contaminated and weaker inducers of genotoxic damage, whereas sediments from sites B (urban influence) and C (affected by industrial effluents and agricultural runoffs) were responsible for a very significant increase in both ENA and DNA-SB, site B being most contaminated with metals and site C mainly with organic pollutants, especially PAHs and PCBs . Analysis of genotoxic effects showed a strong correlation between the concentrations of PAHs and PCBs and both biomarkers at sampling times T(14) and T(28), while the amounts of Cu, As, Cd and Pb were less strongly correlated, and at T(28) only, with ENA and DNA-SB. These results show that organic contaminants in sediment are stronger and faster acting genotoxic stressors. The results also suggest that metals may have an inhibitory effect on genotoxicity when interacting with organic contaminants, at least during early exposure. ENA and DNA-SB do not show a linear relationship, but a strong correlation exists between the overall increase in genotoxicity caused by exposure to sediment, confirming that they are different, and possibly non-linked effects that respond similarly to exposure. Although the Comet assay showed enhanced sensitivity, the two analyses are complementary and suitable for the biomonitoring of sediment contaminants in a benthic species like S. senegalensis. 相似文献
995.
Herbivory can induce changes in plant traits that may involve both tolerance mechanisms that compensate for biomass loss and
resistance traits that reduce herbivore preference. Seagrasses are marine vascular plants that possess many attributes that
may favour tolerance and compensatory growth, and they are also defended with mechanisms of resistance such as toughness and
secondary metabolites. We quantified phenotypic changes induced by herbivore damage on the temperate seagrass Posidonia oceanica in order to identify specific compensatory and resistance mechanisms in this plant, and to assess any potential trade-offs
between these two strategies of defence. We simulated three natural levels of fish herbivory by repeatedly clipping seagrass
leaves during the summer period of maximum herbivory. Compensatory responses were determined by measuring shoot-specific growth,
photosynthetic rate, and the concentration of nitrogen and carbon resources in leaves and rhizomes. Induced resistance was
determined by measuring the concentration of phenolic secondary metabolites and by assessing the long-term effects of continued
clipping on herbivore feeding preferences using bioassays. Plants showed a significant ability to compensate for low and moderate
losses of leaf biomass by increasing aboveground growth of damaged shoots, but this was not supported by an increase in photosynthetic
capacity. Low levels of herbivory induced compensatory growth without any measurable effects on stored resources. In contrast,
nitrogen reserves in the rhizomes played a crucial role in the plant’s ability to compensate and survive herbivore damage
under moderate and high levels of herbivory, respectively. We found no evidence of inducibility of long-term resistance traits
in response to herbivory. The concentration of phenolics decreased with increasing compensatory growth despite all treatments
having similar carbon leaf content, suggesting reallocation of these compounds towards primary functions such as cell-wall
construction. 相似文献
996.
The house mouse, Mus musculus domesticus, exhibits a high level of chromosomal polymorphism because of the occurrence and fast fixation of Robertsonian fusions between telocentric chromosomes. For this reason, it has been considered a classical speciation model to analyse the role of the chromosomal changes in reproductive isolation. In this study, we analysed a parapatric contact area between two metacentric races in central Italy, the Cittaducale race (CD: 2n = 22) and the Ancarano race (ACR: 2n = 24), to estimate gene flow at the boundary. Hybrids between these two races show high levels of structural heterozygosity and are expected to be highly infertile. A sample of 88 mice from 14 sites was used. The mice were genotyped by means of eight microsatellite loci mapped in four different autosomal arms. The results show clear genetic differentiation between the CD and ACR races, as revealed by differences in allele frequencies, factorial correspondence analysis and indexes of genetic population (e.g. F(ST) and R(ST)) along the contact zone. The genetic differentiation between the races was further highlighted by assignation and clustering analyses, in which all the individuals were correctly assigned by their genotypes to the source chromosomal race. This result is particularly interesting in view of the absence of any geographical or ecological barrier in the parapatric contact zone, which occurs within a village. In these conditions, the observed genetic separation suggests an absence of gene flow between the races. The CD-ACR contact area is a rare example of a final stage of speciation between chromosomal races of rodents because of their chromosomal incompatibility. 相似文献
997.
998.
Minvielle MC Molina NB Polverino D Basualdo JA 《Memórias do Instituto Oswaldo Cruz》2008,103(1):98-103
The purpose of this study was to investigate the genotypes of Giardia lamblia from human and animal feces and their epidemiological and clinical characteristics in Argentina, South America. Seventy isolates, 60 from humans (adults and children), eight from dogs and two from cows were processed by polymerase chain reaction-restriction fragment length polymorphism. Data corresponding to demographic, socio-cultural and environmental variables and presence/absence of signs/symptoms were collected. The triosephosphate isomerase gene was amplified from 43 (71.66%) of the 60 human fecal samples. Among these, 3/43 (6.98%) were genotype AII and 40/43 (93.02%) were genotype B. Assemblage AII was detected in three children who lived together in a shantytown and they were oligosymptomatic and none had diarrhea. This genotype was not found in animals. Genotype B showed a high prevalence in both adults and children. It was also found in polysymptomatic people, many of whom presented diarrhea. It was also found only in one dog. The present study represents the first contribution to the knowledge of G. lamblia genotypes in Argentina. 相似文献
999.
Mayoral R Mollá B Flores JM Boscá L Casado M Martín-Sanz P 《The Biochemical journal》2008,416(3):337-346
The effect of COX (cyclo-oxygenase)-2-dependent PGs (prostaglandins) in acute liver injury has been investigated in transgenic mice that express human COX-2 in hepatocytes. We have used three well-established models of liver injury: in LPS (lipopolysaccharide) injury in D-GalN (D-galactosamine)-preconditioned mice; in the hepatitis induced by ConA (concanavalin A); and in the proliferation of hepatocytes in regenerating liver after PH (partial hepatectomy). The results from the present study demonstrate that PG synthesis in hepatocytes decreases the susceptibility to LPS/D-GalN or ConA-induced liver injury as deduced by significantly lower levels of the pro-inflammatory profile and plasmatic aminotransferases in transgenic mice, an effect suppressed by COX-2-selective inhibitors. These Tg (transgenic) animals express higher levels of anti-apoptotic proteins and exhibit activation of proteins implicated in cell survival, such as Akt and AMP kinase after injury. The resistance to LPS/D-GalN-induced liver apoptosis involves an impairment of procaspase 3 and 8 activation. Protection against ConA-induced injury implies a significant reduction in necrosis. Moreover, hepatocyte commitment to start replication is anticipated in Tg mice after PH, due to the expression of PCNA (proliferating cell nuclear antigen), cyclin D1 and E. These results show, in a genetic model, that tissue-specific COX-2-dependent PGs exert an efficient protection against acute liver injury by an antiapoptotic/antinecrotic effect and by accelerated early hepatocyte proliferation. 相似文献
1000.
ELG1 (enhanced level of genome instability) encodes a Replication Factor C (RFC) homolog that is important for the maintenance of genome stability. Elg1 interacts with Rfc2-5, forming the third alternative RFC complex identified to date. We found that Elg1 plays a role in the suppression of spontaneous DNA damage in addition to its previously identified roles in the resistance to DNA damage. Using mutational analysis we examined the function of conserved and unique regions of Elg1 in these roles. We found that the Walker A motif in the conserved RFC region is dispensable for Elg1 function in vivo. The RFC region is important for association with chromatin although residues predicted to mediate interactions with DNA are dispensable for Elg1 function. The unique C-terminus of Elg1 mediates oligomerization with Rfc2-5, nuclear import, and chromatin association, and is critical for the function of Elg1. Finally, we demonstrated that the N-terminus of Elg1 contributes to the maintenance of genome stability, and that one function of this N-terminus is to promote the nuclear localization of Elg1. Together, these studies delineate the regions of Elg1 important for its function in damage resistance and in the suppression of spontaneous DNA damage. 相似文献