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41.
Beauveria bassiana, a mitosporic fungus used for the biological control of many insect species, is recognized as a "species complex" comprising genetically diverse lineages. Being predominantly asexual, mating tests cannot be applied to delimit species in this species complex. Genetic tests offer an indirect means of identifying species among isolates. To this end, molecular genetic analysis of a sample of B. bassiana isolates with 2 subsamples, 1 representing a worldwide collection and another from a localized epizootic population was carried out. DNA markers generated through AFLPs (amplified fragment length polymorphisms) and SSCPs (single-strand conformation poly morphisms) and nucleotide sequence data of different allelic forms of 3 genes (large and small subunits of rRNA and beta-tubulin) were evaluated. The B. bassiana isolates from the worldwide sample showed 11% overall similarity and no closely clustered groups. Phylogenetic trees generated from the AFLP and SSCP data of this sample resolved the different isolates into distinct phylogenetic lineages. In the epizootic B. bassiana population, prevalence of recombination was evident from random association of alleles in multilocus tests and lack of phylogenetic concordance among 3 gene genealogies. Thus, the worldwide sample of B. bassiana exhibits a predominantly clonal structure, hinting at species divergence leading to cryptic speciation with recombination being customary among isolates sharing a close ecological niche.  相似文献   
42.

Background

Association mapping, initially developed in human disease genetics, is now being applied to plant species. The model species Arabidopsis provided some of the first examples of association mapping in plants, identifying previously cloned flowering time genes, despite high population sub-structure. More recently, association genetics has been applied to barley, where breeding activity has resulted in a high degree of population sub-structure. A major genotypic division within barley is that between winter- and spring-sown varieties, which differ in their requirement for vernalization to promote subsequent flowering. To date, all attempts to validate association genetics in barley by identifying major flowering time loci that control vernalization requirement (VRN-H1 and VRN-H2) have failed. Here, we validate the use of association genetics in barley by identifying VRN-H1 and VRN-H2, despite their prominent role in determining population sub-structure.

Results

By taking barley as a typical inbreeding crop, and seasonal growth habit as a major partitioning phenotype, we develop an association mapping approach which successfully identifies VRN-H1 and VRN-H2, the underlying loci largely responsible for this agronomic division. We find a combination of Structured Association followed by Genomic Control to correct for population structure and inflation of the test statistic, resolved significant associations only with VRN-H1 and the VRN-H2 candidate genes, as well as two genes closely linked to VRN-H1 (HvCSFs1 and HvPHYC).

Conclusion

We show that, after employing appropriate statistical methods to correct for population sub-structure, the genome-wide partitioning effect of allelic status at VRN-H1 and VRN-H2 does not result in the high levels of spurious association expected to occur in highly structured samples. Furthermore, we demonstrate that both VRN-H1 and the candidate VRN-H2 genes can be identified using association mapping. Discrimination between intragenic VRN-H1 markers was achieved, indicating that candidate causative polymorphisms may be discerned and prioritised within a larger set of positive associations. This proof of concept study demonstrates the feasibility of association mapping in barley, even within highly structured populations. A major advantage of this method is that it does not require large numbers of genome-wide markers, and is therefore suitable for fine mapping and candidate gene evaluation, especially in species for which large numbers of genetic markers are either unavailable or too costly.  相似文献   
43.
Colicin A (ColA) is a water-soluble toxin that forms a voltage-gated channel in the cytoplasmic membrane of Escherichia coli. Until now, two models were proposed for the closed channel state: the umbrella model and the penknife model. Mutants of ColA, each containing a single cysteine, were labeled with a nitroxide spin label, reconstituted into liposomes, and studied by electron paramagnetic resonance (EPR) spectroscopy to study the membrane-bound closed channel state. The spin-labeled ColA variants in solution and in liposomes of native E. coli lipid composition were analyzed in terms of the mobility of the nitroxide, its accessibility to paramagnetic reagents, and the polarity of its microenvironment. The EPR data determined for the soluble ColA pore-forming domain are in agreement with its crystal structure. Moreover, the EPR results show that ColA has a conformation in liposomes different from its water-soluble conformation. Residues that belong to helices H8 and H9 are significantly accessible for O2 but not for nickel-ethylene diamine diacetic acid, indicating their location inside the membrane. In addition, the polarity values determined from the hyperfine tensor component Azz of residues 176, 181, and 183 (H9) indicate the location of these residues close to the center of the lipid bilayer, supporting a transmembrane orientation of the hydrophobic hairpin. Furthermore, the accessibility and polarity data suggest that the spin-labeled side chains of the amphipathic helices (H1-H7 and H10) are located at the membrane-water interface. Evidence that the conformation of the closed channel state in artificial liposomes depends on lipid composition is given. The EPR results for ColA reconstituted into liposomes of E. coli lipids support the umbrella model for the closed channel state.  相似文献   
44.
45.
The Kok effect refers to the progressive light-induced inhibition of dark respiration at low light intensities, which saturates around the light compensation point. This appears as a sudden break around the light compensation point in the plot of photosynthesis versus light intensity. The magnitude of the break can be considered as a measure of the Kok effect. In the present work, the importance of different components of dark respiration during the Kok effect was investigated by using low concentrations of mitochondrial inhibitors in leaf discs of pea ( Pisum sativum L. cv. Azad P1). The effects of glucose (stimulates respiration) and 0.8 M sorbitol (imposes osmotic stress and inhibits photosynthesis) were also studied for comparison. The magnitude of the break decreased significantly in the presence of antimycin A or oligomycin (inhibitors of cytochrome pathway of mitochondrial electron transport and ATP synthase, respectively). In contrast, there was no significant change with salicylhydroxamic acid (SHAM; an inhibitor of alternative pathway of mitochondrial electron transport). The magnitude of the break increased significantly with glucose, and decreased on exposure to osmotic stress. Our results suggest that the Kok effect (inhibition of dark respiration in light) is modulated by inhibitors of cytochrome pathway and ATP synthesis, but not that of the alternative pathway.  相似文献   
46.
Tobacco dust mainly contains nitrosamines, which are readily absorbed by the body tissues like skin, respiratory epithelium, and mucous membrane of mouth, nose and intestines. Exposure to tobacco dust is known to affect the respiratory tracts in humans. In the present study, cytogenetic effects of exposure to tobacco dust are evaluated in 154 male tobacco factory workers and 138 age and sex matched controls by analysing chromosomal aberrations in their peripheral blood lymphocytes. The workers were in the age group of 20-55 years and were employed in the tobacco processing factory for 1-32 years. Heparinised blood samples were collected from workers and control subjects and lymphocyte cultures were carried out by using standard technique. Slides were prepared and 150 metaphases were screened for each sample for various structural and numerical types of abnormalities. A statistically significant increase was observed in the frequencies of chromosomal aberrations in non-smoking and smoking exposed groups when compared to the respective controls. An increase in the frequencies of chromosomal aberrations was also observed with increase in years of service in the exposed subjects.  相似文献   
47.
Benzylidenehydrazinyl imidazoles ( 3 ) are prepared from 2‐hydrazinyl imidazoles ( 2 ) on treatment with hydrazine. The imine functionality in 3 is utilized to develop 5′‐aryl‐N‐(4‐aryl‐1H‐imidazol‐2‐yl)‐1H‐1,2,3‐triazol‐1‐amines ( 5 ) by 1,3‐dipolar cycloaddition of diazomethane followed by aromatization with I2 in DMSO. Compounds 3 are also explored to prepare 4′‐aryl‐1‐(4‐aryl‐1H‐imidazol‐2‐ylamino)‐3‐chloroazetidin‐2‐ones ( 6 ) on treatment with chloroacetyl chloride. The Molinspiration calculations predicted that 3 , 5 and 6 have molecular hydrophobicity, conformational flexibility, good intestinal absorption and bioactivity scores. The chloro, bromo and nitro substituted imidazolyl azetidinones ( 6c , 6d , 6f ) and nitro substituted imidazolyl triazole ( 5f ) exhibited excellent antibacterial activity on B. subtilis, whereas chloro and nitro substituted imidazolyl triazoles ( 5c , 5f ) showed prominent antifungal activity on A. niger.  相似文献   
48.
The interaction of polymyxin with the producer organism Bacillus polymyxa has been shown to be at the level of membranes, resulting in an enhancement of the activities of its own biosynthetic enzymes. This enhancement has been shown to be due to the solubilization of the membrane-associated multienzyme complex by polymyxin in a specific manner. The relevance of this physiological feature was also indicated by the appearance of the soluble multienzyme complex activity only in cells, which synthesize maximal amounts of polymyxin. Purification of the polymyxin released multienzyme complex from the membranes and the soluble form of the complex from the stationary phase cells has revealed several similarities between them. Both contain two major fractions of the molecular weights of 300,000 and 170,000, harboring all the polymyxin component amino acid-activating enzymes. Their multisubunit nature was established by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis. Using mutants blocked in sporulation and/or antibiotic synthesis, it was shown that the interaction of polymyxin with the producer organism was inoperative when antibiotic production was curtailed. This interaction has been suggested as one of the early sporulation-specific phenemenon.  相似文献   
49.
Piperine is a major component of black (Piper nigrum Linn) and long pepper (Piper longum Linn) used widely in various systems of traditional medicine. We have evaluated the effect of piperine on mitochondrial tricarboxylic acid cycle and phase I and glutathione-metabolizing enzymes in Benzo(a)pyrene induced experimental lung carcinogenesis in swiss albino mice. Lung cancer bearing mice showed a significant decrease in the activities of mitochondrial enzymes-isocitrate dehydrogenase (ICDH), -ketoglutarate dehydrogenase (KDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH) and significantly increased NADPH-Cytochorome reductase (NADPH-C reductase), cytochrome P450 (cyt-p450) and cytochrome b5(cyt-b5). The activities of glutathione-metabolizing enzymes glutathione peroxidase(GPx), glutathione reductase (GR) and glucose-6-phospho dehydrogenase(G6PDH) were significantly lowered in lung-cancer bearing mice when compared with control mice. Piperine supplementation to tumour-induced animals significantly lowered the phase-I enzymes (NADPH-C reductase, cyt-p450 and cyt-b5)) and there was a rise in glutathione-metabolizing enzymes (GPx, GR and G6PDH), which indicated an antitumour and anti-cancer effect. Comparison of normal control mice and mice administered piperine only as drug control showed no significant variations in enzyme activities. Piprine administration to benzo(a)pyrene induced animals significantly increased the activities of mitochondrial enzymes, thereby suggesting its role in mitochondrial energy production.  相似文献   
50.
Maternal vitamin deficiencies are associated with low birth weight and increased perinatal morbidity and mortality. We hypothesize that maternal folate and/or vitamin B12 restrictions alter body composition and fat metabolism in the offspring. Female weaning Wistar rats received ad libitum for 12 weeks a control diet (American Institute of Nutrition-76A) or the same with restriction of folate, vitamin B12 or both (dual deficient) and, after confirming vitamin deficiency, were mated with control males. The pregnant/lactating mothers and their offspring received their respective diets throughout. Biochemical and body composition parameters were determined in mothers before mating and in offspring at 3, 6, 9 and 12 months of age. Vitamin restriction increased body weight and fat and altered lipid profile in female Wistar rats, albeit differences were significant with only B12 restriction. Offspring born to vitamin-B12-restricted dams had lower birth weight, while offspring of all vitamin-restricted dams weighed higher at/from weaning. They had higher body fat (specially visceral fat) from 3 months and were dyslipidemic at 12 months, when they had high circulating and adipose tissue levels of tumor necrosis factor α, leptin and interleukin 6 and low levels of adiponectin and interleukin 1β. Vitamin-restricted offspring had higher activities of hepatic fatty acid synthase and acetyl-CoA-carboxylase and higher plasma cortisol levels. In conclusion, maternal and peri-/postnatal folate and/or vitamin B12 restriction increased visceral adiposity (due to increased corticosteroid stress), altered lipid metabolism in rat offspring perhaps by modulating adipocyte function and may thus predispose them to high morbidity later.  相似文献   
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