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131.
The determination of the genetic structure of microbial populations has, until recently, required the establishment of many independent clonal cultures for genotypic analysis. In such studies it has been necessary to assume that isolates able to grow in laboratory culture are representative of the full range of diversity within the natural population. In order to test this assumption we used the polymerase chain reaction (PCR) to amplify the intergenic spacer region of the Phycocyanin operon (PC-IGS) from filaments of Nodularia taken both from clonal cultures and from natural populations in the Baltic Sea. Analysis of the nucleotide sequences revealed more variation among 16 cultured isolates than within 23 single filaments sampled from a natural population. As a means of rapidly determining population genetic structure we designed and used mixtures of allele-specific amplification primers in diagnostic PCRs to identify which PC-IGS allele was present in single filaments from natural cyanobacterial assemblages. Using this method, we determined the PC-IGS genotype of 156 filaments from 9 sampling stations throughout the central basin of the Baltic Sea in July 1996. Our results show that two distinct genotypes of Nodularia are present in the population at all stations. Although the two types were present in approximately equal numbers, they were not distributed uniformly. 相似文献
132.
Jane C. Schneider Hugly Suzanne Chris R. Somerville 《Plant Molecular Biology Reporter》1995,13(1):11-17
Twenty-one mutants ofArabidopsis thaliana were isolated that developed chlorosis or necrosis upon incubation at low temperature (10°C to 15°C). Crosses among mutants
in different phenotypic classes showed that mutants in three of four classes were found in a small number of loci.
This article is reproduced fromWeeds World, vol. 1. For electronic access toWeeds World, see PMBR 12(4):302–303. 相似文献
133.
Summary Proton chemical shifts of a series of disordered linear peptides (H-Gly-Gly-X-Gly-Gly-OH, with X being one of the 20 naturally
occurring amino acids) have been obtained using 1D and 2D 1H NMR at pH 5.0 as a function of temperature and solvent composition. The use of 2D methods has allowed some ambiguities in
side-chain assignments in previous studies to be resolved. An additional benefit of the temperature data is that they can
be used to obtain ‘random coil’ amide proton chemical shifts at any temperature between 278 and 318 K by interpolation. Changes
of chemical shift as a function of trifluoroethanol concentration have also been determined at a variety of temperatures for
a subset of peptides. Significant changes are found in backbone and side-chain amide proton chemical shifts in these ‘random
coil’ peptides with increasing amounts of trifluoroethanol, suggesting that caution is required when interpreting chemical
shift changes as a measure of helix formation in peptides in the presence of this solvent. Comparison of the proton chemical
shifts obtained here for H-Gly-Gly-X-Gly-Gly-OH with those for H-Gly-Gly-X-Ala-OH [Bundi, A. and Wüthrich, K. (1979) Biopolymers, 18, 285–297] and for Ac-Gly-Gly-X-Ala-Gly-Gly-NH2 [Wishart, D.S., Bigam, C.G., Holm, A., Hodges, R.S. and Sykes, B.D. (1995) J. Biomol. NMR, 5, 67–81] generally shows good agreement for CH protons, but reveals significant variability for NH protons. Amide proton chemical
shifts appear to be highly sensitive to local sequence variations and probably also to solution conditions. Caution must therefore
be exercised in any structural interpretation based on amide proton chemical shifts. 相似文献
134.
Is hydrogen peroxide a second messenger of salicylic acid in systemic acquired resistance? 总被引:18,自引:1,他引:17
Urs Neuenschwander Bernard Vernooij Leslie Friedrich Scott Uknes Helmut Kessmann John Ryals 《The Plant journal : for cell and molecular biology》1995,8(2):227-233
Elevated levels of salicylic acid (SA) are required for the induction of systemic acquired resistance (SAR) in plants. Recently, a salicylic acid-binding protein (SABP) isolated from tobacco was shown to have catalase activity. Based on this finding elevated levels of hydrogen peroxide (H2 O2 ) were postulated to act as a second messenger of SA in the SAR signal transduction pathway. A series of experiments have been carried out to clarify the role of H2 O2 in SAR-signaling. No increase of H2 O2 was found during the onset of SAR. Induction of the SAR gene, PR-1, by H2 O2 and H2 O2 -inducing chemicals is strongly suppressed in transgenic tobacco plants that express the bacterial salicylate hydroxylase gene, indicating that H2 O2 induction of SAR genes is dependent on SA accumulation. Following treatment of plants with increasing concentrations of H2 O2 , a dose-dependent accumulation of total SA species was found, suggesting that H2 O2 may induce PR-1 gene expression through SA accumulation. While the results do not support a role for H2 O2 in SAR signaling, it is suggested that SA inhibition of catalase activity may be important in tissues undergoing a hypersensitive response. 相似文献
135.
The relaxant actions of vaso-active intestinal polypeptide (VIP), acetylcholine (ACh), histamine and papaverine have been compared using circular muscle strips of rat aorta contracted with noradrenaline (NA). Arachidonic acid (AA) in a low dose (6.7 × 10 − 7M) also relaxed the aorta. The relaxant actions of all these substances except papaverine were abolished by removal of the endothelial cells. Higher doses of AA (6.7–13.4 × 10–6M) contracted aortic strips in the absence of NA but the con tractile effect “faded” while AA was still present in the bathing fluid. De-endothelialisation abolished this “fade” portion of the response leaving a sustained contracture. Indomethacin inhibited the contractile effect of AA revealing a weak inhibitory effect. However, it did not affect the relaxations induced by VIP, ACh, histamine or papaverine. ETYA abolished the relaxant actions of all these substances except papaverine. The results are consistent with the hypothesis that VIP, ACh and histamine relax the rat aorta via an endothelial-dependent mechanism which may involve the synthesis of a lipoxygenase product. 相似文献
136.
137.
Isolation and Characterization of a Novel Thermophilic, Freshwater Methanogen 总被引:4,自引:1,他引:3 下载免费PDF全文
A novel thermophilic, coccoid methanogen isolated from nonthermal freshwater sediments is described. Hydrogen plus carbon dioxide and formate were substrates for methanogenesis, and methane production was stimulated by yeast extract, Casamino Acids, and tryptose. Growth also occurred autotrophically. Elevated levels of sodium chloride were not required for maximum growth and were inhibitory above 2%. The minimum doubling time occurred at 57°C, and the upper and lower limits for methane production were 62 and 26°C, respectively. The optimum pH for growth was between 7.0 and 7.5. Inhibitory antibiotics included metronidazole, anisomycin, chloramphenicol, and lasalocid. Colonies were circular, dark yellow, shiny, and convex with entire edges. Cells were 1 to 2.5 μm in diameter, nonmotile, occurring singly or in pairs, and fimbriated. Cells were lysed by pronase or trypsin digestion, glass-distilled water, and 1% sodium dodecyl sulfate. Electron micrographs of thin sections showed a monolayered cell wall ca. 20 nm thick. The DNA base ratio was 49.2 mol% guanine plus cytosine. The whole cell protein pattern differed from that of other named coccoid methanogens. 相似文献
138.
139.
In a continuation of studies on protein intake and aflatoxin B1 (AFB1) metabolism, weanling rats were fed semipurified diets containing either 20% casein or 5% casein for two weeks to determine the effect of dietary protein level on hepatic microsomal epoxide hydrase activity and AFB1 metabolism in an effort to evaluate the role of protein intake on the formation and degradation of the reactive metabolite of AFB1. Styrene oxide was used as substrate for epoxide hydrase since the hypothetical AFB1 2,3-epoxide (AFB-epox) cannot be synthesized because of its lability. Two groups of animals were fed 20% casein diets; one was fed ad libitum and the second was pair fed to the 5% casein group in order to control the effects of total feed intake. The depression of epoxide hydrase activities caused by the 5% casein diets was approximately equivalent to that previously seen with hepatic microsomal mixed function oxidase (MFO) activities with the identical protocol. Similarly, the metabolism of AFB1 to AFQ1 and AFM1 was depressed by the 5% casein diets, with an increase in the production of chromatographically more polar material. The relationship of the MFO and epoxide hydrase activities to AFB1 metabolism and formation of macromolecular adducts is discussed. 相似文献
140.
Leaves of greenhouse grown grasses had free protein amino acid contents of generally less than 5 % total amino acids, while field collected grasses averaged 14.7 % free protein amino acid contents. Taxonomic patterns are detectable in the total leaf amino acid profiles of grasses from both sources, those of pooids being distinguishable from those of chloridoids and panicoids, and those of danthonioids showing an intermediate pattern. Leaf profiles of Oryza, Stipeae, and Ehrharteae resemble one another, and are more like those of pooids than those of panicoids. Variations in Thr and Leu are apparently associated with differences in photosynthetic pathway. Grass leaves are generally low in total amino acid contents (2.2 ? 1.0 g % fr. wt), with Ile, Val and Met + Cys identified as the limiting essential amino acids. However, the nutritional ‘chemical scores’ of grass leaf proteins are high (75 %, based on the WHO scoring pattern). 相似文献