Comparative analysis of glycoprotein and glycolipid composition of virulent and avirulent strain membranes ofMycoplasma hyopneumoniae

The glycoproteins and glycolipids from membranes of virulent strain Z and avirulent strain M ofMycoplasma hyopneumoniae have been compared. The proteins and the glycoproteins were identified by SDS-polyacrylamide gel electrophoresis and concanavalin A-biotin labeling, respectively. The membrane preparation contained approximately 34 protein bands with molecular weights between 20 KD and 100 KD. The concanavalin A-biotin system reacted with a glycoprotein of a molecular weight of approximately 28,000 from avirulent strain M and did not react with the correspondent band from virulent strain Z. The membrane glycolipids of both strains consisted of monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG), and the percentages of 160, 180, and 181 fatty acids comprised more than 80% of the total fatty acids of membrane glycolipids. The 180 fatty acid of MGDG in avirulent strain M was twofold higher than that of virulent strain Z.     

p140trk mRNA marks NGF-responsive forebrain neurons: evidence that trk gene expression is induced by NGF.

Nerve growth factor (NGF) appears to act as a neurotrophic factor for basal forebrain and caudate-putamen cholinergic neurons. The mechanism by which NGF transduces its signal in these neurons is yet to be defined. Recent data indicate that the product of the trk gene, p140trk, is a critical component of the NGF receptor. Herein, we show that p140trk mRNA is highly restricted in its distribution in the adult rat forebrain, that it is present in cholinergic neurons, and that most if not all cholinergic neurons contain p140trk mRNA. Furthermore, induction of trk expression by NGF suggests that neurotrophin-mediated up-regulation of their receptor tyrosine kinases is an important feature of their actions and that neurotrophins may regulate the activity of responsive neurons through increasing the level of their receptors.     

Photoinhibition of holly (Ilex aquifolium) in the field during the winter

The distribution of holly ( Ilex aquifolium ) and its habitat preferences indicate a sensitivity to low temperature, particularly when exposed to high light. Experiments were conducted to determine whether photoinhibition of photosynthesis occurs in holly leaves in the field in United Kingdom during the winter. Photosynthetic efficiency was assessed in holly leaves that were exposed to or shaded from direct sunlight using measurements of photosynthetic oxygen evolution and chlorophyll fluorescence. Field measurements were conducted over 3 weeks during January and February. Correlation of the measurements of photosynthetic efficiency with weather conditions indicated that holly was suffering photoinhibition, particularly in leaves exposed to direct sunlight. Controlled environment studies demonstrated that exposure of leaves to low temperature and high light resulted in reductions in photosynthetic efficiency; however, leaves recovered rapidly when exposed to a higher temperature and reduced light level.     

The Sequence of Change within the Photosynthetic Apparatus of Wheat following Short-Term Exposure to Ozone

The basis of inhibition of photosynthesis by single acute O₃ exposures was investigated in vivo using analyses based on leaf gas exchange measurements. The fully expanded second leaves of wheat plants (Triticum aestivum L. cv Avalon) were fumigated with either 200 or 400 nanomoles per mole O₃ for between 4 and 16 hours. This reduced significantly the light-saturated rate of CO₂ uptake and was accompanied by a parallel decrease in stomatal conductance. However, the stomatal limitation, estimated from the relationship between CO₂ uptake and the internal CO₂ concentration, only increased significantly during the first 8 hours of exposure to 400 nanomoles per mole O₃; no significant increase occurred for any of the other treatments. Analysis of the response of CO₂ uptake to the internal CO₂ concentration implied that the predominant factor responsible for the reduction in light-saturated CO₂ uptake was a decrease in the efficiency of carboxylation. This was 58 and 21% of the control value after 16 hours at 200 and 400 nanomoles per mole O₃, respectively. At saturating concentrations of CO₂, photosynthesis was inhibited by no more than 22% after 16 hours, indicating that the capacity for regeneration of ribulose bisphosphate was less susceptible to O₃. Ozone fumigations also had a less pronounced effect on light-limited photosynthesis. The maximum quantum yield of CO₂ uptake and the quantum yield of oxygen evolution showed no significant decline after 16 hours with 200 nanomoles per mole O₃, requiring 8 hours at 400 nanomoles per mole O₃ before a significant reduction occurred. The photochemical efficiency of photosystem II estimated from the ratio of variable to maximum chlorophyll fluorescence and the atrazine-binding capacity of isolated thylakoids demonstrated that photochemical reactions were not responsible for the initial inhibition of CO₂ uptake. The results suggest that the apparent carboxylation efficiency appears to be the initial cause of decline in photosynthesis in vivo following acute O₃ fumigation.     

Effect of light/dark cycles on expression of nitrate assimilatory genes in maize shoots and roots

The level of nitrate reductase (NR) and nitrite reductase (NiR) varied in both shoot and root tissue from nitrate-fed Zea mays L. grown under a 16-hour light/8-hour dark regime over a 10-day period postgermination, with peak activity occurring in days 5 to 6. To study the effect of different light regimes on NR and NiR enzyme activity and mRNA levels, 6-day-old plants were grown in the presence of continuous KNO₃ (10 millimolar). Both shoot NRA and mRNA varied considerably, peaking 4 to 8 hours into the light period. Upon transferring plants to continuous light, the amplitude of the peaks increased, and the peaks moved closer together. In continuous darkness, no NR mRNA or NR enzyme activity could be detected by 8 hours and 12 hours, respectively. In either a light/dark or continuous light regime, root NRA and mRNA did not vary substantially. However, when plants were placed in continuous darkness, both declined steadily in the roots, although some remained after 48 hours. Although there was no obvious cycling of NiR enzyme activity in shoot tissue, changes in mRNA mimicked those seen for NR mRNA. The expression of NR and NiR genes is affected by the light regime adopted, but light does not have a direct effect on the expression of these genes.     

High plating efficiency and plant regeneration frequency in low density protoplast cultures derived from an embryogenic Brassica napus cell suspension

Protoplasts were isolated from an embryogenic cell suspension culture derived from microspores of Brassica napus cv. Jet Neuf. Protoplast yield varied with the cell suspension growth medium. Optimization of protoplast plating density, manipulation of culture medium, carbon source and medium matrix, and inclusion of Ficoll resulted in protoplast plating efficiencies close to 30%. Placement of the protoplasts close to the gas interface contributed greatly to the elevated plating efficiency. Low density cultures could be induced to regenerate calli at optimum plating efficiencies if grown in the presence of nurse culture. This is of great advantage for manipulation of individual protoplasts or for microinjection. Plants were regenerated directly from the cell suspension or from the protoplast cultures.Abbreviations BA N⁶-benzyladenine - 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-3-acetic acid - NAA naphthaleneacetic acid     

脂质过氧化对人红细胞膜脂流动性的影响

研究枯稀过氧化氢/高铁血红素体系所产生的烷基过氧自由基对红细胞的损伤。测定了脂质过氧化的产物——丙二脂的生成,并证明阿魏酸钠对脂质过氧化的抑制。荧光偏振的结果指出,膜脂过氧化以后降低了膜脂的流动性。人红细胞用5DSA和16DSA标记并用ESR检测膜脂流动性,结果表明,序参数S几乎没有发生变化,旋转相关时间τ值的增加证明膜脂过氧化以后,疏水尾部的物理状态发生了改变。经脂质过氧化以后,红细胞膜中的不饱和脂防酸的减少,可能是降低膜脂流动性的原因之一。     

DNA sequence evidence for polymorphic forms of human serum amyloid A (SAA)

Serum amyloid A (SAA) is an acute-phase reactant and precursor to amyloid A protein, the major constituent of the fibril deposits of reactive amyloidosis. The factors determining whether the 104-amino acid SAA molecule is converted into the 76-amino acid amyloid A protein and deposited as fibrils are not known. As an initial step toward investigating the possibility that a particular primary structure of SAA is involved in amyloid formation, we have cloned and determined the nucleotide sequence of human SAA-specific cDNAs. The first clone, selected using an oligonucleotide probe, was shown to encode the signal peptide and amino-terminal region of SAA. The cDNA of this clone served as probe in the selection of two distinct, full-length SAA cDNAs, initially differentiated by the presence (pSAA21) or absence (pSAA82) of a PstI site in the coding sequence. The complete nucleotide sequence of pSAA82 cDNA was determined. Since there appear to be multiple human SAA alleles, it is conceivable that their differential expression is important to amyloid formation.     

Monoclonal antibody that inhibits infection of HeLa and rhabdomyosarcoma cells by selected enteroviruses through receptor blockade.

BALB/c mice were immunized with HeLa cells, and their spleen cells were fused with myeloma cells to produce hybridomas. Initial screening of culture fluids from 800 fusion products in a cell protection assay against coxsackievirus B3 (CB3) and the CB3-RD virus variant yielded five presumptive monoclonal antibodies with three specificities: protection against CB3 on HeLa, protection against CB3-RD on rhabdomyosarcoma (RD) cells, and protection against both viruses on the respective cells. Only one of the monoclonal antibodies (with dual specificity) survived two subclonings and was studied in detail. The antibody was determined to have an immunoglobulin G2a isotype and protected cells by blockade of cellular receptors, since attachment of [35S]methionine-labeled CB3 was inhibited by greater than 90%. The monoclonal antibody protected HeLa cells against infection by CB1, CB3, CB5, echovirus 6, and coxsackievirus A21 and RD cells against CB1-RD, CB3-RD, and CB5-RD virus variants. The monoclonal antibody did not protect either cell type against 16 other immunotypes of picornaviruses. The monoclonal antibody produced only positive fluorescence on those cells which were protected against infection, and 125I-labeled antibody confirmed the specific binding to HeLa and RD cells. The results suggest that this monoclonal antibody possesses some of the receptor specificity of the group B coxsackieviruses.     

Allometry in the placoderm Bothriolepis canadensis and its significance to antiarch evolution

A set of 18 measurements of the dermal armour of Bothriolepis canadensis Whiteaves (Placodermi, Anti-archa) is analysed with respect to allometric growth patterns. The strongest allometric patterns were found for the orbital fenestra and premedian plate of the head-shield. and the anterior median dorsal plate of the trunk-shield. These are all areas of the greatest importance in antiarch phylogeny and imply a role for ontogenetic effects such as paedomorphosis in the evolution of antiarchs. It is suggested that this is partly a result of the severe constraints on growth in a closed box such as the armour of placoderms, and may be generally true of such arrangements.