Iron transport-mediated antagonism between plant growth-promoting and plant-deleterious Pseudomonas strains

Both plant growth-promoting Pseudomonas B10 and its yellow-green, fluorescent iron transport agent (siderophore) pseudobactin enhance potato growth and biologically control certain soil-borne fungal diseases in part by depriving specific root-colonizing endemic microorganisms including phytopathogens of iron(III), thus inhibiting their growth. The present study examines this mode of iron deprivation. The growth inhibition of certain bean-deleterious fluorescent pseudomonads by specific bean-beneficial fluorescent pseudomonads is due in part to the inability of susceptible strains to utilize siderophores from beneficial strains to transport iron(III). Conversely, deleterious strains which were able to utilize siderophores from beneficial strains were not inhibited. The ability of a given pseudomonad to utilize another pseudomonad's siderophore may depend upon its possessing a specific outer membrane receptor protein for that pseudomonad's ferric siderophore. Siderophore-mediated competition for iron in microbial systems appears to be a widespread phenomenon.     

单面针的生物碱研究

自芸香科(Rutaceae)花椒属植物单面针(Zanthoxylum nitidum var. fastuosum How ex Huang)的根皮中分得五种已知生物碱:乙氧基白屈菜红碱(ethoxychelerythrine)(Ⅰ);氯化光花椒碱(nitidine chloride)(Ⅱ);去甲基白屈菜红碱(des-N-methychelerythrine)(Ⅲ);α—别隐品碱(α-allocryptopine)(Ⅳ);鹅掌揪宁(liriodenine)(Ⅴ).     

悼念李世英教授

中国植物生态学与地植物学家,中国植物学会理事,《植物生态学与地植物学学报》常务编委,中国科学院植物研究所研究员李世英同志,因患鼻咽癌,经多方长期治疗无效,于1985年12月17日零点在北京逝世,终年64岁。李世英同志1945年毕业于前中央大学。研究生肄业后,就职于前巾央林业实验所,从     

利用单克隆抗体鉴定人甲胎蛋白(HAFP)抗原结构可分性

本文利用两株针对HAFP分子不同抗原决定簇的单克隆抗体,鉴定HAFP酶解片断的抗原抗体反应性质,并同完整HAFP分子进行比较。结果表明,酶解片断上失去了一株单克隆抗体所对应的分子部份,完整保留着另一株单克隆抗体所识别的抗原决定簇,从而证实HAFP分子某些抗原结构之间具有可分割性。     

Degradation of Dehydrodivanillin by Anaerobic Bacteria from Cow Rumen Fluid

Dehydrodivanillin (DDV; 0.15 g/liter) was biodegradable at 37°C under strictly anaerobic conditions by microflora from cow rumen fluid to the extent of 25% within 2 days in a yeast extract medium. The anaerobes were acclimated on DDV for 2 weeks, leading to DDV-degrading microflora with rates of degradation eight times higher than those initially. Dehydrodivanillic acid and vanillic acid were detected in an ethylacetate extract of a DDV-enriched culture broth by thin-layer, gas, and high-performance liquid chromatographies and by mass spectrometry.     

Chemical transformation of eremofortin C into PR toxin.

The natural products of both eremofortin C (EC) and PR toxin are secondary metabolites of Penicillium roqueforti. Because the chemical structures of EC and PR toxin are closely related to each other and differ only by a hydroxyl functional group in EC and an aldehyde functional group in PR toxin at the C-12 position, the chemical transformation of EC into PR toxin was investigated. Oxidation with a chromic anhydride-pyridine complex was found to be the most satisfactory method.     

Covalent structure of three phase-1 flagellar filament proteins of Salmonella

Using recombinant DNA techniques, the covalent structure was determined for three flagellar filament proteins produced by Salmonella serotypes with phase-1 antigens a, c and d. Comparison of the results obtained, together with previous results for antigen i, indicated an overall structure in which conservation of amino acid sequence was absolute at both ends of the molecule and proceeded inwards with progressively greater variation. Very few differences in nucleotide sequence were detected in regions of amino acid conservation, which suggested that these areas of the gene may be involved in regulatory functions.     

Channel formation in phospholipid bilayer membranes by the toxin ofHeminthosporium maydis,race T

Summary Southern Corn Leaf Blight is caused by a toxin produced by a virulent form ofHelminthosporium maydis (Race T). The toxin has been shown to uncouple oxidative phosphorylation and dissipate Ca²⁺ gradients in mitochondria isolated from susceptible, but not resistant, corn. The possibility that the toxin acted by increasing the permeability of membranes to ions was tested using a planar bilayer membrane system. Addition of the toxin to the bilayer system, under voltage-clamp conditions, resulted in stepwise increases in current across the phospholipid bilayer, a response characteristic for channel formers. Single-channel conductance in 1m KCl is 27 pS which corresponds to 1.7×10⁷ ions sec^–1 channel^–1 at 100 mV applied potential. The toxin channels are: (i) fairly uniform in conductance, (ii) ideally selective for K⁺ over Cl^–, and (iii) most conductive to H⁺. The channel showed the following selectivity for alkali metal cations: Rb⁺>K⁺>Cs⁺>Na⁺>Li⁺ (169731) based on the most frequently observed conductance in 1m chloride salts. The toxin showed no voltage dependence over the range of –100 to +100 mV. Channel formation was also a property of a synthetic analog (Cmpd IV) of the toxin. The ability of the native toxin to form channels may be a mode of toxin action on mitochondrial membranes from susceptible corn.     

Relationship between bacteriophage T4 and T6 DNA topoisomerases. T6 39-protein subunit is equivalent to the combined T4 39- and 60-protein subunits

T6 DNA topoisomerase has been purified from bacteriophage T6 infected Escherichia coli. Unlike the T4 DNA topoisomerase which has three subunits, it consists of two subunits of molecular weights 75,000 and 51,000. They are the products of T6 genes 39 and 52, respectively. The purified T6 enzyme can stimulate in vitro T6 DNA replication. It has an ATP-dependent DNA relaxation activity similar to the T4 enzyme. Either ATP or dATP can be used in both reactions. Using a "Western blotting" and radioimmuno-detection methods, we show that T6 39 subunit contains protein sequences specified by both the T4 39 and 60 genes. The 52-proteins of both phages appear to be identical. The T4 and T6 topoisomerase genes represent a naturally occurring example of gene separation or fusion.