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排序方式: 共有266条查询结果,搜索用时 171 毫秒
261.
J Korteland N Overbeeke P de Graaff P Overduin B Lugtenberg 《European journal of biochemistry》1985,152(3):691-697
In order to study the structure-function relationship of the PhoE protein pore we have isolated five independent, TC45-resistant, phoE mutants all of which appeared to produce normal amounts of an electrophoretically altered PhoE protein, designated as PhoE* protein. Nucleotide sequence analysis of the DNA fragments carrying the mutations showed that the mutations all correspond to a G.C to A.T transition at the same place within the phoE gene resulting in a deduced change of amino acid residue arginine 158 into histidine. This result shows that the arginine 158 residue plays an important role in the interaction of the PhoE protein pore with phage TC45. Moreover, studies on the channel properties of the PhoE* protein showed that the PhoE channel has lost part of its preference for negatively charged solutes, as a result of the arginine to histidine change. The results are discussed in terms of the structure-function relationship of PhoE protein as well as in terms of the topological organization of the protein channel in the outer membrane. 相似文献
262.
1. Omnivorous predators can protect plants from herbivores, but may also consume plant material themselves. Omnivores and their purely herbivorous prey have previously been thought to respond similarly to host‐plant quality. However, different responses of omnivores and herbivores to their shared host plants may influence the fitness, trophic identity, and population dynamics of the omnivores. 2. The aim of the present study was to show that an omnivorous heteropteran (Anthocoris nemorum L.) and two strictly herbivorous prey species respond differently to different genotypes of their shared host plant, Salix. Some plant genotypes were sub‐optimal for the omnivore, although suitable for the herbivores, and vice versa. 3. The contrasting patterns of plant suitability for the omnivore and the herbivores highlight an interaction between plant genotype and omnivores' access to animal food. Plant genotypes that were sub‐optimal for the omnivore when herbivores were experimentally excluded became the best host plants when herbivores were present, as in the latter situation additional prey became available. By contrast, the quality of plant genotypes that were intrinsically suitable for omnivores, did not improve when herbivores were present as these plant genotypes were intrinsically sub‐optimal for herbivores, thus providing omnivores with almost no additional animal food. 4. The differential responses of omnivores and their prey to the same host‐plant genotypes should allow omnivores to colonise sub‐optimal host plants in their capacity as predators, and to colonise more suitable host plants in their capacity as herbivores. It may thus be difficult for Salix to escape herbivory entirely, as it will rarely be unsuitable for both omnivores and pure herbivores at the same time. 相似文献
263.
Ron R. van Eijsden Flip J. Hoedemaeker Clara L. Díaz Ben J. J. Lugtenberg B. Sylvia de Pater Jan W. Kijne 《Plant molecular biology》1992,20(6):1049-1058
As part of a strategy to determine the precise role of pea (Pisum sativum) lectin, Psl, in nodulation of pea by Rhizobium leguminosarum, mutations were introduced into the genetic determinant for pea lectin by site-directed mutagenesis using PCR. Introduction of a specific mutation, N125D, into a central area of the sugar-binding site resulted in complete loss of binding of Psl to dextran as well as of mannose/glucose-sensitive haemagglutination activity. As a control, substitution of an adjacent residue, A126V, did not have any detectable influence on sugar-binding activity. Both mutants appeared to represent normal Psl dimers with a molecular mass of about 55 kDa, in which binding of Ca2+ and Mn2+ ions was not affected. These results demonstrate that the NHD2 group of Asn125 is essential in sugar binding by Psl. To our knowledge, Psl N125D is the first mutant legume lectin which is unable to bind sugar residues. This mutant could be useful in the identification of the potential role of the lectin in the recognition of homologous symbionts. 相似文献
264.
265.
L van Alphen W van Alphen A Verkleij B Lugtenberg 《Biochimica et biophysica acta》1979,556(2):233-243
The hypothesis that intramembraneous particles, observed in the outer membrane of Escherichia coli by freeze-fracture electron microscopy, are the morphological representation of aqueous pores, was tested. A mutant which is deficient in five major outer membrane proteins, b, c, d, e and the phage lambda receptor protein, contains a largely decreased number of intramembraneous particles and also shows a greatly decreased rate of uptake of several solutes. In derivatives of this strain which contain only one of these proteins in large amounts a strong decrease of the number of intramembraneous particles is observed, which is accompanied by a complete restoration of the rate of uptake of those solutes which use pores in which the protein in question is involved. The results provide strong evidence for the notion that an individual pore contains only one protein species, a property which has been found earlier for individual particles. The observed correlation between particles and equeous pores strongly supports the hypothesis that the particles are the morphological representation of pores. Implications of this hypothesis for the structure of the particles are discussed. 相似文献
266.
S. A. J. Zaat A. A. N. Van Brussel T. Tak B. J. J. Lugtenberg J. W. Kijne 《Planta》1989,177(2):141-150
Nodulation of Vicia sativa subsp. nigra L. by Rhizobium bacteria is coupled to the development of thick and short roots (Tsr). This root phenotype as well as root-hair induction (Hai) and root-hair deformation (Had) are caused by a factor(s) produced by the bacteria in response to plant flavonoids. When very low inoculum concentrations (0.5–5 bacteria·ml-1) were used, V. sativa plants did not develop the Tsr phenotype and became nodulated earlier than plants with Tsr roots. Furthermore, the nodules of these plants were located on the primary root in contrast to nodules on Tsr roots, which were all located at sites of lateral-root emergence. The average numbers of nodules per plant were not significantly different for these two types of nodulation. Root-growth inhibition and Hai, but not Had, could be mimicked by ethephon, and inhibited by aminoethoxyvinylglycine (AVG). Addition of AVG to co-cultures of Vicia sativa and the standard inoculum concentration of 5·105 bacteria·ml-1 suppressed the development of the Tsr phenotype and restored nodulation to the pattern that was observed with very low concentrations of bacteria (0.5–5 bacteria·ml-1). The delay in nodulation on Tsr roots appeared to be caused by the fact that nodule meristems did not develop on the primary root, but only on the emerging laterals. The relationship between Tsr, Hai, Had, and nodulation is discussed.Abbreviations AVG
aminoethoxyvinylglycine
- cfu
colonyforming units
- Had
root-hair deformation
- Hai
root-hair induction
- NB
naringenin-bacteria filtrate
- Tsr
Thick and short roots 相似文献