Plant-microbial interaction under gnotobiotic conditions: A scanning electron microscope study

Inoculation of canola seeds withPseudomonas putida GR12-2 stimulates root elongation under gnotobiotic conditions. Transformation ofP. putida GR12-2 with the broad-host-range plasmid pGSS15 abolishes the enhancement of root elongation. With scanning electron microscopy it was found that both transformed and nontransformedP. putida GR12-2 are capable of binding to canola seed coats. In addition, it was observed that 4 days after the initial inoculation the roots of bothP. putida GR12-2- and GR12-2/pGSS15-treated seedlings were free of adhering bacteria despite the fact that it was subsequently shown that both bacterial strains are capable of binding to roots. Thus, adhesion to roots is not necessary for the initial phase of enhanced root elongation that is induced byP. putida GR12-2 under gnotobiotic conditions.     

刺激中缝背核压抑大鼠小脑浦肯野细胞对苔状和爬行纤维传入的反应

本文在麻醉并制动的大鼠上观察了中缝背核(DR)条件刺激对由苔状和爬行纤维传入引起的小脑浦肯野细胞(PC)诱发反应的影响。主要结果有:(1)刺激大脑皮层感觉运动区可以引起苔状和爬行纤维向对侧小脑皮层第Ⅵ和Ⅶ小叶的传入,因而在该小叶上记录到 PC 的诱发简单锋电位(SS)和复杂锋电位(CS)反应,潜伏期分别是8—25和12—30ms。(2)以不影响PC 自发 SS 和 CS 活动的阈下强度刺激 DR,可显著地压抑 PC 对于刺激感觉运动皮层引起的苔状和爬行纤维兴奋所产生的诱发 SS 和 CS 反应,这种压抑作用可持续数百毫秒。(3)DR条件刺激对 PC 的诱发 SS 和 CS 反应的压抑作用可以被静脉注射5-HT 受体阻断剂羟甲丙基甲基麦角酰胺所减弱或阻断。上述结果表明 DR 的5-HT 能纤维传入可以降低苔状和爬行纤维对 PC 的突触作用效力,抑或降低 PC 对突触传入的反应敏感性,提示中缝-小脑5-HT,能纤维传入系统参与了小脑某些重要的神经活动过程。     

Identification of the products and nucleotide sequences of two regulatory genes involved in the exogenous induction of phosphoglycerate transport in Salmonella typhimurium.

We describe the determination of the nucleotide sequence of two genes (pgtB and pgtC) contained within the 3.4-kilobase DNA segment sandwiched between the transporter gene, pgtP, and the regulatory gene, pgtA. These two genes are involved in the regulation of expression of phosphoglycerate transport in Salmonella typhimurium. The sequence indicates the presence of two large open reading frames, potentially coding for two polypeptides of 397 and 593 amino acid residues. The two gene products were identified by using the bacteriophage T7 RNA polymerase-T7 promoter coupled system of Tabor and Richardson, and the observed apparent mass of 45 and 69 kilodaltons correlated well with the respective open reading frames. The cellular location of these two polypeptides was directly determined, and the polypeptides were found to be associated with the membrane. Although overall these polypeptides appear to be hydrophilic, there is one hydrophobic transmembrane segment in the smaller polypeptide and four such segments in the larger polypeptide which can account for their association with the membrane. In the accompanying paper, we present genetic evidence that pgtB and pgtC genes are involved in the induction of the pgtP expression by modulating derepressor activity.     

Macrophage colony-stimulating factor is produced by human T lymphoblastoid cell line, CEM-ON: identification by amino-terminal amino acid sequence analysis

A subclone, designated CEM-ON, derived from an azaguanine-resistant human leukemic T cell line, CEM-AG(R), constitutively secretes a colony-stimulating factor (CSF) which stimulates the production of macrophages from murine bone marrow progenitor cells. This CSF has been purified from serum-free conditioned medium. Highly purified CEM-ON CSF with a specific activity of 4.7 X 10(7) units/mg protein was obtained. Amino-terminal sequence analysis showed that the first 27 amino acids were identical to the amino-terminal sequence of the M-CSF (CSF-1) based on the cDNAs for human M-CSF. On SDS-PAGE analysis, CEM-ON CSF had an apparent molecular weight of 33,000-43,000; following reduction with 2-mercaptoethanol, this migrated as a 20,000-24,000 subunit, suggesting a homodimer structure. These results show that a human T cell line, CEM-ON, secretes M-CSF into its medium.     

Reduced cyclosporin accumulation in multidrug-resistant cells

Cyclosporin accumulation was reduced by 50% or more in multidrug- resistant CHRC5 CHO cells with high levels of P-glycoprotein expression compared to drug sensitive AuxB1 CHO cells. This difference could be overcome by verapamil which is known to interact with P-glycoprotein and reverse multidrug resistance. The difference in cyclosporin accumulation between sensitive and resistant cells decreased with increasing cyclosporin concentrations suggesting that cyclosporine itself regulated its own accumulation through interaction with P-glycoprotein. Indeed, cyclosporin also reversed differences in vinblastine accumulation between resistant and sensitive cell lines. Since P-glycoprotein is highly expressed in the kidney which is also a target for cyclosporin toxicity, the effects of verapamil on cyclosporin accumulation were studied in two renal cell lines, rat mesangial cells and LLCPK1, cells. Verapamil increased cyclosporin accumulation by approximately 70%. These results suggest that cellular cyclosporine accumulation is regulated at least in part by its interaction with P-glycoprotein.     

Antibodies to peptide determinants in transforming growth factor beta and their applications

Polyclonal antibodies have been raised to a series of synthetic peptides which correspond to essentially all regions of the transforming growth factor beta 1 (TGF-beta 1) molecule. All antisera were evaluated for their abilities to react with TGF-beta 1 and TGF-beta 2 in either the native or reduced form in enzyme-linked immunosorbent assays, Western blots, and immunoprecipitation assays. While all antisera demonstrated some ability to recognize TGF-beta 1 in these systems, there was limited cross-reactivity with TGF-beta 2, suggesting that substantial sequence or conformational differences exist between the two growth factors. On Western blots 5-10 ng of purified human platelet TGF-beta 1 could be detected when probed with affinity-purified peptide antisera generated against peptides corresponding to residues 48-77, 50-75, and 78-109 of the 112 amino acid TGF-beta 1 monomer. Antisera raised against peptides 50-75 and 78-109 were most effective in immunoprecipitating reduced and native 125I-TGF-beta 1, respectively. The antisera also were tested for their effectiveness in blocking the binding of 125I-TGF-beta 1 to its receptor. Anti-peptide 78-109 and anti-peptide 50-75 blocked 80% and 40% of the binding, respectively, while antibodies against amino-terminal peptides were without effect. These data suggest that the carboxyl-terminal region of TGF-beta 1 may play a significant role in the binding of the native ligand to its receptor.     

Fluorometric detection of the bilayer-to-hexagonal phase transition in liposomes

We have used the fluorescent probe N-(7-nitro-2,1,3-benzoxadiazol-4-yl)phosphatidylethanolamine (NBD-PE) to detect the bilayer-to-hexagonal phase transition. The fluorescence intensity of the probe was found to increase during the bilayer-to-hexagonal transition. The bilayer-to-hexagonal transitions of various types of phosphatidylethanolamine or cardiolipin measured by this method are consistent with results obtained by differential scanning calorimetry. To establish this method for wider use, agents known to alter the bilayer-to-hexagonal transition were examined, and the results are comparable with the published data. The added advantage of this fluorometric method over other currently available techniques is that it is applicable not only for aggregated lipid samples but also for dilute liposome suspensions. This is especially important when one of the components of the system under study can partition between lipid and aqueous phase. Since NBD is located near the headgroup region of the bilayer, it most likely detects the change of the environment surrounding that region. On the basis of our present study, it appears that NBD-PE is sufficiently sensitive to detect bilayer-to-hexagonal phase transition.