Multiple determinants influence root colonization and induction of induced systemic resistance by Pseudomonas chlororaphis O6

Colonization of the roots of tobacco by Pseudomonas chlororaphis O6 induces systemic resistance to the soft-rot pathogen, Erwinia carotovora ssp. carotovara SCC1. A screen of the transposon mutants of P. chlororaphis O6 showed mutants with about a fivefold reduction in ability to induce systemic resistance to the soft-rot disease. These mutations disrupted genes involved in diverse functions: a methyl-accepting chemotaxis protein, biosynthesis of purines, phospholipase C, transport of branched-chain amino acids and an ABC transporter. Additional mutations were detected in the intergenic spacer regions between genes encoding a GGDEF protein and fumarate dehydratase, and in genes of unknown function. The mutants in the ABC transporters did not display reduced root colonization. However, the other mutants had up to 100-fold reduced colonization levels. Generally the production of metabolites important for interactions in the rhizosphere, phenazines and siderophores, was not altered by the mutations. A reduced induction of systemic resistance by a purine biosynthesis mutant with a disrupted purM gene correlated with poor growth rate, lesser production of phenazines and siderophore and low levels of root colonization. These studies showed that multiple determinants are involved in the induction of systemic resistance, with there being a requirement for strong root colonization.     

Ceramide Inhibits Cell Proliferation through Akt/PKB Inactivation and Decreases Melanin Synthesis in Mel‐Ab Cells

Ceramide is a bioactive sphingolipid that mediates a variety of cell functions. However, the effects of ceramide on cell growth and the melanogenesis of melanocytes are not known. In the present study, we investigated the actions of cell‐permeable ceramide and its possible role in the signaling pathway of a spontaneously immortalized mouse melanocyte cell line, Mel‐Ab. Our results show that C₂‐ceramide inhibits DNA synthesis in Mel‐Ab cells and G361 human melanoma cells in a dose‐dependent manner. Cell cycle analysis confirmed the inhibition of DNA synthesis by a reduction in the S phase. To investigate the ceramide signaling pathway, we studied whether C₂‐ceramide is able to influence extracellular signal‐regulated kinase (ERK) and/or Akt/protein kinase B (PKB) activation. We demonstrated that phosphorylated Akt/PKB is decreased by C₂‐ceramide, whereas phosphorylated ERK was only slightly affected. Therefore, the C₂‐ceramide‐induced inactivation of Akt/PKB may be closely related to the reduced cell proliferation of Mel‐Ab cells. Furthermore, we assessed the effects of C₂‐ceramide on the pigmentation of Mel‐Ab cells. The results obtained showed that the melanin content of cells was significantly reduced by C₂‐ceramide at concentrations in the range of 1–10 μM, and that the pigmentation‐inhibiting effect of C₂‐ceramide is much greater than that of kojic acid at 1–100 μM. In addition, we found that the activity of tyrosinase is reduced by C₂‐ceramide treatment. Our results demonstrate that C₂‐ceramide reduces the pigmentation of Mel‐Ab cells by inhibiting tyrosinase activity.     

Fine needle aspiration cytology in the work-up of mammographic and ultrasonographic findings in breast cancer screening: an attempt at differentiating in situ and invasive carcinoma.

This study evaluated the results of fine needle aspiration cytology (FNAC) from the first four years of organized mammography screening for breast cancer in Oslo, particularly our policy in differentiating in situ and invasive carcinoma. Lesions were aspirated directly, ultrasound guided, by stereotaxic device or biopsy localization plate. All lesions were aspirated by cytopathologists working with the radiologists at the breast diagnostic centre. Smears were evaluated immediately for assessment of adequacy and a preliminary diagnosis was given to the surgeon. When FNAC revealed malignancy, diagnostic terms were as follows: (1) invasive carcinoma; (2) ductal carcinoma in situ of comedo type (high nuclear grade), cannot evaluate infiltration; (3) ductal carcinoma in situ of low nuclear grade and (4) papillary tumour, cannot evaluate infiltration. There were 953 cases, 70% of which were nonpalpable. Insufficient material was obtained in 5.8%. Absolute and complete sensitivity were 81% and 91%, respectively. Specificity was 85%. There were 448 histologically proven carcinomas. 383 of these were invasive. 362 carcinomas (in situ and invasive) (80.8%) were diagnosed directly on FNAC. Distinction between invasive and in situ carcinoma was possible in 294 of 320 directly diagnosed invasive carcinomas (91.8%). PPV of a diagnosis of invasive carcinoma was 97%. Our data showed that definitive cytological diagnosis of invasive carcinoma was possible in more than 90% of fully diagnostic smears and allowed definitive primary surgery in these women.     

Copper tolerance in the green alga, Chlorella vulgaris

Abstract. The effect of sub-lethal concentrations of copper upon tolerant and non-tolerant strains of Chlorella vulgaris was investigated. Copper concentrations of 0.2 and 0.4 mg dm⁻³ increased the lag phase of both strains, the effect being greater in the non-tolerant strain. No difference was observed in the toxicity of copper to the photosynthetic rates of the isolated chloroplasts of either strain. However, significant differences were shown at the whole cell level.
Lower copper uptake was shown by the tolerant cells. In both strains initial uptake of copper was followed by a phase of desorption before cell division occurred. In cultures of both strains the concentration of ionic copper was decreased by complexation with extracellular organic material. Over a 14 day growth period more organic material was produced by the tolerant cells. The organic material produced by the tolerant cell formed organo-copper complexes which had a higher conditional stability constant.
It is proposed that the cell wall acts as a barrier to copper in the tolerant cells and prevents copper from affecting cell metabolism. Organo-copper complexation occurs at this barrier and this complex is then released into the medium.     

A Molecular Genetic Approach to Understanding the Evolution of Immunoglobulin Gene Structure and Diversity

Immune function in higher vertebrates is mediated primarilyby multimeric glycoproteins found in the serum and on the surfacesof lymphoid cells. These molecules possess common structuralfeatures suggesting that they belong to a supergene family whichmay have originated from a common ancestral gene. Some multigenicmembers of the supergene family undergo unique forms of chromosomalrearrangement during somatic development. We have identifiedimmunoglobulin heavy chainvariable region (V_H) homologs in speciesrepresenting critical points in the vertebrate radiation, examinedtheir nucleotide sequences and found high degrees of organizationalhomology as well as localized regions of extended nucleotide(and amino acid) sequence identity with mammalian V_H genes.The unexpected high degree of nucleotide sequence identity suggeststhat within this multigene family, selection may be operatingat both the DNA and polypeptide levels.Using several differentapproaches, the V_H gene families in lower vertebrates have beenshown to be remarkably complex, discounting the possibilitythat a reduced number of germline genes accounts for the apparentlyrestricted natureof lower vertebrate immune responses. The lowervertebrate germline V_H genes possess prototypic recombinationsignal sequences, implicated in the somatic reorganization ofmammalian immunoglobulin variable region genes, and segmentalreorganizationresembling that seen in mammals has been observed in an elasmobranch.The detection of a recombination element flanked by short, directrepeats within the intervening sequence of one reptilian V_Hgene suggests that these sequences may be mobile, perhaps functioningoutside of the immunoglobulin loci in other developmental processes.The complex nature of the variable region gene families andtheir capacity to undergo structural change during somatic developmentsuggest that unique genetic mechanisms may govern their evolutionarystabilization and diversification.     

Temperature Effects on Maturity Periods in Tetrahymena pyriformis Syngen 1*

Cells of Tetrahymena pyriformis syngen 1 grown at 30 C after conjugation achieve sexual maturity more quickly than do cells grown at 19 C, whether time is measured in numbers of cell divisions or in terms of absolute time. This result is achieved regardless of the temperature at which conjugation and nuclear reorganization occur. These observations differ from those of other workers investigating Paramecium, and suggest that the long term “chronometer” is more tightly coupled to cell division in Paramecium multimicronucleatum and Paramecium caudatum than in Tetrahymena pyriformis.