Water Balance in Cucumis Plants, Measured by Nuclear Magnetic Resonance, II

Nuclear magnetic resonance (NMR) was used to investigate theeffects of changes in root temperature, of changes in the areaof root in contact with culture solution and of day/night rhythmon the water balance of a cucumber and a gherkin plant. Resultsare discussed in terms of water potential, flow rate and resistanceusing a previously presented model of water balance. As longas water uptake alone is varied, flow rate and water content(or potential) will change in the same direction. In contrast,from that model it is predicted that changes in transpirationwill affect flow rate and water content in opposite ways. Anexperimental verification of this prediction was given in theprevious paper. Results obtained by the NMR method are comparedto those determined using a dendrometer. The results demonstratethat the NMR method is a valuable tool to study plant waterbalance and that it can serve as a technique for discriminatingbetween changes in plant water balance that are due to changesin water uptake by roots and those due to changes in transpiration. Key words: Water balance model, Cucumis satious L., flow, water content, NMR, water balance measurement     

A method for the enrichment of auxotrophic mutants of Serratia marcescens with the antibiotic azthreonam

A new method for the enrichment of cultures of Serratia marcescens for auxotrophic mutants has been developed. The method is based on the formation of filaments by growing cells in minimal medium M70 containing azthreonam. Auxotrophic mutants unable to grow in M70 do not form filaments. Mutants are collected from the culture by filtration.     

Cloning, expression, purification, and characterization of the acid alpha-mannosidase from Trypanosoma cruzi

The acid alpha-mannosidase of Trypanosoma cruzi is a broad-specificity hydrolase involved in the catabolism of glycoconjugates, presumably in the digestive vacuole. We have cloned the alpha-mannosidase gene from a T.cruzi epimastigote genomic library. The alpha-mannosidase gene was determined to be single copy by Southern analysis, and similar sequences were not detected in genomic digests of either Trypanosoma brucei or Leishmania donovani. The coding region was subcloned into the Pichia pastoris expression vector pPICZ, and alpha-mannosidase activity was detected in the medium of induced cultures. The recombinant alpha- mannosidase demonstrated a pH optimum, inhibition by swainsonine, Km, and substrate specificity consistent with the characteristics of the alpha-mannosidase previously purified from T.cruzi epimastigotes. The recombinant enzyme was purified 103-fold from the culture medium of Pichia pastoris and had a native molecular mass of 359 kDa by gel filtration. A combination of SDS-PAGE, deglycosylation with endo H, and NH2-terminal sequencing indicates that the enzyme is originally synthesized as a homodimeric polypeptide that is subsequently cleaved to form a heterotetramer composed of 57 and 46 kDa subunits. A polyclonal antibody raised to the recombinant enzyme was shown to immunoprecipitate the alpha-mannosidase from T.cruzi cell extracts and will be used in future immunolocalization studies.      

Aspergillus terreus and its toxic metabolites as a food contaminant in some Egyptian Bakery products and grains

A. terreus isolates isolated from some bakery products, corn and rice were found to be able to produce territrems. 90% of theA. terreus isolated from bakery products were able to produce territrem A, with a mean of 0.09 ppm, while 80% ofA. terreus isolates produce territrem B with a mean of 0.24 ppm. On the other hand 31.8% of the isolates ofA. terreus from corn were able to produce territrem A with a mean of 0.44 ppm. ConcerningA. terreus isolates from rice, 66.7% were found to produce territrem A, with a mean of 5.28 ppm, and 77.8% of the isolates produced territrem B with a mean of 1.79 ppm.     

Evolutionary history of the COII/tRNALys intergenic 9 base pair deletion in human mitochondrial DNAs from the Pacific

Length changes in human mitochondrial DNA (mtDNA) are potentially useful markers for inferring the evolutionary history of populations. One such length change is a nine base pair (9-bp) deletion that is located in the intergenic region between the COII gene and the Lysine tRNA gene (COII/tRNALys intergenic region). This deletion has been used as a genetic marker to trace descent from peoples of East Asian origin. A geographic cline of the deletion frequency across modern Pacific Islander populations suggests that the deletion may be useful for tracing prehistoric Polynesian origins and affinities. Mitochondrial DNA sequence variation within two variable segments of the control region (CR) permits a number of inferences regarding the evolutionary history of the 9-bp deletion that cannot be determined from frequency data alone. We obtained CR sequences from 74 mtDNAs with the 9-bp deletion from Indonesia, coastal Papua New Guinea (PNG), and American Samoa. Phylogenetic and pairwise distribution analysis of these CR sequences pooled with previously published CR sequences reveals that the deletion arose independently in Africa and Asia and suggests possible multiple origins of the deletion in Asia. A clinal increase of the frequency of the 9-bp deletion across the three Pacific populations is associated with a decrease in CR sequence diversity, consistent with founder events. Furthermore, analysis of pairwise difference distributions indicates an expansion time of proto-Polynesians that began 5,500 yr ago from Southeast Asia. These results are consistent with the express train model of Polynesian origins.      

SIMPROT: Using an empirically determined indel distribution in simulations of protein evolution

Background  

General protein evolution models help determine the baseline expectations for the evolution of sequences, and they have been extensively useful in sequence analysis and for the computer simulation of artificial sequence data sets.     

Restriction of de novo nucleotide biosynthesis interferes with clonal expansion and differentiation into effector and memory CD8 T cells

Nucleotide synthesis inhibitors are currently used in neoplastic diseases or as immunosuppressive agents for the prevention of acute rejection in organ transplantation and the treatment of autoimmune disorders. We have previously described that these inhibitors interfere with proliferation and survival of primary T cells in vitro. However, the precise effects of nucleotide restriction on effector and memory functions have not been elucidated. In this study, we investigated the impact of nucleotide synthesis inhibition on CD8 T cell differentiation by using TCR transgenic mice (F5) specific for the influenza virus nucleoprotein 68 peptide presented on the H-2Db molecule. Our results show that methotrexate and 5-fluorouracil prevent the acquisition of effector functions, such as IFN-gamma, granzyme B expression, and cytotoxic function following antigenic stimulation of naive cells. Surprisingly, in the presence of mycophenolate mofetil, activated F5 cells are still able to produce granzyme B and to kill target cells but to a lesser extent compared with control. All three inhibitors interfere with the differentiation of naive cells into memory CD8 T cells. In contrast, the drugs are unable to inhibit the development of improved cytotoxic functions displayed by memory CD8 T cells.