IMPORTANCE OF REFERENCE STANDARDS IN TRAINING PANELISTS

When training a sensory evaluation panel, reference standards play an important role in developing appropriate terminology, establishing intensity ranges and showing the action of an ingredient. In addition, use of reference standards reduces the amount of training time while providing documentation for terminology. Product characteristics can be demonstrated through reference standards for application in plant quality assurance programs as well as for project planning in new product development, product maintenance (i.e., shelf-life), product improvement and cost reduction programs.     

Effects of Selection for Dark Respiration Rate on Enzyme Genotypes in Lolium perenne

Two lines of perennial ryegrass (Lolium perenne) that had previouslybeen selected for ‘fast’ and ‘slow’rates of leaf dark respiration were examined to determine whetherselection had differentiated allelic or genotypic frequenciesof five polymorphic enzyme loci, and determine whether respirationrates differed among genotypes. The lines were differentiatedfor genes coding for phosphoglucose isomerase (PGI) and UDP-glucosepyrophosphorylase (UDP). Respiration rates were heterogeneousamong UDP and 6-phosphogluconate dehydrogenase (6PGD) genotypes.Founder effects may have produced the genetic differentiationof lines at the PGI locus as we detected no differences amonggenotypes for respiration rates. The genetic differentiationamong lines for UDP was consistent with differences in darkrespiration among genotypes. Although we detected large differences(75%) in dark respiration rate among 6PGD genotypes in the fastrespiring line, selection did not differentiate the lines atthis locus. Lolium perenne L., perennial ryegrass, enzyme polymorphisms, dark respiration rate     

Genetic and ecotypic structure of a fluorescent Pseudomonas population

Fluorescent pseudomonads are among the most numerous bacteria found on plant surfaces and the activity of certain isolates can affect plant growth. In 1993, 108 fluorescent Pseudomonas isolates were collected on a single sampling occasion from the leaves of sugar beet plants grown at the Oxford University Field Station, Wytham. Isolates were obtained from 54 different leaves, from nine plants, and characterized using 10 allozyme and 23 biotype markers. Statistical analysis of the combined data revealed five biotypic traits which permitted a rational classification of the sample. Analysis of the allozyme data showed that the population was in overall linkage disequilibrium. Clonality was also observed after subdivision of allozyme data along spatial and habitat levels. However, two genetically defined subgroups were in linkage equilibrium which suggests the possibility of frequent large-scale recombination among certain isolates. A significant correlation between isolate distribution and habitat (leaf type and plot) indicates that the population has ecotypic structure.     

In Vitro Tryptophan Catabolism by Leishmania donovani donovani Promastigotes

ABSTRACT. Metabolism of tryptophan by promastigotes of Leishmania donovani donovani was investigated in cells suspended in a simple buffer solution supplemented with glucose. Metabolites from supernatant and lysed cell pellets were analyzed by capillary gas liquid chromatography and ¹³C nuclear magnetic resonance spectroscopy, with structural confirmation by gas liquid chromatography-mass spectrometry. Tryptophan does not appear to serve as a carbon energy source for L. d. donovani promastigotes since parasites could survive for only short periods in buffer containing tryptophan without glucose, levels of tricarboxylic acid cycle intermediates remained unchanged in the presence of added tryptophan and label from [¹³C]tryptophan was not detected in any of the intermediates. Leishmania d. donovani catabolized l -tryptophan via aminotransferase and aromatic lactate dehydrogenase reactions to form one major end product, indole-3-lactic acid. The activity of aromatic lactate dehydrogenase required manganese and was NADH-dependent in these organisms that lack lactate dehydrogenase. Promastigotes taken from the mid-log stage of growth produced higher concentrations of indole-3-lactic acid than those from the stationary stage. Conservation of a similar tryptophan catabolic pathway among four Leishmania species suggests the pathway is physiologically important to the parasites themselves.