QUANTITATIVE GENETICS OF RESPONSE TO COMPETITORS IN NEMOPHILA MENZIESII: A GREENHOUSE STUDY

To determine the potential for adaptation to a local biotic environment, we examined the magnitude and nature of genetic variation in response to neighboring plants within a natural population of the native California annual, Nemophila menziesii. A total of 22 plants from a natural population were crossed in three reciprocal factorials. The progeny were grown in a greenhouse in nine treatments that varied in conspecific density and in the density of a naturally co-occurring grass species, Bromus diandrus. Increasing the density of each species significantly reduced individual survival, fruit number, and dry weight. Among survivors, we found small to moderate heritability of dry weight within treatments. Additive genetic correlations (r_A) of dry weight between competitive regimes were generally large and positive. In no case were they significantly different from 1, as expected under the null hypothesis that the relative performance of the genotypes under consideration is the same in all environments. On the basis of these results, we cannot conclude that the structure of genetic covariation within this population would promote genetic differentiation in response to locally varying conditions of density of these two species. Aspects of the experiment that may have compromised our ability to detect r_A differing from 1 are discussed.     

Isolation and properties of a soluble sialidase from the culture fluid of Chinese hamster ovary cells

A Soluble sialidase that can degrade recombinant glycoproteinsexpressed in Chinese hamster ovary (CHO) cells has been isolatedand purified to near homogeneity from the cell culture fluidof this host. Purification of     

Are the spatial patterns of weeds scale-invariant?

In previous empirical and modelling studies of rare species and weeds, evidence of fractal behaviour has been found. We propose that weeds in modern agricultural systems may be managed close to critical population dynamic thresholds, below which their rates of increase will be negative and where scale-invariance may be expected as a consequence. We collected detailed spatial data on five contrasting species over a period of three years in a primarily arable field. Counts in 20×20 cm contiguous quadrats, 225,000 in 1998 and 84,375 thereafter, could be re-structured into a wide range of larger quadrat sizes. These were analysed using three methods based on correlation sum, incidence and conditional incidence. We found non-trivial scale invariance for species occurring at low mean densities and where they were strongly aggregated. The fact that the scale-invariance was not found for widespread species occurring at higher densities suggests that the scaling in agricultural weed populations may, indeed, be related to critical phenomena.     

An alternate model of thyroid cytology: practical not perfect

A sample of 384 thyroid cytology specimens prepared by cytospin over a 2.5-year period was classified by original report into inadequate, non-neoplastic and suspicious of neoplasia or worse. This was then compared with subsequent histology. The resulting data showed an inadequacy rate of 33%, a sensitivity of 55%, a specificity of 59%, a positive predictive value of 64% and a negative predictive value of 93%. On review of the cytology, in knowledge of the subsequent histology, the maximum achievable results were determined to have a positive predictive value of 79% and a negative predictive value of 97%. No clinically significant adverse event was detected.     

Overlapping substrate specificities of benzaldehyde dehydrogenase (the xylC gene product) and 2-hydroxymuconic semialdehyde dehydrogenase (the xylG gene product) encoded by TOL plasmid pWW0 of Pseudomonas putida.

Two aldehyde dehydrogenases involved in the degradation of toluene and xylenes, namely, benzaldehyde dehydrogenase and 2-hydroxymuconic semialdehyde dehydrogenase, are encoded by the xylC and xylG genes, respectively, on TOL plasmid pWW0 of Pseudomonas putida. The nucleotide sequence of xylC was determined in this study. A protein exhibiting benzaldehyde dehydrogenase activity had been purified from cells of P. putida (pWW0) (J. P. Shaw and S. Harayama, Eur. J. Biochem. 191:705-714, 1990); however, the amino-terminal sequence of this protein does not correspond to that predicted from the xylC sequence but does correspond to that predicted from the xylG sequence. The protein purified in the earlier work was therefore 2-hydroxymuconic semialdehyde dehydrogenase (the xylG gene product). This conclusion was confirmed by the fact that this protein oxidized 2-hydroxymuconic semialdehyde (kcat/Km = 1.6 x 10(6) s-1 M-1) more efficiently than benzaldehyde (kcat/Km = 3.2 x 10(4) s-1 M-1). The xylC product, the genuine benzaldehyde dehydrogenase, was purified from extracts of P. putida (pWW0-161 delta rylG) which does not synthesize 2-hydroxymuconic semialdehyde dehydrogenase. The amino-terminal sequence of the purified protein corresponds to the amino-terminal sequence deduced from the xylC sequence. This enzyme efficiently oxidized benzaldehyde (kcat/Km = 1.7 x 10(7) s-1 M-1) and its analogs but did not oxidize 2-hydroxymuconic semialdehyde or its analogs.     

Detection of a 65 kDaras binding protein in rat and sheep brain cytosol using a chemical cross linking agent

The ability of aras protein to associate with proteins present in rat brain cytosolin vitro was investigated using chemical cross-linking agents and the¹²⁵I-labelled v-H-ras protein. Two iodinated protein complexes with apparent molecular weights of 40 and 85 kDa were observed when a mixture of rat brain cytosol and [¹²⁵I]ras was treated with the cross-linking agent disuccinimidyl suberate and subjected to SDS-PAGE. Formation of the [¹²⁵I] 85 kDa complex was enhanced by a high concentration of EDTA while generation of the 40 kDa species was abolished by this treatment. Formation of the [¹²⁵I] 85 kDa complex was inhibited by unlabelledras protein, GTP, GTPS, and GDP but not by ATPS and GMP.Chromatography of the cross-linked brain cytosol-[¹²⁵I]ras mixture on DEAE cellulose partially resolved the [¹²⁵I] 85 kDa complex from the [¹²⁵I]ras protein. The [¹²⁵I] 85 kDa complex (formed using ethyleneglycolbis (succinimidylsuccinate) as the cross-linking agent) could be immunoprecipitated using a rabbit anti-ras polyclonal antibody. Treatment of the immunoprecipitate with hydroxylamine to cleave the cross-link yielded [¹²⁵I]-labelledras. A substantial enrichment of the proportion of the [¹²⁵I] 85 kDa complex in the cross-linked extract was achieved by preparative SDS-PAGE. It is concluded that thein vitro chemical cross-linking approach employed here has detected tworas binding proteins in rat brain cytosol: a 65 kDa heat-sensitive and a 20 kDa heat-stable protein. The possibility that the 65 kDaras binding protein is aras regulatory orras effector protein which has not so far been characterised is briefly discussed.Abbreviations DSS disuccinimidyl suberate - EGS ethyleneglycolbis (succinimidylsuccinate) - GTPS guanosine 5-[-thio] triphosphate - ATPS adenosine 5-[-thio] triphosphate     

Autoradiographic localization of ornithine decarboxylase in mouse kidney by use of radiolabeled α-difluoromethylornithine

Summary Ornithine decarboxylase, a key enzyme in polyamine biosynthesis and cell growth, has been localized in mouse kidney by autoradiography after administration of radiolabeled -difluoromethylornithine. This drug is an enzyme-activated irreversible inhibitor of ornithine decarboxylase and forms a covalent bond with the enzyme. It was found that ornithine decarboxylase is present in all cell types studied but that the highest content occurs in the proximal convoluted tubules followed by the distal convoluted tubules and the collecting tubules. The majority of the enzyme is located in the cytoplasm but about 10–15% is present in the nuclei (often associated with nucleolus-like components) of the cells of the proximal and distal convoluted tubules. The labeled ornithine decarboxylase was lost rapidly from both nucleus and cytoplasm of all the cell types examined, and labeling by radioactive -difluoromethylornithine was greatly reduced if the mice were pretreated for 5 h with cycloheximide to block protein synthesis. These results indicate that ornithine decarboxylase turns over rapidly in all of the cells.