Evaluation of Food Additives and Low-toxicity Compounds for the Control of Bean Rust and Wheat Leaf Rust

The efficacy of low‐toxicity chemicals as possible alternatives to synthetic fungicides for the control of Uromyces appendiculatus and Puccinia triticina was evaluated. A preliminary selection of food additives was performed through in vitro and in vivo preliminary screenings. The ED₅₀ and minimum inhibition concentration (MIC) values showed that most of the food additives used in this study were more toxic to U. appendiculatus than to P. triticina. Acetic acid, potassium carbonate, sodium carbonate and sodium molybdate were the food additives that were more toxic to the urediniospores of P. triticina. Selected compounds and concentrations were tested on bean and wheat plants grown in pots under controlled conditions. Acetic acid, ammonium bicarbonate, potassium acetate, potassium benzoate, potassium bicarbonate, potassium carbonate, sodium acetate and sodium citrate at 0.03, 0.09, 0.03, 0.006, 0.012, 0.012, 0.03 and 0.03 m , respectively, significantly reduced the disease severity of U. appendiculatus without causing any injury to bean leaves. Ammonium bicarbonate, potassium bicarbonate, sodium bicarbonate and sodium citrate at 0.12, 0.03, 0.12 and 0.03 m , respectively, were the most effective in reducing the disease severity caused by P. triticina without causing any injury to wheat leaves.     

Photoelectron imaging of viruses and DNA: evaluation of substrates by unidirectional low angle shadowing and photoemission current measurements.

Photoelectron imaging (photoelectron emission microscopy, PEM or PEEM) is a promising high resolution surface-sensitive technique for biophysical studies. At present, image quality is often limited by the underlying substrate. For photoelectron imaging, the substrate must be electrically conductive, low in electron emission, and relatively flat. A number of conductive substrate materials with relatively low electron emission were examined for surface roughness. Low angle, unidirectional shadowing of the specimens followed by photoelectron microscopy was found to be an effective way to test the quality of substrate surfaces. Optimal results were obtained by depositing approximately 0.1 nm of platinum-palladium (80:20) at an angle of 3 degrees. Among potential substrates for photoelectron imaging, silicon and evaporated chromium surfaces were found to be much smoother than evaporated magnesium fluoride, which initially appeared promising because of its very low electron emission. The best images were obtained with a chromium substrate coated with a thin layer of dextran derivatized with spermidine, which facilitated the spreading and adhesion of biomolecules to the surfaces. Making use of this substrate, improved photoelectron images are reported for tobacco mosaic virus particles and DNA-recA complexes.     

Cell cycle regulation of the c-Myc transcriptional activation domain.

The product of the c-myc gene (c-Myc) is a sequence-specific DNA-binding protein that has previously been demonstrated to be required for cell cycle progression. Here we report that the c-Myc DNA binding site confers cell cycle regulation to a reporter gene in Chinese hamster ovary cells. The observed transactivation was biphasic with a small increase in G1 and a marked increase during the S-to-G2/M transition of the cell cycle. This cell cycle regulation of transactivation potential is accounted for, in part, by regulatory phosphorylation of the c-Myc transactivation domain. Together, these data demonstrate that c-Myc may have an important role in the progression of cells through both the G1 and G2 phases of the cell cycle.     

Effects of temperature and photoperiod on development and oviposition of the legume flower thrips, Megalurothrips sjostedti

Chrysomya albiceps, the larvae of which are facultative predators of larvae of other dipteran species, has been introduced to the Americas over recent years along with other Old World species of blowflies, including Chrysomya megacephala, Chrysomya putoria and Chrysomya rufifacies. An apparent correlate of this biological invasion has been a sudden decline in the population numbers of Cochliomyia macellaria, a native species of the Americas. In this study, we investigated predation rates on third instar larvae of C. macellaria, C. putoria and C. megacephala by third instar larvae of C. albiceps in no-choice, two-choice and three-choice situations. Most attacks by C. albiceps larvae occurred within the first hour of observation and the highest predation rate occurred on C. macellaria larvae, suggesting that C. albiceps was more dangerous to C. macellaria than to C. megacephala and C. putoria under these experimental conditions. The rates of larvae killed as a result of the predation, as well as its implications to population dynamics of introduced and native species are discussed.     

Chlorophenol Hydroxylases Encoded by Plasmid pJP4 Differentially Contribute to Chlorophenoxyacetic Acid Degradation

Phenoxyalkanoic compounds are used worldwide as herbicides. Cupriavidus necator JMP134(pJP4) catabolizes 2,4-dichlorophenoxyacetate (2,4-D) and 4-chloro-2-methylphenoxyacetate (MCPA), using tfd functions carried on plasmid pJP4. TfdA cleaves the ether bonds of these herbicides to produce 2,4-dichlorophenol (2,4-DCP) and 4-chloro-2-methylphenol (MCP), respectively. These intermediates can be degraded by two chlorophenol hydroxylases encoded by the tfdB_I and tfdB_II genes to produce the respective chlorocatechols. We studied the specific contribution of each of the TfdB enzymes to the 2,4-D/MCPA degradation pathway. To accomplish this, the tfdB_I and tfdB_II genes were independently inactivated, and growth on each chlorophenoxyacetate and total chlorophenol hydroxylase activity were measured for the mutant strains. The phenotype of these mutants shows that both TfdB enzymes are used for growth on 2,4-D or MCPA but that TfdB_I contributes to a significantly higher extent than TfdB_II. Both enzymes showed similar specificity profiles, with 2,4-DCP, MCP, and 4-chlorophenol being the best substrates. An accumulation of chlorophenol was found to inhibit chlorophenoxyacetate degradation, and inactivation of the tfdB genes enhanced the toxic effect of 2,4-DCP on C. necator cells. Furthermore, increased chlorophenol production by overexpression of TfdA also had a negative effect on 2,4-D degradation by C. necator JMP134 and by a different host, Burkholderia xenovorans LB400, harboring plasmid pJP4. The results of this work indicate that codification and expression of the two tfdB genes in pJP4 are important to avoid toxic accumulations of chlorophenols during phenoxyacetic acid degradation and that a balance between chlorophenol-producing and chlorophenol-consuming reactions is necessary for growth on these compounds.     

Production of a Novel Extracellular Polysaccharide by Lactobacillus sake 0-1 and Characterization of the Polysaccharide

A novel exopolysaccharide (EPS) produced by Lactobacillus sake 0-1 (CBS 532.92) has been isolated and characterized. When the strain was grown on glucose, the produced EPS contained glucose and rhamnose in a molar ratio of 3:2 and the average molecular mass distribution (M(infm)) was determined at 6 x 10(sup6) Da. At a concentration of 1%, the 0-1 EPS had better viscosifying properties than xanthan gum when measured over a range of shear rates from 0 to 300 s(sup-1), while shear-thinning properties were comparable. Rheological data and anion-exchange chromatography suggested the presence of a negatively charged group in the EPS. Physiological parameters for optimal production of EPS were determined in batch fermentation experiments. Maximum EPS production was 1.40 g (middot) liter(sup-1), which was obtained when L. sake 0-1 had been grown anaerobically at 20(deg)C and pH 5.8. When cultured at lower temperatures, the EPS production per gram of biomass increased from 600 mg at 20(deg)C to 700 mg at 10(deg)C but the growth rate in the exponential phase decreased from 0.16 to 0.03 g (middot) liter(sup-1) (middot) h(sup-1). EPS production started in the early growth phase and stopped when the culture reached the stationary phase. Growing the 0-1 strain on different energy sources such as glucose, galactose, mannose, fructose, lactose, and sucrose did not alter the composition of the EPS produced.     

Evaluation of Passive Hemagglutination, Solid-Phase Radioimmunoassay, and Immunoelectroosmophoresis for the Detection of Hepatitis B Antigen

Sensitivity and specificity of passive hemagglutination (RCA), solid phase radioimmunoassay (RIA), and immunoelectroosmophoresis (IEOP) were compared under experimental and clinical conditions. In dilution experiments with sera containing hepatitis B antigen (HB Ag) of known subtypes, the sensitivity for an ad subtype serum was RIA (1), RCA (1/2), IEOP (1/256) and for an ay subtype serum RCA (1), RIA (1/8), IEOP (1/128). An evaluation of the National Institutes of Health, Division of Biologics Standards test panel number 2 demonstrated HB Ag in 34 of 60 samples by RIA, in 33 by RCA, and in 25 by IEOP. HB Ag was detected in 57.5% of 200 outpatients with a tentative diagnosis of hepatitis by RIA, in 54% by RCA, and in 42.5% by IEOP. In 1,661 volunteer blood donors, 13 (0.78%) were "positive" for HB Ag by RIA, 11 (0.66%) by RCA, and 3 (0.18%) by IEOP. However, absorption experiments indicated that at least six of the above RIA positive and five of the RCA positive sera exhibited nonspecific positive reactions.