The effect of chemical modification of Saccharomyces cerevisiae on electrophoretic mobility, cell-wall structure and amphotericin B uptake

Saccharomyces cerevisiae NCYC 239 suspended in solutions of NaCl showed two distinct plateaus in plots of electrophoretic mobility vs. pH, corresponding to pKa values of approx. 2 and 5. This is in contrast to cells suspended in buffer where only a single pKa (4) can be determined. Modification of cells with KI/I2 or nitrous acid led to altered electrophoretic mobility, indicating the presence of sulphydryl and amino groups, respectively, in the yeast cell surface, whereas uranyl nitrate modification had little effect, suggesting phosphate groups to be absent. Electron micrographs showed visible effects of KI/I2 and nitrous acid modification on cell membrane structure, and in these modified cells amphotericin B uptake was rapid. It is suggested that diffusion through the cell wall is the rate-limiting step for amphotericin B uptake. An activation energy of 20 kJ X mol-1 was determined for uptake of amphotericin B by unmodified cells.     

Detection and side-chain specificity of IgE antibodies to flucloxicillin in allergic subjects

Unlike studies on the antigenicity of penicillins in laboratory animals, limited information is available on the allergenicity of penicillins in man, especially with regard to fine structural allergenic differences between the many different penicillins. Inconsistent with the earlier conclusions of others, our studies suggest that side-chain structures to flucloxacillin-reactive IgE antibodies. Quantitative hapten inhibition studies revealed potent inhibition by flucloxacillin and three structurally related penicillins: oxacillin, cloxacillin and dicloxacillin. Analysis of the results showed that the side-chain group of flucloxacillin, 3-2(-chloro-6-fluorophenyl)-5-methyl-4-isoxazolyl, is recognized by some antibodies and that the 5-methyl-3-phenyl-4-isoxazolyl group, with or without halogen substituents, accounts for the reactivity of other antibodies and for the cross-reactions seen with some other penicillins. Since it is the side-chain group that distinguishes the many different types of penicillin, and since IgE antibodies in many of the allergic reactions recognize the side-chain groups, it is becoming clear that specific assays are required for the detection of IgE antibodies to each of the different penicillins.     

Acute toxicity effects of ibuprofen on behaviour and haematological parameters of African catfish Clarias gariepinus (Burchell, 1822)

Indiscriminate discharge of pharmaceutical waste into the aquatic ecosystem may pose serious health challenges to aquatic biota. The effect of acute exposure to ibuprofen was evaluated using changes in behaviour and haematological parameters under static bio-assay method in Clarias gariepinus. Test specimens were exposed to acute concentrations of ibuprofen (0.28, 0.33, 0.38, 0.43 and 0.48 mg l^?1) for 24, 48, 72 and 96 h durations respectively. Behavioural and phenotypic changes were observed in surviving fish. There were significant (p < 0.05) concentration and duration-dependent increases in erythrocyte (RBC), haemoglobin (Hb), pack cell volume (PCV) and leukocytes (WBC) in treated fish compared to the control. Insignificant decreases (p > 0.05) in mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) were observed in treated fish compared to the control. Ibuprofen elicited dose and duration- dependent decrease in neutrophil counts with the decreases being significant (p < 0.05) in the higher doses of 0.43 and 0.48 mg l^?1. Ibuprofen did not elicit any significant changes in monocytes, basophils and eosinophils. Changes observed in this study showed that ibuprofen negatively affected the health of the fish and we recommend that discharge of ibuprofen into the aquatic environment should be monitored and controlled.     

Varicosities of single sympathetic nerve terminals possess syntaxin zones and different synaptotagmin N-terminus labelling following stimulation

A study has been made of the probability of exocytosis of synaptic vesicles at different varicosities in single sympathetic terminal axons in the mouse vas deferens. An antibody (SV2Ab) against SV2, a proteoglycan in synaptic vesicles, labelled an area of individual sympathetic varicosities that was slightly less than that occupied by dextran-rhodamine, previously orthogradely transported into the varicosities. In contrast plasma membrane bound protein syntaxin, found at active zones of motor nerve terminals, occupied an area of the varicosity that was approximately one-third that of SV2. This suggests that sympathetic varicosities possess specialized zones for exocytosis on their plasma membranes. Antibodies against the N-terminal sequence of synaptotagmin 1 (SNAb), a sequence exposed within synaptic vesicles, were used to determine the probability of exocytosis at different varicosities of single terminal branches. The area of SNAb labelling was not significantly different from that of the SV2 labelling, which implies vesicles that have undergone exocytosis may eventually return to the main pool of vesicles. Varicosities belonging to the same terminal axon, and identified with SV2Ab, showed different extents of labelling with SNAb when secretion was evoked with high potassium concentrations (80 mM) for 30 min in the presence of SNAb. There was up to an order of magnitude difference in the average intensity of SNAb labelling between different varicosities of the same terminal axon whereas there was little difference in the average intensity of SV2Ab labelling. These observations suggest that there is considerable variability in the probability of exocytosis at the specialized zones in different varicosities.     

Spatio-temporal dynamics of willow beetle (Phratora vulgatissima) in short-rotation coppice willows grown as monocultures or a genetically diverse mixture

1 Phratora vulgatissima (Chrysomelidae) is the major pest of short-rotation coppice willows in the U.K., capable of causing severe defoliation in monoculture plantations. As this beetle shows feeding preferences between willow clones, knowledge of the spatio-temporal dynamics of P. vulgatissima is needed in order to assess the effects of mixed clonal plantings on the management of this pest. 2 Distribution patterns of adult P. vulgatissima were monitored over a season at a spatial scale of every tree or every other tree in single clone plantings (monocultures) of three willow clones and in a regular row mixture of these clones. 3 Distribution indices (deviation from Complete Spatial Randomness) demonstrated that P. vulgatissima adults were spatially aggregated on favourable clones in the monocultures and the mixture. The degree of aggregation (measured by the k-parameter of the negative binomial) differed between willow clones. Beetles were highly aggregated at the start of the season, but less so later. 4 Dispersal studies of P. vulgatissima adults over time showed a pattern of beetle infestation along rows of the preferred clones in a regularly structured mixture. In the monocultures, movement was less directional. 5 Plantation design offers some potential for more effective non-chemical pest management for P. vulgatissima. Monitoring of the pest must take account of our findings that adults occur in mobile aggregations.     

Simulated beetle defoliation on willow genotypes in mixture and monotype plantations

The effect of simulated beetle damage (0%, 25%, 50% and 75% mechanical defoliation) on 12 willow genotypes, grown in short‐rotation coppice, was studied in a modified criss‐cross experimental design. The design enabled the above‐ground effects of monoculture and mixed planting to be assessed. Repeated measurements were modelled to produce derived variables in terms of time or, more appropriately, in terms of accumulated day length (i.e. ‘developmental time’) units. These derived variables were then analysed using the REsidual Maximum Likelihood (REML) method implemented in GenStat? (2001) . No significant competition effect between the genotypes due to planting regime was detected. Genotypes Salix viminalis × Salix schwerinii‘Beagle’ and S. viminalis × S. schwerinii‘Torhild’ were found to have the greatest rate of increase in leaves regardless of defoliation and also the greatest height prior to defoliation. Genotype Salix dasyclados‘Loden’ showed the highest rate of growth under the stress of defoliation. When assessing height at the end of the growing season, S. viminalis × S. schwerinii‘Olof’ was the highest genotype for 25% and 75% levels of defoliation, but genotypes Salix aurita × Salix cinerea‘Delamere’, Loden and S. viminalis × Salix burjatica‘Ashton Parfitt’ appeared to be most tolerant by having consecutively lower base day lengths (i.e. increasing the accumulation of developmental units and the length of the growing season) for increasing defoliation. Shorter genotypes tended to be more tolerant, but of the higher genotypes reaching a control height of greater than 3 m by the end of the growing season, S. viminalis × S. schwerinii‘Tora’ and Beagle performed best to 50% defoliation.