The cytotoxic and photodynamic inactivation of micro-organisms by Rose Bengal

Rose Bengal was cytotoxic to the following bacteria at the concentrations given in parentheses (highest concentrations of dye in mol/1 at which growth occurred on nutrient medium): Brochothrix thermosphacta and Deinococcus radiodurans (1 times 10^-6 or less); Streptococcus, Micrococcus, Staphylococcus, Bacillus, Arthrobacter and Kurthia spp. (1 times 10^-5–1 x 10^-4), and Pseudomonas spp. and Enterobacteriaceae (5 times 10^-3–1 x 10^-2 or greater). These organisms were killed rapidly when suspended in illuminated (170 μE/m²/s) solutions of Rose Bengal (1 times 10^-4 mol/1) providing oxygen was present. Singlet oxygen was identified as the lethal agent, because the rate of killing was increased by dissolving the dye in deuterium oxide while the organisms were protected against photoinactivation by L-histidine or crocetin. Yeasts from chilled foods were killed in illuminated solutions of Rose Bengal but a light intensity of 315 μE/m²/s was needed for a death rate comparable with that of bacteria. The yeasts present in a range of chilled meat and dairy products failed to form colonies on Rose Bengal (5 times 10^-5 mol/1) media exposed continuously to modest illumination (55–80 μE/m²/s).     

Effects of fungicide spray regimes on incidence of dicarboximide resistance in grey mould (Botrytis cinerea) on strawberry plants

In tunnel experiments, the efficacy of dicarboximide sprays in controlling grey mould of strawberries was greatly decreased by the presence of dicarboximide-resistant forms of Botrytis cinerea. The use of dichlofluanid, as a tank-mix or in an alternating programme, with a dicarboximide fungicide, procymidone, helped to maintain the efficacy of disease control but failed to prevent an increase in the proportion of dicarboximide-resistant forms of the pathogen. Alternative ‘partner’ fungicides (thiram, chlorothalonil) delayed build-up of resistance to dicarboximides. Build-up of resistance was absent or relatively small in unsprayed plots. Application of dichlofluanid alone was always associated with a substantial increase in dicarboximide resistance, although less than in procymidone-treated plots. Monitoring dicarboximide resistance in the tunnels during the winter, when no further sprays were applied, revealed a gradual decline in the proportion of dicarboximide-resistant forms in all previously treated plots. In laboratory studies on inoculated leaf debris, dichlofluanid treatment induced the build-up of dicarboximide-resistant forms of B. cinerea. Leaf-disc tests revealed cross-resistance of dicarboximide-resistant isolates towards dichlofluanid but not towards thiram or chlorothalonil. Dichlofluanid is widely used for control of B. cinerea and the implications of these results for the practical management of dicarboximide resistance in this pathogen are discussed.     

Migration of alate morphs of the bird cherry aphid (Rhopalosiphum padi) and implications for the epidemiology of barley yellow dwarf virus

Suction trapping data indicate three periods of migration of Rhopalosiphum padi in spring, summer and autumn. Four alate morphs are present at different times during the year. A comparison of data from suction traps operating at 12·2 and 1·5 m suggests a different behaviour of females in autumn with more being recorded at 12·2 than 1·5 m. Males, which are only present in autumn, were also more numerous at 12·2 m. During tests to measure barley yellow dwarf virus (BYDV) infectivity, only 9% of female R. padi reproduced on oat seedlings in autumn compared with 74% in summer. Tests on alate female R. padi trapped alive showed that in summer all were exules, but during the first half of September these were largely replaced by gynoparae so that in autumn only 5% of all R. padi trapped at 12·2 m were alate exules. The aerial densities of gynoparae and males were 10 times greater at 12·2 than 1·5 m while densities of alate exules were similar at both heights. It is suggested that gynoparae and males fly higher to increase the chance of finding a taller dispersed host plant. The implications for BYDV epidemiology of the behaviour and presence of the various R. padi alate morphs indicate that autumn-sown cereals emerging before mid-September are particularly at risk from colonisation by alate exules before the transition to a mainly sexual migrant population is complete. Alate exules introduce BYDV from comparatively local sources. The ratio of total R. padi to Sitobion avenae in suction trap samples in autumn usually exceeds 100: 1, but on crops it was only 10: 1. The ratio of alate exule R. padi to S. avenae in suction traps in autumn was only 12: 1, similar to that observed on crops.     

On Gibbs sampling for state space models

We show how to use the Gibbs sampler to carry out Bayesian inferenceon a linear state space model with errors that are a mixtureof normals and coefficients that can switch over time. Our approachsimultaneously generates the whole of the state vector giventhe mixture and coefficient indicator variables and simultaneouslygenerates all the indicator variables conditional on the statevectors. The states are generated efficiently using the Kalmanfilter. We illustrate our approach by several examples and empiricallycompare its performance to another Gibbs sampler where the statesare generated one at a time. The empirical results suggest thatour approach is both practical to implement and dominates theGibbs sampler that generates the states one at a time.     

Epigenetic mechanical factors in the evolution of long bone epiphyses

In developing vertebrate long bones in which endochondral ossification occurs, it is preceded or accompanied by perichondral ossification. The speed and extent of perichondral apposition relative to endochondral ossification varies in different taxa. Perichondral ossification dominates early long bone development in extinct basal tetrapods and dinosaurs, extant bony fish, amphibians, and birds. In mammals and lizards, perichondral and endochondral ossification proceed more synchronously. One of the most important epigenetic factors in skeletogenesis is mechanical loading caused by muscle contractions which begin in utero or in ovo . It has been previously shown that the stress distributions created perinatally in the chondroepiphysis during human skeletal development can influence the appearance of secondary ossification centres. Using finite element computer models representing bones near birth or hatching, we demonstrate that in vertebrates in which perichondral ossification significantly precedes endochondral ossification, the distribution of mechanical stresses in the ossifying cartilage anlagen tends to inhibit the appearance of secondary ossification centres in the ends of long bones. In models representing vertebrates in which endochondral ossification keeps pace with perichondral apposition, the appearance of secondary centres is promoted. The appearance of secondary centres leads to the formation of bony epiphyses and growth plates, which are most common in mammals and extant lizards. We postulate that genotypic factors influencing the relative speed and extent of perichondral and endochondral ossification interact with mechanical epigenetic factors early in development to account for many of the morphological differences observed in vertebrate skeletons.     

Cepaea on Salisbury Plain: patterns of variation, landscape history and habitat stability

Patterns of variation in Cepaea nemoralis and C. hortensis on Salisbury Plain are related to its landscape history. Areas of arable or mixed farming, with hedgerows and woods, show patterns of variation with habitat and topography. Areas of downland, until recently heavily grazed by sheep, show area effects. Cepaea populations in these downland areas would have been much rarer, and more isolated when grazing was intense. This pattern is repeated in other parts of southern England, showing that area effects in Cepaea are strongly associated with areas of habitat instability, where Cepaea survived as small and isolated populations until recently. This evidence enhances the plausibility of explanations of area effects involving isolation, founder effect or local selection, and co-adaptation.     

Radioiodination of Parasite Antigens with 1,3,4,6,-Tetrachloro-3α,6α-diphenylglycoluril (IODOGEN): Studies with Zygotes of Plasmodium gallinaceum

The iodinating reagent 1,3,4,6,-tetrachloro-3α,6α-diphenylglycoluril (IODOGEN³) was used to label antigens on zygotes of Plasmodium gallinaceum with parallel studies using lactoperoxidase-catalyzed radioiodination for comparison. Proteins labeled by the IODOGEN method are most probably on the surface of the zygote, as the pattern of labeled proteins analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis was very similar to the pattern of lactoperoxidase-labeled proteins. Furthermore, the labeled proteins represented only a subset of the total Coomassie Blue-stained proteins. The radioiodinated zygote proteins were immuno-reactive after IODOGEN or lactoperoxidase labeling. The IODOGEN method is technically much more simple than the lactoperoxidase method and does not require the addition of extraneous proteins or H₂O₂. The advantages of IODOGEN labeling, together with the essential equivalence of results obtained by these two, methods, make the IODOGEN method attractive for labeling parasite antigens in general.