Effect of Mixing Conditions on the Behavior of Lipoxygenase,Peroxidase, and Catalase in Wheat Flour Doughs

The effect of mixing has been tested on the extractable activities of lipoxygenase, peroxidase, and catalase from dough after 2, 5, and 20 min of mixing, and 30 min of rest period after 20 min of mixing. Different mixing conditions have been studied including temperature, atmosphere, speed, amount of water added to the dough, buffer solutions between pH 3.6 and 7.5 added to the dough, and different additives (linoleic acid, guaiacol, hydrogen peroxide, ascorbic acid, cysteine, yeast, and sodium chloride). In all the mixing conditions tested, the dough peroxidase activity remains equivalent to the initial flour activity, whereas losses in lipoxygenase and catalase activities largely varied according to mixing conditions. The results show that a self-destruction mechanism as well as physicochemical denaturation are responsible for these losses. Lipoxygenase losses seem mainly associated with the former mechanism, whereas catalase losses are highly increased in acidic conditions (physicochemical denaturation). Therefore, the relative impact of the three oxidoreducing enzymes may be largely modulated by mixing conditions.     

Degradation of [14C]Terbuthylazine and [14C]Atrazine in Laboratory Soil Microcosms

The degradation and formation of major chlorinated metabolites of terbuthylazine and atrazine in three soils (loamy clay, calcareous clay and high clay) were studied in laboratory experiments using molecules labelled with ¹⁴C on the s-triazine ring. Soil microcosms were treated with the equivalent of 1 kg ha^-1 of herbicide and incubated in the dark for 45 days at 20(±1)°C. The quantity of [¹⁴C]carbon dioxide evolved in the soils treated with atrazine was negligible and could not be attributed to mineralization of the parent molecule. The mineralization of terbuthylazine accounted for 0·9–1·2% of the initial radioactivity. In the soils studied, the extrapolated half-lives varied from 88 to 116 days for terbuthylazine and 66 to 105 days for atrazine, with no significant differences for the three soils and the two molecules. The deethyl metabolites of the two s-triazines and the deisopropyl-atrazine metabolite appeared during the incubation in the three soils. The completely dealkylated metabolite was not detected in any of the soils. After 45 days of incubation, the non-extractable soil residues for the high clay, loamy clay and calcareous clay soils represented for terbuthylazine, 33·5, 38·3 and 43·1% and for atrazine, 19·8, 20·8 and 22·3% of the initial radioactivity. © 1997 SCI.     

Scale-dependent determinants of heterogeneity in fire frequency in a coniferous boreal forest of eastern Canada

Despite the recognized importance of fire in North American boreal forests, the relative importance of stochastic and determinist portions of intra-regional spatial variability in fire frequency is still poorly understood. The first objective of this study is to identify sources of spatial variability in fire frequency in a landscape of eastern Quebec’s coniferous boreal forest. Broad-scale environmental factors considered included latitude, longitude, human activities and belonging to a given bioclimatic domain, whereas fine-scale factors included slope, position on the slope, aspect, elevation, surficial deposit and drainage. The average distance to waterbodies was also considered as a potential intermediate-scale source of variability in fire frequency. In order to assess these environmental factors’ potential influence, they were incorporated into a proportional hazard model, a semi-parametric form of survival analysis. We also used a digital elevation model in order to evaluate the dominant aspect within neighborhoods of varying sizes and successively incorporated these covariates into the proportional hazard model. We found that longitude significantly affects fire frequency, suggesting a maritime influence on fire frequency in this coastal landscape. We also found that position on the slope was related to fire frequency since hilltops and upperslopes were subject to a lower fire frequency. Dominant aspect was also related to fire frequency, but only when characterized within a neighborhood delimited by 4,000 to 10,000-m radii (5,027–31,416 ha). A 2–6-fold variation in fire frequency can be induced by geographic and topographic contexts, suggesting a substantial intra-regional heterogeneity in disturbance regime with potential consequences on forest dynamics and biodiversity patterns. Implications for forest management are also briefly discussed. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Atypical scrapie in a Swiss goat and implications for transmissible spongiform encephalopathy surveillance.

Different types of transmissible spongiform encephalopathies (TSEs) affect sheep and goats. In addition to the classical form of scrapie, both species are susceptible to experimental infections with the bovine spongiform encephalopathy (BSE) agent, and in recent years atypical scrapie cases have been reported in sheep from different European countries. Atypical scrapie in sheep is characterized by distinct histopathologic lesions and molecular characteristics of the abnormal scrapie prion protein (PrP(sc)). Characteristics of atypical scrapie have not yet been described in detail in goats. A goat presenting features of atypical scrapie was identified in Switzerland. Although there was no difference between the molecular characteristics of PrP(sc) in this animal and those of atypical scrapie in sheep, differences in the distribution of histopathologic lesions and PrP(sc) deposition were observed. In particular the cerebellar cortex, a major site of PrP(sc) deposition in atypical scrapie in sheep, was found to be virtually unaffected in this goat. In contrast, severe lesions and PrP(sc) deposition were detected in more rostral brain structures, such as thalamus and midbrain. Two TSE screening tests and PrP(sc) immunohistochemistry were either negative or barely positive when applied to cerebellum and obex tissues, the target samples for TSE surveillance in sheep and goats. These findings suggest that such cases may have been missed in the past and could be overlooked in the future if sampling and testing procedures are not adapted. The epidemiological and veterinary public health implications of these atypical cases, however, are not yet known.     

Experimental study on the toxicity of imidacloprid given in syrup to honey bee (Apis mellifera) colonies

Two groups of eight honey bee colonies were fed with two different concentrations of imidacloprid in saccharose syrup during summer (each colony was given 1 litre of saccharose syrup containing 0.5 microg litre(-1) or 5 microg litre(-1) of imidacloprid on 13 occasions). Their development and survival were followed in parallel with control hives (unfed or fed with saccharose syrup) until the end of the following winter. The parameters followed were: adult bee activity (number of bee entering the hive and pollen carrying activity), adult bee population level, capped brood area, frequency of parasitic and other diseases, mortality, number of frames with brood after wintering and a global score of colonies after wintering. The only parameters linked to feeding with imidacloprid-supplemented saccharose syrup when compared with feeding with non-supplemented syrup were: a statistically non-significant higher activity index of adult bees, a significantly higher frequency of pollen carrying during the feeding period and a larger number of capped brood cells. When imidacloprid was no longer applied, activity and pollen carrying were re-established at a similar level for all groups. Repeated feeding with syrup supplemented with imidacloprid did not provoke any immediate or any delayed mortality before, during or following the next winter, whereas such severe effects are described by several French bee keepers as a consequence of imidacloprid use for seed dressing in neighbouring cultures. In any case, during the whole study, mortality was very low in all groups, with no difference between imidacloprid-fed and control colonies. Further research should now address several hypotheses: the troubles described by bee keepers have causes other than imidacloprid; if such troubles are really due to this insecticide, they may only be observed either when bees consume contaminated pollen, when no other sources of food are available, in the presence of synergic factors (that still need to be identified), with some particular races of bees or when colonies are not strong and healthy.     

Histological localization assays for diflubenzuron in Pieris brassicae larva (Lepidoptera), by secondary ion microanalysis

No histochemical reaction is available to localize diflubenzuron in tissues. The insecticide can be localized in Pieris tissues by its fluoride atoms, used as tracers in secondary ion microanalysis, which is very sensitive for such light elements. In diflubenzuron-treated insects, especially in females, fluoride intensities are much higher than in controls; images demonstrate a wide distribution of the insecticide in the insect tissues. Thus, besides target organs, i.e., epidermis, diflubenzuron is present in other tissues, such as fat bodies, which may be related to the general metabolic effects and to a detoxification of the insecticide.     

Oral rabies vaccination of foxes with one or two delayed distributions of SAG2 baits during the spring

During the spring of 1997, various protocols of rabies vaccine bait (SAG2) distribution for foxes were compared: in the first test zone, a first distribution was organised at the end of April, followed by a second distribution two weeks later; in the second test zone, there was a first distribution at the same period as for the previous zone, followed by a second distribution four weeks later, at the end of May. In two control zones, a classical single bait distribution was organised during the same periods as for the second distribution in the respective test zones. No statistical differences were observed for adult foxes or fox cubs sampled in the test and control zones neither for baits uptake nor for seroconversion rate. However, seroconversion rates observed in fox cubs population were significantly higher (P < 0.01) in areas vaccinated at the end of May (43 and 56%) compared with those vaccinated at mid-May (24 and 20%). The vaccinal efficacy of baits was also significantly (P < 0.05) increased for the fox cubs in the areas vaccinated at the end of May (46 and 57%) compared with those vaccinated at mid-May (24 and 25%). This increase in immunological response by fox cubs when vaccinating in late spring must be related to their development. In the early spring, fox cubs are generally too young to have access to baits or to be vaccinated when eating them. For most of these fox cubs, a second distribution will not constitute a booster. Therefore, in order to increase the efficient access of fox cubs to vaccine baits, Spring distribution of baits should preferably be organised during May or June rather than in April.     

Usefulness of single copy genes containing introns in Phytophthora for the development of detection tools for the regulated species P. ramorum and P. fragariae

Introns are generally highly polymorphic regions within genes and were proven to be of great interest for discriminating among phylogenetically-close Phytophthora species. Phytophthora ramorum and P. fragariae are considered as quarantine pathogens by the European Union and accurate detection tools are therefore necessary for their monitoring. From introns located in different single copy genes (GPA1, RAS-like, and TRP1), we developed a series of PCR primers specific to P. ramorum and P. fragariae. The specificity of these primers was successfully checked with a wide collection of Phytophthora isolates and a protocol was developed to detect both pathogens directly in infected plant tissues. These genes should be of particular interest for the development of additional species-specific detection tools within the Phytophthora genus.     

Emerging and re-emerging viruses of the honey bee (Apis mellifera L.)

Until the late 1980s, specific viral infections of the honey bee were generally considered harmless in all countries. Then, with the worldwide introduction of the ectoparasite mite Varroa destructor, beekeepers encountered increasing difficulties in maintaining their colonies. Epidemiological surveys and laboratory experiments have demonstrated that the newly acquired virulence of several viruses belonging to the family Dicistroviridae (acute bee paralysis virus, Kashmir bee virus and Israeli acute paralysis virus) in Europe and the USA had been observed in relation with V. destructor acting as a disseminator of these viruses between and within bee colonies and as an activator of virus multiplication in the infected individuals: bee larvae and adults. Equal emphasis is given to deformed wing virus (DWV) belonging to the Iflaviridae. Overt outbreaks of DWV infections have been shown to be linked to the ability of V. destructor to act not only as a mechanical vector of DWV but also as a biological vector. Its replication in mites prior to its vectoring into pupae seemed to be necessary and sufficient for the induction of a overt infection in pupae developing in non-viable bees with deformed wings. DWV in V. destructor infested colonies is now considered as one of the key players of the final collapse. Various approaches for combating bee viral diseases are described: they include selection of tolerant bees, RNA interference and prevention of new pathogen introduction. None of these approaches are expected to lead to enhanced bee-health in the short term.     

The protective immune response produced in dogs after primary vaccination with the LiESP/QA-21 vaccine (CaniLeish?) remains effective against an experimental challenge one year later

Control of canine leishmaniasis is an important objective for the benefit of dogs living in or visiting endemic areas and for public health because of the zoonotic nature of this disease. Resistance or susceptibility to developing canine leishmaniasis after exposure to Leishmania infantum is primarily determined by the ability of the immune system to develop an appropriate Th1-dominated specific response to the parasite. For this reason there is a need for effective canine vaccines that can decrease the number of dogs developing progressive infections. In this study, we followed the impact of the LiESP/QA-21 canine vaccine (composed of excreted-secreted proteins of L. infantum and the QA-21 saponin adjuvant), recently launched commercially in Europe, on selected humoral and cellular immune parameters following an infectious intravenous challenge with L. infantum promastigotes administered one year after the primary vaccine course. We also followed parasitological parameters to determine the parasitological status of the challenged dogs. In contrast to controls, vaccinated dogs retained significantly stronger cell-mediated immune responses against the parasite despite a virulent challenge and had significantly lower mean parasite burdens at the end of the study, associated with a lower probability of developing active infections. These results confirm that the immune responses generated by vaccination with LiESP/QA-21 are still effective against an intravenous challenge one year after the primary vaccine course.