Influence of partial replacement of nitrate by amino acid nitrogen or urea in the nutrient medium on nitrate accumulation in NFT grown winter lettuce

Two cultivars of lettuce plants (Lactuca sativa L. cvs Berlo and Kirsten) were grown for two months in late fall in NFT under three different nitrogen (N)‐regimes but with the same total N concentration (13.4 mM). A reference treatment with a nutrient solution containing 94% nitrate (NO₃) and 6% ammonium (NH₄) was compared with urea and proteinate treatments in which 20% of the NO₃ of the reference treatment was replaced by either of these two N sources. Proteinate is a fertilizer produced in Turkey containing 8% amino acid N and 8% NO₃‐N. For both cultivars the fresh weights of the harvested plants were unaffected by the N source as was also the total N uptake. Nitrate content, however, was considerably lower in the urea and proteinate plants, values for the three treatments ranging from 3314 to 4579 mg NO₃/kg fresh wt making up from between 44.3% to 55.4% of the total plant N. Of the two cultivars, Berlo accumulated greater concentrations of NO₃ than did Kirsten. The accumulation of chloride (Cl) was in the reverse order of that of NO₃ with greatest concentrations occurring in the proteinate plants.     

Rainfall simulation to identify the storm-scale mechanisms of gully bank retreat

Gully erosion is one of the main causes of soil loss in drylands. Understanding the dominant mechanisms of erosion is important to achieve effective erosion control, thus in this study our main objective was to quantify the mechanisms involved in gully bank retreat as a result of three processes, falling of entire soil aggregates, transport of soil material by splash and by water running along gully banks (runoff), during rainfall events. The study was conducted in the sloping lands of the KwaZulu-Natal province, a region that is highly affected by gully erosion. Artificial rain was applied at 60 mm h⁻¹ for 45 min at the vertical wall of a gully bank typical to the area. The splash material was collected by using a network of 0.045 m² buckets. The sediments in the running water were assessed by sampling the runoff collected from a microplot inserted within the base of the bank, and collecting the fallen aggregates after the rainfall simulation was complete. Results indicated that the overall erosion for the simulation was 721 g m⁻² h⁻¹. Runoff erosion proved to be the dominant mechanism and amounted to 450 g m⁻² h⁻¹, followed by splash and fall down of aggregates (about 170 g m⁻² h⁻¹). Gully bank retreat occurred at a rate of 0.55 mm h⁻¹ and assuming that the soil bulk density is 1.3 g cm⁻³, this corresponds to a retreat of 8.8 mm y⁻¹. Extrapolations to the watershed level, where about 500 m² of gully bank are observed per hectare, would lead to an erosion rate of 4.8 t ha⁻¹ y⁻¹. These limited results based on a simulated storm show that the three main mechanisms (runoff, splash and fall down of aggregates) are responsible for the retreat of gully banks and that to mitigate gully erosion, appropriate measures are required to control all three mechanisms. Further research studies are needed to confirm and to scale up, both in time and space, as these data are obtained at one location and from a single artificial storm.     

Comparison of latex agglutination,enzyme-linked immunosorbent assay,and indicator plants for detection of potato viruses S and X in potatoes

Potato virus S (PVS) was consistently detected by the enzyme-linked immunosorbent assay (ELISA) and the latex agglutination test (LAT) at dilutions (PVS sap: healthy sap) of 1:499 and 1:19, respectively. Mechanical inoculation ofNicotiana debneyi gave variable results with detection possible 38% of the time at dilutions of 1:499. Potato virus X (PVX) was consistently detected by ELISA and LAT at dilutions (PVX sap: healthy sap) of 1:199 and 1:49, respectively. Mechanical inoculation ofGomphrena globosa with PVX resulted in consistent detection of the virus at a dilution of 1:499.     

Rapid digestion of Cry34Ab1 and Cry35Ab1 in simulated gastric fluid

Two genes were identified in Bacillus thuringiensis Berliner (Bt) that code for the proteins that comprise a Cry34Ab1/Cry35Ab1 binary insecticidal crystal protein. Maize, Zea mays L., plants have been transformed to express the Cry34Ab1/Cry35Ab1 proteins, and as a result, these plants are resistant to attack by western corn rootworm, Diabrotica virgifera virgifera LeConte, a major pest in the Midwestern corn-growing area of the U.S.A. As part of the safety assessment for the proteins, digestibility studies were conducted. Digestion experiments with both proteins demonstrated rapid degradation in simulated gastric fluid, comparable to other registered plant-incorporated protectants. Quantitative and qualitative approaches for determining digestibility are illustrated.     

Oxidation of pesticides by purified microsomal FAD-containing monooxygenase from mouse and pig liver

The ability of purified microsomal FAD-containing monooxygenase from mouse and pig liver to oxidize pesticides has been investigated. The kinetic constants, K_m and V_max, were determined for a number of pesticide substrates including thioether-containing organophosphorus compounds and carbamates as well as (di)alkyldithiocarbamates. In general, the mouse liver enzyme had K_m values higher than those of the pig liver enzyme. Values for V_max were similar regardless of substrate, although the V_max typical of the mouse liver enzyme was approximately twice that of the pig liver enzyme. The thioether-containing organophosphorus compounds were the best substrates for both enzymes followed by the thioether-containing carbamates. The (di)alkyldithiocarbamates were relatively poor substrates for both pig and mouse liver microsomal FAD-containing monooxygenases.     

表面活性剂对杀虫剂的增效机制及药效研究

在敌百虫和兴棉宝药液中分别加入φ为０．０１％￣０．０４％的ＡＰＳＡ－８０,表面张力降低４１．８３％￣６０．４３％;在荔枝叶上的接触角降低３７．００％￣６４．２２％,沉积量增加１２．８３％￣３５．４１％;室内毒力试验测定表明,敌百虫与ＡＰＳＡ－８０混用后,ＬＣ５０比单剂分别降低２３．７３％和１３．６９％,增效系数分别为１３１．１１和１１７．５１;田间试验结果表明：ＡＰＳＡ－８０能够明显提高兴棉宝防治     

Comment on "The illusion of invariant quantities in life histories"

Nee et al. (Reports, 19 August 2005, p. 1236) used a null model to argue that life history invariants are illusions. We show that their results are largely inconsequential for life history theory because the authors confound two definitions of invariance, and rigorous analysis of their null model demonstrates that it does not match observed data.     

Laboratory animal medicine — Needs and opportunities for Canadian veterinarians

Laboratory animal medicine is a growing field of veterinary practice that emphasizes animal welfare and refinement of research animal care. The Canadian Association for Laboratory Animal Medicine/L’association canadienne de la medecine des animaux de laboratoire (CALAM/ACMAL) and the Canadian Council on Animal Care (CCAC) provide a framework within which laboratory animal veterinarians practise. Numerous continuing education and post-graduate training opportunities exist in Canada for veterinarians interested in pursuing this specialty.     

Hydatidosis of slaughtered animals in Ngorongoro district of Arusha region,Tanzania

A study on the prevalence of hydatidosis in cattle, goats and sheep was carried out in Ngorongoro district of Arusha region, Tanzania. A 4-years data records from four slaughter slabs were retrieved and analysed. In addition, meat inspection was done in the same slaughter slabs for nine months and 64 households were interviewed to assess the community awareness on hydatidosis. Results showed the overall prevalence of hydatidosis to be 47.9%. Species prevalence of 48.7%, 34.7% and 63.8% in cattle, goats and sheep respectively was recorded. Of 174 cysts examined in cattle, 37 (21.3%) were fertile, 126 (72.4%) were sterile and 11 (6.3%) were calcified. Out of 215 goats and 67 sheep cysts examined, 52 (24.7%) and 26 (38.8%) were fertile, 138 (64.2%) and 38 (56.7%) were sterile, 24 (11.2%) and 3 (4.5%) were calcified respectively. The higher percentage of fertile hydatid cysts in sheep and goats coupled with the practice of backyard slaughter of sheep and goats suggests that, these animals could be important intermediate hosts for the maintenance of the domestic life cycle of E. granulosus in the locality. Questionnaire survey revealed that 17.2% of the respondents were aware of hydatidosis but non of them were knowledgeable on its transmission. Up to 84.4% of the respondents had domestic ruminants and donkeys, while 89.1% had dogs. Of the households with dogs, only 19.3% had their dogs dewormed at least once in life time. Most of the households (87.7%) had their dogs managed freely and 77.2% of the respondents reported school children to be the closest friends of dogs in the family. The prevalence of E. granulosus infection in wildlife and the possible relationship of the domestic cycle to the sylvatic cycle operating in the same area are unknown and need to be studied.