洋葱染色体核型的FISH分析

 挑选洋葱(Allium cepa L．) (2n=2x=16，CC)有丝分裂中期细胞，以洋葱卫星DNA序列(AC—SAT-DNA)为探针，DIG-1 1-dUTP为标记物，用荧光原位杂交(FISH)方法观察其在染色体上的定位，并进行洋葱的核型分析。6号染色体为近端部着丝点染色体，在其长臂末端有一个卫星DNA序列的主要位点。其余每条染色体在其长、短臂的末端都各具有一个主要位点。差异表现在各染色体上卫星DNA序列的次要位点分布不同。根据洋葱8对染色体各自具有的独特的卫星DNA分布位点，可将洋葱8对染色体全部分开。以此为基础，构建了洋葱卫星DNA在染色体上分布的模式图。     

Off-flavors in pond-grown ictalurid catfish: Causes and management options

Ictalurid catfish grown in ponds often acquire undesirable off-flavors prior to harvest. Off-flavors develop when odorous, lipophilic substances in food or water are absorbed across gut or gill epithelium and concentrated in edible tissues. The most common causes of catfish off-flavors are two nontoxic secondary metabolites of planktonic cyanobacteria: geosmin (causing an earthy off-flavor) and 2-methylisoborneol (causing a musty off-flavor). Off-flavored fish are unacceptable for processing, and harvest must be postponed until the source of the odorous compound disappears and the compound purges from edible fish tissue. Harvest delays caused by episodes of off-flavor increase production time, interrupt cash flow, and increase the risk of fish loss. Catfish farmers consider off-flavor to be one of their most important production-related problems. This paper reviews the causes of off-flavor in catfish, pharmacokinetics of uptake and loss of odorous compounds in catfish, seasonality and prevalence of off-flavors, farm- and industry-level impacts, the ecology of cyanobacteria in catfish ponds, and various strategies for preventing or treating cyanobacterial (and other) off-flavors. A decision-making system based on knowledge gained from research is presented as a guide to effective use of the limited tools available to manage off-flavors.     

Longterm effects of soil compaction and tillage on Collembola and straw decomposition in arable soil

Soil core samples were taken from May 1996 to October 1996 at four week intervals to assess the longterm effects of compaction due to soil tillage on Collembola in arable land. Two different tillage systems were studied: conservation tillage (CS) with rotary harrowing to 120 mm depth and conventional tillage (CT) with a mould board plough to 300 mm depth. Soil compaction was achieved by wheeling with graded loads: 0t, 2 × 2.5t and 6 × 5.0t (wheeling frequency × wheel load) in early spring 1995. Litter decomposition rate was investigated by the minicontainer-method, using two different mesh-sizes: 20 μm (excluding mesofauna) and 500 μ (including mesofauna). The substrate used was winter wheat straw, corresponding to the crop cultivated on the field.We recorded 25 species of Collembola. The abundance of Collembola during the growing season was at a minimum in June in both tillage systems. Thereafter, numbers of individuals increased, probably due to better nutrition. Mesaphorura krausbaueri s.l. was eudominant in CS. In CT Folsomia fimetaria and M. krausbaueri s.l. reached high abundances at the end of August. Harvesting and tilling supported population growth in CS, while numbers in CT decreased. The collembolan species showed different preferences in regard to the tillage system and the grade of compaction. During the first 4 weeks of exposure the decomposition rate of straw was highest. The decomposition rate in the minicontainers with 20 μm mesh-size was higher due to better moisture conditions for the microorganisms. After harvest and tilling the decomposition rate increased, especially in the CS-plots, because of aeration and incorporation of residues. Population fluctuation in the minicontainers was caused by migration of Collembola in response to changing moisture conditions. The main species in the minicontainers were large and mobile. Compared to the surrounding soil, species diversity was reduced.     

液体潲食对猪生产性能和健康状况的影响

用液体稻食作为猪口粮,可降低10％～17％的成本有数据表明：液体路食可提高猪生产性能,改善其健康状况并降低死亡率70％液体潲食富合碳水化合物如：液体小麦淀粉,乳酪及熟马铃薯度等液体潲食有一些利于贮藏发酵的特点和优势,发酵可能是由于液体潲食所含合成食品和水份所引起．研究人员采用试验研究5种不同液体饲料贮藏6d后的理化特征变化并统计所有可测变化值,如PN值下降到35－3B;乳酸水平上升为15～30g／kg．本文数据综合自几个试验     

苹果套纸罩对防止果实日灼的效应

试验结果表明，“嘎拉”和“乔纳金”树冠外围果实套纸罩可减弱果实受光强度2／3左右，生长季晴天果实日表面最高温度降低7℃以上，果实日灼率由45％左右降为7％～11％左右。苹果果实日灼易发区在其树冠西南面应适当多留内膛果和半遮荫果，外围裸露果则可套纸罩保护，时间以5月中下旬进行为宜。     

Honey with high levels of antioxidants can provide protection to healthy human subjects

Free radicals and reactive oxygen species (ROS) have been implicated in contributing to the processes of aging and disease. Humans protect themselves from these damaging compounds, in part, by absorbing antioxidants from high-antioxidant foods. This report describes the effects of consuming 1.5 g/kg body weight of corn syrup or buckwheat honey on the antioxidant and reducing capacities of plasma in healthy human adults. The corn syrup treatment contained 0.21 +/- 0.06 mg of phenolic antioxidants per gram, and the two buckwheat honey treatments contained 0.79 +/- 0.02 and 1.71 +/- 0.21 mg of phenolic antioxidants per gram. Following consumption of the two honey treatments, plasma total-phenolic content increased (P < 0.05) as did plasma antioxidant and reducing capacities (P < 0.05). These data support the concept that phenolic antioxidants from processed honey are bioavailable, and that they increase antioxidant activity of plasma. It can be speculated that these compounds may augment defenses against oxidative stress and that they might be able to protect humans from oxidative stress. Given that the average sweetener intake by humans is estimated to be in excess of 70 kg per year, the substitution of honey in some foods for traditional sweeteners could result in an enhanced antioxidant defense system in healthy adults.     

Detection of catfish off-flavour compounds by trained dogs

Six mixed‐breed dogs were trained to detect 2‐methylisoborneol and geosmin in laboratory‐prepared water. The three dogs most responsive to training were selected for further testing to measure their ability to detect these compounds at levels typical of the early stages of an ‘off‐flavour’ event in catfish pond culture. The dogs were given one out of five choices of off‐flavour and ‘on‐flavour’ water samples and were trained to sit at boxes containing off‐flavour sample tubes. At the lowest concentration tested, 10 ng L^?1 of the target compound, the mean correct responses for the three dogs were 37%, 43% and 67%. Additional testing was conducted using off‐flavour pond water samples containing known amounts of these two compounds that occurred naturally. Correct responses for off‐flavour samples varied from 30% to 95%, depending on the sample and the dog. On‐flavour samples were correctly identified with 96% accuracy for all dogs and all samples. Dogs may provide practical early detection of off‐flavour problems in catfish ponds.     

Influence of Soil Organic Carbon on Acute and Chronic Toxicity of Plant Protection Products to Poecilus cupreus (Coleoptera, Carabidae) Larvae (4 pp)

Background, Aims and Scope   Variability of results from terrestrial ecotoxicological tests with arthropods demonstrate the importance of understanding the impact of soil composition has on the bioavailability of pollutants. Beside other soil parameters, the organic C content is known to be relevant to bioavailability. The aim of the present paper was to detect lethal and sublethal effects of plant protection products on soil-dwelling larvae of the carabid beetle Poecilus cupreus under different concentrations of soil organic C. The study was based on a familiar laboratory test method. Methods   Larvae of the laboratory-reared carabid beetle P. cupreus were exposed to dimethoate in a standardised soil (Lufa 2.1), modified to four different concentrations of organic C between 0.5 to 2.8% by admixing peat. Dimethoate was applied to the soil surface at rates ranging between 40 and 250 g a.i./ha. Some larvae were exposed to an application of water to act as a control. One larva was released per test tube, with at least 20 larvae per treatment group. Effects on mortality and developmental time of the larvae and on the hatching weight of adult beetles were recorded. Dimethoate was selected as the test item because some dose-response data for different soils were already available and because the reproducibility of test results with dimethoate had already been shown in a previous ring test. Results and Discussion   With increasing concentration of organic C in the soil substrate, mortality decreased at all tested rates of dimethoate. Consequently, LC50 values increased from 39 to 107 g a.i./ha with increasing organic C content from 0.5 to 2.8%. The results suggest higher bioavailability of dimethoate with decreasing content of organic C. The replication and magnitude of sublethal effects (hatching weight and developmental time) was insufficient to detect a clear interaction between dimethoate and organic C. Conclusion   The results of the experiment reveal that the concentration of organic C in the soil substrate is influential on the effects and, by association, the toxicity of dimethoate to larvae of P. cupreus. For the interpretation of terrestrial ectotoxicological tests with arthropods, the composition of the substrate has to be taken into account. Recommendations and Outlook   For reliable and reproducible test results, a well-defined and thoroughly controlled composition of the test soil is highly recommended. Test results should be used for risk assessments only after having taken the soil composition, especially the organic C content, into account.     

Rapid classification of basil chemotypes by various vibrational spectroscopy methods

The potential of vibrational spectroscopy methods (attenuated total reflectance/Fourier-transform-infrared (ATR/FT-IR), FT-Raman and near infrared (NIR) spectroscopy) for the identification and quantification of valuable as well as carcinogenic substances in different basil chemotypes is described. It is shown that all main volatile components occurring in different basil accessions can be reliably determined in the isolated essential oils or solvent extracts but also in the air-dried herbs. While NIR data can be interpreted only by chemometric methods, IR and Raman spectra present characteristic key bands of the individual volatiles; therefore, in the latter case, a discrimination of basil chemotypes is frequently possible without applying chemometric algorithms. NIR calibrations are successfully established for various terpenoids and phenylpropanoids; on the basis of these data, the content of the two carcinogenic compounds methyleugenol (range: 2-235 microg/100 g) and estragole (range: 34-138 microg/100 g) can be reliably predicted in air-dried basil leaves (R (2) (coefficient of determination) = 0.951; SECV (standard error of cross validation) = 19.1 microg/100 g and R (2) = 0.890; SECV = 12.8 microg/100 g, respectively). The described methods were found to be very useful tools for the efficient selection of special basil single plants, adapted to the new demands set by the legislator and the consumer. Furthermore, they can be applied in industry to very easily control the purifying, blending, and redistilling processes of basil oil.