黑麦草内生真菌对植物病原真菌生长的影响

摘要：为确定黑麦草内生真菌及其发酵产物对病原真菌生长的影响,从不同品种的多年生黑麦草(Lolium perenne)(爱神特、美达丽、顶峰和球道)中分离出N A1、N M2、N P2和N F1共4株Neotyphodium属的内生真菌菌株,分别采用平板对峙培养、菌落生长及孢子萌发等方法对细交链孢(Alternaria alternata)、小麦根腐离蠕孢(Bipolaris sorokiniana)、新月弯孢霉(Curvularia lunata)和德氏霉(Drechslera sp.)等病原真菌进行室内生物测定。结果表明,在平板对峙培养中,不同内生真菌对同一种病原菌的抑制作用不同,不同病原菌对同一内生真菌的敏感程度表现出差异,4株内生真菌对各病原菌的抑制率范围依次为42.51%~46.25%、31.45%~43.97%、34.51%~46.55%和40.19%~46.62%。在对病原菌的生物测定中,4株内生真菌的发酵产物均可抑制病原菌的生长,N F1菌株的抑菌效果显著高于其他3株内生真菌(P＜0.05),对小麦根腐离蠕孢的菌落生长和孢子萌发表现出较强的抑制作用,抑制率分别达到57.20%和86.60%。     

DCD 在不同质地土壤上的硝化抑制效果和剂量效应研究

通过硝化抑制剂抑制土壤硝化作用是实现作物铵硝混合营养和提高氮肥利用率的重要途径之一。本试验采用室内模拟的方法, 在人工气候室(25 ℃)黑暗培养条件下, 应用新疆石灰性土壤研究了不同剂量的双氰胺(dicyandiamide, DCD)在砂土、壤土、黏土3 种不同质地土壤中对土壤硝态氮、铵态氮转化的影响及DCD 的剂量效应和硝化抑制效果。处理30 d 内, 各剂量DCD 处理对砂土的硝化抑制率为96.5%~99.4%(平均值为98.3%), 在黏土上为66.9%~85.6%(平均值为77.6%), 在壤土上为49.3%~79.4%(平均值为67.7%), 总体硝化抑制率表现为砂土>黏土>壤土。在砂土上DCD 的剂量效应不明显, DCD 用量从纯氮的1.0%增加到7.0%时, 土壤中硝态氮含量仅增加1.9~10.7 mg·kg^-1(培养30 d 时); 而在壤土和黏土中, 土壤硝态氮含量随DCD 浓度的增加而显著下降, 存在明显剂量效应。这说明施用DCD 可显著抑制新疆石灰性土壤的硝化作用过程, 在砂土、壤土、黏土中DCD 的最佳浓度分别为纯氮用量的6.0%、7.0%和7.0%, 并在培养30 d 内发挥显著作用。     

检测牛边缘无浆体抗体的竞争抑制ELISA方法的建立

为建立检测牛边缘无浆体(Anaplasma marginale)抗体的方法,本研究以牛A.marginale膜表面重组MSP5蛋白作为包被抗原,抗MSP5单克隆抗体(MAb)作为竞争抗体,建立一种用于检测牛A marginale抗体的重组MSP5蛋白竞争抑制ELISA(CI-ELISA)方法.经优化确定CI-ELISA的最佳反应条件为:抗原包被浓度为2μg/孔,封闭液为2%脱脂乳,MAb的稀释度为1:400,酶标二抗的稀释度为1:1000,阴性和阳性血清临界值分别为33%和40%;该方法具有良好的特异性和重复性;2 348份临床血清样品的检测结果表明,217份为阳性,阳性率为9.2%,与IDEXXA marginale抗体检测试剂盒的阳性符合率为95.3%,阴性符合率为100%.本实验建立的ELISA方法具有较高的特异性和重复性,可用于流行病学调查研究.     

超声波辅助提取槐花总黄酮及其对酪氨酸酶的抑制作用

利用超声波辅助从槐花中提取总黄酮,通过单因素和正交试验确定超声波辅助提取槐花中总黄酮的最佳工艺,并测定槐花提取物对蘑菇酪氨酸酶活性的影响.结果表明,最佳提取工艺条件为2.0 g槐花粉,体积分数60%的乙醇40mL、提取温度80℃、超声波功率300W、提取时间30min,总黄酮得率(16.5±0.4)%.槐花提取物对蘑菇...     

Evaluation of the selective respiratory inhibition method for measuring the ratio of fungal:bacterial activity in acid agricultural soils

A procedure for the measurement of the fungal and bacterial contribution to substrate-induced respiration was tested in three arable soils. Glucose and different amounts of cycloheximide (eukaryote inhibitor) and streptomycin sulfate (prokaryote inhibitor) were added to soil suspensions, and respiration (CO₂ evolution) was measured. Streptomycin sulfate concentrations from 10 to 120 mg ml^–1 soil solution caused a stable inhibition of respiration. Amounts of cycloheximide ranging from 5 to 35 mg ml^–1 showed an increasing inhibition. In a test with separate and combined addition of the antibiotics at maximum inhibitory concentrations, inhibition by streptomycin was completely overlapped by cycloheximide. This indicated non-target inhibition which may lead to overestimation of fungal respiration. Experiments with sterilized soils inoculated with either fungi or bacteria confirmed that streptomycin selectively inhibited bacteria. Cycloheximide, however, did not only inhibit fungal respiration already at 2 mg ml^–1, but also increasingly inhibited bacterial respiration at increasing concentrations. Only at less than 5 mg cycloheximide ml^–1 was the condition of selective fungal inhibition fulfilled. When 2 mg cycloheximide and 10 mg streptomycin sulfate ml^–1 were applied, the sum of the separate inhibitions almost equalled the combined inhibition by the mix of both inhibitors in field samples. This method yielded fungal:bacterial respiration ratios of 0.50 to 0.60, and confirmed the dominance of bacteria in Dutch arable soils. The ratios obtained by the selective inhibitors were not correlated with, and were higher than, ratios of fungal:bacterial biovolume (0.19 to 0.46) as determined by microscopy and image analysis. Similar measurements in a forest soil (A-horizon) raised doubts on the reliability of the fungal inhibition by cycloheximide in this soil. It is concluded that the separate:combined inhibition ratio should always be checked, and comparison with other approaches is recommended. Received: 17 September 1996     

无机氮对高原沼泽甲烷氧化的影响

In a series of laboratory incubations using soils of two contrasting sites from a temperate marsh on the Qinghai-Tibet Plateau, potential methane (CH₄) oxidation rates were measured to study the effects of inorganic N inputs on CH₄ oxidation. For a drained site, subsurface peat (5-15 cm) at an initial 20 μL CH₄ L^-1 showed a significantly different (P < 0.05) CH₄ oxidation rate compared to other soil depths, with a maximal rate of 20.9 ng CH₄ gDW (dry weight)^-1 h^-1; the underlying mineral soil layers (15-30 and 30-50 cm) also had a strong CH₄ oxidation capacity at about an initial 2000 μL CH₄ L^-1. With a waterlogged site, the CH₄ oxidation rate in an aerobic incubation was significantly greater (P < 0.05) in the surface soil layer (0-5 cm) compared to the 15-30 and 30-50 cm depths. There was generally no or a very weak effect from addition of NO₃^- on CH₄ oxidation. In marked contrast, NH₄⁺ salts, such as (NH₄)₂SO₄, NH₄Cl and NH₄NO₃, exhibited strong inhibitions, which varied as a function of the added salts and the initial CH₄ level. Increasing NH₄⁺ usually resulted in greater inhibition and increasing initial CH₄ concentrations resulted in less. NH₄⁺ inhibition on CH₄ oxidation in natural high-altitude, low-latitude wetlands could be as important as has been reported for agricultural and forest soils. The NH₄⁺ effects on the CH₄ oxidation rate need to be further investigated in a wide range of natural wetland soil types.     

Evaluation of the acetylene inhibition method for measuring denitrification in soilless plant culture systems

Denitrification measurements by means of the acetylene inhibition method require a continuous presence of acetylene to block the microbial reduction of N₂0 to N₂. To examine the effect of such steady exposures on the growth of plants, roots of cucumber and tomato seedlings were treated with different acetylene concentrations. Acetylene concentrations of 1 vol% in the gas phase, which were necessary for complete inhibition of N₂ formation, led to a significant retardation of root growth. This was partly due to trace amounts of ethylene contained in the acetylene gas which could not be removed with the usual prescrubbing through a sulfuric acid train. As a result of the growth impairment, oxygen consumption in the root zone decreased after 4 days of exposure. In order to avoid these side effects, the denitrification measurements in soilless cultures were performed on individual plants over a limited period of 2–3 days. The flow-through chamber method proved to be suitable for determining the gaseous N losses in a closed-loop system. It avoided greater air variations from the environmental conditions (substrate temperature, airflow and plant composition) and excluded errors in measurement caused by injury to roots and spatial variability of denitrification activity in the root medium. For exact estimation of the gaseous N losses, preceding 24-h acetylene fumigation was necessary. Subsequently at least three gas samples had to be taken throughout the day, because the N₂O+N₂ emissions were subject to a pronounced diurnal variability.     

The effects of concurrent administration of cytochrome P-450 inhibitors on the pharmacokinetics of oral methadone in healthy dogs

ObjectiveThe objective was to examine the effects of inhibiting cytochrome P450 (CYP) on the pharmacokinetics of oral methadone in dogs.Study designProspective non-randomized experimental trial.AnimalsSix healthy Greyhounds (three male and three female).MethodsThe study was divided into two phases. Oral methadone (mean = 2.1 mg kg^?1 PO) was administered as whole tablets in Phase 1. In Phase 2 oral methadone (2.1 mg kg^?1 PO) was administered concurrently with ketoconazole (13.0 mg kg^?1 PO q 24 hours), chloramphenicol (48.7 mg kg^?1 PO q 12 hours), fluoxetine (1.3 mg kg^?1 PO q 24 hours), and trimethoprim (6.5 mg kg^?1 PO q 24 hours). Blood was obtained for analysis of methadone plasma concentrations by liquid chromatography with mass spectrometry. The maximum plasma concentration (C_max), time to C_max (T_max), and the area under the curve from time 0 to the last measurable time point above the limit of quantification of the analytical assay (AUC_0–LAST) were compared statistically.ResultsThe C_max of methadone was significantly different (p = 0.016) for Phase 1 (5.5 ng mL^?1) and Phase 2 (171.9 ng mL^?1). The AUC_0–LAST was also significantly different (p = 0.004) for Phase 1 (13.1 hour ng mL^?1) and Phase 2 (3075.2 hour ng mL^?1).Conclusion and clinical relevanceConcurrent administration of CYP inhibitors with methadone significantly increased the area under the curve and plasma concentrations of methadone after oral administration to dogs. Further studies are needed assessing more clinically relevant combinations of methadone and CYP inhibitors.     

Exploitation of intestinal colonization-inhibition between salmonella organisms for live vaccines in poultry: potential and limitations

Immunization represents one of the most important methods to increase the resistance of chickens against Salmonella infection. In addition to the development of an adaptive immune response, oral administration of live Salmonella strains to day-old chicks provides protection against infection within hours by intestinal colonization-inhibition. For the exploitation of this phenomenon, practical information on colonization-inhibition between Salmonella organisms is needed. Colonization-inhibition capacity between Salmonella strains from serogroups B, C1, C2, D and G was assessed in chickens. The most profound level of intestinal colonization-inhibition occurred between isogenic strains. Inhibition between strains of the same serovar was greater than that between strains of different serovars. The degree of inhibition between different serovars was not sufficiently high to identify a single strain which might inhibit a wide range of other Salmonella organisms. However, as Salmonella Enteritidis is the dominant serovar in poultry in many countries and because of the profound colonization-inhibition within this serovar there is a considerable potential to exploit this phenomenon in the development of novel live S. Enteritidis vaccines. Treatment of young chicks with mixtures of different Salmonella serovars resulted not only in a very strong growth inhibition of the isogenic strains but also in a substantial inhibition of heterologous serovars. The potential of mixtures of heterologous Salmonella strains as a 'Salmonella Inhibition Culture' and as a 'live Salmonella vaccine' should be further explored.     

辣椒疫霉菌拮抗木霉的筛选及抑菌机制研究

利用生长势和生长抑制率法从61株木霉菌株中筛选出辣椒疫霉拮抗菌株TR39,并对其抑菌机制进行了研究。结果表明:TR39对辣椒疫霉的抑制机制有重寄生和竞争作用,体外可以产生几丁质酶、β-1,3-葡聚糖酶和纤维素酶等细胞壁降解酶;TR39还对11种其它病原真菌具有较强的抑制作用。