The screening toolbox of bioactive substances from natural products: a review

Hunting lead compounds from natural products plays a vital role in finding successful drug candidates. The efficiency of screening campaigns is mainly determined by the validity of selected screening models. To screen desired lead compounds, researchers have developed a plethora of experimental screening models. However, the considerable diversity of screening models from animal models, tissue models, to cell models and so on, may cause some trouble in choosing the suitable one. This review provides a toolbox of experimental screening models that have been used to discover new drug candidates from natural products. Two screening indexes are designed for different research directions in this screening toolbox. Index I is proposed from the direction of screening different objective substance populations, including plant extracts, active fractions and pure compounds; index Π is according to screening different drug properties, including pharmacological properties, pharmacokinetic properties and affinity binding properties. We hope that the abbreviated bibliographies will help readers to quickly retrieve useful information by two screening indexes and provide certain reference value for choosing more appropriate screening models. Finally, we discuss ways of improving model systems, as well as future directions.     

Microbial and microfaunal community structure in cropping systems with genetically modified plants

Soils from field sites at Foulum (DK), Narbons (FR) and Varois (FR) planted with genetically modified maize expressing either the insecticidal Bacillus thuringiensis protein (Bt) or herbicide tolerance (HT), as described elsewhere in this volume, were analysed for nematodes, protozoa and microbial community structure. These analyses were mirrored in single-species testing and in mesocosm experiments, and were coordinated with field samples taken for microarthropods, enchytraeids and earthworms so allowing for cross-comparison and a better understanding of the results observed in the field. Over the first 2 years of the field experiments (in 2002 and 2003), the effect of Bt-maize was within the normal variation expected in these agricultural systems. Sampling in 2004 and 2005 was expanded to include the effects of tillage (i.e. reduced tillage versus conventional tillage) and also the use of HT-maize. Tillage had major effects regardless of soil type (Varois or Foulum), with reduced-tillage plots having a greater abundance of microfauna and a different microbial community structure (measured both by phospholipid fatty-acid analysis (PLFA) and by community-level physiological profiling (CLPP)) from conventionally tilled plots. Grass, as a contrasting cropping system to maize, also had an effect regardless of soil type and resulted in greater microfaunal abundance and an altered microbial community structure. Differences in crop management, which for the Bt-maize was removal of the insecticide used to control European corn borer and for HT-maize was a change in herbicide formulation, were only tested at single sites. There were differences in microbial community structure (CLPP but not PLFA) and sporadic increases in protozoan abundance under the Bt-crop management. The HT-maize cropping system, which covered a shorter period and only one site, showed little change from the conventional system other than an altered microbial community structure (as measured by PLFA only) at the final harvest. The Bt-trait had a minimal impact, with fewer amoebae at Foulum in May 2003, fewer nematodes at Foulum in May 2004 but more protozoa at Varois in October 2002 and an altered microbial community structure (PLFA) at Foulum in August 2005. These were not persistent effects and could not be distinguished from varietal effects. Based on the field evaluations of microfauna and microorganisms, we conclude that there were no soil ecological consequences for these communities associated with the use of Bt- or HT-maize in place of conventional varieties. Other land management options, such as tillage, crop type and pest management regime, had significantly larger effects on the biology of the soil than the type of maize grown.     

Interactions between 14C-labelled atrazine and the soil microbial biomass in relation to herbicide degradation

A laboratory incubation experiment was set up to determine the effects of atrazine herbicide on the size and activity of the soil microbial biomass. This experiment was of a factorial design (0, 5, and 50 g g^–1 soil of non-labelled atrazine and 6.6×10³ Bq g^–1 soil of ¹⁴C-labelled atrazine) x (0, 20, and 100 g g^–1 soil of urea-N) x (pasture or arable soil with a previous history of atrazine application). Microbial biomass, measured by substrate-induced respiration and the fumigation-incubation method, basal respiration, incorporation of ¹⁴C into the microbial biomass, degradation of atrazine, and ¹⁴C remaining in soil were monitored over 81 days. The amount of microbial biomass was unaffected by atrazine although atrazine caused a significant enhancement of CO₂ release in the non-fumigated controls. Generally, the amounts of atrazine incorporated into the microbial biomass were negligible, indicating that microbial incorporation of C from atrazine is not an important mechanism of herbicide breakdown. Depending on the type of soil and the rate of atrazine application, 18–65% of atrazine was degraded by the end of the experiment. Although the pasture soil had twice the amount of microbial biomass as the arable soil, and the addition of urea approximately doubled the microbial biomass, this did not significantly enhance the degradation of atrazine. This suggests that degradation of atrazine is largely independent of the size of the microbial biomass and suggests that other factors (e.g., solubility, chemical hydrolysis) regulate atrazine breakdown. A separate experiment conducted to determine total amounts of ¹⁴C-labelled atrazine converted into CO₂ by pasture and arable soils showed that less than 25% of the added ¹⁴C-labelled atrazine was oxidised to ¹⁴CO₂ during a 15-week period. The rate of degradation was significantly greater in the arable soil at 24%, compared to 18% in the pasture soil. This indicates that soil microbes with previous exposure to atrazine can degrade the applied atrazine at a faster rate.     

Environmental impacts from herbicide tolerant canola production in Western Canada

The commercial production of herbicide tolerant (HT) canola began in Western Canada in 1997. With more than a decade of use, the actual farm-level environmental impact of HT canola can be evaluated. This article reports on a spring 2007 survey of nearly 600 canola farmers in the three prairie provinces of Western Canada. Producers were asked about their crop production experiences for 2005 and 2006 and expected crop planting for 2007. A reduction in the total number of chemical applications over the 3-year period was reported, resulting in a decrease of herbicide active ingredient being applied to farmland in Western Canada of nearly 1.3 million kg annually. Fewer tillage passes over the survey period were reported, improving moisture conservation, decreasing soil erosion and contributing to carbon sequestration in annual cropland. An estimated 1 million tonnes of carbon is either sequestered or no longer released under land management facilitated by HT canola production, as compared to 1995. The value of this carbon off-set is estimated to be C$5 million. Comparisons with similar studies and against non-adoption of HT canola can guide future decisions about HT canola adoption.     

Management of cruciferous cover crops by mowing for soil and water conservation in southern Spain

In recent years, the use of cover crops in Mediterranean olive orchards has increased due to serious soil erosion problems and surface water contamination by herbicides. In these areas, the annual precipitation regime is strongly seasonal, with dry summers that require killing the cover crop before it competes with the trees for water. Cruciferous species are being introduced as cover crops in southern Spain, and their management by mowing could reduce the use of herbicides. However, the use of mowing as a management system requires an understanding of the phenology of these species to identify the most suitable mowing date to derive the greatest possible soil water content. The aims of this study were the following: (1) to assess the susceptibility of cruciferous species to mowing, their regrowth ability and the persistence of their residues on the soil surface after mowing, and (2) to identify the best mowing date for the cover crops in relation to the soil moisture content in the environmental conditions of southern Spain. For these purposes, the emergence, ground cover, biomass and regrowth after two mowing dates of common mustard (Sinapis alba L. subsp. mairei), rocket (Eruca vesicaria), radish (Raphanus sativus) and Ethiopian mustard (Brassica carinata) were evaluated in field trials during 2001/2002. In addition, during 2002/2003 and 2003/2004, the moisture content of soil sowed with common mustard and rocket cover crops was assessed at different mowing dates and compared with a bare soil control. Common mustard was the most favourable species for management by mowing due to its lack of regrowth after mowing. Early mowing (March 10th) reduced soil moisture due to the regrowth of the cover crop, fast decomposition of cover residues and weed proliferation. Late mowing (April 24th) led to little or no regrowth of the cover crops, large biomass and high persistence of cover residues, which provided effective soil ground cover, avoided the emergence of spring-summer weeds and helped retain soil moisture, reaching a similar water content to bare soil. These results suggest that cruciferous cover crops killed by mowing in late April can be used to replace no-tillage bare soil management systems to reduce the use of herbicides and preserve soil and water quality.     

玉米抗除草剂体细胞变异体的筛选及植株再生

将玉米优良自交系齐 31 9和N1 0 - 6产生的胚性愈伤组织 ,转移到加有半致死浓度除草剂绿磺隆的培养基上 ,经 3代筛选 ,获得抗除草剂愈伤组织。在加有除草剂的分化培养基上 ,抗性愈伤组织分化出植株。除草剂对愈伤组织的生长与分化有显著影响。再生植株移栽成活后 ,自交结实 ,获得种子。再生植株农艺性状与对照相似。除草剂抗性鉴定结果表明 ,再生植株及其后代对除草剂绿黄隆的抗性有了明显提高     

筛选和应用拮抗细菌防治稻瘟病的研究

从水稻叶片、稻田土壤、菜地土壤和田间菌核中共分离细菌菌株1228株,经平板测定,对稻瘟病菌有拮抗作用的菌株有246株,其中具有强拮抗作用的菌株有29株。8个代表性的菌株对水稻稻瘟病菌、水稻纹枯病菌和水稻恶苗病菌均表现了强的拮抗作用。田间药效试验表明,菌株V-297在吉安市吉州区和修水县的平均防效分别为55.09%和57.20%;菌株R-122分别为55.61%和54.15%。经初步鉴定,菌株V-297和R-122均为Bacillusspp.;菌株S-96为Pseudomonassp.。     

超高产水稻的高光效特性和高光效材料的筛选

综述了超高产水稻的光合特性、光抑制、光合性状的遗传规律和高光效材料的筛选等内容,比较详细地介绍了光抑制部位及其表现,光抑制的原因以及光抑制中热耗散的可能途径及作用等。由于叶黄素循环在水稻耐光抑制、增加热耗散中起着十分重要的作用,也总结了叶黄素循环的功能。最后,讨论和展望了超高产水稻的高光效育种前景。     

植物病原真菌的拮抗放线菌筛选

[目的]筛选对植物病原真菌有抑制作用的拮抗放线菌。[方法]以棉花枯萎病菌为靶标菌,采用稀释平板法从4份土样中分离放线菌,筛选拮抗放线菌并测定其理化特性和抗菌谱。[结果]分离到113株放线菌,获得拮抗菌株23株,其中6株对棉花枯萎病菌抗性较强。除332#菌株外,其他菌株均可液化明胶。除323#菌株外,其他菌株均可胨化牛奶。6株拮抗放线菌的利用淀粉能力都较强。219#和323#可分解纤维素。121#3、23#3、27#和430#最适生长温度约为28℃,219#和332#分别为28~35℃和35~40℃。6菌株最适生长pH值均为6~7。6菌株对棉花枯萎病菌有较强的抑制作用。菌株121#、219#抗菌谱较广,对真菌抗性明显。[结论]121#3、27#和430#在初步液体培养中生长良好,产生较高抗菌活性物质,可用于抗真菌代谢产物的研究和应用。     

瓜类枯萎病菌拮抗放线菌分离方法的研究

通过对土壤样品进行不同温度、不同孢子激活剂、不同抑制剂、不同培养基等条件的梯度试验,得到对黄瓜枯萎病菌有拮抗作用的土壤放线菌的分离方法:将土壤样品经100℃干热处理1 h,用0.05%的SDS稀释,分别涂布于含有1μg/ml青霉素的高氏合成1号琼脂、淀粉琼脂、腐植酸—维生素琼脂(HVG)组合培养基上,置于28℃培养7 d,并分离到69株瓜类枯萎病的拮抗放线菌。