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1.
Cells and cell-free solutions of the culture filtrate of the bacterial symbiont, Xenorhabdus nematophila taken from the entomopathogenic nematode Steinernema carpocapsae in aqueous broth suspensions were lethal to larvae of the diamondback moth Plutella xylostella. Their application on leaves of Chinese cabbage indicated that the cells can penetrate into the insects in the absence of the nematode vector. Cell-free solutions containing metabolites were also proved as effective as bacterial cells suspension. The application of aqueous suspensions of cells of X. nematophila or solutions containing its toxic metabolites to the leaves represents a possible new strategy for controlling insect pests on foliage.  相似文献   

2.
Cells and cell-free solutions of the culture filtrate of the bacterial symbiont, Xenorhabdus nematophila taken from the entomopathogenic nematode Steinernema carpocapsae in aqueous broth suspensions were lethal to larvae of the diamondback moth Plutella xylostella. Their application on leaves of Chinese cabbage indicated that the cells can penetrate into the insects in the absence of the nematode vector. Cell-free solutions containing metabolites were also proved as effective as bacterial cells suspension. The application of aqueous suspensions of cells of X. nematophila or solutions containing its toxic metabolites to the leaves represents a possible new strategy for controlling insect pests on foliage.  相似文献   

3.
INTRODUCTION Entomopathogenic nematodes of the generaSteinernema and Heterorhabditis have been used tocontrol a wide range of agriculturally important insectpests (Kaya and Gaugler, 1993). The mechanism bywhich these nematodes are able to infect and repro-duce in the insect host involves a mutual relationshipbetween the nematode and the symbiotic bacteria,Xenorhabdus spp. and Photorhabdus spp. (Akhurstand Dunphy, 1993; Forst and Nealson, 1996). Poinarand Thomas (1966) established tha…  相似文献   

4.
1IntroductionNeural stem cells have great potential for use intreating neural damage and neurodegenerative disor-ders such as Parkinson’s Disease and Alzhei mer’s Di-sease.They are undifferentiated elements found inboth the embryonic and adult brain[1].Growth factor-responsive cells fromthe embryonic and adult controlnervous system(CNS)were isolated and culturedinvitrointhe early1990’s[2-4].Thelocation of CNS stemcells in the adult brain were therefore identified[5]mainlyinthe striatum,…  相似文献   

5.
由于细胞间相互作用的复杂性使得建立外电场作用下悬液细胞膜损耗功率计算模型非常困难,提出了用场近似等效方法解决该建模难题.基于有效介质理论,用等效原理,研究了外电场作用下悬液细胞跨膜电压变化规律,然后确定细胞膜内电场分布.最后根据焦耳定律,建立了外电场作用下悬液细胞膜损耗功率计算模型.模型表明:对直流和低频场,悬液细胞膜的能量损耗主要为导电损耗;当外加频率超过细胞膜的弛豫频率时,介质损耗占主导部分.  相似文献   

6.
不同稳定机制对SiC颗粒分散稳定性的影响   总被引：2，自引：0，他引：2  
选用纳米级SiC颗粒为原料，分别采用单一静电稳定机制、加入PEG的空间位阻稳定机制和加入PMAA—NH4的电空间稳定机制，制备固相体积分数为1vol％的SiC水悬浮液，通过Zeta电位、沉降实验和粘度测定及粒度分析等手段，最终分别获得了碱性条件下高分散、高稳定的SiC水悬浮液。  相似文献   

7.
介绍了从菠菜中提取叶绿素B的一种方法,以蔗糖为固定相,乙醚-石油醚(1:9,v/v)溶液作为展开剂从菠菜色素中分离叶绿素B,用紫外-可见光光度计和荧光光谱分别检测分离出的叶绿素B.并研究了叶绿素B在不同溶剂中的荧光光谱.通过研究我们得出:叶绿素B在溶剂中的光谱性质与溶剂的介电常数有关.  相似文献   

8.
Psidium guajava （guava） leaf is a phytotherapic used in folk medicine to treat gastrointestinal and respiratory disturbances and is used as anti-inflammatory medicine. In nuclear medicine, blood constituents （BC） are labelled with technetium-99m （^99mTc） and used to image procedures. However, data have demonstrated that synthetic or natural drugs could modify the labelling of BC with ^99mTC. The aim of this work was to evaluate the effects of aqueous extract of guava leaves on the labelling of BC with ^99mTc. Blood samples of Wistar rats were incubated with different concentrations of guava extract and labelled with ^99mTc after the percentage of incorporated radioactivity （%ATI） in BC was determined. The results suggest that aqueous guava extract could present antioxidant action and/or alters the membrane structures involved in ion transport into cells, thus decreasing the radiolabelling of BC with ^99mTc. The data showed significant （P〈0.05） alteration of ATI in BC from blood incubated with guava extract.  相似文献   

9.
While data are available on the effect of medicinal plants on intestinal motility and their antibacterial action, there is a paucity of information on their mode of action on various aspects of diarrheal pathogenicity, namely colonization to intestinal epithelial cells and production/action of enterotoxins. Crude decoction of dried leaves of Pongamia pinnata was evaluated for its antimicrobial （antibacterial, antigiardial and antirotaviral） effect; and its effect on production and action of enterotoxins （cholera toxin, CT; Escherichia coli labile toxin, LT; and E. coli stable toxin, ST）; and adherence of enteropathogenic E. coli and invasion of enteroinvasive E. coli and Shigellaflexneri to epithelial cells. The decoction had no antibacterial, antigiardial and antirotaviral activity, but reduced production of CT and bacterial invasion to epithelial cells. The observed results indicated that the crude decoction ofP. pinnata has selective antidiarrheal action with efficacy against cholera and enteroinvasive bacterial strains causing bloody diarrheal episodes.  相似文献   

10.
E—P~H图简介     
本文简单的讨论了E—P~H图的作图方法和它在水溶液里的应用.  相似文献   

11.
In October 2003, a new bacterial disease with symptoms similar to those caused by Xanthomonas axonopodis pv.poinsettiicola was observed on poinsettia leaves at a flower nursery in Zhejiang Province of China. Three Xanthomonas strains were isolated from infected plants and classified as X. axonopodis. They were differentiated from the pathotype strain LMG849 of X. axonopodis pv. poinsettiicola causing bacterial leaf spot of poinsettia by comparison of pathogenicity, substrate utilization and BOX-PCR genomic fingerprints.  相似文献   

12.
INTRODUCTION In recent years poinsettia cultivation has blos-somed from a small garden business into a multimil-lion-dollar industry in China. Some fungal diseases, such as Rhizoctonia stem and root rot, Pythium root rot, Fusarium wilt, and Botrytis blight have been reported to cause considerable damage during propagation (Sun et al., 2003). A new bacterial dis-ease characterized by leaf spot appearance was first observed on poinsettia in October 2003, in the Xiaoshan district of Zhej…  相似文献   

13.
针对冀东地区常见的九种树木叶片及相应虫沙,对其叶绿素提取液的吸光度值及吸收光谱进行了对比研究。结果显示：鲜叶乙醇提取液在430nm和663nm有强吸收峰,虫沙乙醇提取液在410nm和663nm有强吸收峰。相同条件下,乙醇对于鲜叶片中叶绿素的提取效果优于丙酮;而丙酮对于各种虫沙中叶绿素的提取效果优于乙醇。  相似文献   

14.
This study focused, for the first time, on the effect of ultrasonic features on the extraction efficiency of secondary metabolites in mustard seed cake(MSC). The nematostatic potential of sonicated seed cake was examined against the second-stage juveniles(J2 s) of root-knot nematode, Meloidogyne javanica. The results show that a 35 ppm(parts per million) concentration of a sonicated extract(SE) sample of MSC caused 65% J2 s mortality at 18 h exposure period in vitro. It also significantly suppressed the root-knot index(RKI=0.94) in tomato roots. The lethal concentration values for SE were 51.76, 29.79, and 13.34 ppm,respectively, at 6, 12, and 18 h of the exposure period, and the lethal concentration values for the non-sonicated extract(NSE)sample were 116.95, 76.38, and 55.59 ppm, respectively, at similar exposure time. Sinapine and gluconapin were identified as the major compounds in ultrasonic-assisted MSC. Because of the high extraction efficiency of metabolites in the SE, all treatments of SE were shown to be antagonistic to J2 s. Thus, this study of ultrasonication activity-based profiling of MSC may help generate target-based compounds at a scale relevant to the control of disease caused by nematodes in economic crops.  相似文献   

15.
The objective of the investigation was to study the application of ultrasound reactor technology （USRT） as a disinfectant for reduction of fungi from sewage effluent. Fungi are carbon heterotrophs that require preformed organic compounds as carbon sources. USRT is an attractive means to improve water quality because of the system simplicity and no production of toxic by-products. An ultrasound reactor produces strong cavitation in aqueous solution causing shock waves and reactive free radicals by the violent collapse of the cavitation bubble. These effects should contribute to the physical disruption of microbial structures and inactivation of organisms. There was significant reduction in fungal growth, with decreased fungal growth with increasing USRT. In this study, ultrasound irradiation at a frequency of 42 kHz was used to expose suspensions of fungi to evaluate the disinfection efficacy of the ultrasound reactor. Also, this study showed that in this system more than 99% reduction of sewage fungi was achieved after 60 min.  相似文献   

16.
The effects of both computer animations of microscopic chemical processes occurring in a galvanic cell and conceptual change instruction based on chemical demonstrations on students' conceptions of current flow in electrolyte solutions were investigated. Preliminary results for verbal conceptual questions suggest that conceptual change instruction was effective at dispelling student misconceptions that electrons flow in aqueous solutions of electrochemical cells. Computer animations did not appear to have an effect on students' responses to visual or verbal conceptual questions. An animation/conceptual change interaction for verbal conceptual questions suggests that animations may prove distacting when the questions do not require students to visualize. Data from this study also suggests that lecture attendance and recitation participations helped students answer visual questions.  相似文献   

17.
Schwertmannite(Sh), a poorly crystalline iron(hydr)oxide that usually appears in acid mine drainage, plays a significant role in the immobilization of As(V). In this study, the effects of UV irradiation and oxalate on the dissolution of Sh with structurally incorporated As(V) [Sh-As(V)] and the subsequent mobilization of As(V) were investigated at pH 3.0. In the dark, more total dissolved Fe was produced(the maximum value was 33.2 mg/L) in the suspensions of Sh-As(V) with oxalate than in those without oxalate. UV irradiation slightly enhanced the mobilization of As(V) for the system of Sh-As(V)-1 and Sh-As(V)-2 in the absence of oxalate compared with that in the dark. However, in the presence of oxalate, UV irradiation caused the concentration of mobilized As(V) to decline by 630-875% compared with that in the dark. This study enhanced our understanding of the mobilization of As(V) and demonstrated that UV irradiation could contribute to the immobilization of As(V) on Sh in aqueous environments containing oxalate.  相似文献   

18.
Alkaloids are plant secondary metabolites that are widely distributed in Nicotiana species and contribute greatly to the quality of tobacco leaves. Some alkaloids, such as nornicotine and myosmine, have adverse effects on human health. To reduce the content of harmful alkaloids in tobacco leaves through conventional breeding, a genetic study of the alkaloid variation among different genotypes is required. In this study, alkaloid profiles in leaves of five Nicotiana tabacum cultivars and Nicotiana tomentosiformis were investigated. Six alkaloids were identified from all six genotypes via gas chromatograph-mass spectrometry (GC-MS). Significant differences in alkaloid content were observed both among different leaf positions and among cultivars. The contents of nornicotine and myosmine were positively and significantly correlated (R 2=0.881), and were also separated from those of other alkaloids by clustering. Thus, the genotype plays a major role in alkaloid accumulation, indicating a high potential for manipulation of alkaloid content through traditional breeding.  相似文献   

19.
Syzygium campanulatum Korth is a plant, which is a rich source of secondary metabolites (especially flavanones, chalcone, and triterpenoids). In our present study, three conventional solvent extraction (CSE) techniques and supercritical fluid extraction (SFE) techniques were performed to achieve a maximum recovery of two flavanones, chalcone, and two triterpenoids from S. campanulatum leaves. Furthermore, a Box-Behnken design was constructed for the SFE technique using pressure, temperature, and particle size as independent variables, and yields of crude extract, individual and total secondary metabolites as the dependent variables. In the CSE procedure, twenty extracts were produced using ten different solvents and three techniques (maceration, soxhletion, and reflux). An enriched extract of five secondary metabolites was collected using n-hexane:methanol (1:1) soxhletion. Using food-grade ethanol as a modifier, the SFE methods produced a higher recovery (25.5%?84.9%) of selected secondary metabolites as compared to the CSE techniques (0.92%?66.00%).  相似文献   

20.
In recent years, the frequent use of suspensions and the racial disparities in their application, particularly for nonviolent behaviors, has created a maelstrom of public pressure for schools to adjust their suspension practices. In an era of increasing institutional accountability for schools, there is evidence that schools may be responsive to policy shifts when they are under institutional pressure to do so. Several school districts have recently revised their out-of-school suspension policies, but researchers know little about (a) if these changes in policy actually change students’ odds of suspension and (b) if so, how these changes might shift racial disproportionality in suspensions. This analysis examines the recent removal of suspensions for low-level infractions from the formal school discipline policy of a large, urban district. I use student-level data to compare the frequency and disproportionality of suspensions before and after the discipline code change. Findings suggest that although suspension rates decrease overall, multiple suspensions per student are more likely. With regard to disproportionality, black girls and white boys are more likely than expected to receive a first suspension in the post period as well. These findings highlight the importance of exploring heterogeneity in outcomes resulting from potential unintended consequences of policy change.  相似文献   

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