双向转换的系统结构调控方法与半干旱地区的农作物布局

一、临猗县农业生产条件特点及存在问题临猗县位于山西西南部,是晋南盆地中的一个大县。全县面积1356km~2,耕地1.0×10~5ha,水浇地5.27×10~4ha,占耕地的52.7%,人均占有耕地0.227ha。地势平坦,土地肥沃,农业生产条件较好。年降水量为500mm 左右,最高年份曾达到849.8mm,其中5—10月份的降雨量为450mm 左右,同期≥10℃的活动积温在     

Spontaneous transformation and immortalization of human endothelial cells

Summary A new cell line from the human umbilical vein has been established and maintained for more than 5 yr (180 generations; 900 population doublings). This strain, designated ECV304, is characterized by a cobblestone monolayer growth pattern, high proliferative potential without any specific growth factor requirement, and anchorage dependency with contact inhibition. Karyotype analysis of this cell line reveals it to be of human chromosomal constitution with a high trisomic karyotype (mode 80). Ultrastructurally, endothelium-specific Weibel-Palade bodies were identified. Although one of the endothelial cell markers, Factor VIII-related antigen (VIIIR:Ag) was negative in this cell line, immunocytochemical staining for the lectin Ulex europaeus I (UEA-I), and PHM5 (anti-human endothelium as well as glomerular epithelium monoclonal antibody) was positive, and angiotensin-converting enzyme (ACE) activity was also demonstrated. In addition, ECV304 displayed negativity for alkaline and acid phosphatase and for the epithelial marker keratin. All of these findings suggest that ECV304 cells originated from umbilical vein endothelial cells by spontaneous transformation. Ultrastructurally, no viruslike particles have been detected intracellularly. Nude mouse tumorigenicity and rabbit cornea tests were both positive. This is a report on a novel case of phenotypic alteration of normal venous endothelial cells of human origin in vitro, and generation of a transformant with indefinite life spans. This line may be useful in studies of some physiologically active factors available for medical use.     

Further Studies on Substrates Inducing Metacyclogenesis in Trypanosoma cruzi

Epimastigotes of Trypanosoma cruzi, Peru strain, incubated in Contreras' artificial triatomine urine transformed into metacyclic trypomastigotes when 10 mM L-glutamine, L-asparagine or D-fructose was added to the medium. Metacyclogenesis with these substrates was comparable to the percent metacyclic morphotype formation induced by L-proline and significantly greater than that stimulated by 10 mM D-glucose. Sodium acetate (10 mM) increased transformation induced by L-proline, and L-hydroxyproline (10 mM) increased transformation induced by D-fructose. Phosphoenolpyruvate (10 mM) inhibited L-proline-induced metacyclic trypomastigote stage formation. Three antimetabolites, azetidine 2-carboxylate (5 mM), malonic acid (1 mM), and desthiobiotin (5 mM), completely inhibited D-fructose-induced but not L-proline-induced transformation. The Costa Rica, Y, and CL strains of T. cruzi showed different patterns of percent metacyclogenesis with substrates that induce transformation in the Peru strain.     

嗜热脂肪芽孢杆菌启动子克隆载体pFDC4和表达型载体pFDC11的构建

以pPL703的衍生质粒pPGV5为载体,从嗜热脂肪芽孢杆菌CU21总DNA的Sau 3A酶切产物中得到1个0.54kb的启动子片段,它能促进载体上的无启动子的cat-86基因在嗜热脂肪芽孢杆菌及枯草芽孢杆菌中表达。这一片段以正、反向插入pPGV5载体,都能使重组质粒转化CU21原生质体的效率提高10~(?)至10(?)倍。Southern杂交实验表明,这一启动子片段与Imanaka等报道的来自CU21中的隐蔽性质粒pBS02的能提高转化效率的1.6kb Eco RI片段是同源的。利用所得到的0.54kb Sau 3A片段构建了新的启动子克隆载体pFDC4和表达型载体pFDC11,二者都能以很高的效率转化CU21原生质体。     

Ethylene production by shoot-forming and unorganized crown-gall tumor tissues of Nicotiana and Lycopersicon cultured in vitro

We have studied ethylene biosynthesis in cloned crown-gall cell lines of Nicotiana tabacum L., N. glutinosa L., and Lycopersicon esculentum (L.) Mill. transformed by the A6 strain of Agrobacterium tumefaciens (Smith and Townsend) Conn. or a tms (shooty) mutant strain, A66. Both the synthesis of the ethylene precursor 1-aminocyclo-propane-1-carboxylic acid (ACC) and the conversion of ACC to ethylene were affected by crown-gall transformation. All A6-transformed cell lines contained about 50 times more ACC than the A66-transformed cell lines, indicating that the tms genes stimulate ACC synthesis. On the other hand, A6-transformed N. tabacum and L. esculentum cell lines showed a very low capacity to convert ACC to ethylene when compared with A66-transformed cells of the same species. These differences in ACC-dependent ethylene formation were stable and could not be modified by supplying auxin to the culture medium. In contrast, both the A6- and A66-transformed N. glutinosa cell lines showed a low capacity for ACC-dependent ethylene production. Thus, the low-ethylene-forming phenotype did not seem to be under direct control of the tms genes and appeared to be part of the host response to crown-gall transformation. All cell lines exhibiting the low-ethylene-forming phenotype grew as unorganized tissues in culture, whereas cell lines showing a high capacity to convert ACC to ethylene formed shoots. Thus, ACC-dependent ethylene formation may be useful for studying host factors important in determining tumor phenotype.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - NAA -naphthalencacetic acid     

Sweet potato (Ipomoea batatas) trypsin inhibitors expressed in transgenic tobacco plants confer resistance against Spodoptera litura

A sweet potato (Ipomoea batatas cv. Tainong 57) trypsin inhibitor gene was introduced into tobacco plants (Nicotiana tabaccum cv. W38) by Agrobacterium tumefaciens– mediated transformation. From 30 independent transformants, three lines with high level of expression were further analyzed. The trypsin inhibitor gene, under control of the 35S CaMV promoter, led to the production of the trypsin inhibitor proteins up to 0.2% of the total protein. In insecticidal bioassays of transgenic tobacco plants, larval, growth of Spodoptera litura (F.), the tobacco cutworm, was severely retarded as compared to their growth on control plants. This observation implied that expression of sweet potato trypsin inhibitor can provide an efficient method for crop protection. Received: 29 July 1996 / Revision received: 15 November 1996 / Accepted: 8 December 1996     

A colony‐to‐lawn method for efficient transformation of Escherichia coli

Aims: To develop a fast, convenient, inexpensive and efficient Escherichia coli transformation method for changing hosts of plasmids, which can also facilitate the selection of positive clones after DNA ligation and transformation. Methods and Results: A single fresh colony from plasmid‐containing donor strain is picked up and suspended in 75% ethanol. Cells are pelleted and resuspended in CaCl₂ solution and lysed by repetitive freeze–thaw cycles to obtain plasmid‐containing cell lysate. The E. coli recipient cells are scraped from the lawn of LB plate and directly suspended in the plasmid‐containing cell lysate for transformation. Additionally, a process based on colony‐to‐lawn transformation and protein expression was designed and conveniently used to screen positive clones after DNA ligation and transformation. Conclusions: With this method, a single colony from plasmid‐containing donor strain can be directly used to transform recipient cells scraped from lawn of LB plate. Additionally, in combination with this method, screening of positive clones after DNA ligation and transformation can be convenient and time‐saving. Significance and Impact of the Study: Compared with current methods, this procedure saves the steps of plasmid extraction and competent cell preparation. Therefore, the method should be highly valuable especially for high‐throughput changing hosts of plasmids during mutant library creation.