Organellar DNA replication inNicotiana tabacum cultured cells

In the diploid vegetative plant cell, the nuclear DNA is present in two copies, whereas the chloroplast and mitochondria genomes are present in a higher and variable copy number. We have studied the replication of the nuclear, chloroplast and mitochondrial DNA in culturedNicotiana tabacum cells using density and radioactive markers. Essentially all the 10 000 chloroplast genomes in a given cell replicate in one cell cycle as do all the mitochondrial DNA molecules. No measurable level of unreplicated organellar DNA molecules can be detected in these cells.     

Mechanisms by which EGF receptor and TGF alpha contribute to malignant transformation

Alterations affecting the epidermal growth factor/transforming growth factor alpha-responsive mitogenic pathway are frequently detected in malignancies. In particular, the epidermal growth factor receptor has been found overexpressed in a number of human tumors. Production and secretion of transforming growth factor type alpha has also been shown in several tumor cells but not in their normal counterparts. In this review we describe the establishment of in vitro model systems to study the transforming potential of these molecules and summarize our current understanding of the mechanisms involved in transformation by genes encoding a growth factor and a growth factor receptor.     

植物群落演替与土壤发展之间的关系

本文运用植物群落中植物优势种的重要值与相对应子群落的土壤特征值直接相关联的分析方法,对湖北宜昌大老岭的桦(Betula)、栎(Quercus)、栗(Castanea)七个群落类型的三个演替途径的土壤动态进行分析,结果表明:在植物群落的演替过程中,土壤中的Ca、pH值减少;离子代换量增加;Na、Mg、NH_4+-N、速效P、速效K、有机质的含量是随着物种的变化而呈不同的趋势。因此,植物群落的演替是生态系统的动态过程。     

控制常绿针叶树叶量对树干生长的促进作用

一、前言近几年,在研究不同树种的修枝过程中,偶然发现,一些常绿针叶树的人工去叶能加快树干材积的生长,这引起了人们新的研究兴趣:控制常绿针叶树的叶量是否能促进树木生长?这一措施有多少可能的前途或弊端?多年来,人类为寻求促进林木生长的有效经营措施,利用各种手段进行了大量实验研究工作,获得了很有意义的成果,抚育间伐是其中的一项重要途径。由于世界各国的日益重视,60年代以来,很多学     

毛喉鞘蕊花的化学成分研究

本文报导了,从产于滇东北的毛喉鞘蕊花(Coleus forskohlii Brig)的根茎中分离到四个二萜化合物,经光谱分析鉴定,其结构分别为1α,6β,7α-triacetyl-coleonol—B(1),I-acetyl—forskolin(2),coleonol-B(3),和deacetyl-forskolin(4)。化合物(1)和(2)是首次从该植物中分离到。     

应用纯化的重组Epstein-Barr病毒早期抗原建立检测鼻咽癌病人血清IgA/EA抗体的ELISA方法

利用凝胶和离子交换柱(Mono Q)两次层析,将大肠杆菌表达的EB病毒早期抗原P138片段多肽纯化。以此P138为抗原,增加鼠抗人IgA单克隆抗体以扩大IgA的反应,建立了三步ELISA法。用本法检查了100例鼻咽癌病人和63例正常人血清中抗EB病毒IgA/EA抗体,病人血清的阳性检出率为86％,正常人有3例阳性(4.7％)。此结果表明,三步ELISA法较常用的间接ELISA法(阳性检出率为71％)敏感。     

人参多肽基因的化学合成和克隆

 本文报道了具有降血糖作用的人参多肽基因的设计及用固相亚磷酰胺法的合成。再以质粒pUC19作为克隆载体,以大肠杆菌JM101为受体菌,克隆了人参多肽基因,并成功地获得了克隆菌株。     

Cobalt stimulates carotid body chemoreceptors

Because cobalt administration is known to elicit erythropoietin response, it is a reasonable hypothesis that cobalt would also stimulate the O2-sensing process in the peripheral chemoreceptors. We tested this hypothesis by measuring the effects of cobalt chloride on carotid chemosensory fibers in pentobarbital-anesthetized cats that were paralyzed and artificially ventilated. Responses of carotid chemoreceptor afferents to graded doses of cobalt given by intra-arterial injections (0.08-2.10 mumols) were measured at constant blood gases. Responses of the same chemoreceptor afferents to hypoxia, before and after a saturation dose of cobalt, were measured. In two experiments carotid body tissue PO2 was also simultaneously measured. The chemosensory fibers showed prolonged excitation after a brief period of inhibition subsequent to cobalt administration. The stimulatory effect showed a dose-dependent saturation response. Cobalt augmented rather than blocked carotid chemoreceptor response to hypoxia. The effect of cobalt was not mediated by tissue PO2. These results are consistent with the hypothesis that cobalt stimulates the O2-sensing mechanism, although a direct effect of cobalt on the excitability of the chemosensory terminal remains a possibility.     

Stabilization of a HemA-LacZ hybrid protein against proteolysis during carbon starvation in atp mutants of Salmonella typhimurium.

Transposon insertions that stabilize the beta-galactosidase activity of a HemA-LacZ hybrid protein following carbon starvation were mapped to the atp operon of Salmonella typhimurium. This effect is similar to that seen with nuo mutants defective in the energy-conserving type I NADH dehydrogenase. Insertions in several other genes, including such highly pleiotropic mutants as rpoS, polA, and hfq, were isolated with the same phenotypic screen, but they do not affect the beta-galactosidase activity of HemA-LacZ. All of these mutants act indirectly to alter the colony color of many different fusion strains on indicator plates.