Formation of Ascorbate Oxidase in Cultured Pumpkin Cells

Ascorbate oxidase activity rapidly increased during callus formationfrom pumpkin fruit tissue. The activity reached a maximum at5 days after transfer and then declined. In callus which hadbeen subcultured at about 4-week intervals for more than oneyear, the activity also increased after transfer to fresh mediumand reached a maximum in the early logarithmic phase of growth.Light had little effect on the appearance of ascorbate oxidaseactivity in pumpkin callus. In the callus grown in the presenceof 10µM CuSO₄, the activity was about 10 times that inthe presence of 0.1 µM CuSO₄, suggesting that the formatonof ascorbate oxidase in pumpkin callus is stimulated by copper,a prosthetic metal of the enzyme. From 45 to 75% of the totalascorbate oxidase activity in pumpkin cell suspension cultureswas found in the medium. Ascorbate oxidase activity in the medium,as well as that in the cells, increased soon after transferto fresh medium, and reached a maximum at about 5 days. (Received July 2, 1987; Accepted November 21, 1987)     

C5 convertase of the alternative complement pathway: covalent linkage between two C3b molecules within the trimolecular complex enzyme

C5 convertase of the alternative C pathway is a complex enzyme consisting of three C fragments--one molecule of a major fragment of factor B (Bb) and two molecules of a major fragment of C3 (C3b). Within this C3bBbC3b complex, the first C3b binds covalently to the target surface, and Bb, which bears a catalytic site, binds noncovalently to the first C3b. In the present investigation, we studied the nature of the convertase that is assembled on E surfaces and obtained evidence that the second C3b binds directly to the alpha'-chain of the first through an ester bond rather than to the target surface. Thus, the alternative pathway C5 convertase could be described as a trimolecular complex in which Bb binds noncovalently to a covalently linked C3b dimer. We also obtained evidence that not only the second C3b but also the first C3b participates in binding C5, that is, covalently-linked C3b dimer acts as a substrate-binding site. Because of this two-site binding, the convertase has a much higher affinity for C5 than the surrounding monomeric C3b molecules. Based on this evidence, a new model of the alternative pathway C5 convertase is proposed. Covalent association of two subunits and the bivalent binding of the substrate are then common properties of the alternative and classical pathway C5 convertases.     

Monoclonal antibodies to mouse complement receptor type 1 (CR1). Their use in a distribution study showing that mouse erythrocytes and platelets are CR1-negative

mAb to murine C receptor type 1 (CR1) were produced and three of them were characterized. One antibody, designated as 8C12, immunoprecipitated a protein of 190,000 Mr from a detergent extract of surface-labeled spleen cells and stained spleen B but not T lymphocytes in fluorescent flow cytometry. It inhibited both CR1-mediated rosette formation and the cofactor activity of CR1 for factor I-mediated cleavage of C3b, suggesting that it recognizes the ligand-binding site of CR1. The two other antibodies, designated as 7G6 and 7E9, recognized different epitopes from that recognized by 8C12, and they cross-reacted with a protein of 150,000 Mr that is present in a spleen extract. The distribution of CR1 in murine hemopoietic cells was studied by binding experiments with radiolabeled 8C12 and fluorescent flow cytometry. When CR1 was not detected by 8C12 alone, the two other antibodies were used in combination with 8C12 to confirm the negative results. Almost all B lymphocytes from the spleen, lymph nodes, and peripheral blood were CR1 positive. Most of the Thy-1-positive lymphocytes from these tissues were CR1 negative. Thymus lymphocytes were also CR1 negative. Peritoneal macrophages and chemotactic factor stimulated but not unstimulated peripheral blood granulocytes were CR1 positive. In contrast to human E, mouse E were CR1 negative. This pattern of distribution was consistent with previous results obtained by rosette assays. Although mouse platelets cause immune adherence hemagglutination with C3b-bearing SRBC, they are CR1 negative. Three other lines of evidence also indicated that platelets are CR1 negative. First, no band of CR1 was demonstrated by immunoprecipitation with 8C12 of an extract of surface-labeled platelets. Second, 8C12, which inhibited rosette formation by lymphocytes, alone or in combination with 7G6 and 7E9, did not inhibit immune adherence between platelets and C3b-bearing SRBC. Third, polyclonal rabbit IgG prepared from anti-mouse CR1 antiserum did not inhibit immune adherence by platelets. These results strongly suggest that the C3b-binding factor(s) on mouse platelets is different from CR1 and that processing of C3b-bearing immune complexes in mouse blood may be mediated by a new and as yet unidentified C3b-binding factor(s).     

从“湖北光敏感核不育水稻”的未受精子房和花药培养出单倍体植株

采用10种诱导培养基,培养湖北光敏感核不育水稻农垦58品种的未受精子房和花药。共培养未受精子房2790个,获得胚囊愈伤组织17块,最高诱导频率达3.33%,其中2块分化出绿苗。培养花药16740个,获得花药愈伤组织15块,最高诱导频率为0.92%,其中3块分化出苗,2丛白苗,1株绿苗。胚囊植株和花粉植株经根尖染色体检查为单倍体,2n=x=12。实验证明,液体培养、2,4-D0.2-0.5 mg/1、低温预处理对诱导胚囊愈伤组织及花粉愈伤组织的形成具良好效果。     

三个与agropine合成相关的基因在大肠杆菌微细胞中的表达

pTiAch 5 TR区与在植物中积累agropine相关的三个基因片段已导入pINIIA或pACYC184,在大肠杆菌微细胞中表达出杂合蛋白。三个基因片段的pINIIA重组质粒的表达得到稳定蛋白、不稳定蛋白和在两个相表达出相似蛋白的三种结果。基因2'HindⅢ片段上的UGAA序列是在两个相表达相似蛋白的原因。从产生的杂合蛋白分子量和读码方式看,pTiAch 5中基因2'和基因1'的结构与pTi 15955近似,但由基因0'片段产生的杂合蛋白分子量比根据pTi15955 DNA序列数据推测的稍大。从表达强度和微细胞操作看,这个系统还不适应从大肠杆菌中方便地纯化杂合蛋白的需要。     

The ontogeny of the vascular cambium inGinkgo biloba roots

Observation was made on early ontogeny of vascular cambium in the developing root ofGinkgo biloba L. After completion of root elongation, the vascular meristem gradually acquires cambial characteristics. Strips of the periclinal division of cells in transverse section are observed on the inner side of phloem when the primary xylem and phloem in the stele have been established. The strips are united into a continuous layer between phloem and xylem. In tangenital section, the procambium shows a homogeneous structure, which is initially composed of short cells with transverse end walls and subsequently, of long cells with tapering ends. Then, the procambium is organized into two systems of cells; axial strands of short cells with transverse end walls resulting from the sporadic transverse divisions of long cells, and long cells with tapering ends. Still later, the short cells are divided frequently in a trasverse plane exhibiting one or a few cells in width and several decades of cells in height, while the long cells are elongated. The frequency of transverse divisions of the short cells decreases in subsequent stages. Eventually, the short cells in axial strands are vertically separated from one another by the elongation of neighboring long cells and by the decrease in the frequency of transverse divisions of short cells themselves. Cambial initials occur in two forms; ray initials a few cells in height and one cell in width derived from the short cells, and fusiform initials with tapering ends derived from the long cells.     

青天葵野生变家栽的探讨——Ⅰ.生物学特性的观察

青天葵是广西特产药材,过去一直处于野生状态,药源日渐枯竭.供不应求。作者通过调查和研究,掌握了它的生态条件和生物学特性。实践证明,青天葵由野生变为人工栽培是可能的。     

植物激素对草莓叶片不定芽形成的影响

用试管内生长的草莓幼嫩叶片作外植体,培养在MS基本培养基上附加1.5—2.5毫克/升6—BA和0.1毫克/升NAA,可直接诱导成不定芽,诱导率可达20%。如果不定芽继代培养在同样浓度的培养基上,继而可形成大量的丛生芽。能使叶外植体形成不定芽的植物激素组合而不能使其愈伤组织分化成芽。IAA与6—BA的不同浓度组合对不定芽形成效果不明显。     

大鼠应激性胃粘膜损害与eAMPCa~2及能量代谢变化的关系

本文采用放射免疫测定法、原子吸收光谱分析法和生化酶分析法,测定了大鼠在经受束缚加浸水急性应激四小时内,胃组织cAMP Ca~(2+)及在ATP、ADP、AMP和能量代谢的短期动态变化,同时观察了胃粘膜的损害程度。结果发现胃粘膜损害面积密度随着应激时间延长而逐渐增加;胃组织cAMP和Ca~(2+)则进行性降低;两者呈密切负相关;胃组织能量代谢却略有增强。若预先给以CaCl_2,再予应激,则有减轻应激性胃粘膜损害的作用。