小麦—天兰偃麦草—黑麦三属杂种花粉植株诱导条件的研究

研究表明,三属杂种处于单核中晚期阶段的花粉最适于诱导形成愈伤组织。低温预处理对促进三属杂种花粉愈伤组织的诱导有一定的作用。利用以马铃薯提取物为基础物质的马铃薯-Ⅱ培养基作诱导培养基,其愈伤组织诱导与分化的频率比目前两个较好的合成培养基要高。同一个三属杂种F_1春、秋播种植株之间在形成愈伤组织的能力上有较大的差异,秋播材料形成愈伤组织的能力明显高于春播材料。F_(?)杂种植株诱导愈伤组织和分化植株的频率均比F_1杂种明显提高。     

维西香茶菜的二萜成分

维西香茶菜Rabdosia weisiensis C. Y. Wu产云南西北部海拔2600米沟谷中,其化学成分的研究未见报道。从该植物叶的乙醚提取物中,分得两个二萜成分,一为已知成分trichorabdal A(2),一为新成分,命名为维西香茶菜甲素weisiensin A(1)。 维西香茶菜甲素weisiensin A(1),C_(26)H_(36)O_9,mp 298—300℃,其~(13)C NMR谱显示存在三个CH_3,三个CH_2,八个CH,三个四取代碳,三个Ac,二个烯碳和一个羰基     

A detailed analysis of early events during in-vitro fertilization of bovine follicular oocytes

Bovine follicular oocytes collected at slaughter were matured and fertilized in vitro with in-vitro capacitated spermatozoa. Analysis of 621 penetrated ova fixed at various times after in-vitro insemination led to definition of 6 stages of early development. A time sequence for sperm penetration, sperm head decondensation, male pronucleus formation, the activation of second meiotic division, female chromosome decondensation and pronucleus development was established. First sperm penetration into the ooplasm was recorded 6 h after insemination; 1-2 h was required for the sperm head to decondense and another 4-6 h to develop into the opposing pronucleus stage. Synkaryosis and first cleavage occurred 28 h after fertilization. Examination of the early stages revealed four types of abnormalities, i.e. polyspermy, polygyny, asynchrony between male and female pronucleus development, and preactivation of cytokinesis.     

Nucleotide sequence, function, activation, and evolution of the cryptic asc operon of Escherichia coli K12.

The cryptic asc (previous called "SAC") operon of Escherichia coli K12 has been completely sequenced. It encodes a repressor (ascG); a PTS enzyme IIasc for the transport of arbutin, salicin, and cellobiose (ascF); and a phospho-beta-glucosidase that hydrolyzes the sugars which are phosphorylated during transport (ascB). ascG and ascFB are transcribed from divergent promoters. The cryptic operon is activated by the insertion of IS186 into the ascG (repressor) gene. The ascFB genes are paralogous to the cryptic bglFB genes, and ascG is paralogous to galR. The duplications that gave rise to these paralogous genes are estimated to have occurred approximately 320 Mya, a time that predates the divergence of E. coli and Salmonella typhimurium.     

Mapping of the SLA complex of miniature swine: mapping of the SLA gene complex by pulsed field gel electrophoresis.

The overall order of the regions of the swine major histocompatibility complex (MHC), the SLA complex, was determined by pulsed field gel electrophoresis (PFGE). It was found that the order of the regions is class II-class III-class I. A class I probe hybridized to a 420 kb Mlu I and a 420 kb Not I fragment as did a class III probe for C2. None of the class II probes hybridized to these fragments. Thus, linkage of class I to class III was shown. The class III C2, Bf, and C4 genes were found to residue in a 190 kb Not I fragment. Linkage of class III and class II genes was shown when both the class III C4 and the class II DR probes hybridized to the same 195 kb Sac II and 340 kb Not I fragments. The class I probe did not hybridize to these fragments. The order of the regions, class II-class III-class I, is similar to that of human MHC genes and may have been conserved in evolution so that coordinated expression of MHC genes could be achieved.     

中更新世以来兽类地理分布的变化及其天文气候学的解释

中更新世以来,兽类的地理分布曾发生过重大的变化,如西伯利亚的兽类曾三次大举西迁,入侵西欧.它们分别发生在氧同位素的第16、6、2-4阶段.如果考察过去73万年以来全球所获得的、北半球冬半年平均的太阳辐射量的变化,那么第16、6、2-4阶段乃是太阳辐射量比较低的时期.故中更新世以来兽类地理分布的变化是受气候变迁的制约的.而后者则是受天文因素的自然变化所控制的.     

西双版纳傣族“龙山”的生态学意义

傣族“龙山”是西双版纳地区傣族的民族植物文化中的一例。其概念是“神居住的地方”,在这个地方的动植物都是神的家园里的生灵,是神的伴侣,是不能砍伐、狩猎和破坏的。人