水资源的忧虑

水是生态系统中生命必需元素得以无限循环的介质。没有水生态系统,生命就不能维持。在当今世界面临的人口、资源、环境三大问题中,水属于人类赖以生存和社会经济发展的重要物质资源,又和其它两个问题有着密切的关系。因此,水资源的开发、利用和管理已成为世界各国普遍重视的一个重要课题。     

鲥鱼的驯养与生物学研究Ⅰ.O~+龄幼鱼的生长与食性

本文主要描述池塘养殖条件下鲥鱼幼鱼的生长与食性。1)1987—1989年8月至11月幼鱼生长迅速,快于同期珠江天然个体的生长速度;2)体长26.6—94.9mm的幼鱼主要摄食浮游动物,轮虫和浮游植物出现率随个体增大而减少。食物共有18个属种,摄食频度为100％;3)幼鱼的平均饱满指数为75.70‰。各类食物重量百分比的顺序为:桡足类>枝角类>无节幼体>虾类溞状幼体>轮虫>藻类。     

浙江产蝮蛇毒(Agkistrodon halys pallas venom)凝血酶样酶的性质及其对血凝和血脂的影响

从浙江产蝮蛇毒中分离出一种凝血酶样酶,该酶能明显地延长全血凝固时间,白陶土部分凝血活酶时间(KPTT),并降低了血浆中的纤维蛋白原水平,同时全血的比粘度和血浆的比粘度及血清中的胆固醇和β脂蛋白均有所下降.该酶不激活凝血因子ⅩⅢ.     

龙栖山自然保护区园林植物资源

本文对龙栖山自然保护区园林植物资源进行了调查,首次确定该区园林植物资源状况,并对其今后的合理开发利用提出看法。     

Further investigation on nuclear transplantation in different orders of teleost: the combination of the nucleus of Tilapia (Oreochromis nilotica) and the cytoplasm of Loach (Paramisgurnus dabryanus).

The nucleus of a blastula cell from Tilapia (Oreochromis nilotica, family Cichlidae, order Perciformes) was transplanted into an enucleated egg of Loach (Paramisgurnus dabryanus, family Cobitidae, order Cypriniformes). From among 3747 nucleo-cytoplasmic hybrid (NCH) eggs two NCH larval fish (0.05%) were obtained; one died on the 6th day and the other died on the 12th day after the operation. Morphological examinations showed that both NCH larval fish had developed normally with an opened mouth except they could not take food after complete utilization of their egg yolk on the 5th day of development. The possible mechanisms for obtaining such inter-order NCH larval fish are discussed. This is the first report indicating that inter-order NCH larval fish can be obtained in spite of their evolutionary divergence.     

Electrostatic destabilization of the cytochrome b6f complex in the thylakoid membrane.

Three of the membrane-spanning polypeptides of the chloroplast cytochrome (cyt) b6f complex were sequentially released from the thylakoid membrane, in the order cyt b6, suIV and Rieske iron-sulfur protein, as the pH was increased from 10 to 12, a protocol usually employed to remove peripheral proteins from membranes. The fourth polypeptide of the cyt b6f complex, cyt f, which spans the membrane once, was apparently not released. The pH values for half-release at low ionic strength were approximately 10.7, 11.1 and 11.3 respectively. The separation of the polypeptides of the complex and the sequential release is readily seen at pH 11, where the loss from the membrane of cyt b6, suIV and Fe iron-sulfur center is approximately 90%, 50% and 20%, respectively. the release of cyt b6 from the membrane was reflected by the absence of its characteristic reduced minus oxidized absorbance signal. The pH values at which the release occurred increased as the ionic strength was raised, implying that the release of the b6f polypeptides arises from extrusion due to repulsive electrostatic interactions probably caused by deprotonation of tyrosine and lysine residues. The lipid content of the released polypeptides was very low, consistent with the observation of a non-membranous state. It is proposed that the pH-dependent extrusion requires two electrostatic effects at alkaline pH higher than approximately 10.5: (i) increased electrostatic repulsion between neighbouring polypeptides of the complex, arising from increased net negative charge in the peripheral segments of these polypeptides, which can cause separation of the polypeptides from the complex; and (ii) ionization of residues such as tyrosine in the membrane-spanning alpha-helices, and neutralization of residues such as lysine which can bind to the negative membrane surface.(ABSTRACT TRUNCATED AT 250 WORDS)     

Construction of synthetic genes using PCR after automated DNA synthesis of their entire top and bottom strands.

A new method is described for the direct construction of synthetic genes by applying a modified version of the polymerase chain reaction (PCR) to crude oligonucleotide mixtures made by automated solid phase DNA synthesis. Construction of the HIV-1 393 bp rev gene and the 655 bp nef gene by this method is illustrated. The sequences for the entire top and bottom strands of rev were each programmed into an automated DNA synthesizer. Following DNA synthesis, the two crude oligonucleotide solutions were mixed together, specific primers were added, and the target gene was amplified by a modified PCR technique. Although the longer (greater than 200 bases) strands comprise a very small percentage of the total DNA after solid phase synthesis, this method uses PCR to 'find' and amplify such strands to create the target gene. The rev gene constructed by this method was found to contain 4 sequence errors, which were subsequently corrected by site-directed mutagenesis. In order to evaluate the source of sequence errors, several nef genes were made from the top and bottom strand DNA synthesis solutions using independent PCR's. Results suggest that sequence errors arose from both DNA synthesis and PCR. The utility of this method in producing a functional gene is demonstrated by expression of rev in E.coli.