C.elegans野生型和par突变体早期胚胎卵裂的观察

不对称分裂在动植物的发育中起到了非常重要的作用。Caenorhabditis elegans（C．elegans）胚胎最早的两次卵裂为研究控制不对称分裂的机制提供了很好的机会。用普通光学显微镜观察了野生型胚胎早期卵裂和par-1、par-2、par-3、par-4突变体胚胎的早期卵裂。野生型胚胎最早的分裂是不等的,产生了两个不同大小的子细胞。两个子细胞又以不同的方向进行第二次分裂。在C．elegans中任意一个par基因的缺失会使胚胎的第一次卵裂丧失不对称性。这会导致一些发育调控因子不能在特定的胚胎细胞中准确地定位,造成细胞分裂纺锤体方向的异常。par类基因参与不对称性的建立,这种不对称性决定了C．elegans身体的前后轴。     

The response of the yeast Saccharomyces cerevisiae to sudden vs. gradual changes in environmental stress monitored by expression of the stress response protein Hsp12p

The response of the yeast Saccharomyces cerevisiae to sudden vs. gradual changes in different environmental stress conditions during both respiratory growth and aerobic fermentative growth in the presence of excess glucose was investigated by monitoring the level and rate of expression of the stress response protein Hsp12p using the fluorescent fusion construct Hsp12p-Gfp2p. The initial expression level and the rate of Hsp12p synthesis was significantly greater under glucose-limited conditions in the chemostat ( D <0.14 h⁻¹) compared with when excess glucose was present in the auxostat. Decreasing the dilution rate and the glucose concentration further in the A-stat resulted in increased Hsp12p expression, which was more marked when a rapid rather than a gradual change was affected. Common stress factors such as NaCl, ethanol and elevated temperature caused stress responses in both D-stat and auxo-accelerostat culture. The magnitude of the stress response depended on the stress factor, cultivation conditions as well as the rate of change of the stress factor. The rate of Hsp12p synthesis increased due to all applied stresses, with the observed increase between 2 and 20 times lower when the stress was applied gradually rather than rapidly. The results suggested that the Hsp12p expression rate is a good indicator of applied stress in S. cerevisiae .     

重组猪源胰蛋白酶原的构建、表达与活性分析

目的：构建、表达重组猪源胰蛋白酶原,并对其进行分离纯化和酶活性分析。方法：利用大肠埃希菌表达系统（pET-28a,宿主菌BL21 DE3）优化天然猪源胰蛋白酶原基因,经乳糖诱导表达重组胰蛋白酶原蛋白,采用阴离子交换色谱法分离纯化,以SDS-PAGE 电泳鉴定目标蛋白,以紫外分光光度法检测重组蛋白的酶活力。结果：测序结果表明,重组猪源胰蛋白酶原基因工程菌构建成功,SDS-PAGE检测显示目的蛋白条带位置与标准猪源胰蛋白酶条带位置一致,且酶活力可达513.09 U?mg-1。结论：成功获得了重组猪源胰蛋白酶原,且酶活力较好,为进一步研究生产提供了基础。     

硝化抑制剂DCD、 DMPP对褐土氮总矿化速率和硝化速率的影响

采用15N库稀释-原位培养法研究了硝化抑制剂DCD、DMPP对华北盐碱性褐土氮总矿化速率和硝化速率的影响.试验在山西省运城市种植玉米的盐碱性土壤上进行,设单施尿素、尿素+DCD、尿素+DMPP 3个处理.结果表明:施肥后2周,DCD、DMPP分别使氮总矿化速率和氮总硝化速率减少了25.5％、7.3％和60.3％、59.1％,DCD对氮总矿化速率的影响显著高于DMPP,两者对氮总硝化速率的影响无显著差异;而在施肥后7周,不同硝化抑制剂对氮总硝化速率的影响存在差异.施肥后2周,3个处理的土壤氮总矿化速率和硝化速率分别是施肥前的7.2 ～10.0倍和5.5 ～21.5倍;NH4+和NO3-消耗速率分别是施肥前的9.1 ～12.2倍和5.1 ～8.4倍,这是由氮肥对土壤的激发效应所致.硝化抑制剂使氮肥更多地以NH4+形式保持在土壤中,减少了NO3-的积累.土壤氮总矿化速率和总硝化速率受硝化抑制剂的抑制是N2O减排的主要原因.     

Improvement of the 15N dilution method for estimation of absorption of NOx by plants supplied with 15N-labelled fertilizer

To develop further the methods for estimation of NOx absorption by plants supplied with ¹⁵N-labelled fertilizer, we proposed a new calculation method, total N fixed method (TNF), and compared with the ¹⁵N dilution method and the classical mass balance method (MB).
Hydroponically grown soybean plants were supplied with ¹⁵N-labelled nitrate and exposed to 200–250 nl l⁻¹ NO₂ for 7 d. The proportions of the N derived from NO₂ to total N in exposed plants were estimated by the three methods.
The reported rates of NO₂ absorption by several plant species, estimated by the ¹⁵N dilution method, were recalculated using the TNF method. The results of the two methods were compared and showed that: (1) The ¹⁵N dilution method overestimated the content of NO₂-N in exposed plants compared with the MB method whilst the TNF method produced estimations of NO₂-N closer to those by the MB method when the plants were supplied with 5 m M nitrate. (2) The differences in estimations between the MB method and either the ¹⁵N dilution method or the TNF method increased with decreasing supply of ¹⁵N-labelled nitrate to roots.     

Radiomarquage in vitro des leucocytes au [F]-fludésoxyglucose : première expérience à l’hôpital d’instruction des armées Val-de-Grâce

^99mTc-HMPAO (technetium^99m-hexamethylpropylene amine oxime) radiolabeled-leukocytes or Indium-111 oxine labeled leukocytes scintigraphy and positron emission tomography with [¹⁸F]-fludeoxyglucose (¹⁸F-FDG) are the reference techniques for infection imaging. These methods have some limits explaining the active research for an ideal infection tracer finding. Because of its potential advantages, leukocyte labeling with ¹⁸F-FDG have been developed but is not routinely used for clinical infection imaging. We report the results of our first experience of leukocyte radiolabeling with ¹⁸F-FDG, managed on 20 healthy subjects. Labeling efficiency, cellular viability and radiolabeling stability have been assessed. Our results exhibit the influence of different parameters on labeling efficiency: presence of glucose during the labeling reaction, number of cells and volumic activity of ¹⁸F-FDG. Stability assessment indicates that 60% of initial cellular activity persist in cells after 1 hour incubation. Our results are similar to literature data and permit us to consider a clinical use of radiolabeled leukocyte with ¹⁸F-FDG. Nevertheless, a clinical use of radiolabeled cells can’t be considered before the radiolabeling induced cellular effects have been assessed.     

Detection of cytokinins in a seaweed extract

trans-Zeatin, trans-zeatin riboside, their dihydro derivatives, isopentenyladenine and isopentenyladenosine have been identified and quantified in Seasol, a commercial extract of Tasmanian Giant Bull kelp, Durvillea potatorum.     

Trophic interactions among heterotrophic microplankton,nanoplankton, and bacteria in Lake Constance

A considerable portion of the pelagic energy flow in Lake Constance (FRG) is channelled through a highly dynamic microbial food web. In-situ experiments using the lake water dilution technique according to Landry & Hasset (1982) revealed that grazing by heterotrophic nanoflagellates (HNF) smaller than 10 µm is the major loss factor of bacterial production. An average flagellate ingests 10 to 100 bacteria per hour. Nano- and micro-ciliates have been identified as the main predators of HNF. If no other food is used between 3 and 40 HNF are consumed per ciliate and hour. Other protozoans and small metazoans such as rotifers are of minor importance in controlling HNF population dynamics.Clearance rates varied between 0.2 and 122.8 nl HNF^–1 h^–1 and between 0.2 and 53.6 µl ciliate^–1 h^–1, respectively.Ingestion and clearance rates measured for HNF and ciliates are in good agreement with results obtained by other investigators from different aquatic environments and from laboratory cultures. Both the abundance of all three major microheterotrophic categories — bacteria, HNF, and ciliates — and the grazing pressure within the microbial loop show pronounced seasonal variations.     

Estimation of residual N effect of faba bean and pea on two succeeding cereals using15N methodology

A field experiment was conducted using¹⁵N methodology to study the effect of cultivation of faba bean (Vicia faba L.), pea (Pisum sativum L.) and barley (Hordeum vulgare L.) on the N status of soil and their residual N effect on two succeeding cereals (sorghum (Sorghum vulgare) followed by barley). Faba bean, pea and barley took up 29.6, 34.5 and 53.0 kg N ha^–1 from the soil, but returned to soil through roots only 11.3, 10.8 and 5.7 kg N ha^–1, respectively. Hence, removal of faba bean, pea and barley straw resulted in a N-balance of about –18, –24, and –47 kg ha^–1 respectively. A soil nitrogen conserving effect was observed following the cultivation of faba bean and pea compared to barley which was of the order of 23 and 18 kg N ha^–1, respectively. Cultivation of legumes resulted in a significantly higher A_N value of the soil compared to barley. However, the A_N of the soil following fallow was significantly higher than following legumes, implying that the cultivation of the legumes had depleted the soil less than barley but had not added to the soil N compared to the fallow. The beneficial effect of legume cropping also was reflected in the N yield and dry matter production of the succeeding crops. Cultivation of legumes led to a greater exploitation of soil N by the succeeding crops. Hence, appreciable yield increases observed in the succeeding crops following legumes compared to cereal were due to a N-conserving effect, carry-over of N from the legume residue and to greater uptake of soil N by the succeeding crops when previously cropped to legumes.