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排序方式: 共有121条查询结果,搜索用时 31 毫秒
1.
用硫酸铵分段盐析、超滤膜分级分离及DEAE-纤维素、Sephadex A-25和Sephadex G-50三种柱层析方法从双胸蚓组织的粗提取液中分离纯化出一种纤溶酶,分子量为29kD,由一条肽链组成。此晦具有强烈的溶解纤维蛋白的作用,对家兎实验性血凝块也具有明显的溶解作用。此酶的最适pH为8.0,在pH7.6~8.4之间活力相差不到2%;酶在PH4.7—11.0范围内稳定;酶作用的最适温度为57℃;此酶热稳定性较好,于25~50℃保温3小时,酶活力基本不变,60℃时,活力保留65%。金属离子Na~(+)、K~(+)、Mg~(2+)等可提高此酶的活力,而Hg~(2+)、Ca~(2+)等金属离子对此酶有不同程度的抑制作用。 相似文献
2.
3.
杂交试验是一项费时费钱的工作,因此在进行试验之前如能进行严密的设计,给出试验所需的样本大小是十分必要的,统计学中常见的估计样本容理的公式不宜应用于杂交试验,本文分两种情况给出了杂交试验中样本容量的估计公式,据此估计出的样本容量安排杂交试验,可在满足试验者要求的条件下,使试验的总成本最低或使试畜的总头数最少。 相似文献
4.
《Revue de Micropaléontologie》2016,59(1):1-17
Palynological and sedimentological analyses were performed on Miocene sediments of North-East Tunisia in order to detect the changes in depositional environments, including those linked to eustasy, along with changes in vegetation and climate. The specific integration of palynological (pollen and dinocysts) and sedimentological (including facies analysis) data indicate that shallow marine settings persisted until the early Burdigalian–Langhian, and that open marine environments developed progressively in the late Langhian. Since the early Serravallian, deltaic environments developed under a fluctuating, but predominantly warm climate. The palynological data support a subtropical climate during the Burdigalian, with tropical conditions prevailing at the Langhian–Serravallian transition. The observed high frequency values of megathermic and mega-mesothermic pollen taxa represent the vegetation response to the Miocene climatic optimum (MCO). 相似文献
5.
The study proposes methodological developments to optimize sampling strategy of resting cysts of Alexandrium catenella to estimate their abundance with a predefined error. This work also aims to provide information on spatial distribution of resting cysts in sediments. The distribution mode of A. catenella resting cysts related to the abundance variability was studied through sediment cores sampling on four different spatial scales and using Ludox CLX gradient density method. The quantification method underestimates by a factor of 2 the resting cysts abundance in one gram of sediment. Application of Taylor's power law allowed us to define a compromise between sampling effort and abundance estimation error. In the case of A. catenella resting cysts from Thau lagoon, the optimal sampling strategy consists of sampling 10 stations on a surface of 2 km2 for a given coefficient of variability (C) of 15%, sampling 3 sediment cores at each station (C = 30%) and counting only one replicate by core (C = 18%). Results related to the application of Taylor's power law are closely dependent on resting cyst density and aggregation in a given sediment. In our area, A. catenella resting cysts are mainly observed in the upper 3 cm of sediment. Horizontally, their heterogeneity is lower on 10 cm2 surface and tends to stabilize itself beyond a surface of 10 m2. Each author has to carry out this pre-sampling effort for his own resting cysts-forming species, in his own area, in order to increase accuracy of resting cyst mapping. 相似文献
6.
7.
We have investigated stem turnover strategy for Lindera umbellata, an understory shrub that sprouts from its rootstock under natural conditions to replace constituent stems, on the basis
of the hypothesis that the multiple-stemmed form of woody species is an adaptation enabling efficient reproduction in high-stress
environments. We tested the hypothesis that the timing of stem replacement maximizes sexual reproduction for the shrub. We
developed a model for the time of optimum replacement of a stem by a daughter stem which maximizes the sexual reproduction
of a shrub and tested the model using L. umbellata growing in the field. From the model, the optimum time of replacement of a stem with a daughter stem is when cumulative sexual
reproduction per unit time for the stem is maximum. In practice, this will be the last age (t
opt) at which annual sexual reproduction in a stem can potentially exceed cumulative sexual reproduction per unit time for the
stem. Half of the stems died at almost t
opt and had sexually mature daughter stems at that time. Other stems, however, died at times more remote from t
opt when daughter stems were sexually immature. It is thought that normal replacement of the latter stems was prevented by accidents
such as breakage. We conclude that clumps of L. umbellata achieve efficient sexual reproduction by stem replacement at the optimum time, although accidents can, to some extent, determine
when the stem actually dies. 相似文献
8.
Seasonal reproduction in some Arctic Laminariales coincides with increased UV-B radiation due to stratospheric ozone depletion and relatively high water temperatures during polar spring. To find out the capacity to cope with different spectral irradiance, the kinetics of photosynthetic recovery was investigated in zoospores of four Arctic species of the order Laminariales, the kelps Saccorhiza dermatodea, Alaria esculenta, Laminaria digitata, and Laminaria saccharina. The physiology of light harvesting, changes in photosynthetic efficiency and kinetics of photosynthetic recovery were measured by in vivo fluorescence changes of Photosystem II (PSII). Saturation irradiance of freshly released spores showed minimal I
k
values (photon fluence rate where initial slope intersects horizontal asymptote of the curve) values ranging from 13 to 18 μmol photons m−2 s−1 among species collected at different depths, confirming that spores are low-light adapted. Exposure to different radiation spectra consisting of photosynthetically active radiation (PAR; 400–700 nm), PAR+UV-A radiation (UV-A; 320–400 nm), and PAR+ UV-A+UV-B radiation (UV-B; 280–320 nm) showed that the cumulative effects of increasing PAR fluence and the additional effect of UV-A and UV-B radiations on photoinhibition of photosynthesis are species specific. After long exposures, Laminaria saccharina was more sensitive to the different light treatments than the other three species investigated. Kinetics of recovery in zoospores showed a fast phase in S. dermatodea, which indicates a reduction of the photoprotective process while a slow phase in L. saccharina indicates recovery from severe photodamage. This first attempt to study photoinhibition and kinetics of recovery in zoospores showed that zoospores are the stage in the life history of seaweeds most susceptible to light stress and that ultraviolet radiation (UVR) effectively delays photosynthetic recovery. The viability of spores is important on the recruitment of the gametophytic and sporophytic life stages. The impact of UVR on the zoospores is related to the vertical depth distribution of the large sporophytes in the field. 相似文献
9.
Longin CF Utz HF Reif JC Schipprack W Melchinger AE 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2006,112(5):903-912
Optimum allocation of resources is of fundamental importance for the efficiency of breeding programs. The objectives of our
study were to (1) determine the optimum allocation for the number of lines and test locations in hybrid maize breeding with
doubled haploids (DHs) regarding two optimization criteria, the selection gain ΔG
k
and the probability P
k
of identifying superior genotypes, (2) compare both optimization criteria including their standard deviations (SDs), and
(3) investigate the influence of production costs of DHs on the optimum allocation. For different budgets, number of finally
selected lines, ratios of variance components, and production costs of DHs, the optimum allocation of test resources under
one- and two-stage selection for testcross performance with a given tester was determined by using Monte Carlo simulations.
In one-stage selection, lines are tested in field trials in a single year. In two-stage selection, optimum allocation of resources
involves evaluation of (1) a large number of lines in a small number of test locations in the first year and (2) a small number
of the selected superior lines in a large number of test locations in the second year, thereby maximizing both optimization
criteria. Furthermore, to have a realistic chance of identifying a superior genotype, the probability P
k
of identifying superior genotypes should be greater than 75%. For budgets between 200 and 5,000 field plot equivalents, P
k
> 75% was reached only for genotypes belonging to the best 5% of the population. As the optimum allocation for P
k
(5%) was similar to that for ΔG
k
, the choice of the optimization criterion was not crucial. The production costs of DHs had only a minor effect on the optimum
number of locations and on values of the optimization criteria.
C. Friedrich H. Longin and H. Friedrich Utz contributed equally to this work. 相似文献
10.
A major issue faced by breeders is how to effectively manage adverse correlations in breeding programs. We present results
of a Monte Carlo allele-based simulation of the changes in response and variance of response under adverse genetic correlations
by using the examples of two contrasting selection methods: the ‘Smith-Hazel’ selection index (SH) and independent culling
(IC). We assumed several gene models, which included linkage and antagonistic pleiotropy as the primary drivers of adverse
genetic correlations. The different behaviors of these selection methods allowed us to identify the mechanism behind the generation
of uncertainty under antagonistic trait selection: IC had the properties of stabilizing selection, while SH behaved more similar
to disruptive selection. Although SH outperformed IC in terms of genetic gain, this advantage happened at the cost of higher
variance of response and loss of heterozygosity. Using an optimum selection algorithm (OS) to prevent the loss of heterozygosity
through a constraint on inbreeding in SH/OS increased marginally the reliability, remaining still below that of IC under equal
conditions. However, SH/OS had lower inbreeding (ΔF) than IC for equivalent levels of genetic gain, so a compromise between
high selection reliability, low ΔF, and gain must be made by a breeder under antagonistic trait selection even with the use
of optimization tools. 相似文献