无融合生殖在植物育种中的应用及细胞胚胎学研究方法

无融合生殖是一种能代替有性生殖而不发生核融合,但能产生种子的生殖方式.它包括:(1)二倍体孢子生殖;(2)生殖细胞性无孢子生殖;(3)不定胚生殖等.这3种类型能固定F_1杂种优势.单倍体孤雌生殖产生的后代遗传性较纯,具有潜在的应用价值.     

脱水污泥高温两相与单相厌氧消化工艺比较研究

采用课题组自主研发的自动控温间歇搅拌高含固厌氧消化反应器,针对合肥市十五里河污水处理厂的脱水污泥(稀释至含固率10%)进行了超高温(70℃)酸化-高温(55℃)甲烷化和高温(55℃)酸化-高温(55℃)甲烷化两相与高温(55℃)单相厌氧消化系统性能的比较研究。结果表明,在污泥停留时间为两相产酸相4 d、产甲烷相16 d,单相20 d的条件下,超高温-高温和高温-高温两相的VS降解率分别为40.5%和40.2%,高温单相则只有34.9%。在总停留时间相等的条件下,两相消厌氧化系统的VS降解率、甲烷产率均比高温单相厌氧消化系统高,而出泥VFA含量小于高温单相厌氧消化系统。总体来说,两相厌氧消化系统运行更为稳定,效果更好,并且有较高的H2可供利用为清洁能源,但较高的H2S含量则须控制。     

植物实验生殖生物学的新天地

有性生殖是植物生活史中承前启后的环节,植物经过传粉受精传宗接代。人类从植物生殖的产品中获得粮食、棉花、油料、果品及花卉,并通过操纵     

活度的两种标准状态与热力势

一、 高温冶金经常存在下列四种平衡反应:(一) 单相的溶液反应,表现在某一元素溶解在另一元素中,造成一溶体合金;(二)二相的气体———金属液反应;(三)二相的金属液——炉渣液反应;和(四)三相的气体——炉渣液——金属液反应。在这些高温反应中,我们常应用到下列四个定律:—— 1.拉乌尔定律; 2.亨利定律; 3.分配定律; 4.质量作用定律。     

分相式气液两相流体等干度分配方法

提出一种新的气液两相流体等干度分配方法--分相分配法.该方法的特点在于,基于单相流体较容易实现均匀分配的特征,首先通过强化两相流体在分配单元内的相分离,将气液混合物分离成单相或接近单相的气体和液体,然后以单相流的形式分别进行分配,最后将分配后的单相气、液进行两两汇合,完成两相流体的等干度分配.在空气一水实验回路上对这种分配方法进行了实验研究,结果表明,在分层流、波状分层流、弹状流和部分环状流的情况下,气液两相流体均能在分配元件内得到较好分离,保证在单相或接近单相的状态下进行分配,支路与主路间的平均干度偏差小于1.6%.     

Al-Fe-Sn三元系合金相图

本文用x射线衍射分析法,电子探针显微分析法,研究和测定了Al-Fe-Sn三元系合金相图的室温截面。此截面包含有10个单相区,17个两相区和8个三相区。β、γ两个单相没有可查觉的固溶度,截面中没有出现新相。     

底水驱动油藏水平井油水两相流产能研究

首先利用镜像反应法和势的叠加原理,对底水驱动油藏水平井稳定渗流进行理论研究,得到只有单相油流流动条件下的底水油藏水平井产能公式;在单相油流流动的基础上,以单相流动时的产量作为水平井的初始产量,再应用势的叠加原理和等值渗流阻力法推导出两相流动时的底水驱动油藏水平井产能公式。     

感性三相负载对单相电度表计量的影响

本文分析了利用两个单相电度表测量二相负载用电量过程中出现的一个问题,并指出了解决的办法.     

双模态过渡池沸腾实验研究

利用控制加热电压和加热面平均温度两种方法,实验研究了常压（0．1MPa）、室温（16℃）条件下除气后的R113在直径60μm细铂丝表面的池沸腾传热现象,观测了单相对流、核态沸腾、双模态过渡沸腾和膜态沸腾4种传热模式中的汽相分布及其传热特征,发现充分发展的核态沸腾传热曲线、膜态沸腾传热曲线及临界热流的数值分别与文献中常用关联式的预测一致,而核态沸腾和膜态沸腾共存的稳定双模态过渡沸腾曲线被一极小值点分为两个连续分支,邻近膜态沸腾的右支上热流与过热度成正比,而邻近核态沸腾的左支上热流则随过热度增长而下降,并且只出现在加热面平均温度受控的实验中．     

宁化县银杏古树种核特征

以福建省宁化县32株古银杏树当年生种核为研究材料,对种核的特征进行了系统的研究。结果表明：(1)依据种核的长宽比,将宁化县境内的32株雌株资源种核类型划分为圆子类、马铃类和梅核类;(2)32个银杏单株种核的单粒质量、单粒体积、核长、核宽、核厚等指标的差异均达极显著水平,其中单粒质量位于前3位的分别为3.041、2.846和2.846 g;(3)所测定的种核各项指标中,与质量相关的指标变异系数较大,与种核形态相关的指标较稳定;(4)相关分析及回归分析表明,种核形态各指标间均存在极显著相关,而单粒质量与核长、核宽、核厚之间存在显著相关。     

Genetic segregation and the maintenance of sexual reproduction

Sexual reproduction confronts evolutionary biology with a paradox: other things being equal, an asexual (all-female) population will have twice the reproductive potential of a competing sexual population and therefore should rapidly drive the sexual population to extinction. Thus, the persistence of sexual reproduction in most life forms implies a compensatory advantage to sexual reproduction. Work on this problem has emphasized the evolutionary advantages produced by the genetic recombination that accompanies sexual reproduction. Here we show that genetic segregation produces an advantage to sexual reproduction even in the absence of an advantage from recombination. Segregation in a diploid sexual population allows selection to carry a single advantageous mutation to a homozygous state, whereas two separate mutations are required in a parthenogenetic population. The complete fixation of advantageous mutations is thus delayed in a heterozygous state in asexual populations. Calculation of the selective load incurred suggests that it may offset the intrinsic twofold reproductive advantage of asexual reproduction and maintain sexual reproduction in diploid populations.     

紧密角管藻的两种类型休眠孢子

从厦门近岸分离的紧密角管藻（ＣＣ１３纯系），在氮限制培养下，首次发现在硅藻生活史中同时出现无性和有性形成两种类型休眠孢子的特殊现象，无性产生的休眠孢子是在孢子母细胞中成对形成，有性产生的休眠孢子是在复大孢子里单个形成．两类休眠孢子的形态有相似之处，亦有区别，无性产生的休眠孢子其形成速度和萌发速度均比有性的快速，而寿命却较短．介质中氮贫乏是该藻形成休眠孢子的必要条件；两类休眠孢子形态上和生理上的差别与不同的生殖方式有关     

Evolution of plant reproduction: From fusion and dispersal to interaction and communication

Based on the existing data concerning the evolution of the sexual reproduction, it is argued that the processes of sex differentiation and interactions play a key role in evolution. From the beginning environment and organism are unified. In a changing dynamic environment life originates and the interaction between life and environment develops from simple to more complex organisms. Sexual reproduction is introduced after the origin of meiosis and is a key process in evolution. The asexual reproduction process prepares to dispersal. Sexual reproduction process adds the genome renewal and the gamete-gamete interaction. Reproduction and dispersal are connected and the process of reproduction has similarities between asexual and sexual reproduction. Unicellular algae develop the physiological and morphological sex differentiation. Sex differentiation is connected with the way of dispersal. The step to multicellular plants introduces cell isolation after meiosis and by the stay on the mother plant within a cell or organ, plant-cell apoplastic interaction originates and by prolonged stay the plant-plant interaction. This stay influences the type of dispersal. A life cycle with alternation of generations and two moments of dispersal permits plants to go on land. In ferns a shift in the moment of sex differentiation to meiospore happens and the stay of the macrospore leads to the seed plants. In water all types of sexual reproduction, interactions and the alternation of generations are prepared and these are used to conquest land. On land the biotic dispersal is realized. The phylogeny of sexual reproduction reveals that the sex differentiation and interaction are the main causes in the evolution of sexual reproduction. Sexual reproduction shows interactions during gamete fusion, between organism and environment and in multicellular plants between organisms. With respect to other types of interaction as in symbiosis or the nutrient chain, interaction is considered as an important action which is based on a persisting cooperation and points to a push during evolution. The push is expressed as communication： the driving force in the evolution. Based on the interactions between organisms and interactions between organisms and the dynamic environment, communication is considered as a driving force leading to the evolution as explained in the development of plant reproduction. Consequences for reproduction, its regulation and the process of evolution are discussed.     

The ecological cost of sex

Why sex prevails in nature remains one of the great puzzles of evolution. Sexual reproduction has an immediate cost relative to asexual reproduction, as males only express their contribution to population growth through females. With no males to sustain, an asexual mutant can double its relative representation in the population in successive generations. This is the widely accepted 'twofold cost of males'. Many studies have attempted to explain how sex can recoup this cost from fitness benefits associated with the recombination of parental genotypes, but these require complex biological environments that cycle over evolutionary timescales. In contrast, we have considered the ecological dynamics that govern asexual invasion. Here we show the existence of a threshold growth rate for the sexual population, above which the invasion is halted by intraspecific competition. The asexual population then exerts a weaker inhibitory effect on the carrying capacity of the sexual population than on its own carrying capacity. The stable outcome of this is coexistence on a depleted resource base. Under these ecological circumstances, longer-term benefits of sex may eventually drive out the asexual competitor.     

Haploidy or diploidy: which is better?

Although the evolutionary advantages of sexual reproduction have been extensively discussed, much less attention has been paid to haploid and diploid phases of the sexual life cycle. The relative lengths of these phases differ greatly in various taxa, including as extremes those with one or the other phase reduced to a single cell. Here we consider the efficiency of elimination of deleterious mutations as an evolutionary force and compare the mutation loads under haploid and diploid selection, Ln and L2n. With truncation-like selection, partial dominance, and heterozygous effect of a mutation less than about 1/4 its hemizygous effect, L2n less than Ln; otherwise L2n greater than Ln. The difference becomes important when the genomic deleterious mutation rate exceeds about 1 per genome. This suggests that the mutation rate, degree of dominance and mode of selection can be important in life-cycle evolution.     

野古草(Arundinella hirta) 对水淹逆境的生殖响应

分析了嘉陵江边不同强度水淹后的1年生野古草个体的有性生殖和无性生殖数量特征，结果表明：野古草有性生殖植株的单株种子质量、粒数和生殖分配等随水淹强度增大而逐渐降低，高强度水淹后野古草没有进行有性生殖．在一定水淹范围内，表征野古草无性生殖的单株质量、分枝数随水淹强度的增大而呈增大的趋势，说明野古草无性生殖随水淹强度的增加呈增强的趋势．在周期性的自然水淹下，无性生殖是野古草适应自然的生殖方式．     

Sexual selection and the maintenance of sexual reproduction

The maintenance of sexual reproduction is a problem in evolutionary theory because, all else being equal, asexual populations have a twofold fitness advantage over their sexual counterparts and should rapidly outnumber a sexual population because every individual has the potential to reproduce. The twofold cost of sex exists because of anisogamy or gamete dimorphism-egg-producing females make a larger contribution to the zygote compared with the small contribution made by the sperm of males, but both males and females contribute 50% of the genes. Anisogamy also generates the conditions for sexual selection, a powerful evolutionary force that does not exist in asexual populations. The continued prevalence of sexual reproduction indicates that the 'all else being equal' assumption is incorrect. Here I show that sexual selection can mitigate or even eliminate the cost of sex. If sexual selection causes deleterious mutations to be more deleterious in males than females, then deleterious mutations are maintained at lower equilibrium frequency in sexual populations relative to asexual populations. The fitness of sexual females is higher than asexuals because there is no difference in the fecundity of sexual females and asexuals of the same genotype, but the equilibrium frequency of deleterious mutations is lower in sexual populations. The results are not altered by synergistic epistasis in males.     

Sexual reproduction between partners of the same mating type in Cryptococcus neoformans

Cryptococcus neoformans is a globally distributed human fungal pathogen that causes life-threatening meningoencephalitis in immunocompromised patients. It has a defined sexual cycle involving haploid cells of alpha and a mating types, yet the vast majority of environmental and clinical isolates are alpha (ref. 3). Sexual recombination is normally expected to occur between isolates of opposite mating type in organisms with two mating types (or sexes). How sexual reproductive potential can be maintained in an organism with a largely unisexual, nearly clonal population genetic structure is unknown. One clue, however, is that alpha strains undergo fruiting, a process that resembles sexual mating but is thought to be strictly mitotic and asexual. We report here that hallmarks of mating occur during fruiting, including diploidization and meiosis. Pheromone response pathway elements and the key meiotic regulator Dmc1 are required for efficient fruiting. Furthermore, fusion and meiosis can occur between non-isogenic alpha strains, enabling genetic exchange. These studies reveal how sexual reproduction can occur between partners of the same mating type. These findings have implications for the evolution of microbial pathogens, as well as for parthenogenesis, cell fusion events and transitions between self-fertilizing and outcrossing modes of reproduction observed in both fungi and other kingdoms.     

海三棱藨草种群的繁殖生态学研究

本文研究了上海市南汇县东海农场场部海堤外侧滩涂上海三棱藤草种群的繁殖生态学,其中包括在三个地带中种群的无性繁殖(无性系生长)与无性系结构,种群的有性繁殖,种子产量与重量,植株在生长季节中的干物质分配动态以及与环境之间的相互关系。通过对海三棱藨草种群的繁殖过程与生活史各阶段之间以及与生态环境之间相互关系的研究,有助于理解和搞清其种群的数量动态规律。     

Higher rates of sex evolve in spatially heterogeneous environments

The evolution and maintenance of sexual reproduction has puzzled biologists for decades. Although this field is rich in hypotheses, experimental evidence is scarce. Some important experiments have demonstrated differences in evolutionary rates between sexual and asexual populations; other experiments have documented evolutionary changes in phenomena related to genetic mixing, such as recombination and selfing. However, direct experiments of the evolution of sex within populations are extremely rare (but see ref. 12). Here we use the rotifer, Brachionus calyciflorus, which is capable of both sexual and asexual reproduction, to test recent theory predicting that there is more opportunity for sex to evolve in spatially heterogeneous environments. Replicated experimental populations of rotifers were maintained in homogeneous environments, composed of either high- or low-quality food habitats, or in heterogeneous environments that consisted of a mix of the two habitats. For populations maintained in either type of homogeneous environment, the rate of sex evolves rapidly towards zero. In contrast, higher rates of sex evolve in populations experiencing spatially heterogeneous environments. The data indicate that the higher level of sex observed under heterogeneity is not due to sex being less costly or selection against sex being less efficient; rather sex is sufficiently advantageous in heterogeneous environments to overwhelm its inherent costs. Counter to some alternative theories for the evolution of sex, there is no evidence that genetic drift plays any part in the evolution of sex in these populations.