Costs and benefits of high mutation rates: adaptive evolution of bacteria in the mouse gut

We have shown that bacterial mutation rates change during the experimental colonization of the mouse gut. A high mutation rate was initially beneficial because it allowed faster adaptation, but this benefit disappeared once adaptation was achieved. Mutator bacteria accumulated mutations that, although neutral in the mouse gut, are often deleterious in secondary environments. Consistently, the competitiveness of mutator bacteria is reduced during transmission to and re-colonization of similar hosts. The short-term advantages and long-term disadvantages of mutator bacteria could account for their frequency in nature.     

Symmetry breaking and the evolution of development

Because of its simplicity, the binary-switch nature of left-right asymmetry permits meaningful comparisons among many different organisms. Phylogenetic analyses of asymmetry variation, inheritance, and molecular mechanisms reveal unexpected insights into how development evolves. First, directional asymmetry, an evolutionary novelty, arose from nonheritable origins almost as often as from mutations, implying that genetic assimilation ("phenotype precedes genotype") is a common mode of evolution. Second, the molecular pathway directing hearts leftward-the nodal cascade-varies considerably among vertebrates (homology of form does not require homology of development) and was possibly co-opted from a preexisting asymmetrical chordate organ system. Finally, declining frequencies of spontaneous asymmetry reversal throughout vertebrate evolution suggest that heart development has become more canalized.     

Scent organ development in creatonotos moths: regulation by pyrrolizidine alkaloids

7-Hydroxy-6,7-dihydro-5H-pyrolizine-1-carboxaldehyde is the major volatile component of the scent organs in males of two species of Creatonotos (Lepidoptera, Arctiidae). The biosynthesis of this presumed pheromone depends on the presence of pyrrolizidine alkaloids in plants that are ingested by the larvae. In addition, these secondary plant substances control the morphogenesis of the scent organs. This morphogenetic effect of an alkaloid has not been observed previously.     

植物花器官发育的分子机理研究进展

植物花器官的发育是由器官特异性基因决定的,这些基因包括ABC模型的A、B、C功能基因,同时还有决定胚珠发育的D功能基因和E功能基因。这些基因的精确表达需要花分生组织特异性基因的激活和多个正负调节因子的调控。在花器官发育过程中,基因存在着复杂的遗传网络调控系统,就此提出了各种调控模型。文章就花发育分子模型的发展和完善、不同模型之间的相互关系以及调控基因之间的相互作用等方面,对植物花器官发育的最新研究进展进行了综述,同时对植物花器官发育机理研究的理论价值和应用前景进行了展望。     

Requirement for RORgamma in thymocyte survival and lymphoid organ development

Most developing thymocytes undergo apoptosis because they cannot interact productively with molecules encoded by the major histocompatibility complex. Here, we show that mice lacking the orphan nuclear hormone receptor RORgamma lose thymic expression of the anti-apoptotic factor Bcl-xL. RORgamma thus regulates the survival of CD4+8+ thymocytes and may control the temporal window during which thymocytes can undergo positive selection. RORgamma was also required for development of lymph nodes and Peyer's patches, but not splenic follicles. In its absence, there was loss of a population of CD3-CD4+CD45+ cells that normally express RORgamma and that are likely early progenitors of lymphoid organs. Hence, RORgamma has critical functions in T cell repertoire selection and lymphoid organogenesis.     

Living with the past: evolution, development, and patterns of disease

Epidemiological observations have led to the hypothesis that the risk of developing some chronic noncommunicable diseases in adulthood is influenced not only by genetic and adult life-style factors but also by environmental factors acting in early life. Research in evolutionary biology, developmental biology, and animal and human physiology provides support for this idea and suggests that environmental processes influencing the propensity to disease in adulthood operate during the periconceptual, fetal, and infant phases of life. This "developmental origins of health and disease" concept may have important biological, medical, and socioeconomic implications.     

Human embryonic kidneys in organ culture: abnormalities of development induced by decreased potassium

Human embryonic kidneys of 5 to 12 weeks of gestation were grown in organ culture. Potassium concentrations of 3 to 6 milliequivalents per liter produced decreased ureteral bud branching, failure of nephron induction, and occasional cystic dilatations of the ureteral bud. Normal development of the kidney occurred at potassium concentrations of 6.5 to 10 milliequivalents per liter. These studies confirm the importance of relative stability of the potassiunm concentration in the development of the embryonic kidney.     

植物花器官发育模型及相关转录因子的研究

论述了有关花器官发育的ABCDE模型的最新进展以及四聚体模型,并对花发育相关的转录因子的研究进展进行了总结,以期为了解花发育的分子机理和遗传基础打下基础.     

辣椒小孢子发育时期与花器形态的相关性

为了直接从花蕾大小或花药的形态特征来判断小孢子的发育时期,对辣椒小孢子发育时期的细胞学,以及小孢子不同发育时期与花萼特征、花蕾大小和花药颜色的关系进行了研究。结果表明,辣椒小孢子发育经四分体时期、单核期和双核期,各时期特征明显。辣椒小孢子发育时期与花蕾的外部形态特征、花药颜色密切相关。供试辣椒品种的小孢子处于单核靠边期时花蕾纵径在4.253-5.074 mm,花蕾横径在4.191-5.367 mm,花瓣与花萼等长或稍长,花药长度在2.020-2.565 mm,花药宽度在0.982-1.417 mm。辣椒同一花蕾小孢子发育存在一定程度的渐续性即不同步。依据花器官形态特征可判断小孢子的发育时期,从而确定花药培养最佳时期所对应的选蕾标准。     

湖北海棠小孢子发育时期与花器形态的相关性

【目的】观察湖北海棠小孢子不同发育时期的花器外部形态及细胞学特征,找出小孢子发育时期与花器外部形态的相关性,为花药或小孢子培养提供细胞学依据。【方法】采摘湖北海棠同一植株固定枝条上大小不同的花蕾作为试验材料,其中一部分取出花药用4′,6-二脒基-2-苯基吲哚（DAPI）荧光染液染色后压片,用于观察小孢子不同发育时期的细胞学特征变化,另一部分用于观测花蕾和花药的大小及颜色,并建立小孢子发育时期与花蕾外部形态特征的关系。【结果】湖北海棠小孢子发育经历四分体时期、单核早中期、单核靠边期和二胞花粉时期,最终发育为成熟花粉,各时期特征明显。小孢子各发育时期与花蕾大小和花药颜色密切相关,当花蕾纵径为1.45～3.43 mm、花药颜色为深红色时,小孢子处于四分体时期;当花蕾纵径为4.46～6.29 mm、花药为红色时,小孢子绝大多数处于单核早中期;当花蕾纵径在7.14～9.86 mm、花药为粉红色时,小孢子大多进入单核靠边期;当花蕾纵径为10.11～12.19 mm、花药颜色逐渐转变为粉黄色时,小孢子大部分处于二胞花粉时期。【结论】花蕾大小及花药颜色可作为判断小孢子发育时期的依据,据此可便捷地找到适宜时期的小孢子。     

不同品种薹用大蒜花薹发育进程及其形态和解剖学观察

以大蒜薹用品种'正月早'、'二水早'和'三月黄'为材料,采用石蜡切片法和显微摄影法对大蒜茎端及蒜薹发育过程进行形态和解剖学观察.结果表明:大蒜茎端生长点的分化进程可分营养生长期、总苞和花序分化期、鳞芽形成期和花芽分化期,其中花芽分化期又可分为花原基分化、苞片分化、气生鳞茎分化以及花器官分化等不同阶段.大蒜鳞芽分化晚于花序分化而早于花器官分化.蒜薹薹身的解剖结构主要由表皮、皮层、维管束和薄壁细胞组成.不同品种大蒜花芽分化和抽薹始期不同,从早到晚依次为'正月早'、'二水早'和'三月黄',与品种特性一致.     

科技进步对广东农业发展作用的研究

运用农业部规定的增长速度方程测算法,对广东省农业科技进步贡献率进行测算与分析,并进一步对农业科技进步贡献率进行二次分离,探求影响科技进步的主次因素,并探讨了提高广东省农业科技进步贡献率的对策建议和措施。     

水稻花器官突变体lfl(leafy lodicules)的鉴定与分析

在杂交育种中发现的一个水稻花器官突变体,经过多代种植,已稳定遗传。以此突变体为父本,以D62A、岗46A、11-32A和金23A为母本配制杂交组合进行遗传分析,根据F2表型及X2测验结果表明,该突变体的性状是由单隐性基因控制的。此突变体除了花器官,其它农艺性状与野生型无异。在同一突变植株中,有正常小花,也有多种花器官突变表型：内颖缺失或弯曲,浆片与异常叶状体相连,雄蕊正常或部分增多退化,部分雌蕊异常、呈双雄蕊或三拄头。所有突变体中浆片都与叶状体相连,呈浆片叶化表型,因此我们将此突变体命名为水稻浆片叶化突变体lfl（leafy lodieules）,形态分析表明￡儿为一个新的水稻花器官发育相关基因。