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1.
衰减作用是细菌辅助阻遏作用的一种精细调控,虽然它们都是调节基因转录,但是两种不同类型的调控方式,它们之间有着许多不同点。以色氨酸操纵子转录的阻遏作用和衰减作用为例,它们的区别归纳起来有如下方面。(1)调控的信号不同阻遏作用的信号物质是Trp;而衰减作用的信号物质严格说来应是TrP-tRNA,因为当氨酰-tRNA合成酶缺损时,TrP的积累不会引起转录的衰减作用。(2)调控的关键不同阻遏作用的关键是阻遏蛋白与信号物质Trp的相互作用;而衰减作用的关键是转录与翻择相偶联。(3)调控的分子基础不同阻遏作用的分子基础是阻遏…  相似文献   

2.
叶黄素的抗癌作用及其研究现状   总被引:10,自引:0,他引:10  
叶黄素是自然界广泛存在的类胡萝卜素,可以提高人体的免疫能力,也是一种抗氧化剂,对老年视黄斑退行性变化有很好的预防作用,但更重要的是研究表明,叶黄素对一些类型的癌症具有预防效果。本综述了近年来有关叶黄素预防癌症作用的流行病学调查、分析,以及与癌症关系的实验研究及作用机制等方面的研究进展。  相似文献   

3.
植物化感物质活性变化及其作用机理研究进展   总被引:16,自引:0,他引:16  
本文综述了化感物质活性的变化、变化的原因及其功能机理。化感物质活性在自然过程中,由于温度、光周期、水和土壤等的不同而变化,在功能过程中随其初始浓度、化合物结构和混合程度不同而变化,在植物体内由于组织器官和成熟程度不同而变化,而研究技术和操作过程也影响化感物质的活性。文章还讨论了未来化感作用研究的发展方向。未来化感作用研究将集焦于如下五方面(1)更有效地在实践中,特别是在农业生产过程中鉴定和提纯化感物质;(2)化感作用在分子结构水平的功能定位;(3)应用化感作用解释植物种间相互作用;(4)化感作用在植被演替过程中的驱动力作用;(5)化感作用在进化过程中的意义。  相似文献   

4.
植物化感物质活性变化及其作用机理研究进展   总被引:1,自引:0,他引:1  
本文综述了化感物质活性的变化、变化的原因及其功能机理.化感物质活性在自然过程中,由于温度、光周期、水和土壤等的不同而变化,在功能过程中随其初始浓度、化合物结构和混合程度不同而变化,在植物体内由于组织器官和成熟程度不同而变化,而研究技术和操作过程也影响化感物质的活性.文章还讨论了未来化感作用研究的发展方向.未来化感作用研究将集焦于如下五方面:(1)更有效地在实践中,特别是在农业生产过程中鉴定和提纯化感物质;(2)化感作用在分子结构水平的功能定位;(3)应用化感作用解释植物种间相互作用;(4)化感作用在植被演替过程中的驱动力作用;(5)化感作用在进化过程中的意义.  相似文献   

5.
节肢动物(arthropod)是动物界中种类数量最多、分布范围最广的类群,现存110万~120万种。节肢动物毒素具有较强的生物学活性及独特的作用机制,其毒素分子能够作用于离子通道、细胞膜、受体和酶等靶点,影响神经、循环、免疫、肌肉等系统,从而进行快速、高效的捕食和防御。本文总结了有毒节肢动物毒素的来源、成分及作用靶点等信息,重点综述了毒素作用机制的分子基础,以及毒素参与的捕食、防御和趋避等生物学作用。  相似文献   

6.
雌激素在中枢神经系统中的作用   总被引:22,自引:0,他引:22  
雌激素对中枢神经系统神经元有多种作用(包括电生理、神经营养和代谢等的作用)。近年来,随着对雌激素作用基因组机制和非基因组机制的研究,人们逐渐加深了其在神经功能方面作用 的认识。目前发现,雌激素在调节下丘脑GnRH神经元功能活动、诱导和维持海马树状棘突,以及保护神经元等诸多方面都发挥着重要作用。流行病学提示,雌激素可以预防绝经妇女患早老性痴呆病(Alzheimer‘sDisease,AD)对神经功能有保护作用,由此可见,雌激素除调节生殖功能活动外,对中枢神经系统还有着更为广泛的作用。  相似文献   

7.
本文通过家兔及大鼠的动物实验证明了,蚯蚓溶栓酶不仅具有明显地抑制血栓形成的作用,更具有很强的血栓溶解作用,其作用性质为激酶和溶酶两种功能。同时证明溶栓酶能明显缩小大脑皮层因结扎大脑中动脉后产生的梗塞灶。从而认为:蚯蚓溶栓酶是一种很有效的溶栓药物。  相似文献   

8.
印楝素乳油对小菜蛾种群的控制作用   总被引:23,自引:2,他引:21  
通过室内外系统试验探讨了印楝素乳油对小菜蛾Plutella xylostella种群的控制作用。结果表明,其控制作用主要表现在对成虫产卵的显忌避作用。对幼虫的拒食作用以及对生长发育的影响和减少幼虫危害为等方面,印楝素乳油0.005mL/59.0%,使小菜蛾种群趋势指数(I值)降为2.4干扰作用控制指数(IIPC)为0.1079,采用状态空间分析法就印楝素乳油施用后小菜蛾种群数量动态的模拟分析亦表明,其显的控制作用表现在种群发展初期对成虫的忌避作用。  相似文献   

9.
本文研究了乳酸杆菌对小鼠腹腔巨噬细胞(PEM)的活化作用及其细胞毒作用。实验结果表明:腹腔注射乳酸杆菌后,PEM体外细胞毒作用及体内细胞毒作用增强,酸性磷酸酶含量及非特异性酯酶含量增加、TNF—α释放量增加。电镜显示:PEM体积增大、伪足增多、线粒体、溶酶体等细胞器数量增多。本研究表明:乳酸杆菌具有较强的活化PEM的作用。  相似文献   

10.
海鞘中的抗肿瘤生物活性物质   总被引:16,自引:0,他引:16  
本文综述了从海鞘中发现的约80种具有抗肿瘤活性的经合物,包括其结构,活性,来源等,对其中较重要者的作用机理作了详细的介绍。  相似文献   

11.
红三叶草总异黄酮对小公鸡生长及血清睾酮水平的影响   总被引:43,自引:1,他引:42  
日粮中添加红三叶草总异黄酮(4.38mg/kg饲料),饲喂45-56日龄红布罗肉用公仔鸡,与对照组比较,总异黄酮实验组公仔鸡日增重提高5.1%,料重比下降9.2%,提高了饲料的利用率。屠宰结果表明,腹脂重、腹脂/胴体显著降低,鸡冠重、睾丸重增加,鸡冠、睾丸和体重间的相关分析,睾丸石蜡切片和血清睾酮含量的放射免疫测定,均表明总异黄酮能提高血清睾酮水平,促进雄性动物生殖系统发育。  相似文献   

12.
Human lipoxygenase (hLO) isozymes have been implicated in a number of disease states and have attracted much attention with respect to their inhibition. One class of inhibitors, the flavonoids, have been shown to be potent lipoxygenase inhibitors but their study has been restricted to those compounds found in nature, which have limited structural variability. We have therefore carried out a comprehensive study to determine the structural requirements for flavonoid potency and selectivity against platelet 12-hLO, reticulocyte 15-hLO-1, and prostate epithelial 15-hLO-2. We conclude from this study that catechols are essential for high potency, that isoflavones and isoflavonones tend to select against 12-hLO, that isoflavons tend to select against 15-hLO-1, but few flavonoids target 15-hLO-2.  相似文献   

13.
在过去的几十年间,人们认为糖皮质激素(glucocorticoid,GC)仅仅是通过改变基因的表达来发挥其生理作用,这个过程需要几个小时来完成。然而,近年来越来越多的证据表明GC对激素分泌、神经元兴奋性、机体行为及细胞形态、糖类代谢等具备快速效应,这些过程往往在数秒钟或者分种内完成,这种作用机制被称为GC的非基因组作用机制。GC的非基因组作用主要可能通过两种不同的机制起作用:(1)通过细胞膜上或者细胞质内结构未知的糖皮质激素受体(glucocorticoid Recptor,GR)来发挥非基因组作用,即为特异性非基因组效应,(2)GC主要通过改变细胞膜理化作用来发挥效应。也称为非特异性非基因组效应(non-specific nongenomic effects,NSNE)。本文通过阐述近年来GC的非基因组的作用的最新研究进展并且讨论了这些非基因组作用临床治疗过程中的联系。对糖皮质激素基因组和非基因组作用机制的深入了解有助于指导我们在临床合理用药并减少其副作用。  相似文献   

14.
大坝的生态效应:概念、研究热点及展望   总被引:11,自引:1,他引:10  
大坝产生的生态效应涉及范围广、周期长,在对社会经济发展起到积极作用的同时,也对生态、环境造成了一定的影响。在评述国内外对大坝生态效应概念和内涵理解的基础上,提出了大坝生态效应链和生态效应网的概念。依据大坝建设和运行的特点,结合流域生态系统的特征分别论述了大坝对水文、局地生态的调节效应以及屏障效应和岛屿化、截留效应、边缘效应、水温效应等国内外研究的热点。最后,提出了今后大坝生态效应的研究方向:1)生态正效应、生态效应链和生态效应网;2)生态系统过程和状态生态效应;3)不同时空尺度下生态效应及其尺度推绎方法等3个方面的研究。  相似文献   

15.
We present the results of a series of computer simulations thatexamined the impact of winner, loser, and bystander effectson hierarchy formation in fused groups. These effects and theirimplications for hierarchy structure and aggressive interactionswere first examined in small four-member groups. Subsequentto this, the two small groups were fused into a single largergroup. Further interactions took place in this fused group,generating a new hierarchy. Our models demonstrate clearly thatwinner, loser, and bystander effects strongly influence boththe structure and types of interactions that emerge from thefusion of smaller groups. Four conditions produced results inwhich the same general patterns were uncovered in pre- and postfusiongroups: (1) winner effects alone, (2) bystander loser effectsalone, (3) winner and bystander winner effects operating simultaneously,and (4) all four effects in play simultaneously. Outside thisparameter space, hierarchy structure and the nature of aggressiveinteractions differed in pre- and postfusion groups. When onlyloser effects were in play, one of the two clear alphas fromthe prefused groups dropped in rank in the eight-member fusedgroup. When bystander winner effects were in play, it was difficultto rank any of the eight individuals in the fused group, andplayers interacted almost exclusively with those that were notin their original four-member group. When loser and bystanderloser effects operated simultaneously, two top-ranking individualsemerged in the fused groups, but the relative rank of the otherplayers was difficult to assign.  相似文献   

16.
栖息地破碎化与鸟类生存   总被引:9,自引:0,他引:9  
邓文洪 《生态学报》2009,29(6):3181-3187
栖息地破碎化给野生动物带来的不良后果是全球生态学家和保护生物学家共同关心的问题.自从提出栖息地破碎化是导致生物多样性丧失的关键因素之一的论点后,近20年来,栖息地破碎化研究一直是生态学和保护生物学最活跃的前沿研究领域之一.栖息地破碎化是一动态过程,可在多尺度上发生并蕴涵着复杂的空间模式变化.栖息地破碎化对鸟类的生态学效应主要体现在面积效应、隔离效应和边缘效应等.这些效应影响着鸟类的分布、基因交流、种群动态、扩散行为、种间关系和生活史特征等,最终影响着鸟类的生存.介绍和总结了栖息地破碎化过程、研究的理论依据及栖息地破碎化对鸟类生存产生的诸多影响.  相似文献   

17.
普通玉米籽粒性状的遗传效应分析   总被引:5,自引:1,他引:4  
采用二倍体种子遗传模型及其分析方法,研究了5个玉米籽粒性状的直接效应、母体效应和细胞质效应.分析结果表明,各性状的遗传同时受种子直接效应和母体效应的影响,细胞质基因对百粒重和粒宽具有极显著影响.除粒长、粒厚的直接显性效应与母体显性效应间的协方差外,直接效应与母体效应间的协方差均不显著.因此,通过母体植株的表现可对这些性状进行有效的选择.S_22和 87-1是改良粒重的优良亲本.选择粒较宽的自交系作母本有利于提高后代选系及F_1的百粒重.  相似文献   

18.
Parental experience alters survival-related phenotypes of offspring in both adaptive and nonadaptive ways, yielding rapid inter- and transgenerational fitness effects. Yet, fitness comprises survival and reproduction, and parental effects on mating decisions could alter the strength and direction of sexual selection, affecting long-term evolutionary trajectories. We used a full factorial design in which threespine stickleback (Gasterosteus aculeatus) mothers, fathers, both, or neither were exposed to a model predator at developmentally appropriate times to test for predator-induced maternal, paternal, and joint parental effects on daughters’ mating behavior. We tested the responsiveness, preferences, and mate choices of adult daughters in no-choice trials with wild-caught males who had varied sexual signals. Maternal and paternal predator exposure independently yielded daughters who preferred males who were intermediate in conspicuousness (with duller nuptial coloration and who courted less vigorously), relaxing the typical preference for the most conspicuous males. The combined effects of maternal and paternal predator exposure were not cumulative; when both parents were predator exposed, single-parent effects on mate preferences were reversed. Thus, we cannot assume that maternal and paternal effects additively combine to produce “parental” effects. Further, joint parental predator exposure yielded daughters who were three times less likely to mate at all. Stress-induced intergenerational parental effects on reproductive decisions such as those observed here may potentiate rapid transgenerational responses to novel and changing mating environments.  相似文献   

19.
Consumption and the Rebound Effect: An Industrial Ecology Perspective   总被引:1,自引:0,他引:1  
Measures taken to protect the environment often have other, unintended effects on society. One concern is that changed behavior may offset part of the environmental gain, something that has variously been labeled "take-back" or "rebound." In energy economics, the rebound effect encompasses both the behavioral and systems responses to cost reductions of energy services as a result of energy efficiency measures. From an industrial ecology perspective, we are concerned about more than just energy use. Any given efficiency measure has several types of environmental impacts. Changes in the various impact indicators are not necessarily in the same direction. Both co-benefits and negative side effects of measures directed to solve one type of problem have been identified. Environment is often a free input, so that a price-based rebound effect is not expected, but other indirect effects not connected to the price, such as spillover of environmental behavior, also occur. If the costs and impact of products that are already environmentally friendly are reduced, the "rebound" can be in the opposite, desired direction. Furthermore, I identify technical spillover effects. Hence a number of related effects, often producing positive results, are not as well understood. Household environmental impact assessments and eco-efficiency assessments take into account the rebound effect, but they do not necessarily take into account these other effects. The analysis hence indicates that the current focus on the rebound effect is too narrow and needs to be extended to cover co-benefits, negative side effects, and spillover effects.  相似文献   

20.
The adaptive value of transgenerational effects (the ancestor environmental effects on offspring) in changing environments has received much attention in recent years, but the related empirical evidence remains equivocal. Here, we conducted a meta‐analysis summarising 139 experimental studies in plants and animals with 1170 effect sizes to investigate the generality of transgenerational effects across taxa, traits, and environmental contexts. It was found that transgenerational effects generally enhanced offspring performance in response to both stressful and benign conditions. The strongest effects are in annual plants and invertebrates, whereas vertebrates appear to benefit mostly under benign conditions, and perennial plants show hardly any transgenerational responses at all. These differences among taxonomic/life‐history groups possibly reflect that vertebrates can avoid stressful conditions through their mobility, and longer‐lived plants have alternative strategies. In addition to environmental contexts and taxonomic/life‐history groups, transgenerational effects also varied among traits and developmental stages of ancestors and offspring, but the effects were similarly strong across three generations of offspring. By way of a more comprehensive data set and a different effect size, our results differ from those of a recent meta‐analysis, suggesting that transgenerational effects are widespread, strong and persistent and can substantially impact the responses of plants and animals to changing environments.  相似文献   

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