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1.
ELECTRON MICROSCOPIC STUDIES OF MITOSIS IN AMEBAE : II. The Giant Ameba Pelomyxa carolinensis
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Dividing nuclei from the giant ameba Pelomyxa carolinensis were fixed in osmium tetroxide solutions buffered with veronal acetate to pH 8.0. If divalent cations (0.002 M calcium, magnesium, or strontium as chlorides) were added to the fixation solution, fibrils that are 14 mµ in diameter and have a dense cortex are observed in the spindle. If the divalent ions were omitted, oriented particles of smaller size are present and fibrils are not obvious. The stages of mitosis were observed and spindle components compared. Fibrils fixed in the presence of calcium ions are not so well defined in early metaphase as later, but otherwise have the same diameter in the late metaphase, anaphase, and early telophase. Fibrils are surrounded by clouds of fine material except in early telophase, when they are formed into tight bundles lying in the cytoplasm unattached to nuclei. Metaphase and anaphase fibrils fixed without calcium ions are less well defined and are not observably different from each other. The observations are consistent with the concept that spindle fibrils are composed of polymerized, oriented protein molecules that are in equilibrium with and bathed in non-oriented molecules of the same protein. Partially formed spindle fibrils and ribosome-like particles were observed in the mixoplasm when the nuclear envelope had only small discontinuities. Remnants of the envelope are visible throughout division and are probably incorporated into the new envelope in the telophase. Ribosome-like particles are numerous in the metaphase and anaphase spindle but are not seen in the telophase nucleus, once the envelope is reestablished, or in the interphase nucleus. 相似文献
2.
广西金钟山鸟类保护区鸟类多样性初步研究 总被引:7,自引:0,他引:7
本文共记录到金钟山鸟类274种,分别隶属于18目57科,其中陆生鸟类251种,水鸟23种;以留鸟为主,共157种;候鸟、旅鸟分别为104种、13种;东洋种为优势类群,共有171种,古北种和广布种分别为4种、27种。这些鸟类中有国家重点保护鸟类39种,中国特有种鸟类3种,列入世界自然保护联盟红皮书名录中的鸟类5种,列入中国濒危动物红皮书名录中的鸟类20种,列入CITES附录中的鸟类34种。本文还对金钟山鸟类保护区的5种不同生境类型的鸟类种类组成作了比较,结果表明灌丛+农田的鸟种多样性指数最高,为3.04;水域的鸟种多样性指数最低,为2.14。 相似文献
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China, under highly varied ecological conditions resulted from wide latitudinal and altitudinal ranges and from the adequate precipitation, has developed a
very rich flora of great diversity. As far as flowering plants are concerned, there are
2980 genera, 214 of which, belonging to 64 families, are endemic. Among these endemic genera, there are 9 genera of taxads and conifers, 19 genera of monocots and
others of dicots. Of the approximately 129 herbaceous endemic genera in the Chinese
flora as a whole, about 22 (17%) are annual and 107 (83%) are biennial or perennial.
In the present paper the ecological distribution, the nature of endemic genera and the
centers of endemism are discussed.
1. Three types of endemic genera are distinguished, neoendemics, palaeoendemics
and active epibiotics, The endemic genera in the flora of China are, for the most part,
considered to be very old ones, and most of them are of temperate nature.
2. the degree of endemism in our 22 floristic regions is shown in Figure 1. The
areas richest in endemic genera in the Chinese flora as a whole are the 13, 16 and 17
regions. The poorest are the 2, 4, 9 and 10 regions, and no one in the 1 and 3 regions
These results on floristic richness are of general applicability.
As shown in table 1, the difference in the degree of endemism among the seven
Chinese floristic subkingdoms are most pronounced. 101 endemic genera are known
to occur in one subkingdom, 72 to occur in two subkingdoms, and 3 to occur in four
subkingdoms, only one genus widely distributed in five subkingdoms. However, there
is no genus occurring in seven subkingdoms. The difference in the degree of endemism
in each subkingdom reveals that the distribution of endemic genera is not well-distributed in the Chinese flora as a whole.
Analysis of the vertical distribution of the 200 endemic genera of the Chinese
flora bears out that there is no evident increase in endemism as a whole with altitude.
3. Three centers of endemism are found (Fig. 2). These are as follows:
a). Eastern Sichuan-western Hubei center.
b). Southeastern Yunnan-western Guangxi center.
c). Western Sichuan-northwestern Yunnan center. The degree of endemism andcharacters of endemic genera in each center are discussed. 相似文献
5.
桂西北典型喀斯特区生态服务价值的环境响应及其空间尺度特征 总被引:6,自引:0,他引:6
Study on ecosystem service values (ESVs) is the bridge of understanding ecosystem and economic decision-making. To investigate the response of ESVs to ambient environment and their spatial scales is an urgent work in the process of ecological restoration and sustainable development in southwest China. Based on the previous research results, the remote images, and weather data of 31 years (1975-2005), the response of ESVs to ambient environment and their spatial scales in a typical karst area of northwest Guangxi, China were evaluated with the method of empirical mode decomposition (EMD) in this paper. The results showed that ESVs had obvious variations with changes in elevation, rocky types and soil types, and had corresponding characteristics of spatial scales. The ESVs in middle and low elevation areas were higher, but they decreased due to human activities such as deforestation. The ESVs in peak-cluster depression areas were lower, and they would increase as influenced by policies such as returning farmland to forestland. The ESVs were influenced by rocky types, showing lower values but an increasing trend in the typical karst regions while higher values but a decreasing trend in non-karst regions. The average ESVs in the west part of the study region, which is not only the main nature reserve for rare wildlife species in Guangxi, but also one of the best preserved natural vegetation regions in China, were more than 15,000 RMB Yuan ha-1,. Comparatively, the ESVs were less than 10,000 Yuan ha-1 in the middle part of the region attributed to low vegetation coverage, serious peak-cluster depression and karst rocky desertification. After about 20 years, that is from 1985 to 2005, the ecosystem conditions had been improved and the ESVs had increased in the middle and eastern part of this study region. On the contrary, in most western part, which was dominated by subtropical evergreen broad-leaved forest, they had been worsened, and the balance values of ESVs were negative. As for the relationships of ESVs with rocky types and soil types, lime soil and red soil were the two main soil types that contributed to ESVs (The total contribution was above 60%, and it is 63.77%,64.37%,64.56%,64.91% respectively in the four years of 1985, 1990, 2000 and 2005.). The variance contribution of intrinsic mode function (IMF) and trend (R) showed that there were obvious special sales for ESVs in this study area, and the main spatial scales were about 2.7 km, 5.5 km, and 11.6 km. The variance contribution ratio was 12.29%, 11.26%, 11.49% respectively, and the trend (R) was high (17.74%). In conclusion, this study indicated that ecosystem conditions in the typical karst area were improved owing to the application of rocky desertification control policies, such as ecological migration and returning farmland to forestland. Besides, the main spatial scales of ESVs in the study area were the interactions of terrain, physiognomy, land use / land cover and human activities. 相似文献
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《Biomass》1983,3(2):77-133
The various possible categories of non-petroleum internal combustion engine fuels are reviewed briefly. The oxygenate fuels (i.e. those containing oxygen in chemical combination) are considered in greater detail. The main types are methanol, ethanol, vegetable oils and mono-esters derived from vegetable oils. The problems involved in applying these fuels to compression-ignition engines are considered.The organisations involved in engine and/or service tests on oxygenate fuels for these engines are listed and a short summary of the nature and extent of the work is given in each case. More than 100 organisations are listed and references are provided in most cases to their published work. Summary tables, showing the activities in each country, are included.The survey covers developments known to the authors by mid-July 1982. Additional organisations and activities, on which information has subsequently become available, are listed in the Appendix. 相似文献
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沙冬青冬季叶绿体的超微结构特征 总被引:2,自引:0,他引:2
韩善华 《分子细胞生物学报》1994,(4)
沙冬青在冬季的叶肉细胞中有丰富的叶绿体,经常聚集在一起,相互重叠,相互嵌合,有的还相互融合。大部分叶绿体为凸透镜形,多余叶绿体主要为V形、蝶形、连婴形和哑铃形。它们的被膜不光滑,常凹凸不平,甚至出现突起和内陷。类囊体十分发达,质体小球很多,但淀粉粒缺乏。大部分叶绿体形态结构正常,有的还在出芽和分裂。少数叶绿体与此不同,它们已经衰老,其中一些正在解体或已经解体。 相似文献
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Experimental intermolecular frequencies in the DNA base complexes 1-methylthymine (1-MT) and cytosine monohydrate (CMH) are analyzed in terms of simple analytic interatomic potentials. Calculations with two different values for the constants of the nonbonded interactions are considered, and the hydrogen bond potentials are determined for each of these models. The observed frequencies in 1-MT are reasonably well described, although corresponding potentials are very different in the two models. The observed frequencies in CMH are less well described, although corresponding hydrogen bond potentials are similar in the two models. Hydration interactions are found to be important in CMH and the role of the water molecule is discussed. Possible reasons for the shortcomings of this simple analysis are considered. 相似文献
9.
RNA binding proteins play significant roles in many bio-macromolecular systems. Aromatic amino acid residues are vital for several biological functions. In the present work, the influences of π–π interactions in RNA binding proteins are analyzed. There are a total of 3,396 π-residues in RNA binding proteins out of which 1,547, 1,241, and 608 are phenylalanine (Phe), tyrosine (Tyr), and tryptophan (Trp), respectively. Among these 945, 634, and 356 Phe, Tyr, and Trp residues, respectively, are involved in π–π interactions. The observations indicate that majority of the aromatic residues in RNA binding proteins are involved in π–π interactions. Side chain–side chain π–π interactions are the predominant type of interactions in RNA binding proteins. These π–π interactions stabilize the core regions within RNA binding proteins. π–π interacting residues are evolutionary conserved. Residue-wise analysis indicates that π–π interacting residues have higher long-range contacts and hence they are important in the global conformational stability of these proteins. 相似文献
10.
经调查粤东地区有中国珍稀濒危保护植物 2 7种 (含栽培种 ) ,分属于 2 4科 2 6属 ,占广东境内分布的中国珍稀濒危保护植物的 4 5 .8% ,占全国分布的 6 .9%。其中蕨类植物 1种 ,裸子植物 6种 ,被子植物 2 0种 ;确定为濒危植物的有 5种 ,稀有的 4种 ,渐危的 18种 ;被列为一级重点保护的 1种 ,二级重点保护的 7种 ,三级重点保护的 19种。有国家重点保护野生植物2 2种 (含栽培种 ) ,分属于 2 0科 2 0属 ,占全国重点保护野生植物的 8.3%。其中蕨类植物 5种 ,裸子植物 6种 ,被子植物 11种 ;被列为一级重点保护的 6种 ,二级重点保护的 16种。其国家保护植物资源具有种类丰富、古老性强、中国特有现象突出等特点。对其名录特点和利用价值也进行了分析 相似文献
11.
云南小孢发属地衣的分类 总被引:3,自引:0,他引:3
报道了云南小孢发属地衣13种,其中中国新记录种6个,它们是:喜马拉雅小孢发,尼泊尔小孢发,光滑小孢发,光亮小孢发,多叉小孢发,波氏小孢发,另外7种的形态及分布也在文中进行了讨论。 相似文献
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中国罗汉松属叶角质层微形态结构及其分类意义 总被引:1,自引:0,他引:1
利用扫描电镜对罗汉松属8种2变种植物叶角质层内外表面进行了细致观察。发现罗汉松属植物叶角质层结构具有许多相似特征,表皮细胞较为规则,长方形或多边形,边缘波状弯曲;气孔器排列成带状,长轴均与叶脉一致,气孔器具较为明显的气孔塞和伏罗林环,气孔器保卫细胞极延伸明显,通常具有2~4个副卫细胞、不具极副卫细胞。但罗汉松属叶角质层结构也具有明显的种间差异,镰叶罗汉松和洛杉矶罗汉松同其它种类差异最大,这两种植物叶两面均具气孔器,角质层内表面垂周壁直,角质层凸缘不明显;贺氏罗汉松最为显著的特征是近轴面和远轴面表皮细胞的垂周壁角质层厚且凸缘均极其发达;小叶罗汉松近轴面表皮细胞排列较为规则,多数为方形,长轴与叶脉垂直,垂周壁之间的角质层突起较为显著,延伸到皮下层;兰屿罗汉松近轴面表皮细胞排列较不规则,多边形,细胞的角端比较钝,没有棱角;大理罗汉松气孔带间隔较小,有时两条气孔带挤在一起,使副卫细胞紧连,近轴面表皮细胞较短,方形或长方形,垂周壁之间的角质层较不发达;海南罗汉松角质层气孔带间隔较宽,气孔器形状为阔椭圆形,近轴面表皮细胞均为细长方形;变种短叶罗汉松和狭叶罗汉松与罗汉松也具有明显差异,短叶罗汉松近轴面表皮细胞排列不规则,垂周壁深波状弯曲,凸缘极为明显,但原种罗汉松近轴面表皮细胞排列较为规则,垂周壁浅波状弯曲,凸缘不明显,而狭叶罗汉松近轴面表皮细胞方形或长方形,比罗汉松的表皮细胞短,垂周壁直或略弯曲,角质层极厚。这些角质层微形态特征差异可以作为罗汉松属内种类分类鉴定的依据。 相似文献
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采用同位素示踪和肠道离体灌流方法,研究了草鱼离体肠道对亮氨酸(Leu)、酪氨酸(Tyr)的吸收转运与利用。实验结果表明:当Leu浓度从1.0mmol/L增加到5.0mmol/L、10mmol/L时,肠道吸收转运的速度表现出“高浓度抑制”效应,运输到肠道外的比例为83%、66%和35%;合成肠道蛋白质的比例为2%、5%和13%;肠道组织内游离形式的比例为9%、28%和49%;其他形式的比例为6%、1%和3%。Tyr浓度从0.5mmol/L增加到1.5mmol/L、2.5mmol/L时,肠道对Tyr的吸收转运速度也随之增加,运输到肠道外的比例为52%、55%和55%;合成肠道蛋白质的比例为17%、15%和16%:肠道组织内游离形式的比例为7%、10%和16%;其他形式的比例为24%、20%和13%。肠道在吸收转运Leu和Tyr的同时,也利用它们合成蛋白质的和其他方面,Leu的吸收利用受灌流试验氨基酸浓度影响较大、而Tyr受影响较小;随着肠道内灌流的试验氨基酸浓度增加,吸收转运到肠道外的比例下降、留存于肠道内的比例增加,肠道合成的蛋白质绝对量也增加。
相似文献
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Ginkgo biloba L. has often been called a living fossil. Significant variations are often seen in its leaf form and structure of the epidermal layer and the morphological differences between the upper and lower layer. In the upper epidermal layer, the cells are rather orderly arranged in the appearance of a smooth surface. However, the cells of the lower layer are very irregularly arranged. The cell wall projects in various directions and is wrinkled. The stomata in the upper layer are rare and are restricted to the base of the leaf blade, for which they are often neglected. However, in some incidences, they are present only in the lower layer. The guard cells are deeply caved in by the surrounding 4—7 subsidiary cells, the upper part of which projects and covers the stoma. In the lower layer, two stomata, or occasionally three, that set close to each other might be observed. These phenomena are scarcely seen in other seed plants. 相似文献
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对分布在浙江天台山的七子花(Heptacodium miconioides)等6种主要阔叶树的光合生理生态特性进行了研究,结果表明:1)夏季6种植物光合日进程均为“双峰”型,有明显的光合“午休”现象。日均净光合速率月变化呈“单峰”型,8月是一年的高峰期。日均和5~11月平均净光合速率最高的是东南石栎(Lithocarpus harlandii),最低的是天台阔叶槭(Acer amplum var. tientaiense),七子花处于中下水平。2)相对常绿树种而言,七子花的光补偿点较高,光饱和点较低,对光 相似文献
17.
The atomic motions from a molecular-dynamics simulation of yeast tRNAPhe are analyzed and compared with those observed in protein simulations. In general, the tRNA motions are of larger amplitude, they are more anisotropic, and they arise from potentials of mean force that are more anharmonic than in the protein case. In both cases, the amplitudes are largest for atoms on the surface of the molecules. On the other hand, the most anisotropic and anharmonic atomic motions are generally found in the interior of the tRNA, while they are found on the surface of the protein. These differences are discussed in terms of the differences in structure between nucleic acids and proteins. 相似文献
18.
中国菊科植物的系统分类与区系的初步研究 总被引:29,自引:2,他引:29
为1993年"菊科植物的系统分类与区系地理的初步探讨"(世界)一文的姊妹篇,重点论述我国菊科的系统分类及其区系地理成分。文中介绍了分布我国的菊科240属隶于2亚科、5超族、11族中的系统位置。论述了我国菊科植物区系地理成分的特点是:1.大洲间共同分布或洲际间断分布的属多,且具明显的热带亲缘;2.与亚洲国家,包括中亚国家或亚洲热带国家共同分布的属多,尤其是成"中亚-青藏高原-喜马拉雅山"地区分布的属多;3.中国特有属多,其中我国西南省区特有属最多。文中还讨论了分布我国菊科各族祖先种的起源、迁移以及我国区系地理热带亲缘和"横断山脉-喜马拉雅山脉(东)森林植物亚区"菊科植物分布的特点。 相似文献
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Giant axons of the spiny lobster, Panulirus argus, are filled with microtubules that are decorated with fine, irregular filaments. Mitochondria and membrane-limited clear vesicles are the only other distinguishable elements in the axoplasm and are located around the periphery of the axon near the axolemma. Neither 100 A neurofilaments nor 70 A microfilaments are evident in fixed, intact axons or in negatively stained axoplasm. Actin-like microfilaments are a prominent constituent of the glial cells that closely ensheathe the axons, and gel electrophoresis studies suggest that most of the actin in the nerve fibers is located in the glia rather than in the axons. Studies of isolated axoplasm indicate that microtubules are the primary elements stabilizing the axoplasm. The microtubules in the isolated axoplasm are disrupted by Ca2+ in the medium in the presence of protease inhibitors. 相似文献