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本文阐明了伏安技术对重组膜的各种电性质测量原理和方法,并用多重扫描技术着重研究了膜电导的可逆跃迁变化,以及扫描速度和电压的影响,结果指出,伏安法可能发展成一种研究重组膜离子通道现象的新手段. 相似文献
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Oil samples from six species of Juniperus include 37 detected components, of which most are quantitatively highly variable. Nine chromatographic patterns were identified, including one for each of two subspecies of J. occidentalis and, surprisingly, two different patterns in both J. californica and J. monosperma. The chemical evidence supports earlier taxonomic conclusions based on morphology and natural history that J. occidentalis subsp. occidentalis and J. occidentalis subsp. australis are indeed subspecies, that the former is intermediate between the latter and J. osteosperma, and that J. californica and J. osteosperma are closely related but distinct species. It is concluded that the techniques of gas chromatography have considerable potential as a taxonomic tool. 相似文献
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John W. Everingham 《The Journal of cell biology》1968,37(2):540-550
Oocytes of four species of ascidians were examined with the electron microscope. Prior to fixation, oocytes were subjected to centrifugal forces of 10–15,000 g for 5–10 min and were compared with uncentrifuged oocytes. Intranuclear annulate lamellae (IAL) are distributed uniformly around the periphery of the nucleus of the uncentrifuged oocyte. Centrifugation produces a marked flattening of the oocyte nucleus, migration of nucleoli to the centrifugal end, and often a condensation of the nucleoplasm at the centrifugal end. In contrast, the distribution of IAL is unchanged by centrifugation. Furthermore, numerous IAL profiles appear to be touching the nuclear envelope, and, in a few of these, direct continuity of the IAL with the nuclear envelope is demonstrated. 相似文献
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THE HETEROCYSTS OF BLUE-GREEN ALGAE (MYXOPHYCEAE) 总被引:1,自引:0,他引:1
V. V. S. TYAGI 《Biological reviews of the Cambridge Philosophical Society》1975,50(3):247-284
1. Heterocysts are found in many species of filamentous blue-green algae. They are cells of slightly larger size and with a more thickened wall than the vegetative cells. 2. Structural details of the heterocyst are: the presence of three additional wall layers, the absence of granules, sparse thylakoid network throughout, except at the poles where a dense coiling of membranes occurs. Other characters include the two pores at opposite poles ‘plugged’ with refractive material called the polar granule. 3. Peculiarities in the pigment composition of the heterocyst include an abundance of carotenoids and absence of phycobilins, and a short-wave form of chlorophyll a. 4. Unique glycolipids and an acyl lipid, not found in the vegetative cells of the algae or in other plant cells, are associated with the heterocyst. The glycolipids constitute the laminated layer of the wall and probably regulate diffusion of substances through it, whereas the acyl lipids are supposed to function as carriers and intermediates in the biosynthesis of the wall. 5. The heterocysts develop from vegetative cells, and the visible changes during differentiation include cell enlargement, synthesis of additional wall layers, disappearance of granules and reorientation and synthesis of the thylakoids. 6. Heterocysts are formed sequentially with characteristic cellular spacing during the growth of cultures in medium free from combined nitrogen. 7. Various sources of combined nitrogen inhibit heterocyst formation when supplied in the culture medium. Ammonium salts are among the most powerful inhibitors. Heterocysts are formed simultaneously and within a short period after transference of ammonia-grown non-heterocystous filaments to ammonia-free medium. 8. Incompletely differentiated heterocysts or proheterocysts are found in cultures grown in the presence of combined nitrogen. If two or more proheterocysts are close together generally a single one develops to maturity after a competitive interaction in medium free from combined nitrogen. This indicates that heterocyst formation is completed in two phases: phase I, synthesis and conservation of macromolecules, which takes place during growth in ammonia-containing medium: and phase 11, morphological differentiation of the heterocyst which is unaccompanied by growth in cell number. In the ammonia-free medium phase 11 quickly succeeds phase 1 and the whole process appears as a continuum. 9. Heterocyst formation shows a definite requirement for light. Red light favours heterocyst formation, whereas green and blue light do not. The effects of light seem to be mainly due to photosynthesis, although some effects may be morphogenetic. 10. Studies with metabolic inhibitors have revealed the involvement of photosynthesis, respiration and protein synthesis in heterocyst formation. Photosynthesis provides carbon skeletons, whereas ATP is most probably supplied by oxidative metabolism. 11. Various functions have been assigned to the heterocyst from time to time. Their role in akinete formation is suggested by (i) the formation of akinetes adjacent to the heterocysts and (ii) prevention of sporulation by detachment of the heterocysts from the vegetative cells (potential akinetes). Despite substantial evidence for such a role, it is not applicable to all akinete-forming genera. 12. Heterocysts are now widely believed to be the site of nitrogen fixation in blue-green algae. The main facts in favour of such a role are: (i) fixation of nitrogen by all heterocystous algae, (ii) inhibition of heterocyst formation by combined nitrogen and (iii) direct observations on acetylene reduction by isolated heterocysts. 13. Some non-heterocystous and unicellular algae, and vegetative cells of heterocystous algae fix nitrogen under microaerophilic conditions suggesting that absence of oxygen favours nitrogenase activity. Heterocysts lack the oxygen-evolving photo-system 11, possess oxidative enzymes, and reduce externally supplied tetrazolium salts - all indicating that they are the most suitable sites for harbouring nitrogenase in aerobic conditions. 14. Heterocysts probably originated in the Precambrian in response to the earth's changing environment and seem to be the first example of morphological differentiation in the plant kingdom. 相似文献
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叶绿素荧光技术在植物环境胁迫研究中的应用 总被引:89,自引:2,他引:89
近年来叶绿素荧光技术在植物,包括藻类对各种环境胁迫响应的机理和应用研究中起着越来越重要的作用.本文简述了这方面的部分工作和进展. 相似文献
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rDNA片段的序列分析在苦苣苔亚科系统学研究中的应用 总被引:18,自引:1,他引:18
本文测定了苦苣苔亚科4族、5属、5种植物的核糖体DNA中的内转录间隔区(ITS)序列及5.8s
rRNA基因的3′端序列。这几种苦苣苔亚科植物的ITS-1的长度范围为234~258 bp,ITS-2的长度范
围为218~246bp。Whytockia bijieensis的ITS-1(258bP)和ITS-2(218 bp)在长度、序列及GC含量上
均与其它几个种有较大差异,其代表的尖舌苣苔族可能很早就自苦苣苔亚科的祖先沿单独的一个分支
演化。以w.bijieensis作为功能性外类群,运用PAUP软件分析仅得到一个最简约树。在简约树上,
Cyrtandra umbelliferm、Briggsia longipes和Anna mollifolia形成一个单系群,bootstrap分析对该分支的
支持强度达97%,Chirita crasslfolia位于该分支的基部。由于系统树上Cyrtandra umbellifera代表的
浆果苣苔族和Anna mollifolid代表的芒毛苣苔族均起源于长蒴苣苔族,结合这3个族在形态上存在过渡系列,建议将浆果苣苔族和芒毛苣苔族均并入长蒴苣苔族。 相似文献
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Burton T. Simpson 《CMAJ》1932,27(6):612-615
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通过论证及重新定义逻辑斯缔方程,本文提出和进一步发展了原始生物大分子动态的数学模型.对该模型的4种竞争增长结果进行分析,得出最有可能的原始生物大分子的发展动态,并由此推导出原始生物圈中较大量存在的只是种类单一的原始生物大分子的结论。对这一结论在生命起源和生物进化中的意义进行了探讨,指出生命起源初期的生物多样性是很低的,原始生物世界是一个重复序列或重复结构的世界,生物进化是通过不断增加和扩展生态位,使生物多样性不断提高。最后,讨论了生态学的概念和方法在微观水平上应用的理论基础,指出从生态学的角度去进行分子生物学的研究是一种发展趋势。 相似文献
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Excised shoot apices of Osmunda claytoniana were grown under controlled sterile conditions. Histological examination of the normal shoot apex shows that it is comprised of: (1) a promeristem, which possesses 1 or more apical initiating cells at its center; (2) a prestelar tissue consisting of an incipient vascular tissue which flanks the pith-mother-cell zone; the pith-mother-cell zone gives rise to the pith rib meristem and subsequently to the fundamental parenchyma of the pith; (3) the fundamental parenchyma of the cortex and the fundamental parenchyma of the dermal system both arising from flank cells of the promeristem. Apical initial cells of meristems irradiated with a 127,000 rad acute exposure of a deuteron beam having a diameter of 25μ, histologically examined at 7-day intervals for a 12-week period, as early as 3 weeks’ postirradiation, showed the apical initiating cell(s) together with certain of the cells of the pith-mother-cell zone to be destroyed. A wound response develops peripherally to the destroyed initials. In addition, an isolated, organized growth center is observed to develop from normal promeristem cells. Incipient vascular tissue and a new pith-mother-cell zone are also observed to develop in association with the new center of growth. Implications of the role of the interrelationships between apical initiating cell(s) and other cells of the meristem and the role they may play in maintenance of meristematic integrity within the shoot meristem are discussed. 相似文献
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In the course of a light and electron microscopy study of spermatogenesis in the European crayfish, Astacus fluviatilis, spermatocytes of abnormal appearance were observed in two instances in individuals that had passed the mating period. The electron microscope showed that the inner membrane of the nuclear envelope of these cells was erupting into a mass of microtubules, 15 to 18 mµ in diameter and 0.5 µ or more in length, while the outer membrane transformed into cytoplasmic vesicles. Stages in the formation of these novel processes were followed. The plasma membrane of the affected cells was seen in some cases to erupt into similar although shorter microtubules. It is concluded that the phenomenon is part of a degenerative process in which the spermatocytes are being absorbed by sustentacular cells. It is suggested that the observations provide further evidence for a fundamental functional as well as a morphological similarity between the membranes bounding the nucleus and the plasma membrane. 相似文献
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A. C. Thompson Barbara W. Hanny P. A. Hedin R. C. Gueldner 《American journal of botany》1971,58(9):803-807
When the chemical constitution of the essential oils of six species within three genera of the family Malvaceae were investigated, the essential oils of Gossypium hirsutum L. and Cienfuegosia rosei Fryxell were found to contain 67.0 % and 58.2 % hydrocarbons, respectively. Those of Hibiscus lasiocarpus (Cav.) and Callirhoe involucrata (Nutt.) Gray contained equal percentages of hydrocarbons (14 %), but that of Cienfuegosia drummondii (A. Gray) Lewt. contained only 2.9 % hydrocarbons. Beta-bisabolol was the major oxygenated component in G. hirsutum (13.7 %), Hibiscus militaris (Cav.) (55.0 %), and Hibiscus lasiocarpus (32.6 %), but the major constituents in the essential oil of C. involucrata were myrtenal (32.0 %) and trans-2-cis-6-nonadienal (12.0 %), and the major oxygenated component in C. rosei was an unknown sesquiterpene alcohol (17.4 %) with chemical and physical properties resembling those of beta-bisabolol. The concentration of total oil was 150.0 ppm in G. hirsutum; 50.0 ppm in H. militaris; 46.3 ppm in C. rosei; 41.0 ppm in H. lasiocarpus; 25. 4 ppm in C. drummondii; and 10.0 ppm in C. involucrata, all based on wet weight. 相似文献