共查询到20条相似文献,搜索用时 31 毫秒
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E. Hamilton 《Cell proliferation》1974,7(4):389-398
Cell proliferation, differentiation and migration have been studied in the sebaceous glands of DBA-2 mice in the resting (telogen) phase of hair growth. Cells labelled by a single injection of tritiated thymidine start to leave the glands of adult male mice 5 days later. About 80% of the proliferative cells in the basal layer have a cell cycle time of 40 hr or less. In 18% of the proliferative cells G1 is at least 4 days long and 16% have a G2 phase longer than 17 hr. The S phase is about 7.5 hr long and cells spend at least 21 hr in the basal layer before migrating into the differentiating cell region. The glands of mature female and immature mice are smaller than those of the mature male. They have fewer, smaller cells and a much lower labelling index. 相似文献
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Antonio Prevosti Luis Serra Griselda Ribo Montserrat Aguade Elisabet Sagarra Maria Monclús M. Pilar Garcia 《Evolution; international journal of organic evolution》1985,39(4):838-844
Drosophila subobscura is a Palearctic species that was first detected in the New World in Puerto Montt (Chile) in February 1978. Since that time, it has spread over a broad area and increased in population density. The South American populations exhibit a high level of chromosomal polymorphism: 20 different arrangements exist, distributed among five chromosomes. Chromosomal arrangement heterozygosity varies from 0.55 to 0.61 in the nine populations examined. Incipient clines in the frequencies of the arrangements are appearing; these clines follow the same latitudinal direction as in the Old World. Wing length significantly decreases with latitude, as it does in Europe. The colonization of South America by D. subobscura appears to be a major natural experiment with outcomes that duplicate the distributional patterns—in chromosomal polymorphism and in wing length—observed in the Old World, thereby strongly supporting the adaptive significance of these patterns. The data show a very rapid effect of natural selection promoting genetic differentiation among natural populations. 相似文献
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无量山种子植物区系的特有现象 总被引:18,自引:6,他引:12
地处滇中南的无量山地区迄今计有种子植物207科,1026属,2540种,其中东亚特有科10个,中国特有属27个,无量山特有种子67个,这一地区不仅植物种类丰富,而且特有现象较为显著,在对科级持有现象进行较细致的研究后,本文认国无量山具有较多的分类系统上隔离的东亚特有科反映了该地作为东亚古老植物区系的一部分,其地质历史与整个东亚是一致的,且与东亚植物区系的发端密切相关,属的特有现象表明,地处中国特有 相似文献
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THE LIFE-HISTORY OF THE PLUM-RUST IN ENGLAND. 总被引:1,自引:1,他引:0
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The formation of aerial tubers in Begonia plants, an SD response,was inhibited by IAA, NAA and IBA applied to their leaves duringthe dark periods. The effectiveness of IAA differed accordingto the time of application during the dark periods, and themost sensitive time varied with daylengths employed. In order to inhibit the tuberization under optimal photoperiods(8-hr SDs), IAA had to be applied during the first 2 days orso of the SDs. Under non-optimal photoperiods, however, IAAwas effective even when applied somewhat later. The auxin activity of leaf extracts from the plants subjectedto 8-hr SDs decreased during the first 2 or 3 days to a minimum,and then increased until finally began to decrease, again; undernon-optimal photoperiods, the minimum of auxin activity wasattained more slowly. The paper-chromatographic study suggestedthat the change in auxin activity was mainly due to the changein IAA content. The number of SDs making the auxin content minimal agreed withthe minimum number of SDs required for tuberization. On the basis of the above results, the part played by endogenousauxin in photoperiodic induction is discussed.
1Present address: Institute for Agricultural Research, TôhokuUniversity, Sendai.
2Present address: Biological Institute, Yamaguchi University,Yamaguchi. 相似文献
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Thomson, Betty F., and Pauline Monz Miller. (Connecticut Coll., New London.) The role of light in histogenesis and differentiation in the shoot of Pisum sativum. III. The internode. Amer. Jour. Bot. 50(3): 219–227. Illus. 1963.—Seedlings of Pisum sativum were grown under constant conditions and exposed daily to red or white fluorescent light or kept in total darkness. Counts and measurements of internodal cells in both transverse and longitudinal directions show that light does not alter the sequence or pattern of tissue differentiation, including the sequence of xylem maturation within the vascular bundle. Light does accelerate the rate of a constant course of differentiation. Light advances the time of division and enlargement of cortex, xylem, phloem, and pith cells in the longitudinal direction but reduces both the final number and the final length attained in all cases. It is concluded that light accelerates all phases of shoot growth and differentiation and that cell division and elongation in the later phases of internodal growth are reduced by light because of accelerated cell maturation. 相似文献
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1. The solvent action of a neutral salt upon a protein, oxyhemoglobin, has been found identical to the solvent action of a neutral salt upon a bi-bivalent or uni-quadrivalent compound. 2. The solubility of oxyhemoglobin in phosphate solutions of varying ionic strength has been defined by the equation: log See PDF for Equation in which µ is the ionic strength, and S
0 is the solubility in the absence of salt. 3. The values of S
0 have been calculated to be 12.2, 11.2, and 13.1 gm. per liter respectively at pH 6.4, 6.6, and 6.8. 4. The relatively great solubility of oxyhemoglobin in water has been ascribed to the strong affinity constants for acid and base of certain groups in oxyhemoglobin. 5. The small change in the solubility of oxyhemoglobin effected by neutral salts suggests that but few such groups are dissociated in oxyhemoglobin in the state in which it crystallizes near its isoelectric point. 6. Certain of the other properties of oxyhemoglobin, such as its low viscosity, are considered in the light of its molecular weight and its valence type. 相似文献