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91.
Deborah Ann Roach 《Genetica》1993,91(1-3):53-64
Senescence is a decline in age-specific survival and reproduction with advancing age. Studies of evolutionary plant senescence are designed to explain this decline in life history components within the context of natural selection. A review of studies of plant demography reveals senescent declines in both annual and perennial plants, but also suggests that there are some plant species which may not be expected to show senescence. Thus, future comparative studies of closely related species, with and without senescence, should be possible. The assumptions of the major evolutionary theories of senescence are evaluated for their validity with respect to plants. Different plant species violate one or more of the assumptions of the theories, yet the consequences of violating these assumptions have never been investigated. Whereas, to date, evolutionary senescence has been studied only indirectly in plants, it is concluded that plants provide good experimental systems for clarifying our understanding of senescence in natural populations. 相似文献
92.
The halotolerant, facultatively chemolithoautotrophic, gramnegative sulphur-oxidizing organism isolated from the gills of Thyasira flexuosa is shown to exhibit pleomorphism consistent with its being a member of the genus Thiomicrospira and not a Thiobacillus as originally classified. Its distinctive morphology, DNA base composition, and similarity of 16S rRNA sequences to that of Thiomicrospira sp. strain L-12 (which differs only in detail from the type species Thiomicrospira pelophila), lead us to reclassify this strain as Thiomicrospira thyasirae DSM5322. 相似文献
93.
Bertrand D. Eardly Mara Cloutier Taejung Chung Sofia Roitman Fabricio R. Vieira Mary Ann V. Bruns 《Restoration Ecology》2023,31(1):e13695
From 1913 to 1980, two zinc smelters in Palmerton, Pennsylvania, emitted large quantities of atmospheric pollutants nearly eliminating forests along a ridge above the town. In 2008, a remediation treatment was applied to the land above one of the smelters that included the planting of several locally adapted plant species. It also included mineral fertilization and mycorrhizal inoculation. One of the species, the Pitch pine (Pinus rigida, Mill.), is a native tree that is both tolerant of metalliferous soils and obligatorily ectomycorrhizal. This report summarizes the results of two observational studies conducted 5 years after the remediation treatment. The first study's objective was to compare ectomycorrhizal communities on treated Pitch pine saplings, with communities on naturally regenerating saplings in an adjacent non-remediated area. The second study's objective was to determine if the composition of the fungal communities on root tips of naturally regenerating Pitch pine saplings differed with distance from the smelters. Fungal community compositions were determined using internal transcribed spacer rRNA sequences. Comparisons of sequences from the remediated and non-remediated sites revealed that communities at the remediated sites had lower taxonomic diversity and were dominated by members of a genus in the remediation inoculant. The results of the smelter-proximity study indicated that although fungal diversity did not differ markedly with distance from the smelters, the relative abundances of some taxa were greater on saplings growing directly above the smelters, where the soils contained highest concentrations of zinc and cadmium. 相似文献
94.
Abdullah Jaffer Brian Harvey Vivienne Ann Russell Machteld Elizabeth Carstens Anna Susanna de Villiers Joshua Joachim Fransua Taljaard 《Neurochemical research》1993,18(10):1057-1061
Chronic treatment of rats with lithium chloride was examined in order to determine its effect on hypothalamic monoamine and metabolite content, basal thyrotropin (TSH) secretion and thyroid function. The hypothalamic concentrations of noradrenaline (NA), dopamine (DA) and its metabolites, dihydroxyphenylacetic acid. (DOPAC) and homovanillic acid (HVA) in the lithium treated rats remained unaltered when compared to control levels. NA turnover and the NA metabolite, 3-methoxy-4-hydroxyphenylglycol (total MHPG), were significantly lower (p<0.01), whereas both serotonin (5-HT) and its metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA), were significantly higher (p<0.01 and p<0.02, respectively) in the lithium treated rat hypothalami than in controls. Chronic lithium treatment significantly elevated basal TSH levels (p<0.05). This effect was antagonized by methylp-hydroxybenzoate (methylparaben, p<0.01), which did not itself affect basal TSH levels. Free serum T3 and T4 levels were not significantly affected by chronic lithium treatment, although T4 tended to be slightly lower than control levels. The monoamine changes observed in the hypothalamus of lithium treated rats did not appear to account for the elevated TSH levels observed in these rats since NA activity which is generally regarded as stimulatory was decreased and 5-HT which has an inhibitory effect on TSH secretion, was increased. The elevated TSH levels may have been due to a reduced negative feedback inhibition of TSH release by the mildly reduced circulating T4 levels caused by chronic lithium treatment. A further possibility is that the pituitary cGMP (and hence TSH) response to TRH may have been enhanced by chronic lithium treatment and methylparaben may have antagonized this effect. 相似文献
95.
[目的]核酸的甲基化修饰是一种常见的化学修饰形式,具有重要的生物学功能,却也在一定程度上给一些核酸研究过程带来了技术难度。tRNA上具有的大量甲基化修饰会阻碍逆转录进程,从而降低荧光定量PCR (real-time fluorescence quantitative polymerase chain reaction,RT-qPCR)和高通量测序对其的检测效率。来自大肠杆菌(Escherichia coli)的AlkB蛋白是一种多功能的脱烷基化酶,可以去除DNA和RNA上多种甲基化为代表的修饰,有望解决以上问题。[方法]针对大肠杆菌来源的AlkB,分别尝试在大肠杆菌和毕赤酵母(Pichia pastoris)表达系统中进行诱导表达和纯化,对纯化获得的AlkB进行酶学性质测定。最后以tRNAUAUIle等两种tRNA为代表,研究AlkB的处理对于荧光定量PCR法检测tRNA表达水平的影响。[结果]AlkB在大肠杆菌中表达时多以包涵体形式存在,但是在毕赤酵母中可以成功分泌表达。使用镍柱分离纯化后获得了纯度高于95%的AlkB蛋白,其酶学性质参数如... 相似文献
96.
Martine de Boer Maaike te Lintel Hekkert Jiang Chang Bibi S. van Thiel Leonie Martens Maxime M. Bos Marion G. J. de Kleijnen Yanto Ridwan Yanti Octavia Elza D. van Deel Lau A. Blonden Renata M. C. Brandt Sander Barnhoorn Paula K. Bautista-Niño Ilona Krabbendam-Peters Rianne Wolswinkel Banafsheh Arshi Mohsen Ghanbari Christian Kupatt Leon J. de Windt A. H. Jan Danser Ingrid van der Pluijm Carol Ann Remme Monika Stoll Joris Pothof Anton J. M. Roks Maryam Kavousi Jeroen Essers Jolanda van der Velden Jan H. J. Hoeijmakers Dirk J. Duncker 《Aging cell》2023,22(3):e13768
97.
An Aedes albopictus dihydrofolate reductase gene was used to construct two chimeric DNA vectors that functioned as dominant selectable markers in transfected, wild type mosquito cells. Stably transformed clones were recovered after 10–15 days in the presence of selective medium containing 1 μM methotrexate. The transformed clones contained an estimated 100–500 copies of transfected DNA per nucleus. Combined data from Southern blots and in situ hybridization to metaphase chromosomes indicated that transfected DNA was likely integrated into chromosomes both as repeated structures and as randomly integrated single copy molecules, with minimal rearrangement of coding sequences. Transfected DNA was stably maintained under selective conditions, but in some cases was lost when cells were maintained for prolonged periods in the absence of methotrexate. These observations provide a general framework for further development of stable gene transfer systems for mosquito cells in culture. 相似文献
98.
Epithelial M cells in the rabbit caecal lymphoid patch display distinctive surface characteristics 总被引:5,自引:0,他引:5
Mark A. Jepson M. Ann Clark Nicholas L. Simmons Barry H. Hirst 《Histochemistry and cell biology》1993,100(6):441-447
The follicle-associated epithelium (FAE) in the rabbit caecal lymphoid patch is characterised by the presence of membranous (M) cells, which are believed to be functionally equivalent to those present at other sites of gut-associated lymphoid tissue (GALT). Caecal patch M cells display distinctive features compared with those of other GALT sites, despite similar general morphology and expression of the M cell marker vimentin, suggesting marked heterogeneity in the apical surface of M cells at discrete GALT sites. Electron microscopy reveals that rabbit caecal patch M cells differ from those in the small intestinal Peyer's patch FAE: the former have a prominent aspect within the epithelium and possess microvilli which are longer than those of adjacent enterocytes. Many of the M cells in peripheral regions of the caecal patch FAE are not associated with leucocytes and may thus represent an immature M cell population. The M cells are also histochemically distinct from adjacent enterocytes and from Peyer's patch M cells, showing greater expression of brush-border alkaline phosphatase activity and affinity for certain lectins (peanut and wheat germ agglutinins, Bandeiraea simplicifolia agglutinin II). The differences in the brush-border morphology and glycocalyx structure between M cells at different GALT sites may affect their function at these sites by influencing the interaction of luminal antigens and microorganisms with the M cell surface. The present data also support the hypothesis that M cells arise directly from differentiation of crypt stem cells and not from the transformation of existing fully differentiated enterocytes. 相似文献
99.
Abstract The thymus of the sole Solea solea contained lymphoblasts and thymocytes within a network of pale and dark epithelial cells. The pale cells were characterized by tonofilaments and desmosomes and some embraced rodlet cells within their cytoplasmic processes. The dark epithelial cells had numerous electron-dense inclusions and electron-lucent vacuoles. Lymphocytes were closely associated with the plasma membrane of both types of epithelial cells and with macrophages. Breakdown of effete lymphocytes appeared to be the main function of the macrophages. Some macrophages were multinucleated. Those containing melanin granules associated with phagosomes were classified as melanomacrophages. Pigment cells including melanophores and guanophores were present along the connective tissue trabeculae and surrounding the blood vessels. A few plasma cells and mucous cells were present. 相似文献
100.
The importance of ecological factors such as sex lability, spatial segregation, and resource allocation in the evolution of dioecy were examined in Schiedea globosa. S. globosa is a subdioecious species with equal numbers of plants possessing strictly male or female function and a small proportion of hermaphrodites. The propensity for labile sex expression was under both environmental and genetic control; some plants with male function became hermaphroditic (by producing female flowers) under better growing conditions in the field and in the greenhouse. There was some spatial segregation of the sexes. Because of sex lability, more hermaphrodites than males occurred on moister slopes. Although there were not measurable sex-related differences in mortality within or between two flowering seasons, more females than males and hermaphrodites occurred at the bottom of slopes. Males and females produced the same number of ramets and inflorescences, but females had a greater number of flowers per inflorescence. Males and females had the same number of ovules (vestigial in males), but females had larger ovules and longer stigmas. Hermaphrodites and males had the same amount of pollen per flower despite the production of fruit by the hermaphrodites. In hermaphrodites, there was no apparent tradeoff within flowers between pollen production and ovule production. These results indicate that spatial segregation, sex lability, and environmental conditions influence allocation patterns of S. globosa, and in combination with high inbreeding depression and selling rates, may promote the further evolution of dioecy in S. globosa. 相似文献