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PETER B. SUHR-JESSEN JOHN M. STEWART LEIF RASMUSSEN 《The Journal of eukaryotic microbiology》1977,24(2):299-303
SYNOPSIS. Using continuous flow cultures based on the chemostat principle, we varied the cell generation times of the ciliate Tetrahymena pyriformis strain GL, from 4.9 to 22.2 hr and studied various parameters of the cell cycle at 28 C. These included: the duration of the periods required for oral morphogenesis, macronuclear division, cell division, G1 S, and G2. The size of individual cells was also measured. Independent of the growth rate, the period of oral morphogenesis occurred during the last 90 min of the cell cycle. In all cases macronuclear and cell divisions took place during the last part of these 90 min, and the final macronuclear separation occurred just before final cell separation. The S-period increased slightly, while the G1 and G2 both increased in roughly the same relative proportion to the increasing generation times. Slowly growing cells (generation time 20.5 hr) were shorter but broader and somewhat larger in volume than quickly growing cells (generation time 4.9 hr). 相似文献
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The effects of DCMU and NaN3 were studied on menadione-mediated photophosphorylation in broken spinach chloroplasts kept in low oxygen tension in Tricine or HEPES buffers at either high or reduced irradiances. – (A) At high irradiance (131 W. m?2) and absence of NaN3 the ATP formation was inhibited by DCMU regardless of the type of buffer used. – (B) At high irradiance and presence of NaN3 some concentrations of DCMU stimulated, whilst others inhibited the ATP formation in a HEPES buffer. The ATP formation was predominantly inhibited by DCMU in a Tricine buffer. – (C) At reduced irradiance (57 W. m?2) the chloroplasts in a HEPES buffer were almost insensitive towards DCMU both in the presence and absence of NaN3. – (D) Chloroplasts in a Tricine buffer were slightly stimulated in their ATP formation by DCMU at reduced irradiance either with or without the presence of NaN3 in the experimental medium. When menadione acts as a terminal electron acceptor, oxygen is consumed on its reoxidation. The results indicate that this process may occur with oxygen released by the splitting of water as the main oxidant. – The data also demonstrate the importance of caution when selecting buffering substances as well as when choosing light intensities for experiments on photophosphorylation in chloroplasts. 相似文献
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Developmental stability in brown trout: are there any effects of heterozygosity or environmental stress? 总被引:1,自引:0,他引:1
LEIF ASBJøRN VLLESTAD KJETIL HINDAR 《Biological journal of the Linnean Society. Linnean Society of London》2001,74(3):351-364
We studied the developmental stability of brown trout, Salmo trutta L., in 10 populations (five acidified, five control) in Norway, measured as fluctuating asymmetry (FA) and departure from the morphological norm. We measured four meristic and four morphometric characters, and scored the level of biochemical heterozygosity at 49 loci (20 polymorphic). We reared eggs of a single population in a hatchery using four different water qualities (three replicates of each treatment) to test the effect of acidification stress on developmental instability. There were no significant differences in the level of FA, in departure from the morphological norm between brown trout sampled from lakes with acidified or control water qualities, or in brown trout hatched at different water qualities. There was no correlation between level of heterozygosity and FA or departure from the morphological norm, either when tested within populations or among populations. There were no single-locus effects on developmental stability tested for 11 loci. We conclude that measures of developmental stability or morphological variability are not useful for detecting acidification stress in brown trout. Furthermore, we conclude that developmental stability in our material varies independently of heterozygosity. 相似文献
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Rise and demise of cold-climate Picea abies forest in Sweden 总被引:1,自引:0,他引:1
LEIF KULLMAN 《The New phytologist》1996,134(2):243-256
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ARNE HERMANSEN TERJE AMUNDSEN GUDMUND TAKSDAL STEINAR DRAGLAND GRY SYNNEVÅG MONS FLØNES LEIF SUNDHEIM 《The Annals of applied biology》1997,131(3):399-411
Four experimental sites located in different climatic regions in Norway were inoculated with Mycocentrospora acerina in 1985. In 1986, crop rotation experiments including carrot, barley, grass, red clover, onion and potato, were established at these sites. Incidence of M. acerina on the foliage and the roots of carrots after storage were recorded in 1989/90 and 1994/95. The 3 yr rotation only slightly reduced the inoculum of M. acerina in the soil. Red clover and grass were the most effective crops in reducing the inoculum, potato and barley were less effective, and onion had no effect on the inoculum. Differences in M. acerina infection on carrots between 3, 6 and 8 yr of rotation with barley and grass were not statistically significant. 相似文献
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MATS NILSSON JÖRGEN SAGERFORS ISHI BUFFAM HJALMAR LAUDON TOBIAS ERIKSSON ACHIM GRELLE LEIF KLEMEDTSSON PER WESLIEN ANDERS LINDROTH 《Global Change Biology》2008,14(10):2317-2332
Based on theories of mire development and responses to a changing climate, the current role of mires as a net carbon sink has been questioned. A rigorous evaluation of the current net C-exchange in mires requires measurements of all relevant fluxes. Estimates of annual total carbon budgets in mires are still very limited. Here, we present a full carbon budget over 2 years for a boreal minerogenic oligotrophic mire in northern Sweden (64°11′N, 19°33′E). Data on the following fluxes were collected: land–atmosphere CO2 exchange (continuous Eddy covariance measurements) and CH4 exchange (static chambers during the snow free period); TOC (total organic carbon) in precipitation; loss of TOC, dissolved inorganic carbon (DIC) and CH4 through stream water runoff (continuous discharge measurements and regular C-concentration measurements). The mire constituted a net sink of 27±3.4 (±SD) g C m−2 yr−1 during 2004 and 20±3.4 g C m−2 yr−1 during 2005. This could be partitioned into an annual surface–atmosphere CO2 net uptake of 55±1.9 g C m−2 yr−1 during 2004 and 48±1.6 g C m−2 yr−1 during 2005. The annual NEE was further separated into a net uptake season, with an uptake of 92 g C m−2 yr−1 during 2004 and 86 g C m−2 yr−1 during 2005, and a net loss season with a loss of 37 g C m−2 yr−1 during 2004 and 38 g C m−2 yr−1 during 2005. Of the annual net CO2-C uptake, 37% and 31% was lost through runoff (with runoff TOC>DIC≫CH4) and 16% and 29% through methane emission during 2004 and 2005, respectively. This mire is still a significant C-sink, with carbon accumulation rates comparable to the long-term Holocene C-accumulation, and higher than the C-accumulation during the late Holocene in the region. 相似文献