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51.
Partially replicated bacteriophage T7 DNA was isolated from Escherichia coli infected with UV-irradiated T7 bacteriophage and was analyzed by electron microscopy. The analysis determined the distribution of eye forms and forks in the partially replicated molecules. Eye forms and forks in unit length molecules were aligned with respect to the left end of the T7 genome, and segments were scored for replication in each molecule. The resulting histogram showed that only the left 25 to 30% of the molecules was replicated. Several different origins of DNA replication were used to initiate replication in the UV-irradiated experiments in which 32P-labeled progeny DNA from UV-irradiated phage was annealed with ordered restriction fragments of T7 DNA (K. B. Burck and R. C. Miller, Jr., Proc. Natl. Acad. Sci. U.S.A. 75:6144--6148, 1978). Both analyses support partial-replica hypotheses (N. A. Barricelli and A. H. Doermann, Virology 13:460--476, 1961; Doermann et al., J. Cell. comp. Physiol. 45[Suppl.]:51--74, 1955) as an explanation for the distribution of marker rescue frequencies during cross-reactivation; i.e., replication proceeds in a bidirectional manner from an origin to a site of UV damage, and those regions of the genome which replicate most efficiently are rescued most efficiently by a coinfecting phage. In addition, photoreactivation studies support the hypothesis that thymine dimers are the major UV damage blocking cross-reactivation in the right end of the T7 genome. 相似文献
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Molecular Genetics and Genomics - The gal3 mutation of E. coli, which arose by the insertion of IS2 in the OP region of the gal operon, reverts spontaneously by excision of the IS2 to produce... 相似文献
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Disentangling the contributions of osmotic and ionic effects of salinity on stomatal,mesophyll, biochemical and light limitations to photosynthesis 下载免费PDF全文
There are conflicting opinions on the relative importance of photosynthetic limitations under salinity. Quantitative limitation analysis of photosynthesis provides insight into the contributions of different photosynthetic limitations, but it has only been applied under saturating light conditions. Using experimental data and modelling approaches, we examined the influence of light intensity on photosynthetic limitations and quantified the osmotic and ionic effects of salinity on stomatal (LS), mesophyll (LM), biochemical (LB) and light (LL) limitations in cucumber (Cucumis sativus L.) under different light intensities. Non‐linear dependencies of LS, LM and LL to light intensity were found. Osmotic effects on LS and LM increased with the salt concentration in the nutrient solution (Ss) and the magnitude of LM depended on light intensity. LS increased with the Na+ concentration in the leaf water (Sl) and its magnitude depended on Ss. Biochemical capacity declined linearly with Sl but, surprisingly, the relationship between LB and Sl was influenced by Ss. Our results suggest that (1) improvement of stomatal regulation under ionic stress would be the most effective way to alleviate salinity stress in cucumber and (2) osmotic stress may alleviate the ionic effects on LB but aggravate the ionic effects on LS. 相似文献
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MIREILLE OKASSA SERGE KREITER SABINE GUICHOU MARIE‐STÉPHANE TIXIER 《Biological journal of the Linnean Society. Linnean Society of London》2011,104(2):393-406
Neoseiulus californicus (McGregor) is a natural enemy of pest mites used worldwide in many crops. Its correct identification is thus essential to ensure biological control success. The present study aimed to characterize molecular and morphological intraspecific variations for assisting in the diagnosis of the species and to build baseline information about expected variations within a commercially important phytoseiid species. Morphological and molecular [12S rRNA, cytochrome b mitochondrial (mt)DNA, and internal transcribed spacer] analyses were carried out on fourteen populations collected worldwide and on one mass‐reared strain. The genetic distances between the specimens of N. californicus and another related species were high and no overlap was observed, sustaining the reliability of such molecular methods for assisting a specific diagnosis. Furthermore, the genetic distances between populations of N. californicus were very low and overlap between intra‐ and interpopulations distances was observed, except for two populations collected in France (Marsillargues and Midi‐Pyrénées). The high mitochondrial differentiation between these two latter populations and the others questions their specific status: do they belong to the species N. californicus or to another cryptic species? However, using nuclear DNA marker analyses, no distinct differences were observed. Furthermore, even if significant morphological differences were observed between the populations, these differences were very small and the standard errors within each population were very low. We thus concluded that all the populations studied belong to the species N. californicus, despite unexpected high mitochondrial variations. The present study thus displays the importance of an integrative taxonomic approach for avoiding misidentifications. A discussion on morphological and mtDNA variations in relation to diagnostic reliability is developped. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 393–406. 相似文献
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SOIZIC MORIN ANNE‐SOPHIE LAMBERT JOAN ARTIGAS MARINA COQUERY STÉPHANE PESCE 《Freshwater Biology》2012,57(8):1658-1666
1. The impact of immigration on the recovery of diatom assemblages after chronic exposure to copper was investigated in laboratory microcosms. 2. We examined the recovery trajectories of copper‐contaminated biofilms after reducing copper stress and with or without the possibility of immigration from unimpaired communities. 3. The biofilms mixed with unimpaired communities returned to a ‘control’ assemblage structure within 6 weeks, with recovery patterns depending on the endpoint considered (i.e. 2 weeks for relative abundances of diatom species but 6 weeks for total diatom biomass). In contrast, no recovery was observed in assemblages placed under control conditions without external immigrants. 4. Immigration has important effects on the recovery of quantitative and qualitative characteristics of biofilms. 相似文献
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DIANA H. WALL MARK A. BRADFORD MARK G. ST. JOHN JOHN A. TROFYMOW VALERIE BEHAN‐PELLETIER DAVID E. BIGNELL J. MARK DANGERFIELD WILLIAM J. PARTON JOSEF RUSEK WINFRIED VOIGT VOLKMAR WOLTERS HOLLEY ZADEH GARDEL FRED O. AYUKE RICHARD BASHFORD OLGA I. BELJAKOVA PATRICK J. BOHLEN ALAIN BRAUMAN STEPHEN FLEMMING JOH R. HENSCHEL DAN L. JOHNSON T. HEFIN JONES MARCELA KOVAROVA J. MARTY KRANABETTER LES KUTNY KUO‐CHUAN LIN MOHAMED MARYATI DOMINIQUE MASSE ANDREI POKARZHEVSKII HOMATHEVI RAHMAN MILLOR G. SABARÁ JOERG‐ALFRED SALAMON MICHAEL J. SWIFT AMANDA VARELA HERALDO L. VASCONCELOS DON WHITE XIAOMING ZOU 《Global Change Biology》2008,14(11):2661-2677
Climate and litter quality are primary drivers of terrestrial decomposition and, based on evidence from multisite experiments at regional and global scales, are universally factored into global decomposition models. In contrast, soil animals are considered key regulators of decomposition at local scales but their role at larger scales is unresolved. Soil animals are consequently excluded from global models of organic mineralization processes. Incomplete assessment of the roles of soil animals stems from the difficulties of manipulating invertebrate animals experimentally across large geographic gradients. This is compounded by deficient or inconsistent taxonomy. We report a global decomposition experiment to assess the importance of soil animals in C mineralization, in which a common grass litter substrate was exposed to natural decomposition in either control or reduced animal treatments across 30 sites distributed from 43°S to 68°N on six continents. Animals in the mesofaunal size range were recovered from the litter by Tullgren extraction and identified to common specifications, mostly at the ordinal level. The design of the trials enabled faunal contribution to be evaluated against abiotic parameters between sites. Soil animals increase decomposition rates in temperate and wet tropical climates, but have neutral effects where temperature or moisture constrain biological activity. Our findings highlight that faunal influences on decomposition are dependent on prevailing climatic conditions. We conclude that (1) inclusion of soil animals will improve the predictive capabilities of region‐ or biome‐scale decomposition models, (2) soil animal influences on decomposition are important at the regional scale when attempting to predict global change scenarios, and (3) the statistical relationship between decomposition rates and climate, at the global scale, is robust against changes in soil faunal abundance and diversity. 相似文献
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