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971.
972.
The chloroplast ATP synthase is strictly regulated so that it is very active in the light (rates of ATP synthesis can be higher than 5 mol/min/mg protein), but virtually inactive in the dark. The subunits of the catalytic portion of the ATP synthase involved in activation, as well as the effects of nucleotides are discussed. The relation of activation to proton flux through the ATP synthase and to changes in the structure of enzyme induced by the proton electrochemical gradient are also presented. It is concluded that the and subunits of CF1 play key roles in both regulation of activity and proton translocation.  相似文献   
973.
The pucC genes of Rubrivivax gelatinosus strain 151 and Rhodopseudomonas acidophila strain 10050 have been identified, cloned and sequenced. In Rubrivivax gelatinosus the arrangement of the pucC gene with regard to the pucBA genes was shown to differ from that found in other species of photosynthetic bacteria. The Rhodopseudomonas acidophila pucC was found downstream of four new pucBA gene pairs, bringing the sequenced pucBA pairs to a total of eight in this strain. The predicted PucC protein sequences were compared to those of PucC from other species and showed high similarity. Similarity was also seen to more distantly related proteins LhaA and orf428 of Rhodobacter capsulatus, orf G115 of Rhodospirillum rubrum and `orf428' from Synechocystis sp. PCC6803. An analysis of the predicted secondary structure of these proteins is given, and their structural similarity to proteins in the Major Facilitator Superfamily is discussed with regard to their possible function. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
974.
Monitoring river health   总被引:14,自引:4,他引:10  
  相似文献   
975.
This article examines the widely reported phenomenon of the efflorescence of magical beliefs and practices, often explained as a response by some societies to their incorporation into the cash and market economy. Rather than accepting this view that the phenomenon is a generalizable response to modernity, I seek to understand it in its own terms as a singular response to the introduction of new forms of wealth into a specific cultural framework. Taking the example of a particular society, the Lelet of Papua New Guinea, I show how the expansion of forms of wealth has led to a loss of control over the processes by which sociality was previously regulated. This discussion proceeds through consideration of Lelet management of valuables and desire, and the importance of visuality in this.  相似文献   
976.
Environmental pollutants and other stressors can haveeffects at many different levels of biologicalorganization and a key step in the design ofecotoxicological studies is the formulation ofhypotheses that explicitly state the level(s) ofbiological organization that the study is meant toaddress. For example, single species studies at theindividual organism level can provide key informationon individual growth rates and physiologicalresponses, while multispecies studies at the communitylevel allow food web investigations to be undertakenand potentially allow indirect effects of toxicants tobe identified. The integration and understanding ofprocesses operating over several different levels ofbiological organization can often be greatlyfacilitated by the incorporation of microcosmexperiments conducted at the appropriate scale. Suchexperiments provide replication as well as greatercontrol over relevant variables which allows morerigorous hypothesis testing and important insight intomechanisms of biotic responses to pollutants. Wesuggest an appropriate use for stream microcosms inecotoxicology is in integrated assessment strategieswhere experimental results are linked with fieldmonitoring data. Under an integrated assessmentscenario, concordance of results between fieldobservations and dose-response exposures in microcosmscan provide important weight-of-evidence for guidancein management action or monitoring programs. We alsoidentify a number of other issues that must be addressedwhen utilizing stream microcosms; these includedecisions on exposure type, relative test duration,experimental design, biota source and type oftaxonomic assemblage, environmental realism, andchoice of end points. This kind of integratedassessment strategy has been applied to the Athabasca,Fraser, and Thompson Rivers in western Canada, wheremeasurement of similar end points in microcosms andfield sites has produced concordance of results and animproved understanding of causality instressor/response relationships.  相似文献   
977.
978.
This paper explores the determinants of extinction of endemic plant taxa in mediterranean-climate regions in South Africa and southwestern Australia. Major threats to biodiversity in these areas include agriculture, deforestation, fragmentation, invasive alien organisms and urbanization. Case studies from the two regions show that synergisms between factors can lead to discontinuous, or non-linear, responses that have increased extinction rates (or threaten to) beyond predictions based on simple deterministic processes.  相似文献   
979.
Genomic complexity and plasticity of Burkholderia cepacia   总被引:6,自引:1,他引:5  
Abstract Burkholderia cepacia has attracted attention because of its extraordinary degradative abilities and its potential as a pathogen for plants and for humans. This bacterium was formerly considered to belong to the genus Pseudomonas in the γ-subclass of the Proteobacteria , but recently has been assigned to the β-subclass based on rrn gene sequence analyses and other key phenotypic characteristics. The B. cepacia genome is comprised of multiple chromosomes and is rich in insertion sequences. These two features may have played a key role in the evolution of novel degradative functions and the unusual adaptability of this bacterium.  相似文献   
980.
In non-reciprocal cross-incompatibility (NRCI), the crossing of a female of a strain A with a male of a strain B results in hybrid offspring, whereas the reciprocal cross produces few or no hybrids. Only females are of hybrid origin in Hymenoptera because they arise from fertilized eggs; males arise from unfertilized (haploid) eggs. Crosses between many strains of Trichogramma deion showed some degree of NRCI. Crosses between a T. deion culture collected in Seven Pines, California (SVP) with one from Marysville, California (MRY) showed an extreme form of NRCI in which practically no female offspring was produced when MRY females were crossed with SVP males. The reciprocal cross produced a close to normal proportion of female and male offspring. Detailed studied of this cross indicated that 1) the female offspring produced in the compatible interstrain cross were not the result of parthenogenesis but were true hybrids, 2) the incompatible interstrain cross did not produce female offspring because fertilized eggs died during development, 3) the death of these eggs could not be prevented by either antibiotic or temperature treatment, 4) cytoplasmically inherited factors causing NRCI could be discounted because backcrossed females with the genome of MRY and the cytoplasm of SVP, exhibit the NRCI relationship characteristic of their genome. Therefore the NRCI between these strains appears to be caused by a modification coded for by the nuclear genes of MRY that results in incompatibility when SVP sperm fertilizes MRY eggs. In addition the level of incompatibility in crosses between the SVP females and MRY males is temperature sensitive, the higher the rearing temperature the lower the level of compatibility.  相似文献   
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