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991.
Background and Aims: Sulfonylurea (SU) herbicides are used extensively in cereal–livestockfarming zones as effective and cheap herbicides with usefullevels of residual activity. These residues can persist beyondthe cropping year, severely affecting legumes in general, andannual medics in particular, resulting in reduced dry matterproduction, lower seed yields and decreased nitrogen fixation.A strand medic cultivar, Medicago littoralis Angel,has been developed via chemical mutagenesis with tolerance toSU soil residues. Identifying the molecular basis of the observedtolerance was the aim of this study. Methods: Two F2 populations were generated from crosses between Angeland varieties of intolerant M. truncatula, the male-sterilemutant tap and the cultivar Caliph. Genetic mappingwith SSR (single sequence repeat) and gene-based markers allowedidentification of the trait-defining gene. Quantitative geneexpression studies showed the activity of the respective alleles. Key Results: Segregation ratios indicated the control of SU-herbicide toleranceby a single dominant gene. SU herbicides inhibit the biosynthesisof the branched-chain amino acids by targeting the acetolactatesynthase enzyme, allowing the choice of a mapping approach usingacetolactate synthase (ALS) gene homologues as candidates. SSR-markeranalysis suggested the ALS-gene homologue on chromosome 3 inM. truncatula. The ALS-gene sequences from Angeland intolerant genotypes were sequenced. In Angel,a single point mutation from C to T translating into an aminoacid change from proline to leucine was identified. The polymorphismwas used to develop a diagnostic marker for the tolerance trait.Expression of the mutant ALS allele was confirmed by quantitativeRT-PCR and showed no differences at various seedling stagesand treatments to the corresponding wild-type allele. Conclusions: The identification of the trait-defining gene and the developmentof a diagnostic marker enable efficient introgression of thiseconomically important trait in annual medic improvement programs. 相似文献
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993.
Laboratory evolution studies provide fundamental biological insight through direct observation of the evolution process. They not only enable testing of evolutionary theory and principles, but also have applications to metabolic engineering and human health. Genome‐scale tools are revolutionizing studies of laboratory evolution by providing complete determination of the genetic basis of adaptation and the changes in the organism's gene expression state. Here, we review studies centered on four central themes of laboratory evolution studies: (1) the genetic basis of adaptation; (2) the importance of mutations to genes that encode regulatory hubs; (3) the view of adaptive evolution as an optimization process; and (4) the dynamics with which laboratory populations evolve. 相似文献
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995.
Max M. Tilzer 《Hydrobiologia》1989,173(2):135-140
An array of factors simultaneously controls phytoplankton photosynthesis and hence the primary production process. Because their relative importance shifts both with depth and with season, the significance of individual factors cannot be resolved by in situ incubations, even if all relevant environmental and biotic variables are measured.Here a procedure is described by which in addition to in situ measurements, photosynthesis is simultaneously assessed in identical subsamples under constant temperature (10 °C) and light (0.66 mol m–2 h–1 PAR conditions, in vitro). By calculating photosynthesis per unit of chlorophyll, effects of shifting biomass on photosynthesis can be eliminated but seasonal variations of light-saturated photosynthesis generated by temperature, and vertical changes of light-requirements (e.g. by light-shade adaptation) remain obscure. Quotients of in situ photosynthetic rates divided by in vitro rates allow the quantification of light-mediated changes. Provided that photosynthesis measured in vitro is light-saturated, quotients in situ: in vitro rates should never exceed unity. They are a measure for the degree of light-limitation. In vitro rates normalized to chlorophyll give information on temporal changes caused by variations in photosynthetic capacity. In Lake Constance, mean cell size appears to control light-saturated assimilation numbers. 相似文献
996.
短尾猴(Macaca arctoides)和猕猴跟骨的功能形态研究 总被引:4,自引:0,他引:4
本文从形态描述和统计入手,对短尾猴(macaca arctoides)和猕猴的跟骨进行了比较研究。结果表明,所研究的跟骨变量无论数值大小还是几何图形结构都存在一定差异。特别是跟骨最大宽、跟长、后距骨连结面长、跟骨高度及相对跟长存在显著性差异水平。猕猴跟骨变量间的相关关系比短尾猴的表现得更为紧密。据其形态与功能的关系,我们认为:与猕猴相较,短尾猴更适应于地栖生活。这似乎与短尾猴具更大的体重有关。 相似文献
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R. R. Sakai P. F. He X. D. Yang L. Y. Ma Y. F. Guo J. J. Reilly C. N. Moga S. J. Fluharty 《Journal of neurochemistry》1994,62(5):2053-2056
Abstract: Antisense Oligonucleotides were developed to study the expression and function of angiotensin type 1 (AT1) receptors in cultured cells and brain. In both liver epithelial WB and neuro-blastoma N1E-115 cells AT1 antisense oligomers substantially decreased AT1 receptor density, whereas angiotensin type 2 (AT2) receptors remained unchanged. Similarly, repeated intracerebroventricular injections of AT1 antisense oligomers in rats decreased AT1 receptor density in hypothalamic-thalamic-septal tissue, and AT2 receptors were unaffected. Intracerebroventricular antisense oligomers also attenuated drinking elicited by intra-cerebroventricular angiotensin II but not the cholinomimetic carbachol. Collectively, these results demonstrate that antisense Oligonucleotides attenuate angiotensin receptor expression and function in behaving animals. 相似文献