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21.
Plants of white lupin (Lupinus albus L cv Multolupa) and soyabean(Glycine max L cv Clarke) were grown in controlled-environmentcabinets, subjected to various stresses and their nodular nitrogenaseactivity and total root respiration measured When these measurementswere used to calculate nodular oxygen diffusion resistance,using a simplified equation for Fick's first law of diffusion,it was found that the apparent resistance of stressed nodulesincreased anomalously with decreases in external oxygen concentrationA new analysis procedure is proposed to alleviate this anomalyThis procedure also uses the simplified Fick's law equationbut includes a respiratory contribution to the total oxygenflux across the diffusion barrier which is not coupled to nitrogenaseactivity Also, resistance is modelled as an exponential functionof external oxygen concentration Use of this analysis procedureproduces realistic values for total resistance and providesa characterisation of this resistance into a minimum value andan adjustment factor for changes in external oxygen It is postulatedthat the additional respiration component represents the activityof nodule cortex cells involved in the diffusion barrier, particularlythat of vascular bundles Oxygen diffusion resistance, nodule, nitrogen fixation, respiration  相似文献   
22.
Abstract. Flux densities of water vapour and carbon dioxide were measured for a Mediterranean macchia canopy. Results show good agreement between the measured available energy and the sum of latent sensible and heat flux densities determined with the eddy correlation technique. Joint evaluation of the Bowen ratio, aerodynamic resistance, canopy resistance and the 'omega factor' suggests that the macchia canopy is intermediate in aerodynamic roughness between coniferous and deciduous canopies. Maximum daytime carbon flux densities ranged from -14 to -22(μnol m−2 s−1 on a ground area basis. The ratio of transpiration to assimilation (E/A) was a function of incident photo-synthetic photon flux density below about 400 μmol m−2s−1 and above it was fairly constant at 272 mol mol−1 (H2O/CO2). The relationship between carbon influx and canopy conductance was linear. Results show promising applications of the eddy correlation technique for evaluating physiological features of canopies, treated as unitary functional systems.  相似文献   
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The human dihydrofolate reductase (DHFR) gene family comprises one functional gene and at least four intronless processed pseudogenes. The functional DHFR gene is on chromosome 5, and DHFRP4 is on chromosome 3. Using in situ hybridization, we have now localized the functional DHFR gene to the region q11.1-q13.3 on chromosome 5. By genomic DNA analysis of a panel of human X rodent somatic-cell hybrids, we determined the chromosomal assignment of the DHFRP1 pseudogene to chromosome 18 and that of the DHFRP2 pseudogene to chromosome 6. The DHFRP1 pseudogene exhibits a novel form of polymorphism in humans in that it is present in the DNA of some individuals and absent in that of others. We investigated the racial distribution of this pseudogene in five racial groups. The allelic frequency as defined by analysis of 180 chromosomes was found to be 94% in Mediterraneans, 77% in Asian Indians, 67% in Chinese, 57% in Southeast Asians, and 32% in American blacks. These data suggest that the transposition of this "perfect" pseudogene occurred prior to the inception of the human racial groups.  相似文献   
25.
Wolterbeek, H. Th. and De Bruin, M. 1986. Xylem and phloem importof Na+, K+ , Rb+, Cs+ and in tomato fruits: differential contributions from stem and leaf.—J.exp. Bot. 37: 928–939. The transport of Na+, K+, Rb+, Cs+ and into developing fruits of tomato (an inbred lineof Lycopersicon esculentum Mill. cv. Tiny Tim) was measured.Element solutions were introduced into the transpiration streamthrough the cut stem bases of plant parts consisting of a stempart with single green fruit, both with and without attachedfully expanded leaf. Measurements were carried out of the accumulationin the fruit of the gamma-ray emitting radiotracers 24Na+, 42K+,86Rb+, 134Cs+ and The transport into the fruit was expressed by a single parameter taking intoaccount volume flows varying with time and experiments. Xylemto phloem transfer in the stem as a source of fruit elementsupply was shown to be inversely related with the velocity offlow of the stem xylem. The results also indicated that thetransfer system in the stem was more rapidly equilibrated thanit was in the leaf. Stem loading of the phloem is suggested as a possible mechanismregulating the solute influx in fruits under varying flow velocitiesof the stem xylem, while fruit influx of phloem solutes, whichwere loaded in the leaf, may play a major role in influx regulationunder conditions of varying solute concentrations. Key words: Alkali ions, tomato fruits, stem and leaf phloem loading  相似文献   
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The RD-114 family of endogenous retroviral sequences in domestic cats has been shown to consist of approximately 20 copies of genetically divergent virogenes per haploid genome. The chromosomal localization for four endogenous sequences (RDV1-4) was accomplished by correlating the occurrence of specific feline chromosomes with diagnostic viral DNA fragments in a panel of cat X rodent somatic cell hybrids. Analysis of the hybrid panel revealed that endogenous RD-114 sequences are dispersed on multiple cat chromosomes, that certain proviral segments are polymorphic with respect to the presence or absence of virus, and that a restriction fragment characteristic of inducible RD-114 resides on a single feline chromosome (B3), probably at a single locus.  相似文献   
28.
Abstract We tested the hypothesis that electrogenic ion pumps, working at the parenchyma symplast/xylem interface of pea hypocotyls, provide the driving force for K+ uptake from the xylem. Solutions of known composition were perfused through a hypocotyl segment. The K+ activity of the solution flowing out of the xylem (K+out) increased (i.e. K+ uptake decreased) when aerobic respiration was inhibited by lack of O2, and this was preceded by a decrease in Vpx (electrical potential difference between parenchyma symplast and xylem). Perfusion with auxin (1AA) and fusicoccin (FC) stimulated the electrogenic activity of the ‘xylem pumps’ (111 and 205% respectively) and stimulated uptake of K + from the xylem (with 71% and 29% respectively). The close correlation between xylem pump activity and K+ uptake corroborated the aforementioned hypothesis. Interestingly, inhibition of pump activity by anoxia was incomplete in the presence of FC. It is thought that FC increases the affinity of the ATP-requiring xylem pump for ATP, thus ensuring that ATP production during fermentation is sufficient to fuel the pump in the absence of O2.  相似文献   
29.
Genetic characterization of human c-rel sequences.   总被引:3,自引:3,他引:0       下载免费PDF全文
We isolated and sequenced a human genomic-DNA segment that is homologous to a portion of v-rel, the transforming gene of reticuloendotheliosis virus (strain T). We also localized the human rel sequences to human chromosome 2 by screening a panel of rodent X human somatic-cell hybrids with the newly described human rel segment.  相似文献   
30.
Eight isolates of Naegleria australiensis were obtained from a small lake in Tulsa, Oklahoma. The eight strains were isolated during the hot summer months of July through September, when water temperatures ranged from 27 to 33°C. All eight isolates were pathogenic for mice. The mean time to death for mice was 10 days (range 6–13 days). This pathogenic free-living ameba has not before been reported from the United States or the Western Hemisphere.  相似文献   
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