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101.
The human T-cell receptor gamma variable pseudogeneV10 is a distinctive marker of human speciation 总被引:1,自引:1,他引:0
Xiao-Min Zhang Guy Cathala Zohra Soua Marie-Paule Lefranc Sylvie Huck 《Immunogenetics》1996,43(4):196-203
The nucleotide sequence data reported in this paper have been submitted to the EMBL/GenBank/DDBJ nucleotide sequence databases and have been assigned the accession numbers X86 558 and X86 709–X86 723 相似文献
102.
Werner B. Herppich Guy Midgley Dieter J. von Willert Maik Veste 《Physiologia plantarum》1996,98(2):485-492
Drought responses of diurnal gas exchange, malic acid accumulation and water status were examined in Delosperma tradescantioides , a succulent that grows in drought-prone microenvironments in summer rainfall and all-year rainfall regions of southern Africa. When well-watered, this species exhibited Crassulacean acid metabolism (CAM)-cycling, but its carbon fixation pattern changed during the development of drought, shifting to either low-level CAM or to CAM-idling. The rate and pattern of this change depended on environmental conditions, duration of water stress and leaf age. At the onset of drought, diurnal malate fluctuation increased, but was strongly depressed (by ca 70%) as drought continued, and when leaf water content and water potential were low (ca 35 and 50% of the initial levels, respectively). When rewatered, rates of growth and photosynthesis, gas exchange and water status recovered fully to pre-stressed values within two days. Whole-shoot carbon uptake rates suggested that leaf growth had continued unabated during a short-term (∼ one week) drought. This emphasises that CAM-idling allows the maintenance of active metabolism with negligible gas exchange when soil water is limiting. It is possible that old or senescent leaves may provide water for the expansion of developing leaves during initial periods of drought. Regardless of the water regime and environmental conditions, leaf nocturnal malate accumulation and water content were positively correlated and increased with leaf age. Thus the gradual loss of water from older mature leaves may induce CAM-idling, which reduces water loss. An important ecological consequence of this combination of CAM modes is the potential to switch rapidly between fast growth via C3 gas exchanges when well-watered to water-conserving CAM-idling during drought. 相似文献
103.
The interactive effects of increased carbon dioxide (CO2) concentration and ultraviolet-B (UV-B, 280–320 nm) radiation on Acacia karroo Hayne, a C3 tree, and Themeda triandra Forsk., a C4 grass, were investigated. We tested the hypothesis that A. karroo would show greater CO2-induced growth stimulation than T. triandra, which would partially explain current encroachment of A. karroo into C4 grasslands, but that increased UV-B could mitigate this advantage. Seedlings were grown in open-top chambers in a greenhouse in ambient (360 μmol mol-1) and elevated (650 μmol mol-1) CO2, combined with ambient (1.56 to 8.66 kJ m-2 day-1) or increased (2.22 to 11.93 kJ m-2 day-1) biologically effective (weighted) UV-B irradiances. After 30 weeks, elevated CO2 had no effect on biomass of A. karroo, despite increased net CO2 assimilation rates. Interaction between UV-B and CO2 on stomatal conductance was found, with conductances decreasing only where elevated CO2 and UV-B were supplied separately. Increases in water use efficiencies, foliar starch concentrations, root nodule numbers and total nodule mass were measured in elevated CO2. Elevated UV-B caused only an increase in foliar carbon concentrations. In T. triandra, net CO2 assimilation rates were unaffected in elevated CO2, but stomatal conductances and foliar nitrogen concentrations decreased, and water use efficiencies increased. Biomass of all vegetative fractions, particularly leaf sheaths, was increased in elevated CO2. and was accompanied by increased leaf blade lengths and individual leaf and leaf sheath masses. However, tiller numbers were reduced in elevated CO2. Significantly moderating effects of elevated UV-B were apparent only in individual masses of leaf blades and sheaths, and in total sheath and shoot biomass. The direct CO2-induced growth responses of the species therefore do not support the hypothesis of CO2-driven woody encroachment of C4 grasslands. Rather, differential changes in resource use efficiency between grass and woody species, or morphological responses of grass species, could alter the competitive balance. Increased UV-B radiation is unlikely to substantially alter the CO2 response of these species. 相似文献
104.
Guy G. Orgambide Saleela Philip-Hollingsworth Pedro F. Mateos Rawle I. Hollingsworth Frank B. Dazzo 《Plant and Soil》1996,186(1):93-98
Axenic seedling bioassays were performed on white clover, vetch, and alfalfa to assess the variety and dose responses of biological activities exhibited by membrane chitolipooligosaccharides (CLOSs) from wild type Rhizobium leguminosarum bv. trifolii ANU843. Subnanomolar concentrations of CLOSs induced deformation of root hairs (Had) and increased the number of foci of cortical cell divisions (Ccd) in white clover, some of which developed into nodule meristems. In contrast, ANU843 CLOSs were unable to induce Had in alfalfa and required a 104-fold higher threshold concentration to induce this response in vetch. Also, ANU843 CLOSs were not mitogenic on either of these non-host legumes. In addition, CLOS action also increased chitinase activity in white clover root exudate. Thus, the membrane CLOSs from wild type R. leguminosarum bv. trifolii are fully capable of eliciting various symbiosis-related responses in white clover in the same concentration range as extracellular CLOSs of other rhizobia on their respective legume hosts. These results and our earlier studies indicate that membrane CLOSs represent one of many different classes of bioactive metabolites made by R. leguminosarum bv. trifolii which elicit more intense symbiosis-related responses in white clover than in other legumes. Therefore, CLOSs evidently play an important role in symbiotic development, but they may not be the sole determinant of host-range in the Rhizobium-clover symbiosis.Abbreviations Ccd
cortical cell division
- CLOS
chitolipooligosaccharide
- Had
root hair deformation 相似文献
105.
Lisa A. Donovan James H. Richards Matthew W. Muller 《American journal of botany》1996,83(12):1637-1646
At Mono Lake, California, we investigated field water relations, leaf and xylem chemistry, and gas exchange for two shrub species that commonly co-occur on marginally saline soils, and have similar life histories and rooting patterns. Both species had highest root length densities close to the surface and have large tap roots that probably reach ground water at 3.4-5.0 m on the study site. The species differed greatly in leaf water relations and leaf chemistry. Sarcobatus vermiculatus had a seasonal minimum predawn xylem pressure potential (ψpd) of -2.7 MPa and a midday potential (ψmd) of -4.1 MPa. These were significantly lower than for Chrysothamnus nauseosus, which had a minimum ψpd of -1.0 MPa and ψmd of -2.2 MPa. Sarcobatus had leaf Na of up to 9.1 % and K up to 2.7 % of dry mass, and these were significantly higher than for Chrysothamnus which had seasonal maxima of 0.4% leaf Na and 2.4 % leaf K. The molar ratios of leaf K/Na, Ca/Na, and Mg/Na were substantially lower for Sarcobatus than for Chrysothamnus. Xylem ionic contents indicated that both species excluded some Na at the root, but that Chrysothamnus was excluding much more than Sarcobatus. The higher Na content of Sarcobatus leaves was associated with greater leaf succulence, lower calculated osmotic potential, and lower xylem pressure potentials. Despite large differences in water relations and leaf chemistry, these species maintained similar diurnal patterns and rates of photosynthesis and stomatal conductance to water vapor diffusion. Sarcobatus ψpd may not reflect soil moisture availability due to root osmotic and hydraulic properties. 相似文献
106.
Measurement of Growth at Very Low Rates ((mu) >= 0), an Approach To Study the Energy Requirement for the Survival of Alcaligenes eutrophus JMP 134 下载免费PDF全文
Alcaligenes eutrophus JMP 134 was grown in a recycling-mode fermenter with 100% biomass retention on 2,4-dichlorophenoxyacetic acid (2,4-D), phenol, and fructose. The growth pattern obtained given a constant supply of substrates exhibited three phases of linear growth on all three substrates. The transition from phase 1 to phase 2, considered to correspond to the onset of stringent (growth) control as indicated by a significant increase in guanosine 5(prm1)-bisphosphate 3(prm1)-bisphosphate (ppGpp), took place at 0.016 h(sup-1) with 2,4-D and at about 0.02 h(sup-1) with phenol and fructose. In the final phase, phase 4, which was achieved after the growth rate on the respective substrates fell below 0.003 to 0.001 h(sup-1), a constant level of biomass was obtained irrespective of further feeding of substrate at the same rate. The yield coefficients decreased by 70 to 80% from phase 1 to phase 3 and were 0 in phase 4. The stationary substrate concentrations s(infmin) in phase 4, calculated from the kinetic constants of the strain, were 1.23, 0.34, and 0.23 (mu)M for 2,4-D, phenol, and fructose, respectively. These figures characterize the minimum stationary substrate concentrations required in a dynamic system to keep A. eutrophus alive. This is caused by a substrate flux which enables growth at a rate >=0 due to the provision of energy to an extent at least satisfying maintenance requirements. According to the constant feed rates of the substrates and the final and stable biomass concentrations, this maintenance energy amounts to 14.4, 4.0, and 2.4 (mu)mol of ATP (middot) mg of dry mass(sup-1) h(sup-1) for 2,4-D, phenol, and fructose, respectively, after correction for the fraction of living cells. The increased energy expenditure in the case of 2,4-D is discussed with respect to uncoupling. 相似文献
107.
A Familial Factor Independent of CAG Repeat Length Influences Age at Onset of Machado-Joseph Disease 总被引:3,自引:0,他引:3 下载免费PDF全文
Anita L. DeStefano L. Adrienne Cupples Patricia Maciel Claudia Gaspar Joao Radvany David M. Dawson Lewis Sudarsky Lee Corwin Paula Coutinho Patrick MacLeod Jorge Sequeiros Guy A. Rouleau Lindsay A. Farrer 《American journal of human genetics》1996,59(1):119-127
Machado-Joseph disease (MJD) is a late-onset, progressive, neurodegenerative disorder caused by the expansion of an unstable trinucleotide (CAG) repeat sequence in a novel gene (MJD1) on chromosome 14. Previous studies showed that age at onset is negatively correlated with the number of CAG repeat units, but only part of the variation in onset age is explained by CAG repeat length. Ages at onset and CAG repeat lengths of 136 MJD patients from 23 kindreds of Portuguese descent were analyzed, to determine whether familial factors independent of CAG repeat length modulate age at onset of MJD. Correlation among sibs for onset age adjusted for CAG repeat length was .43, which indicates that an environmental or genetic factor common to sibs influences onset age. Positive correlations were also observed for avuncular (r = .22) and first-cousin pairs (r = .28), which supports the hypothesis that a genetic factor is influencing age at onset. Commingling analysis of onset ages adjusted for CAG repeat length identified three distributions in this population of affected individuals. Further studies of a much larger sample are needed to determine whether these distributions represent the influence of a genetic or environmental factor. 相似文献
108.
Homogeneous transport in a heterogeneous membrane: water diffusion across human stratum corneum in vivo. 总被引:1,自引:0,他引:1 下载免费PDF全文
The objective of this study was to determine whether a structurally heterogeneous biomembrane, human stratum corneum (SC), behaved as a homogeneous barrier to water transport. The question is relevant because the principal function of the SC in vivo is to provide a barrier to the insensible loss of tissue water across the skin. Impedance spectra (IS) of the skin and measurements of the rate of transepidermal water loss (TEWL) were recorded sequentially in vivo in human subjects as layers of the SC were progressively removed by the serial application of adhesive tape strips. The low-frequency (< or = 100 rad s-1) impedance of skin was much more significantly affected by tape stripping than the higher frequency values; removal of the outermost SC layer had the largest effect. In contrast, TEWL changed little as the outer SC layers were stripped off, but increased dramatically when 6-8 microns of the tissue had been removed. It follows that the two noninvasive techniques probe SC barrier integrity in somewhat different ways. After SC removal, recovery of barrier function, as assessed by increasing values of the low-frequency impedance, apparently proceeded faster than TEWL decreased to the prestripping control. The variation of TEWL as a function of SC removal behaved in a manner entirely consistent with a homogeneous barrier, thereby permitting the apparent SC diffusivity of water to be found. Skin impedance (low frequency) was correlated with the relative concentration of water within the SC, thus providing an in vivo probe for skin hydration. Finally, the SC permeability coefficient to water, as a function of SC thickness, was calculated and correlated with the corresponding values of skin admittance derived from IS. 相似文献
109.
Michal Jarnik Jiang-Qing Tang Maria Korab-Laskowska Ewa Zie
tkiewicz Guy Cardinal Izabella Gorska-Flipot Daniel Sinnett Damian Labuda 《Genomics》1996,36(3):388
We studied two systems of multilocus markers revealed by PCR using primers directing amplification betweenAlurepeats in a tail-to-tail orientation. Genomic polymorphisms were detected as the presence or absence of the electrophoretic bands representing DNA fragments of a given length. A total of 104 such fragments segregating as Mendelian markers in a panel of eight CEPH families were analyzed by two-point linkage analysis. Fifty-one of these fragments were localized with respect to CEPH markers; they represented 33 loci, 7 of which were multiallelic. Locus-specific oligonucleotides were developed and used as hybridization probes to identify the mapped loci within a complex pattern of inter-AluPCR products. A great proportion of inter-AluPCR polymorphisms represented length variants within amplified DNA segments, while others were presumably due to mutations within the priming sites. To describe the expected number of informative loci per typing experiment we introduced a parameter called overall informativity (OI), which provides a single measure of the multiplex ratio and the informativity of markers contributing to a multilocus system (OIof a single locus is equivalent to its heterozygosity and cannot exceed 0.5 for a biallelic codominant marker). HighOIvalues (5.8 and 11.5) of the two presented systems of inter-AluPCR markers of random chromosomal distribution render them suitable for mapping genomic rearrangements such as genomic deletions in tumoral tissues. This was illustrated by the detection of loss of heterozygosity in the 9q22–qter region in sporadic colon cancer. 相似文献
110.