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81.
SO42- Deprivation Has an Early Effect on the Content of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase and Photosynthesis in Young Leaves of Wheat 总被引:2,自引:0,他引:2 下载免费PDF全文
Wheat (Triticum aestivum cv Chinese Spring) supplied with 0.45 mM SO42- for 14 d with relative growth rates (RGR) of 0.22 to 0.24 d-1 was deprived of S for 7 to 8 d. There was no significant effect on RGR or leaf development (leaf 2 length was constant; leaf 3 expanded for 2-4 d; leaf 4 emerged and elongated throughout the experiment) during the S deprivation. In controls the net assimilation rate (A) closely reflected leaf ontogeny. S deprivation affected A in all leaves, particularly leaf 4, in which A remained at 8 to 10 [mu]mol CO2 m-2 s-1, whereas in controls A rose steadily to >20 [mu]mol CO2 m-2 s-1. In leaf 2, with a fully assembled photosynthetic system, A decreased in S-deprived plants relative to controls only at the end of the experiment. Effects on A were not due to altered stomatal conductance or leaf internal [CO2] ([C]i); decreases in the initial slope of A/[C]i curves indicated an effect of S deprivation on the carboxylase efficiency. Measurement of Rubisco activity and large subunit protein abundance paralleled effects on A and A/[C]i in S-deprived leaves. Negative effects on photosynthesis in S-deprived plants are discussed in relation to mobilization of S reserves, including Rubisco, emphasizing the need for continuous S supply during vegetative growth. 相似文献
82.
Endogenous chloride channels of insect sf9 cells. Evidence for coordinated activity of small elementary channel units 总被引:1,自引:0,他引:1 下载免费PDF全文
EH Larsen SE Gabriei MJ Stutts J Fullton EM Price RC Boucher 《The Journal of general physiology》1996,107(6):695-714
The endogenous Cl- conductance of Spodoptera frugiperda (Sf9) cells was studied 20-35 h after plating out of either uninfected cells or cells infected by a baculovirus vector carrying the cloned beta-galactosidase gene (beta-Gal cells). With the cation Tris+ in the pipette and Na+ in the bath, the reversal potential of whole-cell currents was governed by the prevailing Cl- equilibrium potential and could be fitted by the Goldman-Hodgkin-Katz equation with similar permeabilities for uninfected and beta-Gal cells. In the frequency range 0.12 < f < 300 Hz, the power density spectrum of whole-cell Cl- currents could be fitted by three Lorentzians. Independent of membrane potential, >50% of the total variance of whole-cell current fluctuations was accounted for by the low frequency Lorentzian (fc = 0.40 +/- 0.03 Hz, n = 6). Single-Cl- channels showed complex gating kinetics with long lasting (seconds) openings interrupted by similar long closures. In the open state, channels exhibited fast burst-like closures. Since the patches normally contained more than a single channel, it was not possible to measure open and closed dwell-time distributions for comparing single-Cl- channel activity with the kinetic features of whole-cell currents. However, the power density spectrum of Cl- currents of cell-attached and excised outside-out patches contained both high and low frequency Lorentzian components, with the corner frequency of the slow component (fc = 0.40 +/- 0.02 Hz, n = 4) similar to that of whole-cell current fluctuations. Chloride channels exhibited multiple conductance states with similar Goldman-Hodgkin-Katz-type rectification. Single-channel permeabilities covered the range from approximately 0.6.10(-14) cm5/s to approximately 6.10(-14) cm3/s, corresponding to a limiting conductance (gamma 150/150) of approximately 3.5 pS and approximately 35 pS, respectively. All states reversed near the same membrane potential, and they exhibited similar halide ion selectivity, P1 > PCl approximately PBr. Accordingly, Cl- current amplitudes larger than current flow through the smallest channel unit resolved seem to result from simultaneous open/shut events of two or more channel units. 相似文献
83.
Responses of two wheat varieties to sulphur addition and diagnosis of sulphur deficiency 总被引:4,自引:0,他引:4
F. J. Zhao M. J. Hawkesford A. G. S. Warrilow S. P. McGrath D. T. Clarkson 《Plant and Soil》1996,181(2):317-327
Sulphur deficiency has become increasingly widespread in wheat in the U.K. Growth, nutrient content and biochemical responses to S and N supply of a breadmaking wheat variety (Hereward) and a non-breadmaking variety (Riband) were investigated in a pot experiment. Shoot dry matter (DM) at stem extension (Zadok's GS 37) and at maturity was increased markedly by S. Grain production of the Riband variety was more susceptible to the imbalance of N to S than the Hereward variety. At GS 37, the concentrations of total S and sulphate-S of shoots, chlorophyll meter readings and the concentrations of glutathione of the uppermost fully expanded leaves were increased significantly by increasing S supply, whereas the concentrations of nitrate and amides were decreased by S. The greatest relative changes in response to S supply were those of the glutathione and asparagine concentrations. Riband also showed greater response to S than Hereward. Critical values of various diagnostic indices at GS 37 were derived from the relationships between DM yield and different indices. The two varieties showed similar diagnostic curves except that for the ratio of total N to total S (N:S) in shoots. Either total S or sulphate-S can be used alone as a good indicator of deficiency, and with values of 1500 and 190 mg kg-1 DM in shoots for the two indices respectively. There was also a well defined relationship between DM yield and the glutathione concentration, with a critical value of 240 nmol g-1 FW. There were no advantages of using % of total S as sulphate-S. Shoot N:S ratio was found to be less accurate in predicting S deficiency than total S or sulphate-S. For prognostic purposes, a much higher S status at GS 37 was required to ensure no losses of DM yield due to S deficiency at maturity. 相似文献
84.
应用免疫组织化学SP法对4例饲喂黄曲霉毒素B1的Wistar大鼠肝组织中AFB1-DNA加合物的染色及常规HE染色发现,4例肝细胞核均出现异型性,但未见肝细胞坏死、增生灶及肝细胞癌;免疫组化揭示部分肝细胞核出现棕黄色、不均质状的AFB1-DNA加合物,阳性细胞数占10~85%。结果提示免疫组织化学方法可作为一种AFB1的定位方法,AFB1在动物致癌过程中AFB1-DNA加合物可能具有启动作用 相似文献
85.
Isolation of a cDNA from Saccharomyces cerevisiae that encodes a high affinity sulphate transporter at the plasma membrane 总被引:5,自引:0,他引:5
Frank W. Smith Malcolm J. Hawkesford Ian M. Prosser David T. Clarkson 《Molecular & general genetics : MGG》1995,247(6):709-715
Resistance to selenate and chromate, toxic analogues of sulphate, was used to isolate a mutant of Saccharomyces cerevisiae deficient in the capacity to transport sulphate into the cells. A clone which complements this mutation was isolated from a cDNA library prepared from S. cerevisiae poly(A)+ RNA. This clone contains an insert which is 2775 by in length and has a single open reading frame that encodes a 859 amino acid polypeptide with a molecular mass of 96 kDa. Sequence motifs within the deduced amino acid sequence of this cDNA (SUL1) show homology with conserved areas of sulphate transport proteins from other organisms. Sequence analysis predicts the position of 12 putative membrane spanning domains in SUL1. When the cDNA for SUL1 was expressed in S. cerevisiae, a high affinity sulphate uptake activity (Km = 7.5 ± 0.6 M for SO
4
2–
) was observed. A genomic mutant of S. cerevisiae in which 1096 by were deleted from the SUL1 coding region was constructed. This mutant was unable to grow on media containing less than 5 mM sulphate unless complemented with a plasmid containing the SUL1 cDNA. We conclude that the SUL1 cDNA encodes a S. cerevisiae high affinity sulphate transporter that is responsible for the transfer of sulphate across the plasma membrane from the external medium. 相似文献
86.
Intraspecific DNA sequence variation of the mitochondrial control region of white sturgeon (Acipenser transmontanus) 总被引:3,自引:0,他引:3
Intraspecific sequence variation in the D-loop region of mtDNA in white
sturgeon (Acipenser transmontanus), a relict North American fish species,
was examined in 27 individuals from populations of the Columbia and Fraser
rivers. Thirty-three varied nucleotide positions were present in a
462-nucleotide D-loop sequence, amplified using the polymerase chain
reaction. Bootstrapped neighbor-joining and maximum- parsimony trees of
sequences from 19 haplotypes suggest that the two populations have recently
diverged. This is consistent with the hypothesis that the Columbia River, a
Pleistocene refugium habitat, was the source of founders for the Fraser
River after the last glacial recession. On the basis of a divergence time
of 10-12 thousand years ago, the estimated substitution rate of the white
sturgeon D-loop region is 1.1-1.3 x 10(-7) nucleotides/site/year, which is
comparable to rates for hypervariable sequences in the human D-loop region.
Furthermore, the ratio of mean percent nucleotide differences in the D-
loop (2.27%) to that in whole mtDNA (0.54%, as estimated from
restriction-enzyme data) is 4.3, which is similar to the fourfold-to-
fivefold-higher substitution rate estimated for the human D-loop. The high
nucleotide substitution rate of the hypervariable region indicates that the
vertebrate D-loop has potential as a genetic marker in molecular population
studies.
相似文献
87.
Ancient large-scale genome duplications: phylogenetic and linkage analyses shed light on chordate genome evolution 总被引:12,自引:4,他引:8
Pebusque MJ; Coulier F; Birnbaum D; Pontarotti P 《Molecular biology and evolution》1998,15(9):1145-1159
Paralogous genes from several families were found in four human chromosome
regions (4p16, 5q33-35, 8p12-21, and 10q24-26), suggesting that their
common ancestral region underwent several rounds of large- scale
duplication. Searches in the EMBL databases, followed by phylogenetic
analyses, showed that cognates (orthologs) of human duplicated genes can be
found in other vertebrates, including bony fishes. In contrast, within each
family, only one gene showing the same high degree of similarity with all
the duplicated mammalian genes was found in nonvertebrates (echinoderms,
insects, nematodes). This indicates that large-scale duplications occurred
after the echinoderms/chordates split and before the bony vertebrate
radiation. It has been suggested that two rounds of gene duplication
occurred in the vertebrate lineage after the separation of Amphioxus and
craniate (vertebrates + Myxini) ancestors. Before these duplications, the
genes that have led to the families of paralogous genes in vertebrates must
have been physically linked in the craniate ancestor. Linkage of some of
these genes can be found in the Drosophila melanogaster and Caenorhabditis
elegans genomes, suggesting that they were linked in the triploblast
Metazoa ancestor.
相似文献
88.
Abstract The development and physiology of cord-forming saprotrophic basidiomycetes, which form extensive and persistent mycelial networks in woodland ecosystems, can be conveniently studied on non-sterile soil in laboratory microcosms mimicking field conditions. Morphological responses of Phanerochaete velutina mycelial systems to resource encounters, and decay partitioning following encounters, varied according to whether simulated woody litter was unsterile or autoclaved and on whether encounter took place at the mycelial foraging front or behind the margin (simulating litter fall onto established systems in the field). Results show that encounter of discrete resources by P. velutina is rapidly communicated to the entire mycelial system; that resource capture takes high priority at the expense of continued system extension and decay-derived carbon reallocation; and that polarized growth toward newly encountered resources, previously considered to occur infrequently with this species, may be readily detected using image analysis techniques. Potential advantages of polarized development of P. velutina are discussed. 相似文献
89.
90.