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1.
2.
McNulty IB 《Plant physiology》1985,78(1):100-103
The objective of this research was to measure the short term osmotic adjustment of Salicornia europaea L. ssp. rubra (A. Nels) Breitung when suddenly exposed to 100 millimolar NaCl. Plants were grown hydroponically, shocked with 100 millimolar NaCl added to the culture solution, and stem tips analyzed for free inorganic ions and small organic molecules at intervals up to 72 hours. In the first 2 hours, the calculated leaf osmoticum showed a net increase of 158.8 millimolar most of which was free Mg2+ (+135.3 millimolar). Total sugars increased almost 5-fold by the 6th hour, enough to provide sufficient osmoticum for the cytoplasm if only partially confined there. By 24 hours, all measured osmotica had decreased except Na+, Mg2+, Cl−, and proline, with the net increase being 208 millimolar. By 72 hours, there was a net gain of 356 millimolar in osmotica of the stem tips, due to Na+ (+233.3 millimolar), Cl− (+306.7 millimolar), and a small increase in sugar and proline (+3.5 millimolar), with all other osmotica decreasing in concentration. Compatible osmotica did not change sufficiently to account for osmotic balance between vacuole and cytoplasm; consequently, there must have been a reapportionment of osmotica within the cell in the short time duration of this experiment. 相似文献
3.
A comparative description of mitochondrial DNA differentiation in selected avian and other vertebrate genera 总被引:14,自引:1,他引:13
Levels of mitochondrial DNA (mtDNA) sequence divergence between species
within each of several avian (Anas, Aythya, Dendroica, Melospiza, and
Zonotrichia) and nonavian (Lepomis and Hyla) vertebrate genera were
compared. An analysis of digestion profiles generated by 13-18 restriction
endonucleases indicates little overlap in magnitude of mtDNA divergence for
the avian versus nonavian taxa examined. In 55 interspecific comparisons
among the avian congeners, the fraction of identical fragment lengths (F)
ranged from 0.26 to 0.96 (F = 0.46), and, given certain assumptions, these
translate into estimates of nucleotide sequence divergence (p) ranging from
0.007 to 0.088; in 46 comparisons among the fish and amphibian congeners, F
values ranged from 0.00 to 0.36 (F = 0.09), yielding estimates of P greater
than 0.070. The small mtDNA distances among avian congeners are associated
with protein-electrophoretic distances (D values) less than approximately
0.2, while the mtDNA distances among assayed fish and amphibian congeners
are associated with D values usually greater than 0.4. Since the
conservative pattern of protein differentiation previously reported for
many avian versus nonavian taxa now appears to be paralleled by a
conservative pattern of mtDNA divergence, it seems increasingly likely that
many avian species have shared more recent common ancestors than have their
nonavian taxonomic counterparts. However, estimates of avian divergence
times derived from mtDNA- and protein-calibrated clocks cannot readily be
reconciled with some published dates based on limited fossil remains. If
the earlier paleontological interpretations are valid, then protein and
mtDNA evolution must be somewhat decelerated in birds. The empirical and
conceptual issues raised by these findings are highly analogous to those in
the long-standing debate about rates of molecular evolution and times of
separation of ancestral hominids from African apes.
相似文献
4.
Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes 总被引:23,自引:2,他引:21
Statistical methods for computing the standard errors of the branching
points of an evolutionary tree are developed. These methods are for the
unweighted pair-group method-determined (UPGMA) trees reconstructed from
molecular data such as amino acid sequences, nucleotide sequences,
restriction-sites data, and electrophoretic distances. They were applied to
data for the human, chimpanzee, gorilla, orangutan, and gibbon species.
Among the four different sets of data used, DNA sequences for an
895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the
most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979)
gave the least reliable one. The DNA sequence data suggested that the
chimpanzee is the closest and that the gorilla is the next closest to the
human species. The orangutan and gibbon are more distantly related to man
than is the gorilla. This topology of the tree is in agreement with that
for the tree obtained from chromosomal studies and DNA-hybridization
experiments. However, the difference between the branching point for the
human and the chimpanzee species and that for the gorilla species and the
human-chimpanzee group is not statistically significant. In addition to
this analysis, various factors that affect the accuracy of an estimated
tree are discussed.
相似文献
5.
In man folates are catabolized and excreted as inactive cleaved degradation products, a mixture of pteridines and p-aminobenzoylglutamate (pABGlu) or its acetamido derivative (apABGlu). The daily rate of excretion represents the inescapable use of the vitamin in metabolic activity and thus has implications for determining the recommended dietary allowance for the vitamin. Furthermore, the rate of catabolism has been suggested to rise during pregnancy and in certain disease states. A method is described for the quantitative extraction and assay of the folate catabolites pABGlu and apABGlu in human urine. Aliquots of 24-h urine collections are acidified and applied to columns of Dowex 50W cation-exchange resin. The catabolites are selectively batch-eluted with increasing concentrations of HCl. The fraction containing pABGlu is diazotized and then applied to a C18 Sep Pak column for further purification and concentration. The fraction containing apABGlu was deacetylated and reapplied to the Dowex column and then treated identically to the pABGlu fraction. The methanolic concentrates of both extracts were evaporated to dryness and reconstituted with water and pABGlu was regenerated by reductive cleavage of the diazotized material with Zn/HCl. The extracts of the two catabolites were separated by reverse-phase HPLC using a Radial Pak C18 column. Recovery of isolated material was monitored by the addition of high specific activity tritiated labels of both compounds added as internal standards to all urine aliquots prior to purification and analysis. 相似文献
6.
Anonymous nuclear DNA markers in the American oyster and their implications for the heterozygote deficiency phenomenon in marine bivalves 总被引:4,自引:0,他引:4
A puzzling population-genetic phenomenon widely reported in allozyme
surveys of marine bivalves is the occurrence of heterozygote deficits
relative to Hardy-Weinberg expectations. Possible explanations for this
pattern are categorized with respect to whether the effects should be
confined to protein-level assays or are genomically pervasive and expected
to be registered in both protein- and DNA-level assays. Anonymous nuclear
DNA markers from the American oyster were employed to reexamine the
phenomenon. In assays based on the polymerase chain reaction (PCR), two
DNA-level processes were encountered that can lead to artifactual genotypic
scorings: (a) differential amplification of alleles at a target locus and
(b) amplification from multiple paralogous loci. We describe symptoms of
these complications and prescribe methods that should generally help to
ameliorate them. When artifactual scorings at two anonymous DNA loci in the
American oyster were corrected, Hardy-Weinberg deviations registered in
preliminary population assays decreased to nonsignificant values.
Implications of these findings for the heterozygote-deficit phenomenon in
marine bivalves, and for the general development and use of PCR-based
assays, are discussed.
相似文献
7.
8.
9.
A highly conserved nuclear gene for low-level phylogenetics: elongation factor-1 alpha recovers morphology-based tree for heliothine moths 总被引:8,自引:2,他引:6
Cho S; Mitchell A; Regier JC; Mitter C; Poole RW; Friedlander TP; Zhao S 《Molecular biology and evolution》1995,12(4):650-656
Molecular systematists need increased access to nuclear genes. Highly
conserved, low copy number protein-encoding nuclear genes have attractive
features for phylogenetic inference but have heretofore been applied mostly
to very ancient divergences. By virtue of their synonymous substitutions,
such genes should contain a wealth of information about lower-level
taxonomic relationships as well, with the advantage that amino acid
conservatism makes both alignment and primer definition straightforward. We
tested this postulate for the elongation factor-1 alpha (EF-1 alpha) gene
in the noctuid moth subfamily Heliothinae, which has probably diversified
since the middle Tertiary. We sequenced 1,240 bp in 18 taxa representing
heliothine groupings strongly supported by previous morphological and
allozyme studies. The single most parsimonious gene tree and the
neighbor-joining tree for all nucleotides show almost complete concordance
with the morphological tree. Homoplasy and pairwise divergence levels are
low, transition/transversion ratios are high, and phylogenetic information
is spread evenly across gene regions. The EF-1 alpha gene and presumably
other highly conserved genes hold much promise for phylogenetics of
Tertiary age eukaryote groups.
相似文献
10.
Identification of the signalling molecules involved in mesoderm formation in amphibian embryos still presents problems. None of the original candidates, such as activin, have been definitively ruled out, and the new factors, such as the nodal-related genes, have come on to the scene. Of the original candidates, activin has been definitively shown to act as a morphogen, whereas bone morphogenetic protein (BMP)-4 has emerged as a ventral inducer and an inhibitor of neural differentiation. The effects of BMP-4 are antagonized by chordin, a molecule related to the product of the Drosophila gene short gastrulation. 相似文献