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排序方式: 共有100条查询结果,搜索用时 62 毫秒
1.
Adaptation of the tetrazolium method for testing the seed viability, and scanning electron microscopy study of some Western European orchids 总被引:3,自引:0,他引:3
A modified tetrazolium method was formulated for use with seeds of Western European orchids. The sequence of treatments which gave the highest percentage of coloured (i.e. viable) embryos was: (1) pretreatment in a solution of 5% (w/v) Ca(OCl)2 + 1% (v/v) Tween-80, (2) soaking for 1 day in sterile water, (3) the classical tetrazolium test. The optimal duration of the pretreatment in Ca(OCl)2 + Tween-80 depends upon the species, and to investigate the effect a scanning electron microscopy study was performed on the testa of 3 species. For a given species, the optimal pretreatment period was not affected by the year of harvest or the source of the seed lots. 相似文献
2.
We have broadly defined the DNA regions regulating esterase6 activity in
several life stages and tissue types of D. melanogaster using P-
element-mediated transformation of constructs that contain the esterase6
coding region and deletions or substitutions in 5' or 3' flanking DNA.
Hemolymph is a conserved ancestral site of EST6 activity in Drosophila and
the primary sequences regulating its activity lie between -171 and -25 bp
relative to the translation initiation site: deletion of these sequences
decrease activity approximately 20-fold. Hemolymph activity is also
modulated by four other DNA regions, three of which lie 5' and one of which
lies 3' of the coding region. Of these, two have positive and two have
negative effects, each of approximately twofold. Esterase6 activity is
present also in two male reproductive tract tissues; the ejaculatory bulb,
which is another ancestral activity site, and the ejaculatory duct, which
is a recently acquired site within the melanogaster species subgroup.
Activities in these tissues are at least in part independently regulated:
activity in the ejaculatory bulb is conferred by sequences between -273 and
-172 bp (threefold decrease when deleted), while activity in the
ejaculatory duct is conferred by more distal sequences between -844 and
-614 bp (fourfold decrease when deleted). The reproductive tract activity
is further modulated by two additional DNA regions, one in 5' DNA (-613 to
-284 bp; threefold decrease when deleted) and the other in 3' DNA (+1860 to
+2731 bp; threefold decrease when deleted) that probably overlaps the
adjacent esteraseP gene. Collating these data with previous studies
suggests that expression of EST6 in the ancestral sites is mainly regulated
by conserved proximal sequences while more variable distal sequences
regulate expression in the acquired ejaculatory duct site.
相似文献
3.
Nucleotide variation at the hypervariable esterase 6 isozyme locus of Drosophila simulans 总被引:2,自引:0,他引:2
Esterase 6 (Est-6/EST6) is polymorphic in both Drosophila melanogaster and
D. simulans for two common allozyme forms, as well as for several other
less common variants. Parallel latitudinal clines in the frequencies of the
common EST6-F and EST6-S allozymes in these species have previously been
interpreted in terms of a shared amino acid polymorphism that distinguishes
the two variants and is subject to selection. Here we compare the sequences
of four D. simulans Est-6 isolates and show that overall estimates of
nucleotide heterozygosity in both coding and 5' flanking regions are more
than threefold higher than those obtained previously for this gene in D.
melanogaster. Nevertheless, the ratio of replacement to exon silent-site
polymorphism in D. simulans is less than the ratio of replacement to silent
divergence between D. simulans and D. melanogaster, which could be the
result of increased efficiency of selection against replacement
polymorphisms in D. simulans or to divergent selection between the two
species. We also find that the amino acid polymorphisms separating EST6- F
and EST6-S in D. simulans are not the same as those that separate these
allozymes in D. melanogaster, implying that the shared clines do not
reflect shared molecular targets for selection. All comparisons within and
between the two species reveal a remarkable paucity of variation in a
stretch of nearly 400 bp immediately 5' of the gene, indicative of strong
selective constraint to retain essential aspects of Est-6 promoter
function.
相似文献
4.
5.
6.
Thomas GR Chen Z Leukinova E Van Waes C Wen J 《Cancer immunology, immunotherapy : CII》2004,53(1):33-40
We previously characterized the expression of CD80 in different murine head and neck squamous cell carcinoma (HNSCC) clones derived following tumor progression in the absence of T cell–mediated immunity in severe combined immunodeficient (SCID) mice. We found that HNSCCs that did not express CD80 grew as progressors, while those that expressed CD80 were regressors when grown in immune-competent animals. In the present study, we characterized expression of a repertoire of immunoregulatory cytokines in these HNSCC lines, and found that HNSCCs that express cytokines IL-1, IL-6, and GM-CSF do not express CD80, suggesting the hypothesis that these cytokines may down-modulate expression of CD80. Cytokine-conditioned medium from progressor HNSCC and recombinant IL-1, IL-6, and GM-CSF caused a reduction of CD80 expression in regressor HNSCCs without affecting proliferation. Conversely, the decrease in CD80 expression in progressor HNSCCs could be restored by IFN-, a known inducer of CD80 expression. These data strongly suggest that high levels of cytokines IL-1, IL-6, and GM-CSF expressed by tumor cells can down-regulate CD80 expression in HNSCC, and that IFN- can independently stimulate expression. These data provide evidence for a novel mechanism of cytokine-mediated down-modulation of CD80 during malignant progression of HNSCC that can be restored by IFN-. 相似文献
7.
8.
Rod and cone photoreceptors project from the outer retinal surface into a
carbohydrate-rich interphotoreceptor matrix (IPM). Unique IPM
glycoconjugates are distributed around rods and cones. Wheat germ
agglutinin (WGA) strongly decorates the rod matrix domains and weakly
decorates the cone matrix domains. This study characterizes the major
WGA-binding glycoprotein in the human IPM, which we refer to as SPACR
(sialoprotein associated with cones and rods). SPACR, which has a molecular
weight of 147 kDa, was isolated and purified from the IPM by lectin
affinity chromatography. A polyclonal antibody to SPACR was prepared that
colocalizes in tissue preparations with WGA-binding domains in the IPM.
Sequential digestion of SPACR with N- and O- glycosidases results in a
systematic increase in electrophorectic mobility, indicating the presence
of both N- and O-linked glycoconjugates. Complete deglycosylation results
in a reduction in the relative molecular mass of SPACR by about 30%.
Analysis of lectin binding allowed us to identify some of the structural
characteristics of SPACR glycoconjugates. Treatment with neuraminidase
exposes Galbeta1- 3GalNAc disaccharide as indicated by positive peanut
agglutinin (PNA) staining, accompanied by the loss of WGA staining. Maackia
amurensis agglutinins (MAA-1 and MAA-2), specific for sialic acid in
alpha2-3 linkage to Gal, bind SPACR, while Sambucus nigra agglutinin (SNA),
specific for alpha2-6 linked sialic acid, does not, indicating that the
dominant glycoconjugate determinant on SPACR is the O-linked carbohydrate,
NeuAcalpha2-3Galbeta1-3GalNAc. The abundance of sialic acid in SPACR
suggests that this glycoprotein may contribute substantially to the
polyanionic nature of the IPM. The carbohydrate chains present on SPACR
could also provide sites for extensive crosslinking and participate in the
formation of the ordered IPM lattice that surrounds the elongate
photoreceptors projecting from the outer retinal surface.
相似文献
9.
The recent structure determinations of the mammalian effector enzyme adenylyl cyclase reveal the structure of its catalytic core, provide new insights into its catalytic mechanism and suggest how diverse signaling molecules regulate its activity. 相似文献
10.
Dentinogenesis imperfecta is a congenital dentin dysplasia that occurs either isolated or associated with a genetic disorder known as osteogenesis imperfecta. Dentinogenesis imperfecta is inherited in an autosomal dominant pattern. Clinically the teeth color of both dentitions varies from brown to a translucent gray with an opalescent sheen. Shields et al. (1973) proposed a classification of Dentinogenesis imperfecta into three types: type I, associated with osteogenesis imperfecta; type II, hereditary opalescent dentin; type III Brandywine-type. The phenotypes of Dentinogenesis imperfecta are described in regard to their genetic defects, pathology, radiology and histopathology as well as their dental treatment. 相似文献