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81.
The vascular anatomy ofHelminthostachys zeylanica was examined with special reference to anomalous secondary tissue. Primary xylem development gradually takes place centrifugally. In branched rhizomes with destroyed apices, the vascular cylinder apical to the insertion of branch traces is generally composed of primary xylem, accessory xylem, inner parenchyma of radially arranged cells, outer parenchyma of irregularly arranged cells, and partly crushed phloem, listed in order going outwards. The accessory xylem as well as the inner parenchyma ofHelminthostachys zeylanica is probably secondarily produced, partly to contribute to the branch traces, in a position corresponding to that of secondary vascular tissue developed from a normal cambium inBotrychium sensu lato. It is suggested that although a cambium is lacking inHelminthostachys zeylanica, the secondary vascular tissues are comparable between the genera. The phylogenetic implication of this tissue is discussed. 相似文献
82.
Preston Gadson Judy McCoy Ann Charlotte Wikstrm Jan-Ake Gustafsson 《Journal of cellular biochemistry》1990,43(2):185-198
Exposure of fibroblasts derived from keloid tissues, desmoid and dermal tissue from individuals with Gardner's syndrome (GS) to dexamethasone resulted in the suppression of protein kinase C (PKC) activity and [3H]thymidine incorporation into DNA, and a 20-fold induction of glutamine synthetase activity. Treatment of GS and keloid fibroblasts with 0.1 microM dexamethasone for 36 h increased glucocorticoid receptor (GR) synthesis, as determined by [35S]methionine labeling and immunoprecipitation with a monoclonal antibody to the human GR. The suppression of PKC activity by dexamethasone was shown to result from a loss of protein mass as determined by immunoblotting using an antibody to PKC type III. In contrast to these results, exposure of fibroblasts isolated from normal tissues to dexamethasone did not result in the suppression PKC and [3H]thymidine incorporation, there was only a sixfold induction of glutamine synthetase, and a decrease of GR synthesis. As no primary receptor binding defect could be detected, the altered response of tumor cells to steroid-occupied receptor indicates a partial post-receptor binding defect in GS and keloid cells. 相似文献
83.
Medicago truncatula,a model plant for studying the molecular genetics of theRhizobium-legume symbiosis 总被引:7,自引:0,他引:7
David G. Barker Sylvie Bianchi François Blondon Yvette Dattée Gérard Duc Sadi Essad Pascal Flament Philippe Gallusci Gérard Génier Pierre Guy Xavier Muel Jacques Tourneur Jean Dénarié Thierry Huguet 《Plant Molecular Biology Reporter》1990,8(1):40-49
Medicago truncatula has all the characteristics required for a concerted analysis of nitrogen-fixing symbiosis withRhizobium using the tools of molecular biology, cellular biology and genetics.M. truncatula is a diploid and autogamous plant has a relatively small genome, and preliminary molecular analysis suggests that allelic
heterozygosity is minimal compared with the cross-fertilising tetraploid alfalfa (Medicago sativa). TheM. truncatula cultivar Jemalong is nodulated by theRhizobium meliloti strain 2011, which has already served to define many of the bacterial genes involved in symbiosis with alfalfa. A genotype
of Jemalong has been identified which can be regenerated after transformation byAgrobacterium, thus allowing the analysis ofin-vitro-modified genes in an homologous transgenic system. Finally, by virtue of the diploid, self-fertilising and genetically homogeneous
character ofM. truncatula, it should be relatively straightforward to screen for recessive mutations in symbiotic genes, to carry out genetic analysis,
and to construct an RFLP map for this plant. 相似文献
84.
85.
Azotobacter vinelandii was grown diazotrophically in sucrose-limited chemostat cultures at either 12, 48, 108, 144 or 192 M dissolved oxygen. Steady state protein levels and growth yield coefficients (Y) on sucrose increased with increasing dilution rate (D). Specific rate of sucrose consumption (q) increased in direct proportion to D. Maintenance coefficients (m) extrapolated from plots of q versus D, as well as from plots of 1/Y versus 1/D exhibited a nonlinear relationship to the dissolved oxygen concentration. Constant maximal theoretical growth yield coefficients (Y
G) of 77.7 g cells per mol of sucrose consumed were extrapolated irrespective of differences in ambient oxygen concentration. For comparison, glucose-, as well as acetate-limited cultures were grown at 108 M oxygen. Fairly identical m- and Y
G-values, when based on mol of substrate-carbon with glucose and sucrose grown cells, indicated that both substrates were used with the same efficiency. However, acetate-limited cultures showed significantly lower m- and, at comparable, D, higher Y-values than cultures limited by either sucrose or glucose. Substrate concentrations (K
s) required for half-maximal growth rates on sucrose were not constant, they increased when the ambient oxygen concentration was raised and, at a given oxygen concentration, when D was decreased. Since biomass levels varied in linear proportion to K
s these results are interpreted in terms of variable substrate uptake activity of the culture.Abbreviations
D
dilution rate
-
K
s
substrate concentration required for half maximal growth rate
-
m
maintenance coefficient
-
q
specific rate of substrate consumption
-
Y
growth yield coefficient
-
Y
G
maximum theoretical growth yield coefficient 相似文献
86.
Barbara J. Javor 《Archives of microbiology》1988,149(5):433-440
Seven strains of extremely halophilic bacteria (Halobacterium spp., Halococcus spp., and Haloarcula sp.) fixed CO2 under light and dark conditions. Light enhanced CO2 fixation in Halobacterium halobium but inhibited it in Halobacterium volcanii and Haloarcula strain GN-1. Propionate stimulated 14CO2 incorporation in some strains, but inhibited it in others. Semi-starvation in basal salts plus glycerol induced enhanced CO2 fixation rates. 14CO2 fixation in semi-starved cells was stimulated by NH
4
+
or pyruvate and inhibited by succinate and acetate in most strains. No possible reductant was found. In cell-free extracts of H. halobium, NH
4
+
but not propionate stimulated 14CO2 fixation. No RuBP carboxylase activity was detected. The main 14C-labeled -keto acid detected after a 2-min incubation with 14CO2 and pyruvate was pyruvate. Little or no -ketobutyrate was detected among the early products of propionate-stimulated CO2 fixation. Glycine was the major amino acid synthesized during a 2-min incubation with NH
4
+
, propionate, and 14CO2. Propionate-stimulated CO2 fixation was sensitive to trimethoprim and insensitive to avidin. A novel pathway for non-reductive CO2 fixation involving a glycine synthase reaction with CO2, NH
4
+
, and a methyl carbon derived from the -carbon cleavage of propionate is tentatively proposed.Abbreviations used BBS
buffered basal salts
- HEPES
N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid
- MOPS
3-(N-morpholino)propanesulfonic acid
- DNPH
2,4-dinitrophenylhydrazine
- DNP
dinitrophenyl
- TLC
thin-layer chromatography
- FH4
tetrahydrofolate
This work was supported by National Science Foundation grant PCM-8116330 and Petroleum Research Fund grant PRF 13704-AC2 相似文献
87.
Øyvind Skraastad Karl L. Reichelt 《Virchows Archiv. B, Cell pathology including molecular pathology》1988,56(1):321-325
Previous work indicates that the colonic epithelial cell proliferation in mice is reversibly inhibited by the tripeptide pGlu-His-GlyOH
found in aqueous extracts of the intestine. In the present study we examined the possible tissue specificity of the colon
mitosis inhibitor. The mitotic rate in the small intestine, epidermis and forestomach in mice was registered after a single
i.p. injection of the tripeptide. A significantly reduced rate of cell renewal was found at 18 h in the epidermis whereas
no inhibition was observed in the forestomach or ileal epithelium. To investigate whether the amino acid sequence of the tripeptide
is essential for the inhibitory effect, three structurally related bioactive peptides were tested and compared to the effect
of CMI. CMI showed a bell-shaped dose-response relationship as previously shown, whereas the mitotic rate was not reduced
in the colonie epithelium after treatment with either an epidermal mitosis inhibitory pentapeptide, or the dipeptide pGlu-GlyOH,
or an analogue of luteinizing hormone-releasing hormone. The efficacy of the tripeptide was dependent on the basal rate of
cell renewal in the colonie epithelium. When the tripeptide was given at the circadian nadir of cell proliferation a delayed
reduction of the proliferative activity was observed at 6 h after treatment, whereas treatment when the rate of cell proliferation
was at its circadian zenith gave an immediate mitotic inhibition. 相似文献
88.
An extensive analysis of genomic DNA preparations from a number of normal and malignant tissues revealed BglII site polymorphism of the human p53 gene. Approximately 10% of p53 gene alleles were found to contain an additional BglII site localized in a region of intron I. This allelic form of p53 gene was also responsible for p53 protein having altered electrophoretic mobility. Molecular cloning and sequencing of both the alleles of p53 gene revealed a base-pair change in codon 72 causing arginine → proline substitution in the allele with the additional BglII site. Both variants of the p53 gene may occur in homozygous state and are therefore functional. 相似文献
89.
An extensive analysis of genomic DNA preparations from a number of normal and malignant tissues revealed BglII site polymorphism of the human p53 gene. Approximately 10% of p53 gene alleles were found to contain an additional BglII site localized in a region of intron I. This allelic form of p53 gene was also responsible for p53 protein having altered electrophoretic mobility. Molecular cloning and sequencing of both the alleles of p53 gene revealed a base-pair change in codon 72 causing arginine → proline substitution in the allele with the additional BglII site. Both variants of the p53 gene may occur in homozygous state and are therefore functional. 相似文献
90.
A role for haemoglobin in all plant roots? 总被引:4,自引:2,他引:2
Abstract. We have found haemoglobin in plant roots whereas previously it has been recorded only in nitrogen fixing nodules of plants. Haemoglobin occurs not only in the roots of those plants that are capable of nodulation but also in the roots of species that are not known to nodulate. We suggest that a haemoglobin gene may be a component of the genome of all plants. The gene structure and sequence in two unrelated families of plants suggests that the plant haemoglobins have had a single origin and that this origin relates to the haemoglobin gene of the animal kingdom. At present we cannot completely rule out the possibility of a horizontal transfer of the gene from the animal kingdom to a progenitor of the dicotyledonous angiosperms but we favour a single origin of the gene from a progenitor organism to both the plant and animal kingdoms. We speculate about the possible functions of haemoglobin in plant roots and put the case that it is unlikely to have a function in facilitating oxygen diffusion. We suggest that haemoglobin may act as a signal molecule indicating oxygen deficit and the consequent need to shift plant metabolism from an oxidative to a fermentative pathway of energy generation. 相似文献