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951.
Effects of sub-minimal inhibitory concentrations of EDTA on growth of Escherichia coli and the release of lipopolysaccharide 总被引:1,自引:0,他引:1
Christophe Pelletier Pierre Bourlioux Jean van Heijenoort 《FEMS microbiology letters》1994,117(2):203-206
Abstract Release of lipopolysaccharide from E. coli was studied in the presence of sub-minimal inhibitory concentrations of ethylenediaminetetraacetic acid (EDTA). In untreated cells no release was detected with 50 mM Mg2+ in the medium, but a steady release of over 50% of the synthesized lipopolysaccharide was observed with 0.1 mM Mg2+ . EDTA at MIC/8 led to a 2- to 3-fold higher release, presumably by an adjustment of the concentration of unchelated Mg2+ to a value still sustaining normal growth but giving rise to a highly unstable outer membrane. No structural difference was observed between cell-bound and released lipopolysaccharide. 相似文献
952.
Wim van Houten Leo van Raamsdonk Konrad Bachmann 《Plant Systematics and Evolution》1994,190(1-2):49-67
The Chilean annual,Microseris pygmaea, has differentiated in distinct coastal and inland series of populations after long-distance dispersal from western North America. Two plants from the most diverse biotypes were crossed, a large F2 was raised and analysed for segregation of 30 phenotypic characters. Segregation of molecular markers (47 RAPDs, 1 RFLP, 2 isozymes) was determined in a subpopulation of 45 plants which include all extremes for the phenotypic characters. 32 marker/character cosegregations were significant at the 1% level in t-tests between dominant and homozygous recessive marker genotypes. Considering linkage among markers and pleiotropy of certain marker loci, the number of independent quantitative trait loci (QTLs) is reduced to about 18. Interactions among 2 or 3 QTLs affecting one character have been characterized. The phenotypic differentiation ofM. pygmaea during its evolution from a single founder individual begins to be understood at the level of single-gene mutants. 相似文献
953.
Maryna van de Venter Derek Litthauer Willem Oelofsen 《Journal of cellular biochemistry》1994,54(1):1-10
Adipocyte precursors from the stromal vascular fraction of human adipose tissue were allowed to differentiate in serum-free defined medium, whereafter their catecholamine stimulated lipolytic response was compared to that of mature isolated human adipocytes. Seventy-five to ninety percent of the fibroblast-like cells accumulated lipid droplets and glycerol-3-phosphate dehydrogenase activities of 1,000–2,800 mU/mg protein were measured in cell homogenates of differentiated cells. Lipolysis could be stimulated by both isoproterenol and norepinephrine in both differentiated preadipocytes as well as mature adipocytes. The results obtained with β-adrenergic agents suggested the presence of a higher affinity receptor in differentiated preadipocytes as compared to mature adipocytes. Mature adipocytes responded well to β-adrenergic agents, but no antilipolytic α2-adrenergic response was observed in the differentiated preadipocytes. The presence of Gi proteins in the differentiated preadipocytes was suggested by the antilipolytic effect of adenosine as well as the lipolytic activity generated by pertussis toxin. In conclusion, our medium supported the differentiation of a very high percentage of human preadipocytes which developed a sensitive β-adrenergic lipolytic response but which lacked an α2-adrenergic antilipolytic response. 相似文献
954.
The radiosensitivity of spermatogonial stem cells of C3H/HeH × 101/H F1 hybrid mice was determined by counting undifferentiated spermatogonia at 10 days after X-irradiation. During the spermatogenic cycle, differences in radiosensitivity were found, which were correlated with the proliferative activity of the spermatogonial stem cells. In stage VIIIirr, during quiescence, the spermatogonial stem cells were most radiosensitive with a D0 of 1.4 Gy. In stages XIirr−Virr, when the cells were proliferatively active, the D0 was about 2.6 Gy. Based on the D0 values for sensitive and resistant spermatogonia and on the D0 for the total population, a ratio of 45:55% of sensitive to resistant spermatogonial stem cells was estimated for cell killing.
When the present data were compared with data on translocation induction obtained in mice of the same genotype, a close fit was obtained when the translocation yield (Y; in % abnormal cells) after a radiation dose D was described by Y = eτD, with τ = 1 for the sensitive and τ = 0.1 for the resistant spermatogonial stem cells, with a maximal eτD of 100. 相似文献
955.
Organisms inhabiting metal-contaminated areas can be stressed by metal exposure and are possibly subject to selection, resulting
in increased metal tolerance and changes in growth and/or reproduction characteristics. In a previous study it was found that
in the terrestrial isopod Porcellio scaber, sampled from the vicinity of a zine smelter, the body size was small and the brood size was large compared to isopods from
a reference area. To assess whether these differences were due to genetic differentiation between strains, isopods collected
from a reference wood, a zinc smelter area and a lead mine were cultured on non-polluted food, while growth, reproduction
and metal concentrations were studied in first and second laboratory generations. The isopods from the three populations differed
in age and weight at first reproduction, although there were hardly any differences in growth. The females of the mine and
the smelter population started to reproduce earlier, at a lower weight, which resulted in fewer young per female. However,
reproductive allocation (=wight of young relative to the weight of the mother) was higher in mine and smelter isopods. We
conclude that the isopods at the metal-contaminated sites have been selected for early reproduction and increased reproductive
allocation. The results indicate that populations inhabiting metal-polluted sites have probably undergone evolutionary changes.
This study showed that growth and reproduction characteristics of different populations under laboratory conditions may provide
information on selection processes in the field. 相似文献
956.
The rate of senescence and the two-dimensional pattern of soluble proteins from detached oat leaves senescing in either darkness or light were analyzed, and compared to those of leaves in which senescence was delayed by application of the cytokinin benzyladenine or enhanced through the action of abscisic acid.Senescence of detached leaves in light did not differ significantly from senescence in attached leaves on intact plants. In darkness, protein was lost at a higher rate than in light, but several individual proteins showed relative increases. Notably, proteins previously characterized as high-molecular-weight proteins and senescence-associated proteins (Klerk et al., 1992) increased. Changes observed during incubation in light or darkness appeared to be related to this condition rather than the rate or progress of senescence. Cytokinins delayed and abscisic acid accelerated the changes in protein pattern compared to water. Beside changes previously identified in leaves senescing on the plant, detached leaves show alterations that reflect their condition of incubation rather than their developmental progress.Abbreviations 2D-PAG
two-dimensional polyacrylamide gel electrophoresis
- ABA
abscisic acid
- BA
N6-benzyladenine
- BSA
bovine serum albumin
- EDTA
ethylenediamine tetraacetic acid
- IEF
isoelectric focusing
- Rubisco
ribulosebisphosphate carboxylase/oxygenase
- SDS
sodium dodecyl sulfate
- Tris
tris (hydroxymethyl) aminomethane 相似文献
957.
[3H]iso-Pentenyladenine ([3H]iP) was fed for 24 h to the tips of intact and root tip-decapitated Pinus pinea seedlings. Twelve and 24 h after application to the roots of intact plants most of the applied radioactivity (±60%) was transported to the shoot. Root tip removal increased transport of the applied radioactivity to the shoot, but the overall pattern of distribution of radioactivity in the seedling did not change. Large amounts of radioactivity were recovered from the elongation zone of the root. Some radioactivity also accumulated in the older part of the root with well-developed lateral roots. When [3H]iP was applied one day after decapitation, no significant changes in the pattern of radioactivity distribution were found between the intact and decapitated root systems. However, when applied 7 days after decapitation there was a significant increase of radioactivity in the region of the root where lateral roots were emerging. HPLC separation of extracts from the different root sections showed that [3H]iP was extensively metabolized in the root. Six peaks of radioactivity, which co-chromatographed with authentic cytokinin standards, were detected.Abbreviations ABA
abscisic acid
- ADE
adenine
- IAA
indole-acetic acid
- iP
iso-pentenyladenine
- HPLC
high performance liquid chromatography
- [OG]DHZ
O-glycosyldihydrozeatin
- [9R-MP]DHZ
ribosyldihydrozeatin monophosphate
- [9G]iP
iso-pentenyladenine-9-glucoside
- [9R]Z
ribosylzeatin
- [9R]iP
iso-pentenyladenosine
- TLC
thin layer chromatography 相似文献
958.
M. Danin S. J. Upfold N. Levin B. L. Nadel A. Altman J. van Staden 《Plant Growth Regulation》1993,12(3):245-254
The effect of inhibitors of polyamine biosynthesis on the development of embryogenic cell cultures of celery (Apium graveolus L.) was studied. Several developmental stages of somatic embryos were compared for differences in the content and biosynthesis of free polyamines and for cytokinin content. Cyclohexylamine and particularly methylglyoxal bis(guanylhydrazone), inhibited both cell division and the organization of polar embryos from globular embryos. Difluoromethylornithine slightly promoted embryo development, especially cell division.The free putrescine content of globular embryos was 6-fold that of fully differentiated plantlets, and that of spermidine 2-fold. Only a slight increase in the spermine content was found with embryo development. These differences were confirmed by data from polyamine biosynthesis. Incorporation of 14C-arginine into polyamines was slightly higher than that of 14C-ornithine. Over 96% of this incorporation was detected in the putrescine fraction. Incorporation of 14C into putrescine in globular embryos was 3 to 4-fold that in fully-differentiated plantlets. Incorporation into spermidine and spermine was, however, higher in plantlets than in globular embryos.Cytokinin analysis revealed considerable differences in the biological activity between the developmental stages of embryogenesis. This could be due to endogenous cytokinins and/or BA taken up from the maintenance medium. Cytokinin levels decreased with increased embryo development. Most of the detected cytokinin-like activity co-chromatographed with BA and its metabolites. Some as yet unidentified peaks of activity were recorded in the globular embryos.The results are considered with respect to the possible participation of polyamines and cytokinins in the development of embryogenic cell cultures of celery. It is suggested that the onset of embryogenesis is characterized by a high content of putrescine and cytokinins, while a decrease in putrescine synthesis and cytokinin content, and an increase in spermidine and spermine content, accompany further embryo development and plantlet formation.Abbreviation ADC
arginine decarboxylase
- ODC
ornithine decarboxylase
- 2,4-D
dichlorophenoxyacetic acid
- DFMA
difluoromethylarginine
- DFMO
difluoromethylornithine
- MGBG
methylglyoxal bis(guanylhydrazone)
- CHA
cyclohexylamine
- BA
benzyladenine
- BAR
benzyladenine riboside 相似文献
959.
M. V. Wright N. Elwess J. van Houten 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1993,163(4):288-296
Intracellular Ca2+ levels in Paramecium must be tightly controlled, yet little is understood about the mechanisms of control. We describe here indirect evidence that a phosphoenzyme intermediate is the calmodulin-regulated plasma membrane Ca2+ pump and that a Ca2+-ATPase activity in pellicles (the complex of cell body surface membranes) is the enzyme correlate of the plasma membrane pump protein. A change in Ca2+ pump activity has been implicated in the chemoresponse of paramecia to some attractant stimuli. Indirect support for this is demonstrated using mutants with different modifications of calmodulin to correlate defects in chemoresponse with altered Ca2+ homeostasis and pump activity.Abbreviations EGTA
ethyleneglycol tetra-acetate
- ER
endoplasmic reticulum
- IBMX
isobutyl methylxanthine
-
I
che
index of chemokinesis
- Mops
3-[N-morpholino] propanesulfonic acid
- PEI
phosphoenzyme intermediate
- STEN
sucrose, TRIS, EDTA, sodium chloride
- TCA
trichloroacetic acid
- TRIS
tris[hydroxymethyl] aminomethane 相似文献
960.
Although it is well established that the predatory mite Phytoseiulus persimilis Athias-Henriot responds to odour emanating from leaves infested by its phytophagous prey, the two-spotted spider mite Tetranychus urticae Koch, little is known of the behavioural mechanisms elicited by odour perception and how they contribute to finding the prey. In this paper the influence of prey-related odour on orientation to wind direction is discussed. It was analysed by observing the predator's walking paths in still air and in an air stream uniformly permeated either with or without prey-related odour stimuli. The results show that well-fed predator females move upwind in presence of these stimuli, but downwind otherwise. Starved predators always move upwind. The anemotactic responses observed are therefore both odour-conditioned and (feeding) state-dependent.In an attempt to explain these responses it is argued that the anemotactic responses of well-fed predators may contribute to arrestment within the area marked by a cluster of prey-colonized leaves. The anemotactic responses of starved predators may help them to find clusters of spider mite colonies located upwind. Why predatory mites also move upwind in absence of prey-related odour stimuli, is a question that remains to be answered. 相似文献