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101.
Drought stress and recovery of riparian cottonwoods due to water table alteration along Willow Creek,Alberta 总被引:5,自引:0,他引:5
A 5-m-deep gravel pit was excavated from 1996 to 1998 in the floodplain between Willow Creek, Alberta, and a grove of balsam poplars ('cottonwoods', Populus balsamifera L.) and water level at the pit was lowered 2.5 m through pumping. This interrupted the infiltration of stream water into the riparian groundwater and imposed drought stress on the cottonwoods. Trees in the drought-affected grove displayed extensive leaf senescence and abscission in late August 1998, while trees in nearby control groves remained green until autumnal senescence in late September. The precocious senescence was accompanied by a two-thirds reduction in leaf stomatal conductance (g s) but mid-day leaf xylem water potentials (ψl) were only slightly reduced (?1.55 vs 1.42 MPa). Pumping ceased in 1999, the pit was partially refilled, and the hydraulic linkage between the stream and the riparian zone recovered. Subsequently in August 1999, g s and ψl were similar for trees in the affected and control groves and senescence phenologies were similar in 1999 and 2000. Annual branch growth increments varied 3-fold across years between 1994 and 1999, but there was no reduction in these growth increments in the drought-affected trees in 1998 or 1999. This study supports the hydraulic linkage between a stream and the adjacent riparian zone in a semi-arid region and demonstrates the vulnerability of riparian cottonwoods to drought due to water table depletion. It also indicates rapid physiological recovery of cottonwoods following restoration of water availability. 相似文献
102.
Long W Wagner KU Lloyd KC Binart N Shillingford JM Hennighausen L Jones FE 《Development (Cambridge, England)》2003,130(21):5257-5268
The ERBB family of type 1 receptor tyrosine kinases and their ligands have crucial functions during mammopoiesis, but the signaling networks that ultimately regulate ERBB activity in the breast have remained elusive. Here, we show that mice with Cre-lox mediated deletions of both Erbb4 alleles within the developing mammary gland (Erbb4(Flox/Flox)Wap-Cre) fail to accumulate lobuloalveoli or successfully engage lactation at parturition owing, in part, to impaired epithelial proliferation. Analysis of the mammary differentiation factor STAT5 by immunohistochemistry and western blot revealed a complete ablation of STAT5 activation in Erbb4(Flox/Flox)Wap-Cre mammary epithelium at parturition. Consistent with disrupted STAT5 function, Erbb4(Flox/Flox)Wap-Cre mammary glands at parturition failed to express the mammary epithelial differentiation marker NPT2B. Defects in epithelial functional differentiation at parturition were accompanied by a profound reduction in expression of the STAT5-regulated milk genes casein beta and whey acidic protein. We propose that ERBB4 functions as an essential mediator of STAT5 signaling, and that loss of STAT5 activity contributes to the impaired functional differentiation of mammary glands observed in mice containing conditional Erbb4 deletions. 相似文献
103.
Wegrowski Y Gillery P Kotlarz G Perreau C Georges N Maquart FX 《Molecular and cellular biochemistry》2000,205(1-2):125-131
Cell culture in collagen lattice is known to be a more physiological model than monolayer for studying the regulation of extracellular matrix protein deposition. The synthesis of sulfated glycosaminoglycans (GAG) and dermatan sulfate (DS) proteoglycans by 3 cell strains were studied in confluent monolayers grown on plastic surface, in comparison to fully retracted collagen lattices. Cells were labelled with35S-sulfate, followed by GAG and proteoglycan analysis by cellulose acetate and SDS-polyacrylamide gel electrophoresis, respectively. The 3 cell strains contracted the lattice in a similar way. In monolayer cultures, the major part of GAG was secreted into culture medium whereas in lattice cultures of dermal fibroblasts and osteosarcoma MG-63 cells but not fibrosarcoma HT-1080 cells, a higher proportion of GAGs, including dermatan sulfate, was retained within the lattices. Small DS proteoglycans, decorin and biglycan, were detected in fibroblasts and MG-63 cultures. They were preferentially trapped within the collagen gel. In retracted lattices, decorin had a higher Mr than in monolayer. Biglycan was detected in monolayer and lattice cultures of MG-63 cells but in lattice cultures only in the case of fibroblasts. In this last case, an up regulation of biglycan mRNA steady state level and down regulation of decorin mRNA was observed, in comparison to monolayers, indicating that collagen can modulate the phenotypical expression of small proteoglycan genes.Supported by a fellowship from the Centre National de la Recherche Scientifique 相似文献
104.
Common theories of microbial growth and physiology are formulated exclusively in terms of the isolated microorganisms – especially bacteria. This is, however, an inadmissible simplification because it is obvious that the organization of microbial populations and colonies follows certain general rules. Bacterial colonies are able to generate complex interfacial growth patterns similar to those observed during diffusion-limited growth processes in non-living systems. One reason for these patterns is assumed to be the ability of many bacteria to swarm in an active manner on a substrate surface. Therefore the models of bacterial colony growth incorporate “random walkers”, which move actively in response to a gradient in the concentration of nutrients and communicate with each other by means of a chemotactic feedback. A selected number of yeasts were tested with regard to their colony growth patterns depending on the medium parameters such as nutrient concentration. Growth patterns similar to those which were described in literature for bacteria were also found in these experiments. It concerns in particular growth types like compact growth, fractal growth and dense-branching growth. This result allows a hypothesis to be formulated, that – especially in the case of fractal growth patterns – wandering of cells on a substrate surface may be induced by uncontrolled “swimming” on a thin water film caused by the metabolic activity (e.g. respiration) of the cells on the surface of the agar. Furthermore it was found that an interplay between changes in the individual morphology of yeast cells and the morphology transitions takes place. Such growth patterns are known for Candida sp. which are able to form pseudomycel and blastospores. 相似文献
105.
106.
Peter I. Duncan Grigorios Fotopoulos Elisabeth Pasche Nadine Porta Isabelle Masserey Elmelegy Jose-Luis Sanchez-Garcia Gabriela E. Bergonzelli & Irène Corthésy-Theulaz 《FEMS microbiology letters》2009,295(2):218-225
Clostridium difficile is responsible for a large proportion of nosocomial cases of antibiotic-associated diarrhoea and pseudomembranous colitis. The present study provides evidence that yeast, beef and pork extracts, ingredients commonly used to grow bacteria, can counteract C. difficile toxin A enterotoxicity in vitro and in vivo . In model intestinal epithelial cells the individual extracts could prevent the toxin A-induced decrease in epithelial barrier function and partially prevented actin disaggregation and cell rounding. Mice with ad libitum access to individual extracts for 1 week had almost complete reduction in toxin A-induced fluid secretion in intestinal loops. Concomitantly, the toxin A-induced expression of the essential proinflammatory mediator Cox-2 was normalized. Moreover this protective effect was also seen when mice received only two doses of extract by intragastric gavage within 1 week. These results show that yeast, beef and pork extracts have the potential to counteract the intestinal pathogenesis triggered by C. difficile toxin A. 相似文献
107.
Pierre Verhaeghe Nadine Azas Sébastien Hutter Caroline Castera-Ducros Michèle Laget Aurélien Dumètre Monique Gasquet Jean-Pierre Reboul Sylvain Rault Pascal Rathelot Patrice Vanelle 《Bioorganic & medicinal chemistry》2009,17(13):4313-4322
To identify a new safe antiplasmodial molecular scaffold, an original series of 2-trichloromethylquinazolines, functionalized in position 4 by an alkyl- or arylamino substituent, was synthesized from 4-chloro-2-trichloromethylquinazoline 1, via a cheap, fast and efficient solvent-free operating procedure. Among the 40 molecules prepared, several exhibit a good profile with both a significant antiplasmodial activity on the W2 Plasmodium falciparum strain (IC50 values: 0.4–2.2 μM) and a promising toxicological behavior regarding human cells (HepG2/W2 selectivity indexes: 40–83), compared to the antimalarial drug compounds chloroquine and doxycycline. The in vitro antitoxoplasmic and antileishmanial evaluations were conducted in parallel on the most active molecules, showing that these ones specifically display antiplasmodial properties. 相似文献
108.
Türkân Saknç Britta Kleine Nadine Michalski Martin Kaase & Sören G. Gatermann 《FEMS microbiology letters》2009,301(1):28-34
The transferability of a large plasmid that harbors a tetracycline resistance gene tet (S), to fish and human pathogens was assessed using electrotransformation and conjugation. The plasmid, originally isolated from fish intestinal Lactococcus lactis ssp. lactis KYA-7, has potent antagonistic activity against the selected recipients ( Lactococcus garvieae and Listeria monocytogenes ), preventing conjugation. Therefore the tetracycline resistance determinant was transferred via electroporation to L . garvieae . A transformant clone was used as the donor in conjugation experiments with three different L. monocytogenes strains. To our knowledge, this is the first study showing the transfer of an antibiotic resistance plasmid from fish-associated lactic bacteria to L. monocytogenes , even if the donor L. garvieae was not the original host of the tetracycline resistance but experimentally created by electroporation. These results demonstrate that the antibiotic resistance genes in the fish intestinal bacteria have the potential to spread both to fish and human pathogens, posing a risk to aquaculture and consumer safety. 相似文献
109.
110.
Whole‐cell biotransformation of oleanolic acid by free and immobilized cells of Nocardia iowensis: Characterization of new metabolites
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Benjamin Ludwig Doris Geib Christiane Haas Juliane Steingroewer Thomas Bley Kai Muffler Roland Ulber 《Engineering in Life Science》2015,15(1):108-115
In this study, Nocardia iowensis was used to transform oleanolic acid (OA) into oleanane derivatives. The first derivative, which was found after 24 h of cultivation, was the known and already described OA methyl ester. After 1 week, two other derivatives (oleanonic acid methyl ester and an unknown metabolite) were identified as new products of a biotransformation by N. iowensis. These oleanane metabolites were characterized by HPLC, HPLC‐ESI‐MS, and HPLC‐1H NMR spectroscopy. The biotransformation was performed by suspended and immobilized cells (ICs) of N. iowensis. Cells immobilized in alginate beads were used in order to prepare a continuous process. The substrate uptake of free and ICs was similar, whereas the peak area of OA methyl ester of the ICs was only about 10% of the native cells. However, the final product (oleanonic acid methyl ester) concentrations were similar in both approaches, whereas the unknown metabolite 3 was only detected transiently in the medium of ICs. Based on these results, a new biosynthetic pathway for the biotechnological production of oleanonic acid methyl ester is proposed. 相似文献