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341.
Electrical activity was recorded from single cells in the olfactorybulb when electrically stimulating the medial and lateral olfactorytract and when stimulating the olfactory epithelium with aminoacids. Bulbar units excited by stimulation of the medial olfactorytract were found in the medial and middle parts of the bulb.Neurones in the dorso-lateral part of the bulb were excitedby stimulation of lateral tract. Units inhibited by stimulationof the lateral or medial olfactory tracts had a reversed distributionwith the majority found in the medial or lateral parts of thebulb respectively. The chemicals tested induced changes in thedischarge of units mainly situated in the lateral part of thebulb. 相似文献
342.
Dany S.S.L. Amaral Madelaine Venzon Marcus V.A. Duarte Fernanda F. Sousa Angelo Pallini James D. Harwood 《Biological Control》2013,64(3):338-346
Habitat manipulation has long been used as strategy to enhance beneficial insects in agroecosystems. Non-crop weed strips have the potential of supplying food resources to natural enemies, even when pest densities are low. However, in tropical agroecosystems there is a paucity of information pertaining to the resources provided by non-crop weeds and their interactions with natural enemies. In this study we evaluated (a) whether weeds within chili pepper fields affect the diversity and abundance of aphidophagous species; (b) whether there are direct interactions between weeds and aphidophagous arthropods; and (c) the importance of weed floral resources for survival of a native and exotic coccinellid in chili pepper agroecosystems. In the field, aphidophagous arthropods were dominated by Coccinellidae, Syrphidae, Anthocoridae, Neuroptera and Araneae, and these natural enemies were readily observed preying on aphids, feeding on flowers or extrafloral nectaries, and using plant structures for oviposition and/or protection. Survival of native Cycloneda sanguinea (Coleoptera: Coccinellidae) differed between plant species, with significantly greater survival on Ageratum conyzoides and Bidens pilosa. However, no evidence was gathered to suggest that weed floral resources provided any nutritional benefit to the exotic Harmonia axyridis (Coleoptera: Coccinellidae). This research has provided evidence that naturally growing weeds in chili pepper agroecosystems can affect aphid natural enemy abundance and survival, highlighting the need for further research to fully characterize the structure and function of plant resources in these and other tropical agroecosystems. 相似文献
343.
Werner G. Siems Anke Schwendel Tilman Grune Hermann-Georg Holzhütter Rolf Uhlig 《Cell biochemistry and function》1994,12(1):1-9
Mouse hepatocytes from healthy control mice and from Ehrlich ascites tumour-bearing mice were used for tracer-kinetic studies of purine catabolism of liver cells during different periods of tumour growth. The dynamics of the radioactive tracers were modelled mathematically by a system of differential equations. Computer simulations, i.e. direct fitting of numerical solutions of these equations to the observed time-courses of metabolites and specific radioactivites, enables one to estimate unknown kinetic parameters of a simplified model of pathways of hepatic purine catabolism in tumour-bearing mice. There occurred great differences of metabolic flux rates between control hepatocytes, hepatocytes of mice during the proliferating period of tumour growth (6th day after inoculation of the tumour) and hepatocytes of mice during the resting period of tumour growth (12th day after inoculation of the tumour). The final purine degradation of hepatocytes prepared during the proliferating period was lower in comparison with that of control hepatocytes, but it was markedly higher in hepatocytes prepared during the resting period of tumour growth. The changes in hepatocyte purine catabolism during the proliferating period of tumour growth argue for transitions which aim at the maintenance of high purine nucleotide levels in the liver itself rather than for an increased nucleoside and nucleobase supply for the tumour. This suggestion is in accordance with the increased ATP level of the liver during the proliferating phase of tumour growth. The drastic acceleration of the final steps of hepatic purine catabolism forming uric acid and allantoin during the resting period of tumour growth was predominantly due to increased flux rate from xanthosine and guanine in accordance with increased catabolism of monophosphorylated nucleotides. 相似文献
344.
G. L. Mendz Andrew J. Shepley Stuart L. Hazell Mark A. Smith 《Archives of microbiology》1997,168(6):448-456
The requirements for purine nucleotide synthesis, the effects of purine analogues, and the metabolism of adenine in the bacterium
Helicobacter pylori were investigated employing cell culture techniques and one-dimensional NMR spectroscopy. Bacterial cells grew and proliferated
in media lacking preformed purines, indicating that H. pylori can synthesize purine nucleotides de novo to meet its requirements. Blocking of this pathway in the absence of sufficient
preformed purines for salvage nucleotide synthesis led to cell death. Analogues of purine nucleobases and nucleosides taken
up by the cells were cytotoxic, suggesting that salvage routes could be exploited for therapy. Adenine or hypoxanthine were
able to substitute for catalase in supporting cell growth and proliferation, suggesting a role for these bases in maintaining
the microaerophilic conditions essentially required by the bacterium.
Received: 23 May 1997 / Accepted: 17 July 1997 相似文献
345.
Microbial Synthesis of Antiviral Nucleosides Using Escherichia coli BL21 as Biocatalyst 总被引:5,自引:0,他引:5
Marí a C. Rogert Jorge A. Trelles Silvia Porro Elizabeth S. Lewkowicz Adolfo M. Iribarren 《Biocatalysis and Biotransformation》2002,20(5):347-351
Experimental conditions such as shaking (aeration) rate, concentration of reagents and extent of culture growth for the optimal synthesis of adenosine using Escherichia coli BL21 as biocatalyst were assessed, achieving 95% yield in 30 min of reaction using microorganisms harvested from late exponential phase. The ability of E. coli BL21 to synthesise purine nucleosides containing sugar residues such as 2'-deoxyribose, 2',3'-dideoxyribose and arabinose was also verified. 2'-Deoxyribo- and arabinonucleosides could be prepared in high yield, while the results obtained with 2',3'-dideoxyribonucleosides were not satisfactory. In the case of 2'-deoxyadenosine, using thymidine as a starting material, a yield of 94% was achieved at 45°C. 相似文献