Regulation of urease activity in Rhizobium meliloti

Abstract Using an ureC-lacZ fusion, the expression of urease structural genes of the soil bacterium Rhizobium meliloti strain AK631 was studied in response to different nitrogen sources and nickel contents in the growth medium. The expression of urease genes is repressed by ammonia and is not inducible by urea. Urease activity depends on the nickel concentration of the medium. Nickel uptake is repressed in medium containing ammonia and is not affected by the genes located in the urease operon investigated.     

DasFestuca vivipara-Problem in den Alpen

The differences betweenFestuca vivipara (tetraploid) andF. ovina subsp.supina (diploid), two often confused taxa, are demonstrated in regard to morphology, leaf anatomy, ecology and distribution. New maps illustrate the distribution ofF. vivipara in the Alps and the Northern Hemisphere. The development of different polyploidy levels withinF. vivipara as a consequence of occasional sexual processes is discussed. (English Summary on p. 39.)

     

Harn-steroidprofile hirsuter frauen

Urine steroid profiles of hirsute womenSteroid profiles of women suffering from idiopathic hirsutism show in more than 50% of the cases a 10–100 fold increase in the excretion of dehydroepiandrosterone (DHEA) compared with normal values.The excretion of DHEA was reduced much more than that of other 17-ketosteroids if the adrenals (NNR) were suppressed by dexamethasone (DXM). Within one week they reached values at the compound noise level of the gas chromatograms. If the ovaries were stimulated with human chorionic gonadotropin during continued suppression of the NNR with DXM no increase of DHEA could be detected.     

Zur Mutagenit?t von Urethanen

Summary By making a tongue-slit in the shaft of the inflorescence ofArabidopsis thaliana 7 different urethanes (1/200 mol+1/200 mol KCl) were forced into the buds through the transpiration stream. After this treatment with 6 of these substances the frequency of the monohybrid segregating mutations was significantly raised 5- to 10times over the control as determined by seedling tests.The mutation frequency was positively correlated with the size of the urethan molecule and seemed to be little affected by its chemical substitution. The mutants were of the same type than those obtained after irradiation with X-rays.These results are in agreement with the conception that the mutagenic effect of the urethanes is indirect and probably due to general disturbances of different metabolic processes in the cell.

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