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991.
Summary We used lambda and plasmid vectors containing the am
+ gene in an insert of from 2.7 to 9.1 kb, to transform am point mutant and deletion strains. A total of 199 transformants were examined with the potential to yield am
– transformants by homologous recombination. When we used vectors that had 9.1 kb of homology with the chromosomal DNA, 30% of the transformants obtained were the result of homologous recombination regardless of whether the vector was a lambda molecule, a circular plasmid, or a plasmid that had been linearized prior to transformation. When vectors with up to 5.1 kb of homology were used, very few transformants (1 of 89 tested) resulted from homologous recombination. Of a sample of 29 ectopic integration events obtained by transformation with the 9.1 kb fragment cloned in a vector, 18 included a major part (usually almost all) of both arms of lambda with the entire Neurospora 9.1 kb insert between them. Four included only long arm sequence together with an adjacent segment of the insert containing the am gene. The remaining seven were the result of multiple integrations. There was no evidence of circularization of the vector prior to integration. All transformants that had multiple copies of the am gene appeared to be subject to the RIP process, which causes multiple mutations in duplicated sequences during the sexual cycle. 相似文献
992.
993.
Control of barley root respiration 总被引:8,自引:0,他引:8
Evidence from barley [ Hordeum distichum (L.) Lam. cv. Maris Mink], and from many other species, suggests that respiration is controlled by either supply of carbohydrate or demand for ATP. The relationship between root respiration rate (measured as O2 consumption or CO2 production) and ethanol-soluble carbohydrate content altered with time following selective pruning, and the change could not be accounted for by buffering of the cytoplasmic carbohydrate concentration by sugars in the vacuole. Exogenous sucrose supplied to the roots prevented any decline of the respiration rate in shoot-pruned plants, and if supplied for 24 h stimulated the respiration rate after any treatment. Root extension responded to sucrose in a similar manner. We suggest that respiration is under fine control by adenylates, but the capacity of the respiratory system is fixed by the supply of sucrose, possibly via coarse control of the respiratory machinery, or of the processes requiring metabolic energy. 相似文献
994.
995.
996.
Leslie matrix simulations were performed, employing idealized ungulate life histories and density-independent, either random or periodic, variation in calf survival, p0. Long-term average rate of increase was reduced whenever variation was added to p0. The iteroparous life histories strongly buffered high-frequency vital rate variations, so that large fluctuations in p0 resulted in relatively small fluctuations in population size. The buffering effect was greatest for species with the longest lifespans. The results suggest that wild ungulate populations will not fluctuate greatly in response to density-independent, environmental-driven vital rates. Such populations will reach high densities, thus experiencing strong density-dependent regulation, only a few times in many generations. 相似文献
997.
Lisa J. Samuelson Ben H. Cazell John R. Seiler 《Environmental and Experimental Botany》1990,30(4):469-473
The use of nitrogen-fixing trees such as black alder (Alnus glutinosa L. Gaertn.) as forest silvicultural tools has recently been recognized. The potential benefit of black alder in silvicultural practices may be reduced by nitrate fertilization. Fifteen-month-old, nodulated, black alder rooted cuttings were fertilized for 6 days with 0, 7.5 or 15 mM NO3 to determine the influence of nitrate on acetylene reduction, nodule respiration and net photosynthesis. Acetylene reduction, net photosynthesis and nodule respiration were measured on the second, fourth and sixth days of nitrate application. Nitrate treatment significantly reduced acetylene reduction and nodule respiration by day 4. Acetylene reduction was 75% lower and nodule respiration 36% lower for the 15 mM NO3 treatment when compared to that of the control treatment. By day 6, net photosynthesis and nodule respiration were significantly reduced by 29 and 59%, respectively, for seedlings treated with 15 mM NO3. This study suggests that nitrate fertilization has a profound influence on nitrogenase activity and that nitrogen-fixing tree species may respond to nitrate fertilization by shifting photosynthetic rates. 相似文献
998.
H L Bank J John M K Schmehl R J Dratch 《Applied and environmental microbiology》1990,56(12):3888-3889
Studies were designed to evaluate the effectiveness of pulsed modulated UV light waveforms for killing bacteria. Exposure of five strains of bacteria to the modulated information encoded in the light decreased the colony population from a confluent lawn to less than 20 colonies. However, approximately 2,000 colonies survived treatment with the same intensity and time of exposure to UV light lacking the modulated information. 相似文献
999.
1000.