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81.
Six-year-old cloned Betula pubescens Ehrh. trees, grown outdoors at 65 degrees 01' N, were cut on six dates during the growing season to study coppice shoot development in relation to root-produced cytokinin-like compounds. Bleeding sap was collected over timed intervals for two days after cutting, and endogenous cytokinin-like compounds were measured by ELISA assay in HPLC-purified fractions of xylem sap. Initiation and development of coppice shoots on the clonally propagated plants were comparable to those in seedlings. Coppice shoot initiation was affected by the time of cutting, diminishing significantly after June. Of the cytokinin-like compounds detected in the xylem sap, zeatin riboside-like (ZR) compounds were present in the highest concentrations, and the concentrations of dihydrozeatin riboside-like (DHZR) and isopentenyladenoside-like (IPA) compounds were approximately one third and one eighth of the ZR concentrations, respectively. The concentration of cytokinin-like compounds was positively correlated with xylem sap flow rate. The export of cytokinin-like compounds, especially DHZR- and ZR-types, was positively correlated with the initiation and elongation rate of coppice shoots, the number of lateral branches, and the radial growth of the more slowly growing coppice shoots. The export of cytokinin-like compounds collected immediately after cutting may represent the basal value for each tree. This value is probably affected by the size and activity of the root system and may be a relevant estimate for predicting the success of coppicing. 相似文献
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Hellemans A 《Science (New York, N.Y.)》1994,266(5182):26-27
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Waner T Nyska A 《Veterinary clinical pathology / American Society for Veterinary Clinical Pathology》1994,23(3):78-80
Serum concentrations of glucose, cholesterol, triglycerides, and serum alkaline phosphatase activity were measured over different periods of time of food deprivation in male rats. Thirty percent of non-fasted rat's sera was found to be lipemic. At 16 hours of fasting, glucose levels dropped by 30% compared to the level of the non-fasting control group, and remained at a relatively constant level for up to 48 hours of fasting. Triglyceride concentrations decreased at 16 hours after fasting. Serum cholesterol levels were not changed at any of the fasting periods compared to the non-fasted control group. Alkaline phosphatase activity was decreased at 8 hours of fasting, with further declines in activity of the serum enzyme seen at 16, 24, and 48 hours of fasting. It was concluded that at 16 to 18 hours fasting, a non-absorptive state had been reached in male rats. 相似文献
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