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In the leaf succulent Asclepiad Hoya carnosa (L.) R. Br., CAM photosynthesis occurred under well-watered conditions, as characterized by diurnal gas exchange and changes in titratable acidity. Following 10–12 days of severe water stress, the plants shifted from CAM to a modified CAM-idling mode of metabolism. CAM-idling was characterized by complete or almost complete stomatal closure accompanied by CAM-like diurnal changes in titratable acidity. H. carnosa plants maintained this CAM-idling mode of photosynthesis for at least 8 weeks. Upon reirrigation, the plants returned to the original CAM mode within 1 week. These results suggested that CAM-idling is a reversible, intermediate form of sustained metabolism which enables plant survival under conditions of extended drought.This work was supported in part by NSF Grant PCM 8200366 and in part by the Science and Education Administration of the United States Department of Agriculture under Competitive Grant 5901-0420-8-0018-0. 相似文献
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Cristina Rinaldi-Garaci Enrico Garaci Vera Del Gobbo Cartesio Favalli Teresa Jezzi Allan L. Goldstein 《Cellular immunology》1983,80(1):57-65
The effects of thymosin-α1 on the stimulation of specific release of prostaglandin E2 (PGE2) from splenic lymphocytes and thymocytes were studied. Experiments were also performed to study in parallel the absolute levels of thymosin-α1 in the blood and the induction of serum FTS activity and of azathioprine sensitivity of spleen cells from adult thymectomized (ATx) mice. A significant difference in the release of PGE2 between normal splenocytes and splenocytes from ATx mice was observed. Thymosin-α1 at certain concentrations was able to stimulate PGE2 release from lymphocytes of ATx mice while inhibiting release in lymphocytes of normal mice. Also, thymocytes were stimulated to release PGE2 after incubation with α1 in a manner similar to that seen in spleen cells of ATx mice. Approximately the same concentration of α1 was found to also correct the low azathioprine sensitivity of splenocytes from ATx mice. Determinations of FTS-like activity in the blood and the pharmacokinetics of α1 after administration of this synthetic molecule show a clear dissociation. A maximum peak of α1 activity was obtained after 1 hr, while maximal FTS-like activity was observed after 24 hr. The inhibition of the induction by α1 of FTS-like activity and of Thy 1.2 antigen by indomethacin suggests that the action of α1 requires prostaglandin biosynthesis. 相似文献
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Unequal synthesis of globin chains after extended incubation of rabbit reticulocytes with L-O-methylthreonine 总被引:1,自引:0,他引:1
Rabbit reticulocytes were incubated in vitro as long as 20 hr with l-O-methyl threonine, the OMT was removed, and the capacity of the cells to synthesize α- and β-globin chains was determined. After 20 hr incubation in vitro, OMT-treated cells can make β chains about twice as well as cells incubated for 20 hr without OMT. However, the capacity of OMT-treated cells to synthesize α chains was only about 60% that of cells incubated without OMT for 20 hr. These results suggest that the capacity of reticulocytes to produce a specific globin chain after an in vitro incubation correlates positively with the number of ribosomes associated with the specific messenger RNA for that chain during the incubation. 相似文献
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