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51.
52.
The aerial parts of P. canadensis afforded a new germacran-8,12-olide and several diterpenic acids. The stereochemistry of the lactone could be established only by careful 1H NMR investigations of the corresponding pyrazolines formed by addition of diazomethane, while the natural compound and its acetate only show very uncharacteristic NMR spectra. The diterpenes all belong to the rare isokaurene type. The chemotaxonomic aspects are discussed briefly. 相似文献
53.
Ferdinand Bohlmann Christa Zdero Wolf-Rainer Abraham Antoinette Suwita Michael Grenz 《Phytochemistry》1980,19(5):873-879
The investigation of 25 further Helichrysum species afforded in addition to known compounds a new diterpene, an oxo-geranyllinalol, a second one, most probably a cembrene derivative, and three dihydrochalkone derivatives. The distribution of the constituents in South African Helichrysum species is discussed briefly. 相似文献
54.
Ferdinand Bohlmann Christa Zdero Robert M. King Harold Robinson 《Phytochemistry》1980,19(12):2663-2668
The investigation of three Eremanthus species afforded, in addition to known compounds, several new sesquiterpenelactones, a cumambrin B isobutyrate, four lactones related to the eremantholides, two to zexbrevin and one to goyazensolide. Furthermore, a new coniferyl alcohol derivative was isolated. The overall picture of the genus is very uniform. The occurrence of eremanthine and germacranolides with a furanone ring seems to be especially typical. 相似文献
55.
Atretic follicles regularly occur in the ovary of the house fly, Musca domestica. The frequency of ovarian follicular atresia and the proportion of atretic follicles per ovary are related to the stage of oögenesis and to the age of the females. Only vitellogenic follicles may become atretic. The atresia may occur at any stage of vitellogenesis, though most follicles become atretic in mid-vitellogenesis. Atretic follicles are completely resorbed within 24–36 hr. The follicle cells may play a synthesizing role during growth and disintegrating one during follicle resorption. The induction of glycogen synthesis by the cessation of RNA and protein synthesis and by vitellogenesis in normal follicles is discussed. The same processes occur prematurely in the atretic follicle which can be thus distinguished by a high content of glycogen. 相似文献
56.
57.
Repression of Diaminopimelic Acid Decarboxylase in Escherichia coli: Gene Dosage Effects and Escape Synthesis 总被引:1,自引:1,他引:0
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Gene dosage and escape synthesis experiments support the hypothesis that diaminopimelate decarboxylase repression by lysine involves a repressor molecule in a negative control system. 相似文献
58.
The biology of insularity: an introduction 总被引:5,自引:0,他引:5
Donald R. Drake Christa P. H. Mulder David R. Towns & Charles H. Daugherty 《Journal of Biogeography》2002,29(5-6):563-569
59.
Nitrogenase activity in composting horse bedding and leaves 总被引:1,自引:1,他引:0
To date little or no nitrogen fixation has been found in composting materials. However, some materials have high C:N ratios and thus might be expected to support nitrogen fixation. We examined windrows of composting horse bedding and leaves for nitrogenase activity via acetylene reduction and used carbon monoxide controls to differentiate ethylene evolved by nitrogenase from that evolved by endogenous processes. In both piles temperatures were substantially elevated and partial pressures of oxygen greatly reduced thus indicating vigorous microbial activity. In the horse bedding, there were only low rates of ethylene evolution and little of this was due to nitrogen fixation. In contrast, much higher rates of ethylene evolution were measured in the leaf pile and 94% of this was due to nitrogenase activity. We estimate that the leaf pile fixed approximately 0.062 mg N/g leaves during a 5-week period. 相似文献
60.
Abbracchio Maria P. Jacobson Kenneth A. Müller Christa E. Zimmermann Herbert 《Purinergic signalling》2020,16(2):137-149
Purinergic Signalling - 相似文献