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1.
Evidence is presented which supports the postulate that the photobilirubins IIA and IIB are diastereoisomers in which the C-3 vinyl group has cyclized intramolecularly. The evidence comes principally from proton n.m.r. spectroscopy at 400 MHz and from chemical considerations. The cyclic structures require the E-configuration at the C-4 double bond in the precursor; this is the first structural evidence for the Z leads to E isomerization in bilirubin and supports the view that the precursor (photobilirubin IA or IB) is (4E, 15Z)-bilirubin. Brief irradiation of photobilirubin II gives bilirubin, a new compound (photobilirubin III) and unchanged starting material. The various photoisomers are discussed in terms of their inter-relationships and biological fates. 相似文献
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Waltraud Kofer Kristina Glimelius Howard T. Bonnett 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1991,81(3):390-396
Summary Fusion of two cytoplasmic male-sterile cultivars of Nicotiana tabacum, one with N. bigelovii cytoplasm and one with N. undulata cytoplasm, resulted in the restoration of male fertility in cybrid plants. All male-fertile cybrids exhibited fused corollas, which is characteristic for the cultivar with N. undulata cytoplasm, while their stamen structures varied from cybrid to cybrid, some producing stamens with anthers fused to petal-like appendages and one producing stamens of a normal appearance for N. tabacum. Restriction enzyme digestion and agarose gel electrophoresis of mitochondrial DNA showed that mitochondrial DNA of the fertile cybrids was more similar to the male-sterile cultivar with the cytoplasm of N. undulata than to the cultivar with N. bigelovii cytoplasm. Some restriction fragments were unique to the male-fertile cybrids. Comparisons between stamen structure and mitochondrial DNA for eight fertile progeny from one cybrid plant led to the identification of several restriction fragments that appeared at enhanced levels in connection with normal stamen development. 相似文献
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The fine structure of young root hairs of radish was studied, with special attention to cytoplasm-wall relationships. Hairs up to 130 µ in length were examined after fixation of root tips in glutaraldehyde followed by osmium tetroxide. Microtubules occur axially aligned in the cytoplasm just beneath the plasmalemma, and extend from the base of the hair to within 2 to 3 µ of the tip. Poststaining with uranyl acetate and lead citrate clearly reveals in thin sections the presence of the two layers of cellulose microfibrils known from studies on shadowed wall preparations: an outer layer of randomly arranged microfibrils arising at the tip, and a layer of axially oriented microfibrils deposited on the inside of this layer along the sides. The youngest microfibrils of the inner, oriented layer first appear at a distance of about 25 µ from the tip. Although the microfibrils of the inner layer and the adjacent microtubules are similarly oriented, the oriented microtubules also extend through the 20- to 25-µ zone near the tip where the wall structure consists of random microfibrils. This suggests that the role of microtubules in wall deposition or orientation may be indirect. 相似文献
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R Bonnett D G Buckley D Hamzetash G E Hawkes S Ioannou M S Stoll 《The Biochemical journal》1984,219(3):1053-1056
An improved preparation of photobilirubin II in ammoniacal methanol is described. Evidence is presented which distinguishes between the two structures proposed earlier for photobilirubin II in favour of the cycloheptadienyl structure. Nuclear-Overhauser-enhancement measurements with bilirubin IX alpha and photobilirubin II in dimethyl sulphoxide are complicated by the occurrence of negative and zero effects. The partition coefficient of photobilirubin II between chloroform and phosphate buffer (pH 7.4) is 0.67. 相似文献
7.
The deposition of radiocaesium from nuclear weapons testing and the Chernobyl accident upon the Llyn Llygad Rheidol catchment in mid-Wales is described. Inventories of soil cores from the catchment support estimates of total atmospheric fallout. The mean inventory of weapons testing 137Cs in lake sediment cores is broadly similar to that in soil cores. The inventory of Chernobyl fallout in sediment cores is significantly lower and raises questions concerning the residence time of 137Cs in the catchment soils and lake waters. 137Cs and 241Am activities in a sediment core record the 1963 peak of fallout from nuclear weapons testing. The association of the peak activities of 137Cs and 241Am in the sediments with the falloot maximum is confirmed by 210Pb dating. The 210Pb dates also reveal a significant increase in sediment accumulation rates over the past 20 years. 相似文献
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S. A. F. Bonnett M. S. A. Blackwell R. Leah V. Cook M. O'Connor E. Maltby 《Geobiology》2013,11(3):252-267
Soils are predicted to exhibit significant feedback to global warming via the temperature response of greenhouse gas (GHG) production. However, the temperature response of hydromorphic wetland soils is complicated by confounding factors such as oxygen (O2), nitrate () and soil carbon (C). We examined the effect of a temperature gradient (2–25 °C) on denitrification rates and net nitrous oxide (N2O), methane (CH4) production and heterotrophic respiration in mineral (Eutric cambisol and Fluvisol) and organic (Histosol) soil types in a river marginal landscape of the Tamar catchment, Devon, UK, under non‐flooded and flooded with enriched conditions. It was hypothesized that the temperature response is dependent on interactions with ‐enriched flooding, and the physicochemical conditions of these soil types. Denitrification rate (mean, 746 ± 97.3 μg m?2 h?1), net N2O production (mean, 180 ± 26.6 μg m?2 h?1) and net CH4 production (mean, 1065 ± 183 μg m?2 h?1) were highest in the organic Histosol, with higher organic matter, ammonium and moisture, and lower concentrations. Heterotrophic respiration (mean, 127 ± 4.6 mg m?2 h?1) was not significantly different between soil types and dominated total GHG (CO2eq) production in all soil types. Generally, the temperature responses of denitrification rate and net N2O production were exponential, whilst net CH4 production was unresponsive, possibly due to substrate limitation, and heterotrophic respiration was exponential but limited in summer at higher temperatures. Flooding with increased denitrification rate, net N2O production and heterotrophic respiration, but a reduction in net CH4 production suggests inhibition of methanogenesis by or N2O produced from denitrification. Implications for management and policy are that warming and flood events may promote microbial interactions in soil between distinct microbial communities and increase denitrification of excess with N2O production contributing to no more than 50% of increases in total GHG production. 相似文献
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J?Craig CohenEmail author Lennart?KA?Lundblad Jason?HT?Bates Michael?Levitzky Janet?E?Larson 《BMC genetics》2004,5(1):21