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排序方式: 共有166条查询结果,搜索用时 31 毫秒
121.
122.
Thomas Hartmann Claudine Theuring Till Beuerle Elizabeth A. Bernays 《Chemoecology》2004,14(3-4):207-216
Summary. The alkaloid profiles of the life history stages
of the highly polyphagous arctiid Estigmene acrea were
established. As larvae individuals had free choice between
a plain diet (alkaloid-free) and a diet that was supplemented
with Crotalaria-pumila powder with a known content and
composition of pyrrolizidine alkaloids (PAs). Idiosyncratic
retronecine esters (insect PAs) accounted for approximately
half of the PAs recovered from the larvae. These alkaloids
were synthesized by the larvae through esterification of dietary
supinidine yielding the estigmines, and esterification of
retronecine yielding the creatonotines. The retronecine is
derived from insect-mediated degradation of the sequestered
pumilines (macrocyclic PAs of the monocrotaline type).
With one exception, the PA profiles established for larvae
were found almost unaltered in all life-stages as well as
larval exuviae and pupal cocoons. The exception is the
males, which in comparison to pupae and adult females,
showed a significantly decreased quantity of the creatonotines
and pumilines. These data support the idea that
the creatonotines are direct precursors of the PA-derived male
courtship pheromone, hydroxydanaidal. Crosses of PA-free
males with PA-containing females and vice versa confirmed
an efficient trans-mission of PAs from males to females and
then from females to eggs. In single cases a male bestowed
almost his total PA load to the female, and a female her total load
to the eggs. The results are discussed with respect to pheromone
formation, PA transmission between life-stages, and the
defensive role of PAs against predators and parasitoids 相似文献
123.
Jason K. Levy Jens Hartmann Kevin W. Li Yunbi An Ali Asgary 《Journal of the American Water Resources Association》2007,43(2):346-358
Abstract: Flood management problems are inherently complex, time‐bound and multi‐faceted, involving many decision makers (with conflicting priorities and dynamic preferences), high decision stakes, limited technical information (both in terms of quality and quantity), and difficult tradeoffs. Multi‐Criteria Decision Support Systems (MCDSS) can help to manage this complexity and decision load by combining value judgments and technical information in a structured decision framework. A brief overview of MCDSS is presented, an original MCDSS architecture is put forth, and future research directions are discussed, including extensions to Multi‐Criteria Spatial Decision Support Systems and group MCDSS (as flood management involves shared resources and broad constituencies). With application to the September 11‐12, 2000 Tokai floods in Japan, the proposed multi‐criteria decision support instruments enhance communication among stakeholders and improve emergency management resource allocation. In summary, by making the links among flood knowledge, assumptions and choices more explicit, MCDSS increases stakeholder satisfaction, saves lives, and reduces flood management costs, thereby increasing decision‐making effectiveness, efficiency and transparency. 相似文献
124.
125.
Comparison of the biosynthesis of the methanobacterial pseudomurein and the eubacterial murein 总被引:4,自引:0,他引:4
From cell extracts of the archaebacterium Methanobacterium thermoautotrophicum 11 putative precursors of the pseudomurein were isolated and characterized. On the basis of the isolated intermediates, a biosynthetic pathway of the pseudomurein is proposed. Compared to the eubacterial murein the biosynthetic stages follow different pathways as indicated by the occurrence of a nucleotide-activated disaccharide and nucleotide-activated peptides. 相似文献
126.
127.
128.
First presented at the European Symposium Photomorphogenesis in Plants, Freiburg/Br., September 24–29, 1989, West Germany. 相似文献
129.
Increased UDP-Glucuronyltransferase in putative preneoplastic foci of human liver after long-term use of oral contraceptives 总被引:1,自引:0,他引:1
Previous research by the authors had suggested that uridine-diphosphate-glucuronyl-transferase (UDP-GT) is a useful preneoplastic marker in chemical carcinogenesis. Recently the authors report that they found typical clear cell foci in a macroscopically normal liver surrounding focal nodular hyperplasia with a 6 cm diameter in a 27-year old woman who had been using oral contraceptives (OCs) containing ethinyl-estradiol and lynestrenol for 9 years. These foci were further characterized by a reduction of canalicular and cytoplasmic ATPase activity, an increased glycogen content, and a positive immunohistochemical reaction for UDP-GT. OC users develop 2 basic types of benign liver tumors: hepatic adenoma and focal nodular hyperplasia. Hepatic adenoma appears to be caused by OCs, whereas the relationship between OC use and focal nodular hyperplasia is less clear. The tumorigenic action of OCs has been ascribed to a promotor action on liver cells; however, there is no evidence that OCs are initiators of liver tumors. The case reported shows 2 manifestations of toxic lesions promoted by OC use: the development of focal nodular hyperplasia and enzyme-altered foci comparable to those seen in experimental liver carcinogenesis. Further studies are needed to get more information about the preneoplastic potential of these foci in humans. Since enzyme-altered foci could not be identified in the liver tissue of healthy women, these foci may be of prognostic significance in longterm OC users. 相似文献
130.
Fruits of Garden Lettuce, imbibed in 0.01 M KNO3, were depleted of maternal active phytochrome B by saturating deep-red exposure and photosensitized by chilling for 1 week
at 4 °C. Twenty saturated fluence-response curves for photoinduced germination were elaborated between 300 and 800 nm, using
exposure periods from 6 to 600 s at 22.5 °C; there is linear and closely parallel regression in the logarithmic probability
net. The reciprocals of the half-response fluences obtained gave the apparent conversion spectrum of the controlling pigments
and this was corrected for the transmittance of the seed-coat. It is a phytochrome spectrum of P
r with photoconversion cross-sections of 1.2·109 and 4.5·103 m2 mol–1 at 666 and 800 nm, respectively. This means that for half-saturated germination of sensitized seed, fewer than 1 out of 200,000
phytochrome A molecules have to be photoconverted to P
fr, and no photo-reversibility by deep-red was found. Therefore, all spectral colours of nightly moon- or skylight should stimulate
the germination of sensitized weed seeds if they are exposed at the soil surface between sequential tillage operations.
Received: 28 April 2000 / Accepted in revised form: 28 July 2000 相似文献