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排序方式: 共有754条查询结果,搜索用时 15 毫秒
1.
Robert J. Pryce 《Phytochemistry》1973,12(7):1745-1754
Allogibberic acid (I) has been identified as the compound responsible for the inhibition of flowering, increase in frond multiplication rate and decrease in frond size produced in Lemna perpusilla 6746 by autoclaved, unbuffered aqueous solutions of gibberellic acid (VII). 13-Deoxyallogibberic acid (IV), a product of autoclaving aq. GA7 (VIII) solutions, also inhibits flowering in L. perpusilla and is about 10 times more active than allogibberic acid. 相似文献
2.
A modification of the trap assay (Woodard et al., 1989) was used to evaluate the response of Drosophila melanogaster (Meigen) to food media containing menthol. Dose-response curves for flies to mentholic foods were produced for flies that had been pre-exposed to menthol, during development and adult life, and flies that had not been exposed to menthol before the assay. Mentholic food media were less attractive to Drosophila than plain food medium. Rearing flies on a medium containing menthol reduced their aversion to some concentrations of menthol. The rearing effect was not simply due to lowered general activity levels resulting from developing in a medium containing menthol. There was a threshold concentration of menthol in the rearing medium below which we found no induced behavioural change. 相似文献
3.
Functional zooplankton bioassays based on ingestion, reproduction and respiration are described, with methods for a new ingestion bioassay included. All bioassays are compared using three indices, including the variability of controls, the range of experimental responses, and a listing of contaminants causing inhibition/stimulation of response. The ingestion bioassay showed the greatest range of response, and was sensitive to pesticides, PCBs and heavy metals. It was also commonly characterized by a hormesis response. The reproduction bioassay showed the lowest variability, illustrated a reduced range of response, and was sensitive to nutrients and heavy metals. In one study, the respiration bioassay was sensitive only to PCBs. 相似文献
4.
Lampert Winfried Fleckner Walter Pott Eckart Schober Ursula Störkel Karl-Ulrich 《Hydrobiologia》1989,(1):415-424
Bioassays of different complexity were compared with respect to their capability to predict the environmental impact of the herbicide atrazine in aquatic systems. Acute toxicity tests with Daphnia did not yield meaningful results. Sublethal tests with Daphnia (feeding inhibition, reduction of growth and reproduction) were more sensitive, but effective concentrations of atrazine were still rather high (2 mg/L). A relatively complicated artificial food chain system that incorporated direct and indirect effects on Daphnia yielded significant reduction of daphnid population growth at 0.1 mg/L. Enclosure experiments with natural communities were by far the most sensitive tools. Community responses could be measured at concentrations as low as 1 µg/L and 0.1 µg atrazine/L. At the lowest concentration, however, communities recovered after three weeks. We conclude that in complex systems indirect effects can be more important than direct effects, so that, contrary to the conditions in simple tests, non-target organisms may be the better indicators of herbicide stress to natural communities. 相似文献
5.
Experimental effects of elevated salinity on three benthic invertebrates in Pyramid Lake,Nevada 总被引:7,自引:7,他引:0
Salinity of Pyramid Lake increased from 3.7 to 5.5 between 1933 and 1980. Concern over future reductions in overall species richness prompted experiments to assess responses of dominant lake organisms to elevated salinity. Salinity tolerances of three important benthic invertebrates, Hyalella aztecta, Chironomus utahensis, and Heterocypris sp., were tested in controlled laboratory bioassays and also in a semi-natural environment consisting of large (47 m3) mesocosms.Densities of H. azteca in mesocosms were significantly lower at salinities of 8.0 and 11.0 compared with 5.6 controls in year one, but not in 8.5 salinity mesocosms in year two. The 96-h LC50 for H. azteca was high at 19.5. Short-term mortalities of C. utahensis were 100% at salinities of 13.3 and greater. Fifty-seven percent fewer larvae matured from third to fourth instar at 8.9 than at 5.5 salinity in 17 day subacute bioassays. Furthermore, larval chironomid densities and emergence of adults from mesocosms were significantly reduced at salinities of 8.0 and higher compared with controls. Mortality of Heterocypris sp. was 50% at a salinity of 18.6 in laboratory bioassays and populations in mesocosms ranged between 40 and 100% lower at salinities of 8.0 and 11.0 than in controls.Multiple generation mesocosm experiments indicated all three invertebrates were more sensitive to elevated salinity than results of short-term bioassays. Our studies suggest populations of these invertebrates may be reduced from present levels if Pyramid Lake's salinity were to double, although none are expected to be extirpated. Food habit shifts and reduced production of lake fishes are likely consequences of salinity-induced disruption in the benthic invertebrate forage base. 相似文献
6.
7.
Twelve singly embedded isolates (SEV) and two multiply embedded isolates (MEV) of nuclear polyhedrosis viruses from Heliothis larvae were compared by time-mortality assays in neonate H. zea larvae. The isolates could be separated into six groups based on differences in the 50% survival time (ST50) values. Isolates with identical restriction endonuclease (REN) profiles did not differ significantly in their ST50 values, whereas isolates with several different REN cleavage sites also had significantly different ST50 values. With the exception of one isolate from India, the singly embedded isolates acted faster than the multiply embedded isolates. 相似文献
8.
用离体血管电场刺激收缩模型观察到强啡肽明显抑制电场刺激引起的兔耳中心动脉及兔肠系膜上动脉的收缩效应,且呈剂量反应关系,而对股动脉的电场刺激收缩反应无明显影响,强啡肽抑制血管收缩达50%时的用量(IC_(50)值)分别为8.5±1.2×10~(-6)mol/L、5.02±1.3×10~(-7)mol/L及>10~(-6)mol/L。 用药物分析法看到,酚妥拉明(10~(-6)mol/L)可取消电场刺激及去甲肾上腺素引起的血管收缩作用,而强啡肽仅抑制电场刺激致血管收缩作用。 用HPLC法测定孵育液中去甲肾上腺素的含量变化时看到,应用强啡肽(5×10~(-7)mol/L)后孵育液中去甲肾上腺素的含量从对照组的340.56±73.13pg/ml下降至67.91±10.26pg/ml,两组差别有极显著意义(P<0.01)。纳洛酮(10~(-6)mol/L)可完全拮抗强啡肽的这一抑制效应。 以上结果提示强啡肽可能通过抑制交感神经末梢释放去甲肾上腺素,从而产生抑制血管的收缩作用。 相似文献
9.
Laurence Dinan Pensri Whiting Dorothée Alfonso Ilias Kapetanidis 《Entomologia Experimentalis et Applicata》1996,80(2):415-420
Sixteen withanolides isolated from Iochroma gesnerioides (Kunth) Miers (Solanaceae) have been assessed for their activities as ecdysteroid agonists and antagonists. None of the compounds showed any agonistic activity, but several showed significant antagonistic activity. With a 20-hydroxyecdysone concentration of 5 × 10–8 M, the ED50 values for 2,3-dihydro-3-methoxywithaferin A, 2,3-dihydro-3-methoxywithacnistine, 2,3-dihydro-3-methoxyiochromolide and 2,3-dihydro-3-hydroxywithacnistine are 3.5 × 10-5 M, 1 × 10–5 M, 5 × 10–6 M and 2.5 × 10–6 M, respectively. 相似文献
10.
JOHN B. MAHONEY JULIE A. McGHEE J. KNEELAND McNULTY 《The Journal of eukaryotic microbiology》1995,42(6):715-721
ABSTRACT. Alexandrium tamarense (Lebour) Balech (= Gonyaulax tamarensis Lebour) has been widely distributed and occasionally abundant in coastal waters of Long Island, New York in recent years. However, the distribution on the New Jersey coast has been sparse and this fact cannot be explained by this dinoflagellate's ability to migrate, or by its nutritional and physiological characteristics, or by the region's general suitability for phytoplankton. Therefore, the possibility that New Jersey coastal waters might be chemically exclusionary for A. tamarense seemed worth exploring. In a limited approach, we tested for water quality detrimental to the species in one New Jersey site (Great Bay) with a series of annual assays. Parsonage Creek, Long Island, New York, was assayed for comparison; this creek is assumed to have had at least marginal suitablity for A. tamarense , based on its reported long-term presence. Results provide tentative support for our working hypothesis, i.e. Great Bay chemical water quality is generally unfavorable for A. tamarense. Inhibition of A. tamarense growth, or culture decline, occurred in both assay series, but was substantially greater in Great Bay water. Inimical water quality was the most important factor distinguishing the two sites. Chelation with EDTA had greatest overall benefit in Great Bay assays, suggesting that lower availability of a natural chelator in the bay could be a secondary factor. Assay metal response is problematic, but we believe it permits speculation that essential metals could be partially limiting to A. tamarense in Great Bay, but would not be a critical regulator. 相似文献