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81.
Marc Pagano Lucien Saint-Jean Robert Arfi Marc Bouvy Daniel Guiral 《Hydrobiologia》1998,390(1-3):83-98
Gut fluorescence, feeding and egg production rates of zooplankton assemblages were measured in a shallow, eutrophic brackish-water
pond for 24 days. Brachionus plicatilis, Hexarthra intermedia and Apocyclops panamensis successively developed and exhibited
differences in food selectivity. Rotifers selected small particles but also had a preference for larger particles (15–21 μm,
Equivalent Spherical Diameter, ESD). B. plicatilis appeared less selective than H. intermedia, which fed mostly on particles
<6 μm. A. panamensis adults showed a selectivity for 6–21 μm ESD particles. Laboratory experiments suggested that A. panamensis
adults were able to shift from seston to carnivorous feeding, depending on the availability of these food resources. Measurements
of gut fluorescence and grazing gave comparable ingestion rates. Rotifers displayed the highest ingestion rates (up to 486%
body C d-1). Despite high total phytoplankton and seston biomasses, the high ingestion rates and selective grazing of rotifers
induced auto food-limitation phenomena and caused major changes in seston abundance and size structure. Grazing impact was
less important when A. panamensis dominated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
82.
Chloride channels in the luminal membrane of exocrine gland acini from frog skin (Rana esculenta) constituted a single homogeneous population. In cell-attached patches, channels activated upon exposure to isoproterenol, forskolin, or dibutyryl-cAMP and isobutyl-1-methyl-xanthine rectified in the outward direction with a conductance of 10.0 ± 0.4 pS for outgoing currents. Channels in stimulated cells reversed at 0 mV applied potential, whereas channels in unstimulated cells reversed at depolarized potentials (28.1 ± 6.7 mV), indicating that Cl− was above electrochemical equilibrium in unstimulated, but not in stimulated, cells. In excised inside-out patches with 25 mM Cl− on the inside, activity of small (8-pS) linear Cl−-selective channels was dependent upon bath ATP (1.5 mM) and increased upon exposure to cAMP-dependent protein kinase. The channels displayed a single substate, located just below 2/3 of the full channel amplitude. Halide selectivity was identified as PBr > PI > PCl from the Goldman equation; however, the conductance sequence when either halide was permeating the channel was GCl > GBr >> GI. In inside-out patches, the channels were blocked reversibly by 5-nitro-2-(3-phenylpropylamino)benzoic acid, glibenclamide, and diphenylamine-2-carboxylic acid, whereas 4,4-diisothiocyanatostilbene-2,2-disulfonic acid blocked channel activity completely and irreversibly. Single-channel kinetics revealed one open state (mean lifetime = 158 ± 72 ms) and two closed states (lifetimes: 12 ± 4 and 224 ± 31 ms, respectively). Power density spectra had a double-Lorentzian form with corner frequencies 0.85 ± 0.11 and 27.9 ± 2.9 Hz, respectively. These channels are considered homologous to the cystic fibrosis transmembrane conductance regulator Cl− channel, which has been localized to the submucosal skin glands in Xenopus by immunohistochemistry (Engelhardt, J.F., S.S. Smith, E. Allen, J.R. Yankaskas, D.C. Dawson, and J.M. Wilson. 1994. Am. J. Physiol. 267: C491–C500) and, when stimulated by cAMP-dependent phosphorylation, are suggested to function in chloride secretion. 相似文献
83.
Studies that have examined the effect of experimental increases in predation risk on diet selectivity have shown both decreased
and increased diet selectivity. A possible explanation for these disparate results emerges from an examination of the prey
sets used in these studies, which differed in the relationship between the values of risk components associated with the capture
of different prey types (‘danger’) and their profitabilities. When less profitable prey were more dangerous, selectivity increased
with predation risk. When prey were equally dangerous, selectivity did not change. Finally, when the more profitable prey
were also more dangerous, selectivity decreased with risk. Here, we examine theoretically the influence of a forager's estimate
of the probability that a predator is present (φ) on the selection of diets from prey sets with varying danger–profitability
relationships. A dynamic programming model is used to determine the maximum attack time (or distance) for each of two types
of prey, differing in their energetic content, for a range of forager energy state and φ levels. The diets which would result
if foragers attacked prey according to the rules provided by the dynamic model are then determined. The model results indicate
that the prey danger–profitability relationship determines the diet selectivity response to φ, confirming that variation in
this relationship could be responsible for the range of experimental results.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
84.
A system of capillary silica monolith with bovine serum albumin (BSA) functionalized through two approaches for affinity monolithic capillary electrochromatography (AMCEC) was developed. Covalent immobilization conditions for two different Schiff base methods, which employed 3-glycidopropyl trimethoxysilane (GPTS) and 3-aminopropyl trimethoxysilane (APTS) as starting materials, respectively, were investigated to obtain good and stable chiral separation. The BSA immobilized silica monoliths were evaluated in terms of morphology, electroosmotic flow, retention time, column efficiency and resolution of model compound (±)-tryptophan. The columns exhibited satisfactory run-to-run, column-to-column repeatability and maintained their enantioselectivity for more than 3 months. Both developed methods can baseline separate tryptophan enantiomers, whereas shorter retention time, better column efficiency, and enantiomeric recognition between two pairs of drug enantiomers (pantoprazole and atenolol) were obtained by the GPTS method. 相似文献
85.
Athanasios C. Kimbaris Antonios Michaelakis Angeliki F. Martinou Moschos G. Polissiou 《Biocontrol Science and Technology》2010,20(4):411-422
The comparative toxicity of five essential oil vapours was tested against four aphid species, the black bean aphid Aphis fabae, the pea aphid Acyrthosiphon pisum, the chrysanthemum aphid Macrosiphoniella sanborni, the green peach aphid Myzus persicae and on two of the most common coccinellid predators, the seven-spotted ladybird Coccinella septempunctata and the two-spotted ladybird Adalia bipunctata. All essential oils were highly toxic to the aphid species tested with LC50 and LC99 values ranging between 0.17 and 1.92 and 0.44 and 4.83 µL/L air, respectively, depending on the aphid species and on the essential oil. Coccinellid predators were also highly susceptible to the essential oil vapours and the selective toxicity ratio varied depending on aphid species, coccinellid predator and essential oil. The possibilities for the utililization of essential oils as aphicides, especially in IPM programmes in glasshouses are discussed with regard to the present findings. 相似文献
86.
Michael Carland Murray J. Cairns Vanessa J. Roknic W. David McFadyen 《Journal of inorganic biochemistry》2010,104(8):815-819
Three platinum complexes in which substituted (7-OMe, 9-NH2; 7-F, 9-NH2; and 7-H, 9-NH(CH2)2OH) 9-aminoacridine-4-carboxamides were tethered to a platinum(II)diamine moiety were synthesised and characterised at the chemical and biological level. These variants showed a decrease in cytotoxicity, as measured by IC50 values in HeLa cells, when compared with the parent 7-H, 9-NH2 compound. The 7-F and 9-NH(CH2)2OH substituents gave rise to a small decrease in cytotoxicity, and the 7-OMe substituent resulted in a larger decrease in cytotoxicity. Their binding to purified pUC19 plasmid DNA was investigated and it was found that the addition of 7-F, 9-NH(CH2)2OH and especially the 7-OMe substituents, resulted in reduced DNA binding. This correlated well with the IC50 cytotoxicity values. However, the DNA sequence selectivity was unaffected by the addition of these moieties. 相似文献
87.
Citric acid production from sucrose using a recombinant strain of the yeast Yarrowia lipolytica 总被引:1,自引:0,他引:1
Förster A Aurich A Mauersberger S Barth G 《Applied microbiology and biotechnology》2007,75(6):1409-1417
The yeast Yarrowia lipolytica is able to secrete high amounts of several organic acids under conditions of growth limitation and carbon source excess.
Here we report the production of citric acid (CA) in a fed-batch cultivation process on sucrose using the recombinant Y. lipolytica strain H222-S4(p67ICL1) T5, harbouring the invertase encoding ScSUC2 gene of Saccharomyces cerevisiae under the inducible XPR2 promoter control and multiple ICL1 copies (10–15). The pH-dependent expression of invertase was low at pH 5.0 and was identified as limiting factor of the CA-production
bioprocess. The invertase expression was sufficiently enhanced at pH 6.0–6.8 and resulted in production of 127–140 g l−1 CA with a yield Y
CA of 0.75–0.82 g g−1, whereas at pH 5.0, 87 g l −1 with a yield Y
CA of 0.51 gg−1 were produced. The CA-productivity Q
CA increased from 0.40 g l −1 h−1 at pH 5.0 up to 0.73 g l −1 h−1 at pH 6.8. Accumulation of glucose and fructose at high invertase expression level at pH 6.8 indicated a limitation of CA
production by sugar uptake. The strain H222-S4(p67ICL1) T5 also exhibited a gene–dose-dependent high isocitrate lyase expression
resulting in strong reduction (<5%) of isocitric acid, a by-product during CA production. 相似文献
88.
89.
NaCl胁迫对黄瓜幼苗体内K+、Na+和Cl-分布的影响 总被引:1,自引:0,他引:1
采用营养液水培,以2个耐盐性不同的黄瓜品种为材料,研究了不同浓度NaCl处理下幼苗植株体内K 、Na 和Cl-在器官间的区域化分布及其吸收和运输特性的变化。结果表明:NaCl胁迫下,黄瓜植株体内K 含量下降,Na 和Cl-含量升高,变化幅度随NaCl浓度的升高而增大;不同器官间,茎中Na 和Cl-含量最高,上位叶中Na 和Cl-含量最低、K 含量下降幅度最小。与耐盐性较弱的“津春2号”相比,耐盐性较强的“长春密刺”根向茎运输的SK,Na值较高,根系对Na 的截留作用较强,茎向上位叶运输的SK,Na和SCl,Na值均较高,叶片中K 含量下降幅度较小,K/Na和Cl/Na比值均较高,功能叶中盐分离子尤其是Na 积累较少,植株生物量较高。说明根系对Na 的截留能力较强且向上位叶运输Na 的选择性较低,是“长春密刺”耐盐性较强的主要原因之一。 相似文献
90.