The adhesion rate of cells under charge regulation onto a spherical collector with constant potential is investigated in this paper. Particularly, the effect of the presence of cationic electrolytes in the suspension medium on the adhesion rate is examined. The result reveals that the presence of cationic electrolytes in the suspension medium raises the electrostatic repulsion force between cell and collector surface, when the separation distance between them is small than a critical value. This has the effect of decreasing the adhesion rate of cells. The adhesion rate of cells is quite sensitive to the value of Hamaker constant, especially at a high ionic strength value. 相似文献
It is critical for spring wheat (Triticum aestivum L.) production in the semi-arid Loess Plateau to understand the impact of nitrogen (N) fertilizer on changes in N metabolism, photosynthetic parameters, and their relationship with grain yield and quality. The photosynthetic capacity of flag leaves, dry matter accumulation, and N metabolite enzyme activities from anthesis to maturity were studied on a long-term fertilization trial under different N rates [0 kg ha?1(N1), 52.5 kg ha?1 (N2), 105 kg ha?1 (N3), 157.5 kg ha?1 (N4), and 210 kg ha?1 (N5)]. It was observed that N3 produced optimum total dry matter (5407 kg ha?1), 1000 grain weight (39.7 g), grain yield (2.64 t ha?1), and protein content (13.97%). Our results showed that N fertilization significantly increased photosynthetic parameters and N metabolite enzymes at all growth stages. Nitrogen harvest index, partial productivity factor, agronomic recovery efficiency, and nitrogen agronomic efficiency were decreased with increased N. Higher N rates (N3–N5) maintained higher photosynthetic capacity and dry matter accumulation and lower intercellular CO2 content. The N supply influenced NUE by improving photosynthetic properties. The N3 produced highest chlorophyll content, photosynthetic rate, stomatal conductance and transpiration rate, grain yield, grain protein, dry matter, grains weight, and N metabolite enzyme activities compared to the other rates (N1, N2, N4, and N5). Therefore, increasing N rates beyond the optimum quantity only promotes vegetative development and results in lower yields.
The nasuta subgroup of Drosophila consists of 12 known species classified within the immigrans group. D. nasuta and D. albomicans are two sibling species widely distributed throughout the Indo-Pacific tropics, which, although morphologically indistinguishable, have different meta-phase-chromosome configurations: chromosomes X and 3 are attached in D. albomicans, so that about 60% of its genes are sex-linked. Our experiments show that, at least in the laboratory, there is no sexual, mechanical, or gametic isolation between the two species. There is, however, hybrid “breakdown” expressed in three ways: 1) reduction in the number of F2 hybrids produced per culture; 2) reduction in the fertility of F2 (males) and F3 (males and females) hybrid progenies; and 3) abnormal sex ratios in the progenies of crosses between strains of certain localities. In experimental populations, the karyotypes of both species are still present in substantial frequencies after 20 generations, although the frequencies of the two karyotypes vary depending on the geographic origin of the strains. Our results support the hypothesis that, in allopatry, the evolution of postzygotic isolation precedes that of prezygotic isolation. The mtDNA is polymorphic in both D. nasuta and D. albomicans and fairly similar between them. Assuming typical rates of mtDNA evolution, the two species would have diverged from each other about 500,000 years ago, whereas the African and Indian populations of D. nasuta (considered to be different subspecies by some authors) might have diverged some 350,000 years ago. 相似文献
Intergeneric hybridization between Pleurotus ostreatus and Schizophyllum commune was studied using PEG-induced fusion. The fusion of protoplasts from auxotrophic mutant strains resulted in the formation of fusion hybrids in the frequencies of 3.6 to 7.3×10–5. Most of these fusion hybrids were monokaryotic and sterile and no heterokaryosis occurred. Most fusants showed a significantly higher nuclear DNA content when compared to parental strains and no diploids (parent 1 genome plus parent 2 genome) were found. Some fusion hybrids revealed both parental fragments in nuclear and mitochondrial rDNA PCR profiles. AP-PCR (Arbitrarily-primed Polymerase Chain Reaction) fingerprints also indicated that most of the fusion products were recombinant hybrids. 相似文献
Treatment of cultured bovine carotid artery endothelial cells with 0.1 µM human plasmin has been reported to induce a receptor-mediated short burst of arachidonate release, which is a pertussis toxin-sensitive and extracellular calcium-dependent reaction. Plasmin-induced calcium influx in cells was significantly inhibited by pretreatment with pertussis toxin, indicating that the former was coupled with a pertussis toxin-sensitive guanosine 5-triphosphate (GTP)-binding protein. Plasmin significantly induced the formation of lysophosphatidylcholine but not lysophosphatidylethanolamine. A cellular phospholipase A2 with an arachidonyl specificity at the sn-2 position of phosphatidylcholine, which required submicromolar calcium, was identified as a cytosolic phospholipase A2 by immunoblot analysis. By a cell-free enzyme activity assay and immunoblot analysis, plasmin was found to induce a translocation of the cytosolic phospholipase A2 from the cytosol to the membrane. Taken together, the results suggest that plasmin bound to its putative receptor and activated a GTP-binding protein coupled to calcium influx channel, followed by translocation and activation of cytosolic phospholipase A2 in endothelial cells. 相似文献
Abstract: Microsomal fractions of cerebral cortices of 15-day-old rabbits were used to study the 1-alkyl- sn -glycero-3-phosphate (AGP) acetyltransferase that generates 1-alkyl-2-acetyl- sn -glycero-3-phosphate in the de novo path of platelet-activating factor synthesis. The AGP acetyltransferase activity was inhibited by small concentrations of medium-long chain fatty acyl-CoA thioesters. In contrast, the AGP acyltransferase used oleoyl-CoA as substrate and was not inhibited by the presence of acetyl-CoA in high molar excess. The inhibition of AGP acetyltransferase was seen at concentrations of oleoyl-CoA as low as 0.5 µ M using 12.5 µ M AGP and 200 µ M acetyl-CoA. The inhibition by oleoyl-CoA was noncompetitive for the acetyl-CoA substrate. However, there was evidence that the oleoyl-CoA was competing with AGP in the acetyltransferase reaction, as the inhibition was lessened by increasing the AGP substrate concentration. Several acyl-CoA thioesters were effective as inhibitors of the AGP acetyltransferase, including oleoyl-, palmitoyl-, lauroyl-, and octanoyl-CoA. Propionyl- and butyryl-CoA were less effective as inhibitors, and propionyl-CoA was found to be a competitive inhibitor for acetyl-CoA. We have noted earlier that MgATP is an effective inhibitor of the AGP acetyltransferase and here we show that the inhibition by oleoyl-CoA can be increased by the presence of 0.1 m M MgATP. In brain ischemia, a decline in ATP levels would likely lead to a corresponding fall in acyl-CoA concentrations, thereby relieving the inhibition of AGP acetyltransferase and permitting the flow of AGP into the de novo pathway of platelet-activating factor synthesis. 相似文献
The interaction of bovine prothrombin with Ca2+ and Mg2+ ions was investigated by following H+ release as a function of metal ion concentration at pH 6 and pH 7.4 at high and low ionic strength. Prothrombin Ca2+ and Mg2+ binding is characterized by high- and low-affinity sites. M2+ binding at these sites is associated with intramolecular conformational changes and also with intermolecular self-association. The pH dependence of H+ release by M2+ is bell shaped and consistent with controlling pKa values of 4.8 and 6.5. At pH 6 and low ionic strength, both Ca2+ and Mg2+ titrations following H+ release clearly show independent low- and high-affinity binding sites. Laser light scattering reveals that at pH 7.4 and low ionic strength, and at pH 6.0 and high ionic strength, the prothrombin molecular weight is between 73 and 98 kD. At pH 7.4 and high ionic strength, prothrombin is monomeric in the absence of metal ions, but appears to dimerize in the presence of M2+. At pH 6.0 and low ionic strength prothrombin exists as a dimer in the absence of metal ions and is tetrameric in the presence of Ca2+ and remains dimeric in the presence of Mg2+. These results and those for metal ion-dependent H+ release indicate that H+ release occurs concomitantly with association processes involving prothrombin.Abbreviations GLA
-carboxyglutamic acid; fragment 1. amino terminal residues 1–156 of bovine prothrombin
- MES
2-(N-morpholino) ethanesulfonic acid
- MOPS
3-(N-morpholino) propanesulfonic acid
- PS/PC
phosphatidylserine/phosphatidylcholine vesicles
-
ionic strength 相似文献