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81.
Murine histocompatibility antigens were solubilized from the spleens and lungs of C57BL/6 (H-2b) animals with hypertonic salt (3 M KC1). Aggregate-free soluble antigens were incubated with nonadherent lymph node cells from BALB/c (H-2d) mice for 18 hr prior to their use as responder cells in the mixed-lymphocyte reaction (MLR). It was found that the generation of cytotoxic cells was suppressed while the proliferative response was not affected. The observed suppression was not due to a shift in the kinetics of the generation of cytotoxicity as determined throughout a 10-day culture period. The suppression was specific in that the response in MLR to unrelated H-2f stimulator cells and the subsequent generation of cytotoxic cells were unchanged. Using various H-2 recombinant strains as target cells in the assay of cell-mediated lympholysis, suppression of cytotoxicity was observed when the D end, but not the K end, was shared with the C57BL/6 strain from which the antigens were derived. 相似文献
82.
S SPIEGEL D HOLLAND Y TAM I BAR-YAAKOV L MASLENIN A ROSNER 《The Annals of applied biology》2004,144(2):229-236
Prunus necrotic ringspot virus (PNRSV) was detected in almonds, plum and apricot germplasm accessions and local almond cultivars in Israel. PNRSV was widespread both in wild and cultivated almond trees and uncommon in wild apricots and plums. The possible variation among the PNRSV isolates was initially evaluated by restriction analysis of PCR products representing the CP gene with the endonuclease RsaI and followed by nucleotide sequence analysis of selected isolates. It was concluded that all 13 isolates belong to group PV96, the largest cluster of PNRSV isolates, described previously. Two PNRSV isolates, one from a plum accession and one from an almond cultivar, were found to be distinct members of group PV96 with unique nucleotide modifications not found in other documented isolates of this virus. However, no PNRSV isolate typical to a specific host and/or to the Middle East region could be identified. This study expands the body of data on variability of PNRSV isolates and highlights the importance of assessing the virus status of germplasm collections by applying reliable diagnostic and differentiating methods. 相似文献
83.
Jonathan A. Newman 《Global Change Biology》2004,10(1):5-15
Experimental evidence regarding the responses of cereal aphids to rising atmospheric CO2 has been ambiguous. Some studies suggest increased population sizes under future CO2 levels, others suggest decreased population sizes, and still others suggest little or no difference. Recently, Newman et al. (2003) constructed a general mathematical model of the aphid–grass interaction to investigate whether or not we should, in fact, expect a general aphid response to rising CO2. They concluded that aphid populations are likely to be larger under future CO2 concentrations if soil N levels are high, the aphid species' nitrogen requirement is low and the aphid species' density‐dependent response in winged morph production is weak. In that model, and in field experiments, CO2 concentration influences aphid population dynamics through the effect it has on plant quality. However, future CO2 concentrations are also likely to be accompanied by higher ambient temperatures, a combination that has received little focus to date. In the present paper, the Newman et al. model is used to consider the combined effects of increased CO2 concentrations and temperature on aphid population sizes. It is concluded that, when both factors are elevated, aphid population dynamics will be more similar to current ambient conditions than expected from the results of experiments studying either factor alone. This result has important implications for future experimentation. 相似文献
84.
85.
Anton Pauw Sunshine A. Van Bael Halton A. Peters Steven D. Allison José L. C. Camargo Miguel Cifuentes-Jara Aurlstela Conserva Teresa Garcia Restom Tamara Heartsill-Scalley Scott A. Mangan Gabriela Nunez-lturri Elsie Rivera-Ocasio Mark Rountree Susanne Vetter Carolina Volkmer de Castllho 《Biotropica》2004,36(3):410-413
86.
I. A. Catalán † E. Berdalet † M. P. Olivar † C. Roldán † 《Journal of fish biology》2007,70(2):391-405
Six condition indices based on RNA, total soluble protein and two metabolic enzymes [lactate dehydrogenase (LDH) and citrate synthase (CS)] were analysed in muscle tissue of individual larvae, post-flexion reared sea bass Dicentrarchus labrax using DNA and total soluble protein as standards for size. In addition, the effect of 2 days of food deprivation on the cell proliferation rates was assessed. The RNA:DNA best reflected short-term changes in feeding conditions. If standardized by DNA content, LDH activity was a better indicator of condition than any other index but RNA:DNA. Further, the analysis of cell proliferation rates in muscle from 26 day-old larvae proved useful in distinguishing continuously fed larvae from individuals subjected to 2 days of fast. 相似文献
87.
Sodium-induced calcium deficiency in salt-stressed corn 总被引:9,自引:5,他引:4
Abstract The effect of the Na+/Ca2+ ratio in the root media on salt-stressed corn (Zea mays L. cvs DeKalb XL-75 and Pioneer 3906) was determined in greenhouse experiments. Plants grown in a complete nutrient solution salinized with 86.5 mol m?3 NaCl exhibited severe Ca2+ deficiency symptoms at the four-leaf stage. The symptoms disappeared when part of the NaCl was replaced with 10 mol m?3 CaCl2 (Na+/Ca2+ molar ratio = 5.7). Salt stress at an iso-osmotic potential of ?0.4 MPa substantially decreased shoot growth at all solution Na+/Ca2+ ratios from 34.6 to 0.26. However, the dry weights of blades at 26 d of age were much less when plants were salinized with NaCl alone, particularly that of DeKalb XL-75 which was more susceptible to Na-induced Ca2+ deficiency than was Pioneer 3906. The growth of sheaths was similarity reduced by sail stress at all Na+/Ca2+ ratios. The symptoms of Ca2+ deficiency were correlated with low Ca2+ concentrations in the leaf tissue. Ca2+ concentrations in the developing blades of NaCl-stressed plants were much lower than in control plants. As the Na+/Ca2+ ratio in the solution was decreased, Ca2+ levels increased in both the blades and sheaths while Na+ concentrations greatly decreased. DeKalb XL-75 was much less effective than Pioneer 3906 in restricting the uptake of Na+. The results clearly indicate that NaCl stress may cause lesions and unique plant responses that are not manifested on agronomic plants grown on saline soils. 相似文献
88.
89.
The lateral diffusion of lectin-labelled glycoconjugates was studied in the human colon carcinoma cell line HT29 using fluorescence photobleaching techniques. HT29 cells were grown in either Dulbecco's modified Eagle's medium with glucose (25 mM; DMEM-Glu) or with galactose (25 mM; DMEM-Gal). Cell cultivation in the DMEM-Gal medium was assumed to promote a transformation of the cells to become small-intestinal-like with characteristic microvilli and associated enzymes. The diffusion of glycoconjugates labelled with fluoresceinated Triticum vulgaris agglutinin (Wheat germ agglutinin; WGA), Ricinus communis agglutinin-I (RCA-I), Concanavalia ensiformis agglutinin (ConA), Ulex europaeus agglutinin-I (UEA-I) and Arachis hypogaea agglutinin (PNA) was in all cases rapid, with a diffusion constant (D) ranging between 0.4 and 0.8×10-8 cm2 s-1. As a comparison the diffusion of the fluorescent synthetic lipid analog diI-C14 was characterized by D=0.8 – 1.0 × 10–8 cm2 s-1. The diffusion of lectin-labelled surface components could not be related to the presence of microvilli on HT29 cells grown in DMEM-Gal, which ought to yield an apparently lower diffusion rate. The results indicate either that surface glycoconjugates in HT29 cells are dominated by glycolipid, or that the labelled glycoproteins are more or less free to diffuse in the plane of the membrane. 相似文献
90.
Tatsuro Koike 《Journal of neurochemistry》1987,49(6):1784-1789
The binding and internalization of 125I-nerve growth factor (NGF) by PC12 pheochromocytoma cells was studied as a function of extracellular potassium concentration. Both surface-bound and internalized fractions of 125I-NGF associated with the cells under depolarizing conditions (50 mM K+) increased to 144 +/- 28% (average +/- SEM, six different cell preparations) and to 176 +/- 12% (n = 6), respectively, of those observed at 6.0 mM K+. Scatchard-type analysis of the data indicates increased sites for the binding and internalization of iodinated NGF by the cells. Similar enhancement was observed for cells treated with NGF as well. This voltage-dependent phenomenon was reversible, and also observed in the presence of veratridine. Moreover, withdrawal of extracellular Ca2+ abolished high K+-induced modulation of 125I-NGF binding and internalization, indicating that this effect may be mediated by Ca2+. 相似文献