Characterization of soybean bradyrhizobia for which serogroup affinities have not been identified

The USDA, ARS National Rhizobium Germplasm Collection contains 143 accessions of slow-growing soybean strains among which there are 17 distinct serological groups. However, 11 strains appear to have no serological affinity with the 17 serogroups. Therefore, we determined whether these strains were diverse and examined their phylogenetic placement. Nine strains formed nitrogen-fixing symbioses with soybean indicating that these accessions were not contaminants. We concluded from results of amplified fragment length polymorphism (AFLP) analysis, using 3 selective primers with 8 strains, that they were genetically dissimilar. Nine strains were examined for their fatty acid composition using fatty acid methyl ester (FAME) derivatives. The FAME results with 5 strains and serotype strains of Bradyrhizobium elkanii were similar, while results with each of the remaining 2 pairs were either similar to the type strain of Bradyrhizobium japonicum (USDA 6) or to USDA 110. Evolutionary history of 9 strains was reconstructed from sequence divergence of a combination of the complete 16S rRNA gene, the internally transcribed spacer region, and about 400 bases of the 5' end of the 23S rRNA gene. Placement of 5 strains was nested within B. elkanii, 2 with USDA 110, and the other 2 with USDA 6. We concluded that soybean isolates that cannot be placed within one of the 17 established serogroups are phenotypically and genetically as diverse as the serotype strains.     

不同农作措施下红壤坡耕地土壤钾素流失特征的研究

研究了6种农作措施下红壤坡耕地土壤钾素的流失特征．结果表明。红壤坡耕地土壤钾素的地表流失主要是以推移质形式和径流形式流失的;在泥砂流失量较小的等高农作、等高土埂处理的坡耕地。土壤钾素主要以径流形式流失;休闲处理的坡耕地通过径流流失的钾素和推移质流失的钾素基本相当。而在泥砂流失量较大的顺坡农作处、水平草带、水平沟处理的坡耕地土壤钾素主要以推移质形式流失．在径流流失的钾素中。又以泥砂结合态为主．除顺坡农作处理以外,其它农作措施均有控制土壤钾素流失的作用。等高农作、休闲、等高土埂等农作措施优于水平草带和水平沟农作措施．2000年红壤坡耕地土壤钾素的流失时间主要集中在5～8月份．     

Accumulation of potassium by human red cells

1. A method is described for measuring the accumulation of K at 37°C. by washed human red cells in glucose-containing systems in which the pH is kept constant, the K content of the cells being compared with that of the cells of systems which contain no added glucose but which are otherwise treated similarly. 2. In systems containing added glucose, the accumulation of K begins shortly after the cells have been warmed to 37°C., proceeds to a maximum which is reached after about 10 hours, and then falls exponentially. The maximum rate of accumulation is found during the first 3 hours. In systems which contain no added glucose, the K content of the cells appears to decrease exponentially with time for about 18 to 24 hours; thereafter the K content of the cells may decrease rapidly and the systems may show considerable hemolysis. Sometimes a small accumulation effect is observed during the first 2 to 3 hours; this may be the result of the washed cells not having been completely freed of glucose. 3. The accumulation process proceeds at its maximum rate at pH 7.4 to 7.6, which is also the pH at which the K loss from the red cells is at a minimum in systems containing no added glucose. 4. When red cells are stored at 4°C. for increasing lengths of time, the storage is accompanied by increasing K loss and the maximum rate of accumulation observed when the cells are warmed to 37°C. at first becomes greater. If the storage at 4°C. is continued for more than 3 to 4 days, the rate of the accumulation which occurs at 37°C decreases again, the accumulation mechanism showing progressive deterioration with time even at low temperatures. This deterioration has a counterpart in the progressive deterioration (deduced from the analysis of the curves relating K content and time) of the accumulation mechanism with time at 37°C. 5. The accumulation of K occurs at a maximum rate when the concentration of glucose in the system is between 50 and 200 mg./100 ml. Its temperature coefficient over the range 27–37°C. is 2.4. In the presence of glucose and at pH 7.6, accumulation of K takes place from isotonic mixtures of KCl and LiCl or of KCl and CsCl only a little less actively than from mixtures of KCl and NaCl; i.e., the accumulation of K under optimum conditions seems to be an active process which is at least partly independent of the excretion of Na.     

Vinculin and 36 kDa protein are not tyrosine-phosphorylated in Rous sarcoma virus infected cells which have been treated with interferon

The expression of membrane-associated transformation-specific parameters was analyzed in de novo Rous sarcoma virus (strain SR-RSV-D) infected chicken embryo fibroblasts pretreated with homologous interferon. Cellular morphology, hexose transport, microfilament organization, and tyrosine-phosphate content of two primary substrates of the transformation-generating viral kinase, pp60src, were found indistinguishable from non-infected controls. These observations support the hypothesis that vinculin and possibly 36 kDa protein are involved in microfilament organization and that tyrosine-phosphorylation of these structural proteins is a prerequisite for the rearrangement of microfilaments during transformation. In de novo infection, interferon pretreatment reduces viral protein synthesis and pp60src activity as compared to non-treated, SR-RSV-D infected cells. However, the phosphotyrosine content of total cellular proteins as measured under steady state conditions is as high in interferon-pretreated as in nontreated transformed cells.     

Cotransport of lithium and potassium in human red cells

This paper reports the presence of human red cells of an additional ouabain-insensitive transport pathway for lithium ions, the Li-K cotransport. Several kinds of observations support this conclusion. Cells loaded to contain only K, Na, or Li do not exhibit furosemide- sensitive efflux. Simultaneous presence of K and Li on the same side of the membrane mutually stimulates furosemide-sensitive Li and K fluxes from that side. Cells loaded with both Na and Li exhibit no furosemide- sensitive Li efflux. Thus, Li can apparently replace Na but not K on the outward Na-K cotransport system in human red cells. Furthermore, Lio, like Ko, inhibits outward Na-K cotransport. Additional proof for coupled Li-K cotransport is provided by the observation that an outwardly directed K electrochemical potential gradient can drive net outwardly directed K electrochemical potential gradient can drive net outward Li movement against its gradient. There are several differences between Li-K cotransport and Li-Na countertransport. The cotransport system has an apparent affinity for Li that is about one-half that for Na and 30 times lower than the counter-transport system. Furosemide and chloride replacement inhibit cotransport but do not affect countertransport. The PCMBS loading procedure irreversibly inhibits countertransport but not cotransport. Furthermore, the two systems can apparently function at maximal rates simultaneously. Present evidence, than, indicates that the two pathways can be separated operationally as two different systems.     

Outward sodium and potassium cotransport in human red cells

Summary This paper reports some kinetic properties of Na–K cotransport in human red cells. All fluxes were measured in the presence of 10^–4 M ouabain. We measured Na and K efflux from cells loaded by the PCMBS method to contain different concentrations of these ions into a medium that contained neither Na nor K (MgCl₂-sucrose substitution) in the absence and presence of furosemide. Furosemide inhibited 30–60% of the total efflux depending on the internal ion concentration and the individual subject. We took the furosemide-sensitive fluxes to be a measure of Na–K cotransport. The ratio of Na to K cotransport was 1 over the entire range of internal Na and K concentrations studied. When Na was substituted for K as the only internal cation, cotransport was maximally activated when the Na and K concentrations were between 20 and 90 mmol/liter cells. The concentration of internal Na required to produce half-maximal cotransport was about 13±4 mmol/liter cells (n=4), while the comparable concentration of K was somewhat lower. The activation curve was definitely sigmoid in character, suggesting that at least two Na ions are involved in the transport process. The maximum of Na–K cotransport was about 0.5±0.15 mmol/liter cells × hr (n=5); it had a flat maximum in the medium at about pH 7.0, decreasing in both the acid and alkaline sides. furosemide-resistant effluxes were found to be linear functions of internal Na and K concentrations and to yield rate coefficients of 0.019±0.002 hr^–1 and 0.014±0.002 hr^–1 (n=7), respectively. These values are of the same order of magnitude expected of ions moving across phospholipid bilayers.Charge de Recherches CNRS.     

High strength binding of P815 mastocytoma cells is not necessary for their lysis by macrophages which have been primed and triggered in vitro

We have examined the hypothesis that binding of P815 mastocytoma cells is a necessary step in lysis of these cells by macrophages which are both "primed" and "triggered" in vitro, Macrophages "primed" by conditioned media containing IFN-gamma, or by rIFN-gamma have an increased ability to bind P815. However, adding either heat-killed Listeria or endotoxin to trigger the primed macrophages has opposite effects on lysis and binding of P815. Lysis is increased. Binding is dramatically decreased. This is true when centrifugal forces of 200 x g, 400 x g, and 800 x g are used to disrupt P815-macrophage binding. Although 100% of P815 cells bound by cytotoxic macrophages are lysed, a large additional population of unbound P815 is also lysed. Detailed kinetic studies indicate that macrophages do not rapidly bind and lyse several cycles of P815. There is an initial lag period of 4 to 6 h before P815 lysis can be detected, and completion of lytic events then occurs within 12 to 14 h. Lysis of P815 bound to cytotoxic macrophages is slightly slower than lysis of the total population of bound and unbound P815. In contrast, D3.1, a cloned CD4+ T cell line, is tightly bound to macrophages but not lysed efficiently. When macrophages are simultaneously confronted with P815 and macrophage-bound D3.1, only the former are lysed. Altogether, the data indicate that P815-macrophage binding, as operationally defined by our assay, is not a necessary step for lysis. These results, by use of macrophages primed and triggered in vitro, are in contrast to previously reported experiments examining P815 binding and lysis by macrophages activated in vivo by infection with bacillus Calmette-Guérin.