莲藕干物质和氮磷钾养分的累积与分配研究

连续2年采用盆栽试验研究了莲藕（Nelumbo nucifera Gaertn）干物质和氮磷钾养分的累积与分配规律。结果表明：莲藕苗期以叶片生长并积累光合产物为主,膨大根状茎成型后,叶片、叶柄和根状茎中的干物质不断运输并贮存到膨大根状茎中,以产量形成为主,干物质累积总量增长呈＂慢-快-稳定＂的变化趋势;氮磷钾累积量与干物质累积量变化趋势一致,并与之呈极显著正相关,莲藕氮磷钾养分累积总量之比为1∶0.12∶1.31。移栽后97-160 d是莲藕产量形成的关键时期,不仅叶片、叶柄和根状茎中的氮磷钾随同干物质运输并贮存到膨大根状茎中,根系还从土壤中吸收更多的氮磷钾直接运输并贮存到膨大根状茎中,后者分别占同期氮磷钾累积量的69.8%、79.2%和75.0%。160 d膨大根状茎中干物质、氮、磷和钾累积量分别平均占植株总累积量的81.1%、85.2%、88.8%和80.2%。     

Crystal structure and dimerization equilibria of PcoC, a methionine-rich copper resistance protein from Escherichia coli

PcoC is a soluble periplasmic protein encoded by the plasmid-born pco copper resistance operon of Escherichia coli. Like PcoA, a multicopper oxidase encoded in the same locus and its chromosomal homolog CueO, PcoC contains unusual methionine rich sequences. Although essential for copper resistance, the functions of PcoC, PcoA, and their conserved methionine-rich sequences are not known. Similar methionine motifs observed in eukaryotic copper transporters have been proposed to bind copper, but there are no precedents for such metal binding sites in structurally characterized proteins. The high-resolution structures of apo PcoC, determined for both the native and selenomethionine-containing proteins, reveal a seven-stranded beta barrel with the methionines unexpectedly housed on a solvent-exposed loop. Several potential metal-binding sites can be discerned by comparing the structures to spectroscopic data reported for copper-loaded PcoC. In the native structure, the methionine loop interacts with the same loop on a second molecule in the asymmetric unit. In the selenomethionine structure, the methionine loops are more exposed, forming hydrophobic patches on the protein surface. These two arrangements suggest that the methionine motifs might function in protein-protein interactions between PcoC molecules or with other methionine-rich proteins such as PcoA. Analytical ultracentrifugation data indicate that a weak monomer-dimer equilibrium exists in solution for the apo protein. Dimerization is significantly enhanced upon binding Cu(I) with a measured delta(deltaG degrees )相似文献   

Insulin increases H<Subscript>2</Subscript>O<Subscript>2</Subscript>-induced pancreatic beta cell death

Insulin resistance results, in part, from impaired insulin signaling in insulin target tissues. Consequently, increased levels of insulin are necessary to control plasma glucose levels. The effects of elevated insulin levels on pancreatic beta (β) cell function, however, are unclear. In this study, we investigated the possibility that insulin may influence survival of pancreatic β cells. Studies were conducted on RINm, RINm5F and Min-6 pancreatic β-cells. Cell death was induced by treatment with H₂O₂, and was estimated by measurements of LDH levels, viability assay (Cell-Titer Blue), propidium iodide staining and FACS analysis, and mitochondrial membrane potential (JC-1). In addition, levels of cleaved caspase-3 and caspase activity were determined. Treatment with H₂O₂ increased cell death; this effect was increased by simultaneous treatment of cells with insulin. Insulin treatment alone caused a slight increase in cell death. Inhibition of caspase-3 reduced the effect of insulin to increase H₂O₂-induced cell death. Insulin increased ROS production by pancreatic β cells and increased the effect of H₂O₂. These effects were increased by inhibition of IR signaling, indicative of an effect independent of the IR cascade. We conclude that elevated levels of insulin may act to exacerbate cell death induced by H₂O₂ and, perhaps, other inducers of apoptosis.     

In vitro T lymphopoiesis: A model system for stem cell gene therapy for AIDS

Abstract: Stable introduction of therapeutic genes into hematopoietic stem cells has the potential to reconstitute immunity in individuals with HIV infection. However, many important questions regarding the safety and efficacy of this approach remain unanswered and may be addressed in a non-human primate model. To facilitate evaluation of expression of foreign genes in T cells derived from transduced hematopoietic progenitor cells, we have established a culture system that supports the differentiation of rhesus macaque and human CD34⁺ bone marrow derived cells into mature T cells. Thymic stromal monolayers were prepared from the adherent cell fraction of collagenase digested fetal or neonatal thymus. After 10–14 days, purified rhesus CD34⁺ bone marrow-derived cells cultured on thymic stromal monolayers yielded CD3⁺CD4⁺CD8⁺, CD3⁺CD4⁺CD8^?, and CD3⁺CD4^?CD8⁺ cells. Following stimulation with mitogens, these T cells derived from CD34⁺ cells could be expanded over 1,000-fold and maintained in culture for up to 20 weeks. We next evaluated the ability of rhesus CD34⁺ cells transduced with a retroviral vector containing the marker gene neo to undergo in vitro T cell differentiation. CD34⁺ cells transduced in the presence of bone marrow stroma and then cultured on rhesus thymic stroma resulted in T cells containing the retroviral marker gene. These studies should facilitate both in vitro and in vivo studies of hematopoietic stem cell therapeutic strategies for AIDS.     

Oxygen-18 studies of the mechanism of pyrophosphoryl group transfer catalyzed by phosphoribosylpyrophosphate synthetase.

The formation of phosphoribosylpyrophosphate (PRPP) and adenosine 5′-monophosphate (AMP) from ribose 5-phosphate and adenosine 5′-triphosphate, catalyzed by purified PRPP synthetase from Salmonella typhimurium, was conducted in ¹⁸O-enriched water. The products were isolated, and inorganic phosphate was isolated from AMP and the pyrophosphoryl moiety of PRPP. Oxygen-18 was incorporated into PRPP but not into AMP. These results indicate that PRPP synthesis proceeds with scission of a βPO bond of adenosine 5′-triphosphate. Oxygen-18 enters PRPP by prior exchange of H₂¹⁸O into ribose 5-phosphate; the rate of this exchange was measured by combined gas chromatography-mass spectrometry of the trimethylsilyl derivative of ribose 5-phosphate.     

Hypodontia: Prevalence amongst Jewish populations of different origin

The teeth of 10,371 male and 11,013 female Israel Jews were examined. Prevalence of all hypodontia was 4.60% with no significant difference between the sexes; 2.11% lacked upper lateral incisors, the females having a significantly higher prevalence than males. Second premolars were missing in 1.87% of the population, with no significant differences between the sexes. Missing lower incisors was diagnosed in 0.68% of the children, with a higher prevalence in males. Prevalence of missing lower incisors was similar in the Ashkenazi and in the non-Ashkenazi. The teeth most frequently missing in descending order were the upper lateral incisors and the lower second premolars.     

Plasmid macro-evolution: selection of deletions during adaptation in a nutrient-limited environment

A study was made of the intra-and inter-population variability of the main traits involved in Trichogramma (T. brassicae and T. cacoeciae) efficiency in host exploitation: longevity, fecundity, progeny viability, progeny sex ratio and progeny allocation. The analysis of isofemale strains shows that differences in progeny viability, progeny sex ratio and progeny allocation are transmissible and relatively stable over two successive generations. Comparison of three strains of T. brassicae originating from different locations, demonstrates differences in fecundity, progeny sex ratio and progeny allocation. Differences in host exploitation strategies also exist between two sympatric populations of T. brassicae and T. cacoeciae. No significant correlation appears between the traits which discriminate populations. The ecological and evolutionary significance and the agronomical importance of the results are discussed.