Composition and Distribution of Free Amino Acids in Flatpea (Lathyrus sylvestris L.) as Influenced by Water Deficit and Plant Age

Drought-stressed flatpea (Lathyrus sylvestris L.) plants from8 to 22 weeks old were analysed for nitrogen, soluble proteinand free amino acids. An increase in nitrogen and free aminoacid concentrations and a decrease in soluble protein levelwere observed in roots of plants up to 16 weeks old. The cumulativeconcentration of free amino acids increased with drought stress.Tissue concentrations of 2, 4-diaminobutyric acid (1.6–2.6%of the dry weight) were highest in leaves. Levels increasedsteadily, nearly doubling, in leaves and stems between weeks10 and 16. Levels in drought-stressed leaves were, on average,11.9% higher than those of controls. Estimated concentrationsof a mixture of 4-aminobutyric acid and an unknown amino acidwere highest in stems, increased in this tissue with age andtended to increase in stems and leaves and decrease in rootsin response to water deficit. Levels of the mixture of homoserineand another unidentified amino acid were not influenced by ageor water status of the plants. Root concentrations of asparagine,arginine, glutamine, aspartate, and another prominent, unidentifiedamino acid increased with plant age and reached a peak at thetime of flowering (14 to 18 weeks). Only the concentration ofthe unknown compound was elevated following drought stress.Concentrations of valine, isoleucine, leucine, phenylalanine,and methionine also increased during this period and were elevatedin drought-stressed plants. Proline levels increased with plantage and drought stress, but proline accounted for only about10% of the total free amino acids in the drought-stressed plants. Key words: 2, 4-Diaminobutyric acid, drought, flatpea     

厚壳贻贝whirlin类贝壳基质蛋白的重组表达与功能分析

贝壳历来是生物工程和材料学研究的重要对象。贝壳中的贝壳基质蛋白质在贝壳的形成与发育过程中具有重要的调控作用。Whirlin类蛋白质(Whirlin-like protein,WLP)是一种从厚壳贻贝(Mytilus coruscus)中鉴定的新型贝壳基质蛋白质。序列分析结果显示,该蛋白质含有PDZ(postsynaptic density/Discs large/Zonula occludens)结构域,而该结构域对贝壳生物矿化的影响目前尚无报道。为深入了解WLP在贝壳形成中对碳酸钙晶体的影响,在序列分析基础上,采用密码子优化结合原核重组表达,获得其重组表达产物后,开展了重组WLP对碳酸钙晶体形貌及晶型的影响研究,结晶速度抑制以及碳酸钙晶体结合分析。分析结果表明,重组WLP能诱导文石型碳酸钙晶体的形貌和方解石型碳酸钙晶体的晶型发生改变;同时重组WLP对碳酸钙晶体具有结合作用,且能抑制碳酸钙晶体的结晶速度。上述结果表明,WLP对贝壳的形成及发育具有重要影响,并可能在贝壳肌棱柱层的形成中发挥了重要作用。     

电刺激杏仁复合体诱发心律失常及其下行神经通路的初步探讨

电刺激杏仁复合体能诱发心律失常。心律失常的类型为心动过缓伴室性或结性期外收缩。刺激杏仁复合体不同亚核均能诱发心律失常,不同类型的心律失常在核内具有相应的代表点。心律失常发作与杏仁局部区域诱发的爆发性后放电有关。推测杏仁复合体内神经元过度激活可能通过杏仁-迷走神经运动背核及杏仁-下丘脑外侧区等通路下行,使心率减慢、房室传导阻滞而导致心律失常。     

利他林对戊巴比妥钠深麻醉家兔呼吸的兴奋效应及机制

在125只呼吸受戊巴比妥钠抑制并切断双侧颈迷走神经的家兔,分析了利他林(MP)呼吸效应的中枢部位及可能的递质。静脉注射 MP(2mg/kg)引起呼气时程显著缩短和呼吸频率显著增加。去除颈动脉体不影响 MP 兴奋呼吸的效应。将浸有2%MP 溶液的滤纸(2×2mm~2)贴敷在第四脑室底闩附近,或微量注射2%MP 2μl 到延髓 NTS 区,均可引起上述效应,但 NA区、NPBM 区和皮层体感运动区则无效。第四脑室或 NTS 区微量注射酚妥拉明均可阻断 MP兴奋呼吸的效应,但第四脑室注射心得安却不能阻断。结果提示,MP 可能作用于 NTS 区,在肾上腺素能α受体的参与下,受戊巴比妥钠抑制的家兔发生呼吸频率增快的效应。     

Half-att site substrates reveal the homology independence and minimal protein requirements for productive synapsis in lambda excisive recombination

The early events in site-specific excisive recombination were studied with phage lambda half-att sites that have no DNA to one side of the strand exchange region; they carry a single core-type integrase binding site and either P or P' arm flanking DNA. These half-attR and half-attL sites exhibit normal properties for the initial (covalent) top-strand transfer and form stable intermediates independent of later steps in the reaction. With these novel substrates we show that Xis specifically promotes the first strand exchange and that attL enhances Int cleavage at the top-strand site of attR. It is also shown that synapsis and initial strand transfers do not require DNA-DNA pairing but are mediated by protein-protein and protein-DNA interactions. These involve the two top-strand Int binding sites (required for the first strand exchange) and, in addition, one of the two bottom-strand sites (C') responsible for the second strand exchange.