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991.
用柱层析和TLC分离小麦PGIP和植保素 总被引:1,自引:0,他引:1
植物抗病能力大小的测定需要比较准确可靠且相对简便的办法。采用接种病菌于植物上观察染菌情况虽然直观,但受病菌本身的生理状态及外界环境影响很大,且不便于定量的表述。因此,选择合适的生理生化指标作为植物抗性大小的衡量标准,对于植物病理的研究具有重要的意义。选择了小麦体系的两种抗性物质- 小麦植保素和 P G I P作为小麦的抗性指标来分离分析 相似文献
992.
B S Mankoo N S Collins P Ashby E Grigorieva L H Pevny A Candia C V Wright P W Rigby V Pachnis 《Nature》1999,400(6739):69-73
The skeletal muscles of the limbs develop from myogenic progenitors that originate in the paraxial mesoderm and migrate into the limb-bud mesenchyme. Among the genes known to be important for muscle development in mammalian embryos are those encoding the basic helix-loop-helix (bHLH) myogenic regulatory factors (MRFs; MyoD, Myf5, myogenin and MRF4) and Pax3, a paired-type homeobox gene that is critical for the development of limb musculature. Mox1 and Mox2 are closely related homeobox genes that are expressed in overlapping patterns in the paraxial mesoderm and its derivatives. Here we show that mice homozygous for a null mutation of Mox2 have a developmental defect of the limb musculature, characterized by an overall reduction in muscle mass and elimination of specific muscles. Mox2 is not needed for the migration of myogenic precursors into the limb bud, but it is essential for normal appendicular muscle formation and for the normal regulation of myogenic genes, as demonstrated by the downregulation of Pax3 and Myf5 but not MyoD in Mox2-deficient limb buds. Our findings show that the MOX2 homeoprotein is an important regulator of vertebrate limb myogenesis. 相似文献
993.
Nucleosome mobilization catalysed by the yeast SWI/SNF complex. 总被引:18,自引:0,他引:18
994.
Auditory collusion and a coupled couple of outer hair cells. 总被引:7,自引:0,他引:7
The discrepancies between measured frequency responses of the basilar membrane in the inner ear and the frequency tuning found in psychophysical experiments led to Bekesy's idea of lateral inhibition in the auditory nervous system. We now know that basilar membrane tuning can account for neural tuning, and that sharpening of the passive travelling wave depends on the mechanical activity of outer hair cells (OHCs)3, but the mechanism by which OHCs enhance tuning remains unclear. OHCs generate voltage-dependent length changes at acoustic rates, which deform the cochlear partition. Here we use an electrical correlate of OHC mechanical activity, the motility-related gating current, to investigate mechano-electrical interactions among adjacent OHCs. We show that the motility caused by voltage stimulation of one cell in a group evokes gating currents in adjacent OHCs. The resulting polarization in adjacent cells is opposite to that within the stimulated cell, which may be indicative of lateral inhibition. Also such interactions promote distortion and suppression in the electrical and, consequently, the mechanical activity of OHCs. Lateral interactions may provide a basis for enhanced frequency selectivity in the basilar membrane of mammals. 相似文献
995.
996.
Structure of Cdc42 in complex with the GTPase-binding domain of the 'Wiskott-Aldrich syndrome' protein. 总被引:16,自引:0,他引:16
N Abdul-Manan B Aghazadeh G A Liu A Majumdar O Ouerfelli K A Siminovitch M K Rosen 《Nature》1999,399(6734):379-383
The Rho-family GTP-hydrolysing proteins (GTPases), Cdc42, Rac and Rho, act as molecular switches in signalling pathways that regulate cytoskeletal architecture, gene expression and progression of the cell cycle. Cdc42 and Rac transmit many signals through GTP-dependent binding to effector proteins containing a Cdc42/Rac-interactive-binding (CRIB) motif. One such effector, the Wiskott-Aldrich syndrome protein (WASP), is postulated to link activation of Cdc42 directly to the rearrangement of actin. Human mutations in WASP cause severe defects in haematopoletic cell function, leading to clinical symptoms of thrombocytopenia, immunodeficiency and eczema. Here we report the solution structure of a complex between activated Cdc42 and a minimal GTPase-binding domain (GBD) from WASP. An extended amino-terminal GBD peptide that includes the CRIB motif contacts the switch I, beta2 and alpha5 regions of Cdc42. A carboxy-terminal beta-hairpin and alpha-helix pack against switch II. The Phe-X-His-X2-His portion of the CRIB motif and the alpha-helix appear to mediate sensitivity to the nucleotide switch through contacts to residues 36-40 of Cdc42. Discrimination between the Rho-family members is likely to be governed by GBD contacts to the switch I and alpha5 regions of the GTPases. Structural and biochemical data suggest that GBD-sequence divergence outside the CRIB motif may reflect additional regulatory interactions with functional domains that are specific to individual effectors. 相似文献
997.
998.
Metamorphic core complexes are domal uplifts of metamorphic and plutonic rocks bounded by shear zones that separate them from unmetamorphosed cover rocks. Interpretations of how these features form are varied and controversial, and include models involving extension on low-angle normal faults, plutonic intrusions and flexural rotation of initially high-angle normal faults. The D'Entrecasteaux islands of Papua New Guinea are actively forming metamorphic core complexes located within a continental rift that laterally evolves to sea-floor spreading. The continental rifting is recent (since approximately 6 Myr ago), seismogenic and occurring at a rapid rate ( approximately 25 mm yr-1). Here we present evidence-based on isostatic modelling, geological data and heat-flow measurements-that the D'Entrecasteaux core complexes accommodate extension through the vertical extrusion of ductile lower-crust material, driven by a crustal density inversion. Although buoyant extrusion is accentuated in this region by the geological structure present-which consists of dense ophiolite overlaying less-dense continental crust-this mechanism may be generally applicable to regions where thermal expansion lowers crustal density with depth. 相似文献
999.
1000.
心跳间隔增量序列的多尺度分析及临床应用 总被引:1,自引:0,他引:1
通过对心跳间隔序列、心跳间隔增量序列的多尺度熵和多尺度标准差分析, 发现心跳间隔序列的多尺度熵主要反映年龄对心脏活动水平的影响, 不足以作为区分充盈性心衰的诊断依据. 然而, 心跳间隔增量序列的多尺度熵分析却显示充盈性心衰和房颤患者心率变异性的复杂性较健康人有显著降低, 揭示两种疾病的心率变异性有着共同的潜在动力学性质. 提出了以心跳间隔增量序列在尺度4下的样本熵作为充盈性心衰和房颤的诊断依据并给出了参考值. 通过分析不同心功能分级对结果的影响, 发现即使是轻度心衰也能显著区别于健康人, 意味着该参数可以用于心衰的早期诊断. 相似文献