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81.
用电生理细胞内记录的方法记录了10个以上小叶神经元对闪光、运动光斑及运动光栅刺激的电生理反应特点,结果表明:(1)小叶神经元对闪光刺激具有特征性反应,细胞对给光和撤光刺激都会表现出不同程度的去极化和超极化,反应的波形不随闪光时间的改变而改变,两次去极化之间的时间间隔与闪光刺激的时间长度成线性关系;(2)小叶神经元对运动光斑的运动速度非常敏感,而对光斑的运动方向的改变却不敏感,尽管有的细胞存在一个能使反应的变化更快的优势方向,但并没有明显的运动方向选择性;(3)小叶神经元对运动光栅的响应频率受光栅的空间频率和运动速度的双重调制,与光栅的运动方向无关。 相似文献
82.
自然免耕下的稻田生态系统 总被引:15,自引:0,他引:15
自然免耕是一种新型的稻田耕作法,通过人为改变地表微地形,建立了一个适合水旱作物复种轮作,鱼、萍、鸭周年共生的稻田生态系统.自然免耕促进了土壤内、外环境的物质、能量和信息交换,水、热、气、肥谐调.并通过环境网络效应,强化了环境与生物区系间的缓冲-调节力.提高了土壤自调能力和土壤有序度. 相似文献
83.
Arabidopsis COP8, COP10, and COP11 genes are involved in repression of photomorphogenic development in darkness. 总被引:16,自引:6,他引:10 下载免费PDF全文
Wild-type Arabidopsis seedlings are capable of following two developmental programs: photomorphogenesis in the light and skotomorphogenesis in darkness. Screening of Arabidopsis mutants for constitutive photomorphogenic development in darkness resulted in the identification of three new loci designated COP8, COP10, and COP11. Detailed examination of the temporal morphological and cellular differentiation patterns of wild-type and mutant seedlings revealed that in darkness, seedlings homozygous for recessive mutations in COP8, COP10, and COP11 failed to suppress the photomorphogenic developmental pathway and were unable to initiate skotomorphogenesis. As a consequence, the mutant seedlings grown in the dark had short hypocotyls and open and expanded cotyledons, with characteristic photomorphogenic cellular differentiation patterns and elevated levels of light-inducible gene expression. In addition, plastids of dark-grown mutants were defective in etioplast differentiation. Similar to cop1 and cop9, and in contrast to det1 (deetiolated), these new mutants lacked dark-adaptive change of light-regulated gene expression and retained normal phytochrome control of seed germination. Epistatic analyses with the long hypocotyl hy1, hy2, hy3, hy4, and hy5 mutations suggested that these three loci, similar to COP1 and COP9, act downstream of both phytochromes and a blue light receptor, and probably HY5 as well. Further, cop8-1, cop10-1, and cop11-1 mutants accumulated higher levels of COP1, a feature similar to the cop9-1 mutant. These results suggested that COP8, COP10, and COP11, together with COP1, COP9, and DET1, function to suppress the photomorphogenic developmental program and to promote skotomorphogenesis in darkness. The identical phenotypes resulting from mutations in COP8, COP9, COP10, and COP11 imply that their encoded products function in close proximity, possibly with some of them as a complex, in the same signal transduction pathway. 相似文献
84.
Louis Faso Richard S. Trowbridge Wei Quan Xiu-Lan Yao Edmund C. Jenkins Alma Maciulis Thomas D. Bunch Henry M. Wisniewski 《In vitro cellular & developmental biology. Animal》1994,30(4):226-235
Summary A strain of cerebral endothelial cells was established from isolated cortical microvessels of caprine brain. These cells,
which are referred to as ECl cells, can be routinely subcultured to 32 passages without the loss of differentiated morphologic
and immunologic traits. The ability to routinely subculture ECl cells is an important asset, given that isolated cerebral
endothelial cells in mammals generally lose their differentiated traits after only 2 to 3 passages.
ECl cells were shown to contain Factor VIII-related antigen, which is a specific marker for cells of endothelial origin. ECl
cells morphologically demonstrated a scarcity of pinocytotic vesicles on their apical surfaces, a lack of trans-cytoplasmic
vesicles, and the ability to form in culture confluent monolayers with tight junctional complexes. Therefore, ECl cells possess
specific antigenic and ultrastructural features which classify them as being small vessel endothelial cells of the blood-brain
barrier type. Cytogenetic evaluation of ECl cells demonstrated a normal female goat 60,XX karyotype and confirmed the apparent
non-transformed nature of ECl cells due to the lack of chromosome abnormalities or rearrangements. Using scanning electron
microscopy, ECl cells were also shown to form confluent monolayers on mixed nitrocellulose filters, a feature that will enable
the development of an in vitro system to study trans-endothelial transport. Given that ECl cells are readily subcultured and
grow well on nitrocellulose filters, and that they resemble cerebral endothelium in vivo, it seems evident that ECl cells
can be used as a versatile model for the study of blood-brain barrier function, regulation, and pathology. 相似文献
85.
Some of the early genes of Bacillus subtilis bacteriophage SPO1 were hypothesized to function in the shutoff of host biosyntheses. Two of these genes, e3 and e22, were cloned and sequenced. E22 showed no similarity to any known protein, while E3, a highly acidic protein, showed significant similarity only to other similarly acidic proteins. Each gene was immediately downstream of a very active early promoter. Each was expressed actively during the first few minutes of infection and was then rapidly shut off and its RNA rapidly degraded. An e3 nonsense mutation severely retarded the degradation of e3 RNA. Expression of a plasmid-borne e3 gene, in either B. subtilis or Escherichia coli, resulted in the inhibition of host DNA, RNA, and protein syntheses and prevented colony formation. However, the e3 nonsense mutation caused no measurable decrease in either burst size or host shutoff during infection and, in fact, caused an increased burst size at high multiplicities of infection. We suggest that e3 is one of several genes involved in host shutoff, that its function is dispensable both for host shutoff and for phage multiplication, and that its shutoff function is not entirely specific to host activities. 相似文献
86.
Through simple model analysis, the mass action kinetic model for lipolytic enzymes in biphasic aqueous-organic systems can be simplified using the quasi-steady state assumption (or the quasi-equilibrium state assumption) for the adsorbed enzyme E* or the enzyme-substrate complex E*S. Some parameter combinations leading to the above assumptions are derived confirmed by full numerical integration of the whole enzymatic process. The results may be classified into three categories: (1) the quasi-equilibrium state assumption for E*, (2) the quasi-steady state assumption for E*, and (3) the quasi-steady state assumption for E*S. Further simplification for both E* and E*S is also discussed. (c) 1993 Wiley & Sons, Inc. 相似文献
87.
本文研究探讨了进化地位不同的三种动物的短时空间记忆功能及其与前额叶背侧部进化水平的相关性。结果表明,在延缓反应作业中,经1000次训练后,7只恒河猴对空间位置的记忆时间平均为7.7±3.2min,懒猴为3.8±0.44min,而树鼩即使在延缓时间几乎为零秒的延缓反应中,其正确反应率也未达到90%标准。一种延缓时间仅测试一个单元,即不经训练的实验表明,恒河猴在延缓期为“0”—5min的各测试单元中,正确反应率稳定在80%以上;懒猴在延缓时间为“0”—4min的各测试单元中,平均正确反应率与恒河猴无明显差异,而当延缓时间增加到5min时,在延缓反应作业中取得的成绩显著下降;树鼩在延缓时间为1—5min的作业中取得的正确反应率在70%以下。3种动物在视觉辨别学习作业中却无明显差异。形态学研究表明,灵长类大脑前额叶的面积和结构的复杂性在进化过程中逐渐增大,如恒河猴大脑前额叶的表面积占大脑半球表面积的11.5%(Brodmann,1929),其内颗粒层发达,背侧部明显凸起,主沟区发达;懒猴的前额叶表面积占其大脑半球表面积的8.3%,背侧部凸起不显著,主沟未形成,额极内颗粒层分化明显,背侧部的内颗粒层较内侧部的发达程度差(Sanides,1967);树鼩的前额叶表面积占7.5%,额极的内颗粒层分化不明显,为非颗粒化区,此区之后为颗粒区 相似文献
88.
89.
本文对蛋白质中二硫键附近的残基进行了计算机统计分析,结果发现平行和反平行残基间存在着特异的配对规律。这种残基间的相互作用或识别,可能与蛋白质折叠过程中正确地形成二硫键有关。该结果有助于蛋白质工程设计。 相似文献
90.
本研究在改进后短程序基础上,对氨基酸分离柱进行了改进。改进后的分离柱长为10cm。比原来20cm长柱分离3—MH的时间缩短了近1/2。实验所得的(回收率为97.59%,分离度0.89±0.02。变异系数1.17)这些指标较国外用其它方法所得的结果有良好的相关性。多次测定结果说明长柱与短柱比较无明显差异。证明了短柱对3—MH含量无影响。这一改进所建立的方法大大地缩短了样品的分析时间,节约了大量进口试剂,开展这方面的工作将有利益提高严重烧伤、创伤后蛋白质代谢和营养学等方面的研究水平。 相似文献