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71.
背联体贻贝棘尾虫的每一虫腹面含有相当于正常棘尾虫的腹面纤毛系统,背联两虫任意一侧属于一虫的背面有4列背触毛,它们的排列分布相似于正常棘昆虫的第1—4列背触毛,另一虫背面打2列背触毛,它们相似于正常棘尾虫的第5、6列背触毛。结果表明,背联体棘尾虫是其中两虫各以背面第4列和第5列背触毛之间的皮层区相联接形成的。也有的背联体中背部皮层联接区有变化。无性分裂中背联两虫皮层纤毛结构的形态发生相似于正常棘尾虫,并且两者其皮层纤毛器如口围带、额腹横棘毛、左、右缘棘毛和背触毛等相应结构的发育是同步进行的,推测背联两虫的皮层发育既是相对独立的,又有某种机制控制着相互间的协调。背联体棘昆虫在无性生殖周期中总是经历着一个调节成单体的过程,认为这于背联两虫都具有一套结构功能正常的运动胞器(特别是口围带),而产生向不同方向运动的“不协调”的力有关。 相似文献
72.
Foraging aphid parasitoids,Diaeretiella rapae M'Intosh, were exposed to sublethal doses of the insecticides pirimicarb, permethrin and malathion on brusslls sprouts plants.
Observations on wasp distribution over time revealed that wasps spent less time on sprayed plants, relative to controls and,
while on these plants, tended to concentrate activity on unsprayed surfaces. For permethrin and malathion, pesticide residues
reversed the stereotypic upward foraging pattern of the wasp. Negative consequences of sublethal pesticide doses for parasitoid
foraging efficiency are discussed.
相似文献
73.
Characterization of Inhibitor-Sensitive and -Resistant Adenosine Transporters in Cultured Human Fetal Astrocytes 总被引:1,自引:1,他引:0
Abstract: The kinetic characteristics of [3H]adenosine uptake, the extent to which accumulated [3H]adenosine was metabolized, the effects such metabolism had on measurements of apparent Michaelis-Menten kinetic values of KT and Vmax, and the sensitivities with which nucleoside transport inhibitors blocked [3H]adenosine accumulations were determined in cultured human fetal astrocytes. KT and Vmax values for accumulations of [3H]-labeled purines using 15-s incubations in the absence of the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) and the adenosine kinase inhibitor 5′-iodotubercidin (ITU) were 6.2 µM and 0.15 nmol/min/mg of protein for the high-affinity and 2.6 mM and 21 nmol/min/mg of protein for the low-affinity components respectively. In the presence of EHNA and ITU, where <4% of accumulated [3H]adenosine was metabolized, transport per se was measured, and kinetic values for KT and Vmax were 179 µM and 5.2 nmol/min/mg of protein, respectively. In the absence of EHNA and ITU, accumulated [3H]adenosine was rapidly metabolized to AMP, ADP, and ATP, and caused an appearance of “concentrative” uptake in that the intracellular levels of [3H]-labeled purines (adenosine plus its metabolites) were 1.4-fold higher than in the medium. No apparent concentrative accumulations of [3H]adenosine were found when assays were conducted using short incubation times in the absence or presence of EHNA and ITU. The nucleoside transport inhibitors dipyridamole (DPR), nitrobenzylthioinosine (NBI), and dilazep biphasically inhibited [3H]adenosine transport; for the inhibitor-sensitive components the IC50 values were 0.7 nM for NBI, 1.3 nM for DPR, and 3.3 nM for dilazep, and for the inhibitor-resistant component the IC50 values were 2.5 µM for NBI, 5.1 µM for dilazep, and 39.0 µM for DPR. These findings, in cultured human fetal astrocytes, represent the first demonstration of inhibitor-sensitive and -resistant adenosine transporters in nontransformed human cells. 相似文献
74.
Isolation and expression in Escherichia coli of hepB and hepC, genes coding for the glycosaminoglycan-degrading enzymes heparinase II and heparinase III, respectively, from Flavobacterium heparinum. 下载免费PDF全文
Upon induction with heparin, Flavobacterium heparinum synthesizes and secretes into its periplasmic space heparinase I (EC 4.2.2.7), heparinase II, and heparinase III (heparitinase; EC 4.2.2.8). Heparinase I degrades heparin, and heparinase II degrades both heparin and heparan sulfate, while heparinase III degrades heparan sulfate predominantly. We isolated the genes encoding heparinases II and III (designated hepB and hepC, respectively). These genes are not contiguous with each other or with the heparinase I gene (designated hepA). hepB and hepC were found to contain open reading frames of 2,316 and 1,980 bp, respectively. Enzymatic removal of pyroglutamate groups permitted sequence analysis of the amino termini of both mature proteins. It was determined that the mature forms of heparinases II and III contain 746 and 635 amino acids, respectively, and have calculated molecular weights of 84,545 and 73,135, respectively. The preproteins have signal sequences consisting of 26 and 25 amino acids. Truncated hepB and hepC genes were used to produce active, mature heparinases II and III in the cytoplasm of Escherichia coli. When these enzymes were expressed at 37 degrees C, most of each recombinant enzyme was insoluble, and most of the heparinase III protein was degraded. When the two enzymes were expressed at 25 degrees C, they were both present predominantly in a soluble, active form. 相似文献
75.
包囊游仆虫休眠包囊中,各类纤毛器的纤毛基体上方的大部分纤毛杆退化,或仅保留毛基体,有时部分额腹棘毛的毛基体也瓦解消失。残留纤毛的纤毛杆周围微管和中央微管仍具有“9 2”结构特征,也有少数纤毛杆出现2套“9 2”微管共处于一层纤毛膜内的现象。毛基体中周围三联体微管的中央形成微管形结构聚合体,基体附属结构仅存在基体间连接及纤毛器托架的残余物;非纤毛区皮层表膜下未见微管层。纤毛区皮层含纤毛器腔周围微管层(相当于表膜下微管层)、纤毛器深部及附近的微管束和分散的微管群。并且,纤毛区皮层囊泡内含有呈不同形态的纤毛杆结构;大核核孔明显变大,核孔数目减少,核孔内膜附着染色质。 相似文献
76.
Calcium ions play critical roles in neuronal differentiation. We have recorded transient, repeated elevations of calcium in embryonic Xenopus spinal neurons over periods of 1 h in vitro and in vivo, confocally imaging fluo 3-loaded cells at 5 s intervals. Calcium spikes and calcium waves are found both in neurons in culture and in the intact spinal cord. Spikes rise rapidly to approximately 400% of baseline fluorescence and have a double exponential decay, whereas waves rise slowly to approximately 200% of baseline fluorescence and decay slowly as well. Imaging of fura 2-loaded neurons indicates that intracellular calcium increases from 50 to 500 nM during spikes. Both spikes and waves are abolished by removal of extracellular calcium. Developmentally, the incidence and frequency of spikes decrease, whereas the incidence and frequency of waves are constant. Spikes are generated by spontaneous calcium-dependent action potentials and also utilize intracellular calcium stores. Waves are produced by a mechanism that does not involve classic voltage-dependent calcium channels. Spikes are required for expression of the transmitter GABA and for potassium channel modulation. Waves in growth cones are likely to regulate neurite extension. The results demonstrate the roles of a novel signaling system in regulating neuronal plasticity, that operates on a time scale 104 times slower than that of action potentials. © 1995 John Wiley & Sons, Inc. 相似文献
77.
植物定植图微机显示与管理系统 总被引:1,自引:0,他引:1
介绍了运用软件工程的方法和数据库技术研究开发的南京中山植物园植物定植图微机显示与管理系统。详细介绍了系统的目标,系统的实现,应用软件的研制及应用效果。 相似文献
78.
鳗鱼肌肉的氨基酸及营养价值 总被引:7,自引:1,他引:6
孔晓荣 《氨基酸和生物资源》1995,17(2):33-35
通过对优质食用鱼类—鳗鱼肌肉的氨基酸进行测定证实,鳗鱼较之其它鱼类是一种营养价值更高、滋味更鲜美的鱼类。并且,根据结果氨基酸组成比例,可为鳗鱼的人工饲养等方面的研究提供理论依据。 相似文献
79.
地衣霉素对细胞膜表面运铁蛋白受体功能的影响 总被引:1,自引:0,他引:1
应用抑制糖蛋白N-糖链合成的地衣霉素处理SMMC-7721人肝癌细胞,3H甘露糖掺入实验显示细胞膜表面糖蛋白N-糖链的合成受到显著抑制,但细胞膜表面运铁蛋白受体内吞再循环的过程无显明变化,进一步的研究表明受体与运铁蛋白的亲和力亦无改变,但细胞膜表面运铁蛋白受体数减少。结果提示用地衣霉素处理细胞后,在内质网合成的无N-糖链的运铁蛋白受体影响其运输到细胞膜表面表达。 相似文献
80.
新的生物杀虫剂螨虫素对棉花、蔬菜害虫的毒力评价及应用技术研究 总被引:2,自引:0,他引:2
本文通过生物杀虫剂螨虫素对棉花、蔬菜害虫的毒力评价及田间应用研究表明,它对棉朱砂叶螨和菜青虫两种害虫杀伤力最强,其中LC90分别为0.078ppm和0.013ppm。兼有胃毒、触杀作用,残效期较长,分别达13天和9天。田间小区试验认为防治菜青虫和茄朱砂叶螨以2ppm浓度为宜。防治适期为卵孵化初期或低龄幼(若)虫(螨)期,其防效能达90%以上。该药特点用药量低、效果好、无公害、值得推广。 相似文献