具收获与投放的三种群Volterra模型的周期轨道

本文在文〔2〕的基础上,研究三维动力系统的Lyapunov分枝问题．放宽了文〔2〕中关于向量场函数的限制,相应地给出从空间闭轨族扰动产生孤立周期解的判定方法．应用判定定理及椭圆函数的积分技巧,研究了具有收获与投放的三种群Volterra模型,得到了存在周期轨道的充分条件．     

DNA fingerprinting of human cell lines using PCR amplification of fragment length polymorphisms

Summary Methods for monitoring cell line identification and authentication include species-specific immunofluorescence, isoenzyme phenotyping, chromosome analysis, and DNA fingerprinting. Most previous studies of DNA fingerprinting of cell lines have used restriction fragment length polymorphism analysis. In this study, we examined the utility of an alternative and simpler method of cell line DNA fingerprinting—polymerase chain reaction (PCR) amplification of fragment length polymorphisms. Fourteen human cell lines previously found by other methods to be either related or disparate were subjected to DNA fingerprinting by PCR amplification of selected fragment length polymorphism loci. Cell identification patterns by this method were concordant with those obtained by isoenzyme phenotyping and restriction fragment length polymorphism-DNA fingerprinting, and were reproducible within and between assays on different DNA extracts of the same cell line. High precision was achieved with electrophoretic separation of amplified DNA products on high resolution agarose or polyacrylamide gels, and with fragment length polymorphism (FLP) loci-specific “allelic ladders” to identify individual FLP alleles. Determination of the composite fingerprint of a cell line at six appropriately chosen fragment length polymorphism loci should achieve a minimum discrimination power of 0.999. The ability of PCR-based fragment length polymorphism DNA fingerprinting to precisely and accurately identify the alleles of different human cell lines at multiple polymorphic fragment length polymorphism loci demonstrates the feasibility of developing a cell line DNA fingerprint reference database as a powerful additional tool for future cell line identification and authentication.     

内蒙古草原退化群落恢复演替的研究II. 恢复演替时间进程的分析

 根据内蒙古典型草原地带的羊草+大针茅草原退化变型一冷蒿群落封育12年(1983—1994)的动态监测数据进行分析,对群落恢复演替轨迹取得以下认识： 1．依据群落优势种的更替及主分量分析结果可将恢复演替过程划分为冷蒿优势阶段、冷蒿+冰草阶段、冰草优势阶段、羊草优势阶段。 2;退化草原群落在恢复演替过程中,群落生产力的变化表现出阶梯式跃变和亚稳态阶面相间的特点。第一次跃变发生在1984年,上升到第二个阶面,第二次跃变发生在1990年,进入了第三个阶面,已接近于原生群落的生产力。 3．群落生产力与水资源量的关系因恢复演替阶段不同而异。第一亚稳态时期,群落地上现存生物量大体处于166g·m-2的水平上,生长季降水量达176mm以上时,增加降水对群落生产力的提高不发生显著影响。第二亚稳态时期,群落生物量与降水量之间的相关性显著。可推算出群落于物质生产用水量介于1.1～1.6mm·g-1之间。此值在1.1mm·g-1时,群落对水资源的利用效率最高,而在1.6mm·g-1时群落生物量达到最大值。 4．在恢复演替进程中,群落密度的位点常数约为271.5株·m-2,循此常数上下波动,表现出拥挤与稀疏交替发生的过程,构成了恢复演替的节奏性变化。群落生物量的跃变与亚稳态的形成,以及群落密度的拥挤与稀疏交替作用是群落恢复演替的内在机制。恢复演替的速度,到第10年发生了1.78个半变的生态距离。5．草原退化群落恢复演替过程中,按照其节奏性及生产力跃变与亚稳态的规律,调控放牧利用强度或采取技术措施,调节群落拥挤和稀疏的交替过程可加速恢复演替进程。     

龟纹瓢虫对豆蚜的捕食功能反应及寻找效应研究

龟纹瓢虫雌虫和雄虫对豆蚜的功能反应符台Holling Ⅱ型模型,其模型为：Na=0．9233N／(1 0．0171N)(雌虫)和Na=0．8641N／(1 0．0164N)(雄虫),瓢虫捕食豆蚜的数量随豆蚜密度增加而增加．但寻找效应随豆蚜密度增加而降低。日最大捕食量和最佳寻找密度分别为37.42(雌)、34．11头(雄)和17．25（雌)、15．8头(雄)。龟纹瓢虫寻找效应随自身密度的增加而降低,其数学模型为：E=0．3032·P^-15634(雌)和E=0．3048·P^-1.1697(雄)。干扰反应的教学模型为：E=0．8104·P^-2.1721(雌),E=0．7125·P^-2.2660,E=0．5963·P^-2.1751(雌雄混台种群)。     

Caloric Restriction: Conservation of in Vivo Cellular Replicative Capacity Accompanies Life-Span Extension in Mice

In male mice of a long-lived hybrid strain (B6D2F1), long-term 40% caloric restriction (CR) extended both mean and maximum life spans by 36 and 20%, respectively, over that of ad libitum fed (AL) controls. Measurements of entry into S-phase were made in vivo of six different cell types in five different organs using 2-week exposures to BrdU. The labeling index (L.I.) in all organs studied was lower in young CR mice than in young AL fed mice. In most cases, the L.I. in AL mice fell to the levels of that in the CR mice by 13 months of age, and the two groups then remained so through old age. However, when the L.I. was measured in old CR mice which had been placed on the AL diet for a period of 4 weeks (this was termed refeeding (RF)), it was found to be above that of similar age AL or CR mice and almost at the level of young AL mice. This was still true, but to a lesser degree, in a repeat study using an 8-week period of RF. In a separate but parallel in vitro study (companion paper, this volume), the superiority of CR over AL for retention of cellular replication capacity was confirmed by clone size distribution measurements made in several cell types in mice of several age groups. These results indicate that: (1) the rate of cell replication in AL diet mice diminishes greatly by early middle age in all organ sites studied and then plateaus or declines much more slowly; (2) CR broadly preserves in vivo cellular replicative capacity but often requires the energy levels provided by a switch to AL feeding to demonstrate this late in life; (3) accordingly, the replicative deficit in AL fed mice appears to be cumulative and is significant only in old age. The mechanism(s) involved is yet to be discovered but may be related to, or even the same as, that which extends life spans in CR animals. Correspondingly, and with corroborative data from our in vitro companion study, (W. R. Pendergrass et al., 1995. Exp. Cell. Res. 217, 309-316), we suggest that cell populations sustain an accrual of biochemical damage or physiological alterations which increasingly limit their replicative capacity as the animal ages, and that CR reduces the accrual of this damage.     

Effects of acute hyperoxic exposure on solute fluxes across the blood-gas barrier in rat lungs

Zheng, Lu P., Rui Sheng Du, and Barbara E. Goodman.Effects of acute hyperoxic exposure on solute fluxes across the blood-gas barrier in rat lungs. J. Appl.Physiol. 82(1): 240-247, 1997.We investigatedeffects of acute hyperoxia on solute transport from air space tovascular space in isolated rat lungs. Air spaces were filled withKrebs-Ringer bicarbonate solution containing fluoresceinisothiocyanate-labeled dextran (FD-20; mol wt 20,000) and either²²Na⁺and [¹⁴C]sucrose, orD-[¹⁴C]glucoseandL-[³H]glucose.Apparent permeability-surface area products for tracers over time (upto 120 min) were calculated for isolated perfused lungs from controlrats (room air) and rats exposed to >95%O₂ for 48 or 60 h immediatelypostexposure. After O₂ exposures,mean fluxes for[¹⁴C]sucrose and FD-20were significantly higher than in room-air control lungs. However,amiloride-sensitive Na⁺ and activeD-glucose fluxes were unchangedafter hyperoxic exposure. Therefore, it is unlikely that decreases innet solute transport in this lung-injury model contributed to pulmonaryedema resulting from O₂ toxicity.Increased net solute transport shown to help resolve pulmonary edemaafter acute hyperoxic exposure must therefore begin during the recoveryperiod. In summary, our data show increases in passive solute fluxesbut no changes in active solute fluxes immediately after acutehyperoxic lung injury.

     

小麦中期染色体银染蛋白的分析

对小麦中期染色体中银染蛋白的大小、形状和分布频率进行图像分析,看到：染色体顺的银染蛋白以颗粒状的形式存在,其大小不同,分布不均匀,数量差异也较大;从形状来看,大的银粒为点状,小的银粒有的为点状,有的实际为短纤维状,结果表明：染色体骨架在小麦中是真实存在的,骨架蛋白以颗粒和纤维状的形式分布于整个染色体中。     

经血管灌流生长抑素对大鼠离体胃运动的抑制作用

采用血管灌流大鼠离体胃模型,探讨生长抑素对胃运动的影响。结果表明：（１）生长抑素能明显抑制胃窦自发和胃动素兴奋的胃运动;（２）生长抑素可抑制离体胃内源性胃泌素释放;（３）抗生长抑素血清和前列腺素合成酶抑制剂消炎痛可阻断生长抑素对胃窦运动的抑制作用。上述结果提示：生长抑素的抑制作用除通过直接作用于生长抑素受体外,还可能通过胃窦局部前列腺素介导来抑制胃的运动。     

乙型脑炎病毒NS2A-C60A位点突变对其生物学特性影响研究*

目的:旨在探索Ⅰ型日本乙型脑炎病毒传代致弱后基因组突变NS2A-C60A对乙脑病毒生物学特性的影响。方法:首先通过对传代致弱及原始乙脑毒株基因组序列进行测序比对、结构预测分析并利用Western blotting(WB)确定了目标研究位点NS2A-C60A;然后使用反向遗传定点突变技术构建拯救了包含NS2A-C60A单点突变的病毒株;最后利用噬斑形态观察、生长曲线、双萤光素酶分析,WB以及炎性因子检测和动物实验研究了该单点突变对于乙脑病毒生物学特性的影响。结果:首次研究发现Ⅰ型乙脑病毒传代致弱会导致NS1'蛋白表达的显著下降以及可能的相关位点NS2A-C60A,并成功拯救获得了NS2A-C60A单点突变毒株rJEV-C60A,研究发现NS2A-C60A突变对乙脑病毒的生长特性及噬斑形成没有显著影响,但是能够显著降低乙脑病毒NS1'蛋白的表达,并且该位点突变能够轻微阻碍乙脑病毒对细胞炎性因子表达的抑制,动物实验结果显示NS2A-C60A点突变病毒与原毒株具有相似的神经毒力,说明该位点突变不是影响乙脑病毒毒力致弱的关键位点。结论:新发现的NS2A-C60A位点突变能够显著减少乙脑病毒NS1'蛋白的表达,但是对其增殖、诱导炎症及神经毒力等生物学特性没有显著影响。     

Release of heat pretreatment-induced dormancy in lettuce seeds by ethylene or cytokinin in relation to the production of ethylene and the synthesis of 1-aminocyclopropane-1-carboxylic acid during germination

The germination of lettuce (Lactuca sativa L.) seeds was greatly reduced when the seeds were heated at 97°C for 30 h prior to imbibition. This dormancy was effectively released when ethylene (1–100 ppm) or benzyladenine (BA) (0.005–0.05 mM) was applied during the imbibition period. Ethylene was not required during the early part of imbibition, but was essential during the period immediately prior to radicle protrusion. Treatment with 1-aminocyclopropane-1-carboxylic acid (ACC) (0.1–10 mM) stimulated germination, but was not as effective as ethylene or cytokinin treatment. During the germination of nondormant lettuce seeds, ethylene production increased rapidly and reached a peak at 24 h, which coincided with the emergence of the radicle, and then declined; the level of ACC increased as ethylene production rate increased, but remained at a high level after radicle protrusion. In heat-pretreated dormant lettuce seeds, the increases in percent germination, ethylene production, and ACC levels were all delayed and lower than those of nondormant seeds, and these increases were accelerated by treatment with ethylene or cytokinin.