Killing of Escherichia coli cells modulated by components of the stability system ParD of plasmid R1

Summary The proteins P10 and P12 have been shown to be gene products of a new stability system, ParD, of plasmid R1. It is now shown that an R1 miniplasmid, pAB112, carrying a trans-complementable amber mutation in the gene of the P10 protein, is lethal for the host in the absence of suppression. This lethal effect is suppressed in a supF background and also by deletions in pAB112 that affect the gene of the P12 protein. These data indicate that the P12 protein has a lethal effect on the host and that this effect is neutralized by the P10 protein. The possibility that the stabilization conferred by the ParD system could be due to a counterselection, mediated by P12, of cells that lose the plasmid at cell division, is discussed.     

Response of aromatic-pathway enzymes to changing physiological states of growth in suspension cultures of Nicotiana silvestris

The activity levels of enzymes of aromatic amino acid biosynthesis respond to changing physiological states of growth, as illustrated by results obtained from suspension-cultured cells of Nicotiana silvestris Speg. et Comes line ANS 1 (2N=24). The experimental system provides a foundation for interpretations about overall regulation of enzyme levels in relationship to growth physiology. Levels of activity for shikimate dehydrogenase (EC 1.1.1.25), prephenate aminotransferase and arogenate dehydrogenase were followed throughout a growth cycle obtained by a conventional subculture protocol. Enzyme date were also obtained from cell cultures maintained in continuous exponential growth for greater than 10 generations (EE cells). Both shikimate dehydrogenase and prephenate aminotransferase exhibited elevated stationary-phase levels of enzyme, much of which was carried over into a subsequent subculture. At least 4 generations of exponential growth were required before diminution of the latter two enzymes to the levels characteristic of truly exponential-phase growth (EE cells) occurred. This is reminiscent of the overall behavior of 3-deoxy-D- arabino -heptulosonate 7-phosphate (DAHP) synthase (EC 4.1.2.15), specifically attributed to the properties of the cytosolic isozyme species (DAHP synthase-Co). Elevation of arogenate dehydrogenase also occurred in stationary-phase cells, but diminished rapidly during lag phase to reach the level characteristic of EE cells.     

Total root length as estimated from small sub-samples

A method is proposed for estimating the total length of a root system from sub-samples. This method is based on the measurement of the length and diameter of small pieces of roots, and on the measurements of the bulk density of root sub-samples. It is assumed that roots are cylinders with a given bulk density. The length and diameter of small root pieces are measured by image analysis. A weighted quadratic mean (W.Q.M.) root diameter is then calculated and used in estimating the root length. This W.Q.M. diameter is defined as the real mean diameter of an equivalent single root with the same length and volume as the tested root system. The accuracy of prediction is demonstrated for one theoretical root system. The standard deviation of estimation can be calculated using sampling simulations.     

拟澳洲赤眼蜂生殖系统的研究

拟澳洲赤眼蜂(Trichogramma confusum)的体长约0.6mm,腹部长度约0.3mm.雌蜂生殖系统(包括卵巢、生殖腔、受精囊及三种附腺)位于腹部后端,约占腹腔的2/3.成熟的卵巢由两条多滋式的卵巢管组成.两条成熟卵巢的端段细长,扭卷成一条疏松索,基部膨大,内脏贮存大量卵粒.成对的侧输卵管较短,分别开口于生殖腔后方的两侧,中输卵管缺如.受精囊呈梨形,开口于生殖腔后方.雌性生殖系统三种附腺中,第一种附腺是成对的,呈锤状,分别连接于生殖腔前方两侧;第二种附腺,腺体呈球状,其前端以短曲的小管通进膨大的贮腺囊,贮腺囊端部成柄状的弯曲小管,连接于产卵管的基部开口处.第三种附腺的腺体呈棒状,前端为细长的小管,开口于第二种附腺贮腺囊的前端.雄性生殖系统由成对的睪丸,输精管、贮精囊、附腺及单一的射精管组成.蛹的早期到后期至成虫期睾丸的形态结构,各有不同变化.     

Leaf ultrastructure of C4 species possessing different Kranz anatomical types in the cyperaceae

The leaf ultrastructure of NADP-malic enzyme type C₄ species possessing different anatomical features in the Cyperaceae was examined: types were the Rhynchosporoid type, a normal Kranz type in which mesophyll cells are adjacent to Kranz cells, and Fimbristyloid and Chlorocyperoid types, unusual Kranz types in which nonchlorophyllous mestome sheath intervenes between the two types of green cells. They show structural characteristics basically similar to the NADP-malic enzyme group of C₄ grasses, that is, centrifugally located chloroplasts with reduced grana and no increase of mitochondrial frequency in the Kranz cells. However, the Kranz cell chloroplasts of the Fimbristyloid and Chlorocyperoid types exhibit convoluted thylakoid systems and a trend of extensive development of peripheral reticulum, although those of the Rhynchosporoid type do not possess such particular membrane systems. The suberized lamella, probably a barrier for CO₂ diffusion, is present in the Kranz cell walls of the Rhynchosporoid type and in the mestome sheath cell walls of the other two types, and tightly surrounds the Kranz cells (sheaths) that are the sites of the decarboxylation of C₄ acids. These ultrastructural features are discussed in relation to C₄ photosynthetic function.     

射击过程中主要生理特征的研究

八名射击运动员(手枪2人,步枪6人),在实弹射击训练中,连续同步地记录了脑电、心电、心率、阻抗呼吸波。同时记录了受试者持枪稳定的程度。 分析表明,射击环数是五项独立无关的指标综合作用的结果。本文首次对射击时生理指标和射击环数进行系统辨识建模分析,求出每个人的系统参数_i值。找出了每人射击时最佳生理参数,为指导射击练习和反馈训练,提供了客观生理依据。 本文设计的激光光点录相方法,可反映持枪稳定的程度,简单、方便,可在射击训练中采用。     

猪肺血管紧张素转换酶的提纯

本文报道了猪肺血管紧张素转换酶(ACE)的提纯方法及其鉴定,并讨论了方法的改进。肺匀浆经1.6—2.6mol/L硫酸铵沉淀,Sephadex G-200凝胶过滤,DEAE-Sephaeel及羟基磷灰石柱层析步骤,从168克肺中获得4.5毫克酶蛋白纯品。活力回收45.2％,比活力15.6单位/毫克蛋白;和匀浆上清比较,提纯390倍。经聚丙烯酰胺凝胶电泳(pH8.3)鉴定为一条带。按SDS聚丙烯酰胺凝胶电泳(SDS-PAGE)测得其分子量为132,000道尔顿。酶蛋白在-30℃貯存10月,比活力丢失30％。     

A replication study of human exposure to 60-Hz fields: effects on neurobehavioral measures.

The purpose of this study was to reproduce and extend an earlier investigation of the effects of human exposure to combined, 60-Hz electric and magnetic fields. This paper presents the neurobehavioral results. Thirty men participated in one training session and four testing sessions. Subjects were randomly assigned to two groups. The 18 subjects in Group I were exposed (9 kV/m, 20 microT) and sham exposed in two counterbalanced orders. In Group II, half of 12 subjects were exposed (9 kV/m, 20 microT) every session, and the remaining half were sham exposed every session. The study was doubly blinded. Measures of cardiac interbeat interval, event-related brain potentials, and performance were obtained before, during, and after exposures. As in the earlier study, exposure to the combined field resulted in a statistically significant slowing of heart rate, in changes in late components of event-related brain potentials, and in decreased errors on a choice reaction-time task. In addition, field effects on several other measures approached statistical significance. The physiological measures obtained during exposure indicated that effects were greatest soon after the field was switched on, and again when it was switched off. The data indicate that changes in exposure level may be more important than duration of exposure for producing effects in human beings.