Ice Encasement Injury to Microsomal Membranes from Winter Wheat Crowns : I. Comparison of Membrane Properties after Lethal Ice Encasement and during a Post-Thaw Period

The functional and physical properties of cellular membranes isolated from Triticum aestivum, cvs Norstar and Fredrick, were altered coincident with changes in composition after a lethal ice-encasement stress and further during a 6 hour post-thaw period. Crowns encased in ice for a duration which inhibited regrowth, exhibited enhanced rates of electrolyte leakage. Furthermore, the recovery of total microsomal protein and phospholipid declined, suggesting that some membrane degradation had been induced during the anoxic stress. The microviscosity of microsomes and liposomes prepared from such membranes increased during stress, and this was correlated with a 2- to 4-fold increase in the free fatty acid levels in the microsomal fraction. There was, however, only a relatively minor change in fatty acid unsaturation during the ice-encasement stress. The process continued during a 6 hour aerobic post-thaw treatment, but the pattern was somewhat different. During this phase, the leakage of electrolytes was further increased and the recovery of microsomal protein and phospholipid continued to decline, indicating general degradation; but, in contrast to the anoxic phase, the degree of fatty acid unsaturation declined markedly, indicating lipid peroxidation.     

兔栓尾线虫成虫体表结构的扫描电镜观察

本虫最初由Rudolphi在1819年定名为Oxyurts ambigua,随后由Dujardin于1845年修订为Pa ssalurus ambiguus。本虫种在光镜下的形态已有描述,但迄今尚无电子显微镜观察报道。本文报告兔拴尾线虫成虫在扫描电子显徽镜下的体表徽细结构。     

苹果“长富2”和安徽珍稀“软子石榴”休眠条的催芽及其芽离体繁殖和生根

(一)植物名称:苹果(Malus pumila)日本着色系富士“长富2”材料类别:高接于成年苹果树上的一年生“长富2”休眠条及其萌发的新枝芽节培养条件:1986年1月剪取“长富2”休眠条,在冰箱6±1℃冷藏一个月,然后将其插在不同溶液中(2％蔗糖、1mg/16-BA、蔗糖2％与6-BA 1mg/1混合液及蒸馏水),在室温23—25℃,每天16小时     

玉米叶片生长规律的观察

供试品种玉米各叶位的生长有严格的顺序性,叶面积大小与延续生长期呈正相关。叶面积系数最高值为3.14,增长期51天,稳定期37天。单位叶面积叶绿素含量在第9、13叶出现两个高峰,其中第1峰与单位面积鲜重的高峰重合。     

有壳变形虫在我国第四纪古环境研究中的意义

有壳变形虫在我国第四纪地层中广泛分布,常见种有旋匣壳虫、无棘匣壳虫、针棘匣壳虫和砂壳虫未定种等。作为能在低pH环境下抗溶蚀的原生动物,它们在缺乏钙质化石的地层中是特别有用的环境标志。在我国,有壳变形虫在沿海平原与陆架海区是辨认海相、陆相和海陆过渡相沉积的宝贵标志。此外,有壳变形虫对于营养水平、沉积速率和其它环境参数反应灵敏,是第四纪地层古湖泊学的潜在指示化石。但是为了将有壳变形虫用于我国古湖泊学研究,需要对其现代分布进行定量的研究。 本文描述了一个新种,即亚洲鸟嘴虫Hoogenraadia asiatica。     

南海表层沉积物中微体动物群的分布及沉积环境特征的探讨

根据沉积物中微体动物群及小壳类遗壳的分布与海洋沉积环境关系,记述在不同的沉积相中各类生物群的种类组成,分布特点及环境意义。     

Growth dynamics of a methylotroph (Methylomonas L3) in continuous cultures. II. Growth inhibition and comparison against an unstructured model

High methanol concentrations have a negative effect on the growth rate and the biomass yield of growth transients induced by methanol pulses in continuous cultures of Methylomonas L3. The physiological basis of this effect is investigated by measuring the effect of the methanol pulse on the cell energy charge (EC) and ATP, ADP, and AMP concentrations, and by comparing the results of the pulse transients against an unstructured model. The methanol pulse is shown to lead to increased values of the cell EC and ATP concentration, and thus, inhibition and reduced availability of biosynthetic energy are excluded as causes of inhibition. When the biomass and methanol profiles of the transient experiments are compared in phase-plane diagrams against computer simulations based on the model, satisfactory agreement between experimental data and model predictions is found in single-substrate, high-dilution-rate experiments. Conversely, poor agreement between experimental data and simulation results indicates a more severe growth inhibition than the model predicts at low dilution rates and a less severe one in mixed-substrate experiments. Based on these findings and other relevant physiological information, we propose that the large variations in the negative effect of methanol on growth result from the fact that cells accumulate methanol to widely different concentrations depending on their physiological state. In their effort to detoxify from the high intracellular methanol and formaldehyde concentrations, cells oxidize considerably more methanol than they can incorporate into biomass. This leads to a useless ATP surplus, which the cells must hydrolyze without doing any useful biosynthetic work, and this results in lower biomass yields.     

Effect of cycling on final mixed culture fate

Cycling in feed substrate concentration and dilution rate is examined as a means of modifying the final fate of a mixed culture. It is shown for the case where the specific growth rate of one species is always greater than that of the second that no cycling strategy will provide the desired extinction of the faster growing species unless time delay is included in the modeling. To account for the time lag in adjusting organism metabolic activities to environmental changes, an adaptability parameter is introduced. Numerical simulations are carried out and an operating diagram indicating the conditions under which the desired extinction occurs is constructed. Cycling in feed substrate concentration and dilution rate are both found to produce the desired result.     

A model for growth of Saccharomyces cerevisiae containing a recombinant plasmid in selective media

A major problem in the use of plasmids as recombinant vectors is the problem of plasmid-free cell generation from plasmid shedding and subsequent growth. A common technique for controlling the population of plasmidfree cells is the use of selective media against these cells using an auxotrophic host and a plasmid that has the ability to produced the essential metabolite. A distributed model describing the growth of Saccharomyces cerevisiae containing a recombinant plasmid in selective media was developed. The model allows for growth and production of a metabolite by the plasmid-carrying strain and growth of the plasmid-free cells on resulting metabolite concentrations. Through a determination of system constants and numerical solution to the equations, experimental batch and continuous culture results for cell concentration transients could be simulated by the model. The results indicated that despite selective pressure, plasmid-free cell growth was significant.