Enzyme activities and membrane lipids in Artemia cysts after a long duration space flight

In the Free Flyer Biostack Experiment (L.D.E.F. mission) investigations have shown that biological objects in a resting state can survive more than 5.5 years of exposure to the space factors in particular microgravity and cosmic rays. We have measured enzyme activities involved in metabolic pathways of sugar and lipid degradation and determined phospholipid composition. Pyruvate kinase and glucose-6-phosphate dehydrogenase activities in space-exposed cysts were higher than in earth controls after 1 hour incubation. In controls, total phospholipids remained unchanged, on the contrary they increased significantly in space-exposed cysts. The rate of metabolism of various phospholipid components was unchanged in controls allowing the development while the level of most of them decreased in space-exposed cysts except for phosphatidylcholine. Enzyme activities (acetylhydrolase, phospholipase A₂ and lyso phospholipase) involved in phospholipid degradation increased; however, activities were much higher in space-exposed cysts. In conclusion, the long duration space flight resulted in an increase of the metabolic activity correlated with a faster development within the first 20 hours of post flight incubation.     

Calcium signaling in plant cells in altered gravity.

Changes in the intracellular Ca2+ concentration in altered gravity (microgravity and clinostating) evidence that Ca2+ signaling can play a fundamental role in biological effects of microgravity. Calcium as a second messenger is known to play a crucial role in stimulus-response coupling for many plant cellular signaling pathways. Its messenger functions are realized by transient changes in the cytosolic ion concentration induced by a variety of internal and external stimuli such as light, hormones, temperature, anoxia, salinity, and gravity. Although the first data on the changes in the calcium balance in plant cells under the influence of altered gravity have appeared in 80th, a review highlighting the performed research and the possible significance of such Ca2+ changes in the structural and metabolic rearrangements of plant cells in altered gravity is still lacking. In this paper, an attempt was made to summarize the available experimental results and to consider some hypotheses in this field of research. It is proposed to distinguish between cell gravisensing and cell graviperception; the former is related to cell structure and metabolism stability in the gravitational field and their changes in microgravity (cells not specialized to gravity perception), the latter is related to active use of a gravitational stimulus by cells presumebly specialized to gravity perception for realization of normal space orientation, growth, and vital activity (gravitropism, gravitaxis) in plants. The main experimental data concerning both redistribution of free Ca2+ ions in plant cell organelles and the cell wall, and an increase in the intracellular Ca2+ concentration under the influence of altered gravity are presented. Based on the gravitational decompensation hypothesis, the consequence of events occurring in gravisensing cells not specialized to gravity perception under altered gravity are considered in the following order: changes in the cytoplasmic membrane surface tension --> alterations in the physicochemical properties of the membrane --> changes in membrane permeability, --> ion transport, membrane-bound enzyme activity, etc. --> metabolism rearrangements --> physiological responses. An analysis of data available on biological effects of altered gravity at the cellular level allows one to conclude that microgravity environment appears to affect cytoskeleton, carbohydrate and lipid metabolism, cell wall biogenesis via changes in enzyme activity and protein expression, with involvement of regulatory Ca2+ messenger system. Changes in Ca2+ influx/efflux and possible pathways of Ca2+ signaling in plant cell biochemical regulation in altered gravity are discussed.     

Biological effects of heavy ions from the standpoint of target theory.

The biological effect of heavy ions is best described through the action cross section, as a function of the end-point of interest and the charge and speed of the ion. In track theory this is called the "ion-kill" cross section, for it is the effect produced by a single heavy ion and its delta rays. As with nuclear emulsions the biological track structure passes from the grain count regime to the track width regime to the thindown region with an increase in LET. With biological cells, as with any detector capable of storing sublethal damage, with low LET irradiation the action cross section (in the ion-kill mode) is increasingly obscured by the effect of "gamma-kill", by the influence of overlapping delta rays from neighboring heavy ions. Thus at low LET response is dominated by the gamma-kill mode, so that the RBE approaches 1. The theory requires 4 radiosensitivity parameters for biological detectors, extracted from survival curves at several high LET bombardments passing through the grain count regime, and at high doses. Once these are known the systematic response of biological detectors to all high LET bombardments can be unfolded separating ion kill from gamma kill, predicting the response to a mixed radiation environment, and predicting low dose response even at the level of a single heavy ion. Cell killing parameters are now available for a variety of cell lines. Newly added is a set of parameters for cell transformation.     

全球电离层发电机方程的一种数值解法

为了将建立在赤道为对称面假设基础上的二维半球域对称）电离层发电机理论扩展到全球,本文在解发电机方程时,去掉赤道对称面这一假设条件和两极附加的边界条件,使通常的边值问题变成一种“无边界’问题．它更合理地描述了电离层发电机过程,而且可以给出半球发电机理论所不能给出的特征,例如,可以对Ｓｑ电流体系的ＵＴ变化、季节变化、非偶极子地磁场部分的发电机效应等南北半球不对称的情况进行数值计算．计算实例表示,在简单的赤道对称情况下,它可以复现二维半球（对称）发电机模型的结果．在不对称情况下,电流体系的强度、焦点位置、电流方向等显示出较为复杂的变化,而半球发电机理论则无法解释这些特征．     

基于模型参考模糊自适应的转台摩擦力矩补偿研究

为克服某型伺服转台在摩擦力矩干扰下引起的低速“爬行”问题,设计了基于模型参考模糊自适应的摩擦补偿控制方法;并基于所建立的数学模型对该摩擦补偿方法进行了lyapunov稳定性证明,采用Matlab进行了仿真试验分析。仿真结果表明,该摩擦补偿方法能够有效抑制摩擦干扰的不利影响,提升了转台低速跟踪的平稳性,从而显著提高了转台的低速伺服精度。     

Survival and death of the haloarchaeon Natronorubrum strain HG-1 in a simulated martian environment

Halophilic archaea are of interest to astrobiology due to their survival capabilities in desiccated and high salt environments. The detection of remnants of salty pools on Mars stimulated investigations into the response of haloarchaea to martian conditions. Natronorubrum sp. strain HG-1 is an extremely halophilic archaeon with unusual metabolic pathways, growing on acetate and stimulated by tetrathionate. We exposed Natronorubrum strain HG-1 to ultraviolet (UV) radiation, similar to levels currently prevalent on Mars. In addition, the effects of low temperature (4, −20, and −80 °C), desiccation, and exposure to a Mars soil analogue from the Atacama desert on the viability of Natronorubrum strain HG-1 cultures were investigated. The results show that Natronorubrum strain HG-1 cannot survive for more than several hours when exposed to UV radiation equivalent to that at the martian equator. Even when protected from UV radiation, viability is impaired by a combination of desiccation and low temperature. Desiccating Natronorubrum strain HG-1 cells when mixed with a Mars soil analogue impaired growth of the culture to below the detection limit. Overall, we conclude that Natronorubrum strain HG-1 cannot survive the environment currently present on Mars. Since other halophilic microorganisms were reported to survive simulated martian conditions, our results imply that survival capabilities are not necessarily shared between phylogenetically related species.     

Induction of hypoxic root metabolism results from physical limitations in O2 bioavailability in microgravity.

Numerous spaceflight experiments have noted changes in the roots that are consistent with hypoxia in the root zone. These observations include general ultrastructure analysis and biochemical measurements to direct measurements of stress specific enzymes. In experiments that have monitored alcohol dehydrogenase (ADH), the data shows this hypoxically responsive gene is induced and is associated with increased ADH activity in microgravity. These changes in ADH could be induced either by spaceflight hypoxia resulting from inhibition of gravity mediated O2 transport, or by a non-specific stress response due to inhibition of gravisensing. We tested these hypotheses in a series of two experiments. The objective of the first experiment was to determine if physical changes in gravity-mediated O2 transport can be directly measured, while the second series of experiments tested whether disruption of gravisensing can induce a non-specific ADH response. To directly measure O2 bioavailability as a function of gravity, we designed a sensor that mimics metabolic oxygen consumption in the rhizosphere. Because of these criteria, the sensor is sensitive to any changes in root O2 bioavailability that may occur in microgravity. In a KC-135 experiment, the sensor was implanted in a moist granular clay media and exposed to microgravity during parabolic flight. The resulting data indicated that root O2 bioavailability decreased in phase with gravity. In experiments that tested for non-specific induction of ADH, we compared the response of transgenic Arabidopsis plants (ADH promoted GUS marker gene) exposed to clinostat, control, and waterlogged conditions. The plants were grown on agar slats in a growth chamber before being exposed to the experimental treatments. The plants were stained for GUS activity localization, and subjected to biochemical tests for ADH, and GUS enzyme activity. These tests showed that the waterlogging treatment induced significant increases in GUS and ADH enzyme activities, while the control and clinostat treatments showed no response. This work demonstrates: (1) the inhibition of gravity-driven convective transport can reduce the O2 bioavailability to the root tip, and (2) the perturbation of gravisensing by clinostat rotation does not induce a nonspecific stress response involving ADH. Together these experiments support the microgravity convection inhibition model for explaining changes in root metabolism during spaceflight.     

The effects of space flight on some rat liver enzymes regulating carbohydrate and lipid metabolism

We have examined, in the livers of rats carried aboard the Cosmos 936 biosatellite, the activities of about 30 enzymes concerned with carbohydrate and lipid metabolism. In addition to the enzyme studies, the levels of glycogen and of the individual fatty acids in hepatic lipids were determined. Livers from flight and ground control rats at recovery (R₀) and 25 days after recovery (R₂₅) were used for these analyses.

For all parameters measured, the most meaningful comparisons are those made between flight stationary (FS) and flight centrifuged (FC) animals at R₀. When these two groups of flight rats were compared at R₀, statistically significant decreases in the activity levels of glycogen phosphorylase, -glycerol phosphate acyl transferase, diglyceride acyl transferase, aconitase and 6-phosphogluconate dehydrogenase and an increase in the palmitoyl CoA desaturase were noted in the weightless group (FS). The significance of these findings was strengthened by the fact that all enzyme activities showing alterations at R₀ returned to normal 25 days postflight. When liver glycogen and total fatty acids of the two sets of flight animals were determined, significant differences that could be attributed to reduced gravity were observed. The weightless group (FS) at R₀ contained, on the average, more than twice the amount of glycogen than did the centrifuged controls (FC) and a remarkable shift in the ratio of palmitate to palmitoleate was noted. These metabolic alterations, both in enzyme levels and in hepatic constituents, appear to be characteristic of the weightless condition. Our data seem to justify the conclusion that centrifugation during flight is equivalent to terrestrial gravity.     

Investigating the cellular effects of isolated radiation tracks using microbeam techniques.

Studies of the effects of radiation at the cellular level have generally been carried out by exposing cells randomly to the charged-particle tracks of a radiation beam. Recently, a number of laboratories have developed techniques for microbeam irradiation of individual cells. These approaches are designed to remove much of the randomness of conventional methods and allow the nature of the targets and pathways involved in a range of radiation effects to be studied with greater selectivity. Another advantage is that the responses of individual cells can be followed in a time-lapse fashion and, for example, processes such as "bystander" effects can be studied clearly. The microbeam approach is of particular importance in mechanistic studies related to the risks associated with exposure to low fluences of charged particles. This is because it is now possible to determine the actions of strictly single particle tracks and thereby mimic, under in vitro conditions, exposures at low radiation dose that are significant for protection levels, especially those involving medium- to high-LET radiations. Overall, microbeam methods provide a new dimension in exploring mechanisms of radiation effect at the cellular level. Microbeam methods and their application to the study of the cellular effects of single charged-particle traversals are described.     

Influence of long-term hyper-gravity on the reactivity of succinic acid dehydrogenase and NADPH-diaphorase in the central nervous system of fish: a histochemical study.

In the course of a densitometric evaluation, the histochemically demonstrated reactivity of succinic acid dehydrogenase (SDH) and of NADPH-diaphorase (NADPHD) was determined in different brain nuclei of two teleost fish (cichlid fish Oreochromis mossambicus, swordtail fish Xiphophorus helleri), which had been kept under 3g hyper-gravity for 8 days. SDH was chosen since it is a rate limiting enzyme of the Krebs cycle and therefore it is regarded as a marker for metabolic and neuronal activity. NADPHD reactivity reflects the activity of nitric oxide synthase. Nitric oxide (NO) is a gaseous intercellular messenger that has been suggested to play a major role in several different in vivo models of neuronal plasticity including learning. Within particular vestibulum-connected brain centers, significant effects of hyper-gravity were obtained, e.g., in the magnocellular nucleus, a primary vestibular relay ganglion of the brain stem octavolateralis area, in the superior rectus subdivision of the oculomotoric nucleus and within cerebellar eurydendroid cells, which in teleosts possibly resemble the deep cerebellar nucleus of higher vertebrates. Non-vestibulum related nuclei did not respond to hyper-gravity in a significant way. The effect of hyper-gravity found was much less distinct in adult animals as compared to the circumstances seen in larval fish (Anken et al., Adv. Space Res. 17, 1996), possibly due to a development correlated loss of neuronal plasticity.     

微重力对拟南芥长势影响的代谢网络流平衡分析

微重力作为典型的空间环境因素,对植物生长发育的影响机制是空间生命科学的研究热点。微重力环境直接或间接影响植物代谢,并引起许多生理适应。 随着系统生物学的发展,代谢网络模型使微重力环境下的植物代谢建模成为可能。采用流平衡分析方法对模式植物拟南芥不同组织的代谢网络进行分析,研究微重力对拟南芥生长发育的影响机制。通过比较空间与地面条件下拟南芥的生物质产量,发现空间条件下拟南芥黄化幼苗、幼苗、芽、根、下胚轴的生物量分别下降了33.00%,51.52%,6.89%,12.53%,11.70%,与空间环境下拟南芥的长势变化趋势一致。代谢通路富集分析发现,微重力使得拟南芥的碳固定等通路下调,而磷酸戊糖途径上调,初步解析了微重力对拟南芥生长发育的影响机制,也验证了流平衡方法用于微重力生物学效应研究中的可行性。      

Have deoxyribonucleotides and DNA been among the earliest biomolecules?

Unlike ribose chemistry, the chemistry of 2-deoxyribose precludes its formation or at least its incorporation into nucleotides under accepted "primordial soup" conditions; therefore RNA and DNA could not develop in parallel during the evolution of protocells. However, deoxyribonucleotides might have been formed abiotically by direct reduction of ribonucleotides in a primitive version of the biochemical pathway. This sequence of events, in which DNA lagged behind RNA in the assembly of genetic information for an unknown--probably short--period of time is suggested by the primitive traits (i.e., nucleotide binding, thiol redox chemistry, and metal ion catalysis) of present-day enzyme systems of deoxyribonucleotide biosynthesis. The reaction should be amenable to experimental study.     

基于图染色理论的并行测试任务调度算法

目前的自动测试系统大多数采用串行测试的工作方式,测试效率很低.针对这个问题,建立了基于图论的测试任务关系模型,用"图"来描述测试任务占用仪器资源的情况,将测试任务调度的工程问题转化为图论中的数学问题.在测试任务关系模型的基础上,提出了两个任务调度算法:CTG算法和CTG-T算法.对于多个测试任务,利用这两个算法可以得到并行度最大或者测试时间最短的任务分组方案,能有效地实现并行测试.这两个算法是基于图的染色理论得到的,对其正确性进行了理论分析和实例仿真.两个算法已经在实际系统中得到了实验验证,结果表明能够大大提高自动测试系统的测试效率.      

基于时间-多资源占用的工作负荷评估模型

为了测量和评估航天员在轨维修的工作负荷,在时间线分析法和多资源占用理论的基础上,确定了用间接获取的资源需求占用率、直接测量的占用时间2个维度来进行工作负荷主客观综合评估,并提出基于动态时间窗口的时间-多资源占用的工作负荷评估模型。为了验证模型的有效性,搭建典型在轨维修任务——液体回路子系统的维修试验环境,招募被试,获取主观工作负荷数据,进行维修视频采集和动素时间测定。结果表明,本文模型的工作负荷值与主观工作负荷评估值显著相关且吻合较好,验证了其有效性。     

太阳高纬探测器的借力飞行轨道设计

行星借力飞行技术可以节省深空探测任务的能量消耗.针对借助内行星引力向太阳高纬度发射探测器这一科学任务,分别以金星和地球为借力星体,运用圆锥曲线拼接法,通过求解兰伯特问题绘制能量等高线图,搜索多天体交会发射机会,设计探测器与借力体轨道周期之比为1∶ 1或2∶ 3的多次借力行星际轨道,获得相对黄道面成大倾角的目标轨道.分析表明,采用多天体交会借力相比单天体借力可大大降低发射能量;3次借用金星或者地球的引力可以使探测器轨道相对黄道面的倾角达到30°左右;3次地球借力轨道性能为最优,需要的地球发射能量更低,而且飞行器进入目标轨道之前的转移时间较短.      

The radio recombination lines of hydrogen

The impact theory of spectral line broadening is used to obtain complete profiles for radio recombination lines broadened by electron and proton impact. Electron impact dominates but proton impact becomes increasingly significant as Δn$\mathrm{\Delta }n$ increases. Thus these new calculations essentially confirm previous results and so a longstanding discrepancy between observation and theory remains unresolved.     

Cellular responses to gravity: extracellular, intracellular and in-between.

Our understanding of gravitational effects (inertial effects in the vicinity of 1 x g) on cells has matured to a stage at which it is possible to define, on the basis of experimental evidence, extracellular effects on small cells and intracellular effects on eukaryotic gravisensing cells. Yet undetermined is the nature of response, if any, of those classes of cells that are not governed solely by extracellular physical events (as are prokaryotes) and are devoid of obvious mechanical devices for sensing inertial forces (such as those possessed by certain plant cells and sensory cells of animals). This "in-between" class of cells needs to be understood on the basis of the combination of intracellular and extracellular gravity-dependent processes that govern experimentally-measurable variables that are relevant to the cell's responses to modified inertial forces. The forces that certain cell types generate or respond to are therefore compared to those imposed by approximately 1 x g in the context of cytoskeletal action and symmetry-breaking pathways.     

A study of chemical systems using signal flow graph theory.

Photochemistry of giant planets and their satellites is characterized by numerous reactions involving a lot of chemical species. In the present paper, chemical systems are modeled by signal flow graphs. Such a technique evaluates the transmission of any input into the system (solar flux, electrons ... ) and gives access to the identification of the most important mechanisms in the chemical system. This method is applied to the production of hydrocarbons in the atmospheres of giant planets. In particular, the production of C2H6 in the atmosphere of Neptune from the photodissociation of CH4 is investigated. Different pathways of dissociation of CH4 are possible from L alpha radiation. A chemical system containing 14 species and 30 reactions including these different pathways of dissociation is integrated. The main mechanism of production of C2H6 is identified and evaluated for each model of dissociation. The importance of various reaction pathways as a function of time is presented.     

Soybean cotyledon starch metabolism is sensitive to altered gravity conditions.

We have demonstrated that etiolated soybean seedlings grown under the altered gravity conditions of clinorotation (1 rpm) and centrifugation (5xg) exhibit changes in starch metabolism. Cotyledon starch concentration was lower (-28%) in clinorotated plants and higher (+24%) in centrifuged plants than in vertical control plants. The activity of ADP-glucose pyrophosphorylase in the cotyledons was affected in a similar way, i.e. lower (-37%) in the clinorotated plants and higher (+22%) in the centrifuged plants. Other starch metabolic enzyme activities, starch synthase, starch phosphorylase and total hydrolase were not affected by the altered gravity treatments. We conclude that the observed changes in starch concentrations were primarily due to gravity-mediated differences in ADP-glucose pyrophosphorylase activity.