中国微重力科学研究回顾与展望

微重力科学主要研究微重力环境中物质运动的规律,以及不同重力环境中重力对物质运动的影响.中国微重力科学研究起步于20世纪60年代,兴起于80年代中后期,经过多年发展,目前已初具规模,在一些重要方向具有明显特色和一定优势.本文回顾了中国微重力科学研究的早期历程,评述了近年来中国微重力科学研究进展,特别是利用实践十号科学实验卫星、天宫二号空间实验室等空间平台开展的微重力科学与技术应用研究取得的最新成果,并对中国载人空间站时代微重力科学发展的前景予以瞻望,推动微重力科学与应用研究在中国的快速、可持续发展.      

微重力环境中哺乳动物细胞分子生物学效应研究进展

随着载人航天事业的不断发展,空间失重环境引起的航天员健康问题（心血管疾病、免疫抑制、肌肉萎缩、骨质疏松等）日益突出,这已成为人类探索空间的一大阻碍.越来越多的研究关注到微重力条件下机体及细胞的变化.近期的研究表明,在细胞水平上,微重力会引起细胞降解,改变细胞骨架,并造成细胞在分子水平（如细胞增殖、分化、迁移、粘附、信号转导等过程）的一系列改变.本文对微重力条件下免疫细胞、内皮细胞、骨细胞、癌细胞的相关研究进行了归纳总结,研究结果可为微重力条件下机体及相关细胞的研究提供指导,为治疗或缓解微重力条件造成的疾病提供方法和思路.      

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。      

Genetic and physiological damage induced by cosmic radiation on dry plant seeds during space flight

Total evaluation of cosmic radiation effect with or without discrimination of individualized HZE-ion effects in dry seeds flown for 10 days on STS-9, yielded significant evidence for radiation damage in space. They depend on the biological criteria tested (seed germination, morphogenesis, embryo lethality, mutation rate) which stand for early, physiological and late genetic effects. They are also related to the radiation shielding environment in the space shuttle. Proceeding from these results three direct questions can be posed for present (LDEF-1) and future (ERA-1, D-2) experiments in space: What is the influence of cosmic radiation on cytogenetic repair and ontogenetic restitution processes? Does microgravity disorder the morphogenesis (i.e. growth and cell differentiation)? Is there an interaction between the effects of cosmic radiation and microgravity in eukaryotic plant systems?     

The effects of microgravity on induced mutation in Escherichia coli and Saccharomyces cerevisiae.

We examined whether microgravity influences the induced-mutation frequencies through in vivo experiments during space flight aboard the space shuttle Discovery (STS-91). We prepared dried samples of repair-deficient strains and parental strains of Escherichia (E.) coli and Saccharomyces (S.) cerevisiae given DNA damage treatment. After culture in space, we measured the induced-mutation frequencies and SOS-responses under microgravity. The experimental findings indicate that almost the same induced-mutation frequencies and SOS-responses of space samples were observed in both strains compared with the ground control samples. It is suggested that microgravity might not influence induced-mutation frequencies and SOS-responses at the stages of DNA replication and/or DNA repair. In addition, we developed a new experimental apparatus for space experiments to culture and freeze stocks of E. coli and S. cerevisiae cells.     

微重力量值对气液两相流相分布及液相湍流统计量影响的数值研究

气液两相流在空间领域具有广阔的应用前景, 深入理解微重力量值(微重力大小)对相分布和液相湍流的影响十分必要. 采用欧拉elax-elax拉格朗日双向耦合模型深入研究了不同微重力量值对相分布和液相湍流的影响. 液相速度场通过直接数值模拟求解, 气泡的运动轨迹由牛顿运动方程跟踪. 研究表明, 气泡分布和液相湍流与微重力量值均具有直接联系. 在低微重力量值下, 气泡近似均匀分布在槽道内, 且对液相湍流统计量几乎没有影响; 然而当微重力量值较高时, 大量气泡聚集在壁面附近, 液相湍流由于气泡的注入受到极大调制.      

An experimental system for determining the influence of microgravity on B lymphocyte activation and cell fusion.

The influence of microgravity on lymphocyte activation is central to the understanding of immunological function in space. Moreover, the adaptation of groundbased technologies to microgravity conditions presents opportunities for biotechnological applications including high efficiency production of antibody forming hybridomas. Because the emerging technology of microgravity hybridoma generation is dependent upon activation and cultivation of B lymphocytes during flight, we have adapted mitogen-driven B lymphocyte stimulation and culture that allows for the in vitro generation of large numbers of antibody forming cells suitable for cell fusion over a period of 1-2 weeks. We believe that this activation and cultivation system can be flown on near-term space flights to test fundamental hypotheses about mammalian cell activation, cell fusion, metabolism, secretion, growth, and bio-separation.     

Microgravity effects on "postural" muscle activity patterns.

Changes in neuromuscular activation patterns associated with movements made in microgravity can contribute to muscular atrophy. Using EMG to monitor "postural" muscles, it was found that free floating arm flexions made in microgravity were not always preceded by neuromuscular activation patterns normally observed during movements made in unit gravity. Additionally, manipulation of foot sensory input during microgravity arm flexion impacted upon anticipatory postural muscle activation.     

Accumulation of stress protein 72 (HSP72) in muscle and spleen of goldfish taken into space.

Using Western blot analysis, here, we report the levels of HSP72 in several organs from goldfish which were taken into space on the NASA space shuttle. A remarkable accumulation of HSP72 was detected in muscle and spleen of those fish taken into space as compared with controls. These results suggested that the HSP72 induction is a kind of stress response at the molecular level introduced by the space environment consisting of microgravity and/or cosmic radiation as stressors.     

Possible mechanism of microgravity impact on Carausius morosus ontogenesis.

Experiments aboard "Spacelab-D1" and "Cosmos-1887" revealed an adverse effect of space flight on Carausius morosus embryos. The main influencing factor for stick insect eggs turned out to be microgravity, while the contribution of HZE particles of cosmic radiation was relatively low. Flight experiments indicated an increased vulnerability of stick insect eggs to microgravity at intermediate stages of development, that could support the "convection" hypothesis.     

Evaluation of upper body muscle activity during cardiopulmonary resuscitation performance in simulated microgravity

Performance of efficient single-person cardiopulmonary resuscitation (CPR) is vital to maintain cardiac and cerebral perfusion during the 2–4 min it takes for deployment of advanced life support during a space mission. The aim of the present study was to investigate potential differences in upper body muscle activity during CPR performance at terrestrial gravity (+1Gz) and in simulated microgravity (μG). Muscle activity of the triceps brachii, erector spinae, rectus abdominis and pectoralis major was measured via superficial electromyography in 20 healthy male volunteers. Four sets of 30 external chest compressions (ECCs) were performed on a mannequin. Microgravity was simulated using a body suspension device and harness; the Evetts–Russomano (ER) method was adopted for CPR performance in simulated microgravity. Heart rate and perceived exertion via Borg scores were also measured. While a significantly lower depth of ECCs was observed in simulated microgravity, compared with +1Gz, it was still within the target range of 40–50 mm. There was a 7.7% decrease of the mean (±SEM) ECC depth from 48 ± 0.3 mm at +1Gz, to 44.3 ± 0.5 mm during microgravity simulation (p < 0.001). No significant difference in number or rate of compressions was found between the two conditions. Heart rate displayed a significantly larger increase during CPR in simulated microgravity than at +1Gz, the former presenting a mean (±SEM) of 23.6 ± 2.91 bpm and the latter, 76.6 ± 3.8 bpm (p < 0.001). Borg scores were 70% higher post-microgravity compressions (17 ± 1) than post +1Gz compressions (10 ± 1) (p < 0.001). Intermuscular comparisons showed the triceps brachii to have significantly lower muscle activity than each of the other three tested muscles, in both +1Gz and microgravity. As shown by greater Borg scores and heart rate increases, CPR performance in simulated microgravity is more fatiguing than at +1Gz. Nevertheless, no significant difference in muscle activity between conditions was found, a result that is favourable for astronauts, given the inevitable muscular and cardiovascular deconditioning that occurs during space travel.     

Plant reproduction systems in microgravity: experimental data and hypotheses.

Elucidation of the possibilities for higher plants to realize complete ontogenesis, from seed to seed, and to propagate by seeds in microgravity, is a fundamental task of space biology connected with the working of the CELSS program. At present, there are results of only 6 spaceflight experiments with Arabidopsis thaliana, an ephemeral plant which will flower and fruit in orbit. Morphogenesis of generative organs occurs normally in microgravity, but unlike the ground control, buds and flowers mainly contain sterile elements of the androecium and gynoecium which degenerate at different stages of development in microgravity. Cytological peculiarities of male and female sterility in microgravity are similar to those occurring naturally during sexual differentiation. Many of the seed formed in microgravity do not contain embryos. Hypotheses to explain abnormal reproductive development in microgravity are: 1) nutritional deficiency, 2) insufficient light, 3) intensification of the influence of the above-mentioned factors by microgravity, 4) disturbances of a hormonal nature, and 5) the absence of pollination and fertilization. Possible ways for testing these hypotheses and obtaining viable seeds in microgravity are discussed.     

Spaceflight results in increase of thick filament but not thin filament proteins in the paramyosin mutant of Caenorhabditis elegans

We have investigated the effect of microgravity during spaceflight on body-wall muscle fiber size and muscle proteins in the paramyosin mutant of Caenorhabditis elegans. Both mutant and wild-type strains were subjected to 10 days of microgravity during spaceflight and compared to ground control groups. No significant change in muscle fiber size or quantity of the protein was observed in wild-type worms; where as atrophy of body-wall muscle and an increase in thick filament proteins were observed in the paramyosin mutant unc-15(e73) animals after spaceflight. We conclude that the mutant with abnormal muscle responded to microgravity by increasing the total amount of muscle protein in order to compensate for the loss of muscle function.     

Alkylating agent (MNU)-induced mutation in space environment.

In recent years, some contradictory data about the effects of microgravity on radiation-induced biological responses in space experiments have been reported. We prepared a damaged template DNA produced with an alkylating agent (N-methyl-N-nitroso urea; MNU) to measure incorrect base-incorporation during DNA replication in microgravity. We examined whether mutation frequency is affected by microgravity during DNA replication for a DNA template damaged by an alkylating agent. Using an in vitro enzymatic reaction system, DNA synthesis by Taq polymerase or polymerase III was done during a US space shuttle mission (Discovery, STS-91). After the flight, DNA replication and mutation frequencies were measured. We found that there was almost no effect of microgravity on DNA replication and mutation frequency. It is suggested that microgravity might not affect at the stage of substrate incorporation in induced-mutation frequency.     

Capillary movement of liquid in granular beds in microgravity.

A more complete understanding of the dynamics of capillary flow through an unsaturated porous medium would be useful for the development of an effective water and nutrient delivery system for the growth of plants in space. An experiment was conducted on the Mir Space Station that used an experimental cuvette called "Capillary Test Bed" to compare fluid migration under terrestrial laboratory conditions by positioning the cuvette such that the hydrostatic force is negated and on Mir under microgravity conditions. Differences in fluid migration in the cuvette were observed with migration being slower in microgravity compared with some ground control experiments.     

空间站微重力流体实验设备需求分析

对国际空间站和中国科学实验卫星及载人飞行器上开展的微重力流体实验情况进行论述和分析,重点分析了国际空间站（ISS）微重力流体科学实验设备情况.根据中国空间微重力流体物理科学发展需求,结合国际空间站微重力流体科学实验对设备的需求,提出了未来在中国空间站开展微重力流体实验时空间实验设备需要重点考虑和解决的问题,同时提出相关设计建议.      

In vitro plant cell growth in microgravity and on clinostat.

For the study of gravity's role in the processes of plant cell differentiation in-vitro, a model "seed-seedling-callus" has been used. Experiments were carried out on board the orbital stations Salyut-7 and Mir as well as on clinostat. They lasted from 18 to 72 days. It was determined that the exclusion of a one-sided action of gravity vector by means of clinostat and spaceflight conditions does not impede the formation and growth of callus tissue; however, at cell and subcellular levels structural and functional changes do take place. No significant changes were observed either on clinostat or in space concerning the accumulation of fresh biomass, while the percentage of dry material in space is lower than in control. Both in microgravity (MG) and in control, even after 72 days of growth, cells with a normally developed ultrastructure are present. In space, however, callus tissue more often contains cells in which the cross-section area of a cell, a nuclei and of mitochondria are smaller and the vacuole area--bigger than in controls. In microgravity a considerable decrease in the number of starch-containing cells and a reduction in the mean area of starch grains in amyloplasts is observed. In space the amount of soluble proteins in callus tissue is 1.5 times greater than in control. However, no differences were observed in fractions when separated by the SDS-PAGE method. In microgravity the changes in cell wall material components was noted. In the space-formed callus changes in the concentration of ions K, Na, Mg, Ca and P were observed. However, the direction of these changes depends on the age of callus. Discussed are the possible reasons for modification of morphological and metabolic parameters of callus cells when grown under changed gravity conditions.     

Water movement on the convex surfaces of porous media under microgravity

A plant growth system for crop production under microgravity is part of a life supporting system designed for long-duration space missions. A plant growth in soil in space requires the understanding of water movement in soil void spaces under microgravity. Under 1G-force condition, on earth, water movement in porous media is driven by gradients of matric and gravitational potentials. Under microgravity condition, water movement in porous media is supposed to be driven only by a matric potential gradient, but it is still not well understood. We hypothesized that under microgravity water in void spaces of porous media hardly moved comparing in void spaces without obstacles because the concave surfaces of the porous media hindered water movement. The objective of this study was to investigate water movement on the convex surfaces of porous media under microgravity. We conducted parabolic flight experiments that provided 20–25?s of microgravity at the top of a parabolic flight. We observed water movement in void spaces in soil-like porous media made by glass beads and glass spheres (round-bottomed glass flasks) in the different conditions of water injection under microgravity. Without water injection, water did not move much in neither glass beads nor glass spheres. When water was injected during microgravity, water accumulated in contacts between the particles, and the water made thick fluid films on the particles surface. When the water injection was stopped under microgravity, water was held in the contacts between the particles. This study showed that water did not move upward in the void spaces with or without the water injection. In addition, our results suggested that the difficulty of water movement on the convex (i.e. particle surfaces) might result in slower water move in porous media under microgravity than at 1G-force.     

Development of plant protoplasts during the IML-1 mission.

During the 8 day IML-1 mission, regeneration of cell walls and cell divisions in rapeseed protoplasts were studied using the Biorack microscope onboard the Space Shuttle "Discovery". Samples from microgravity and 1g protoplast cultures were loaded on microscope slides. Visual microscopic observations were reported by the payload specialist Roberta Bondar, by down-link video transmission and by use of a microscope camera. Protoplasts grown under microgravity conditions do regenerate cell walls but to a lesser extent than under 1g. Cell divisions are delayed under microgravity. Few cell aggregates with maximum 4-6 cells per aggregate are formed under microgravity conditions, indicating that microgravity may have a profound influence on plant cell differentiation.     

Embryogenesis and organogenesis of Carausius morosus under spaceflight conditions

The influence of cosmic radiation and/or microgravity on insect development was studied during the 7 day German Spacelab Mission D1. Eggs of Carausius morosus of five stages differing in sensitivity to radiation and in capacity to regeneration were allowed to continue their development in the BIORACK 22°C incubator, either at microgravity conditions or on the 1 g reference centrifuge. Using the Biostack concept - eggs in monolayers were sandwiched between visual track detectors - and the 1 g reference centrifuge, we were able to separate radiation effects from microgravity effects and also from combined effects of these two factors in space. After retrieval, hatching rates, growth kinetics and anomaly frequencies were determined in the different test samples. The early stages of development turned out to be highly sensitive to single hits of cosmic ray particles as well as to the temporary exposure to microgravity during their development. In some cases, the combined action of radiation and microgravity even amplified the effects exerted by the single parameters of space. Hits by single HZE particles caused early effects, such as body anomalies, as well as late effects, such as retarded growth after hatching. Microgravity exposure lead to a reduced hatching rate. A synergistic action of HZE particle hits and microgravity was established in the unexpectedly high frequency of anomal larvae. However, it cannot be excluded, that cosmic background radiation or low LET HZE particles are also causally involved in damage observed in the microgravity samples.