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第28回宇宙利用シンポジウム (2012年1月23-24日. 日本学術会議), 港区, 東京都, Space Utilization Research (January 23-24, 2012. Science Council of Japan), Minato-ku, Tokyo Japan, 資料番号: SA6000032079, レポート番号: L39

We have investigated to know the limit where the life on the earth can be resistant against various kinds of the extreme environmental factor in the space. Spores and leaves of a moss may be extremely resistant against them, so we have chosen three kinds of moss, and investigated the effect of three kinds of extreme environmental factors: vacuum (1 x 10(exp -3) Pa), nitrogen-exchanged air (1 Pa), and ultrahigh pressure (7.5 GPa). Ratio of budding in the spores and leaves exposed to vacuum for two months was not different from that of the control groups not exposed to vacuum. Budding of the group exposed to nitrogen-exchanged air for one month did not show any difference from that of control groups. Furthermore, 20 percent of spores were resistant against ultrahigh pressure exposed for one week. These results indicate that spores and leaves of the moss have much stronger resistibility against extreme environmental factors that the 'tun' of Milnesium tardigradum we have studied up to now. Spores and leaves of the moss may be a very good material for the resistivity of the life on earth against extreme environmental conditions in space., 資料番号: AA0063706088

Criptobiosis is a feature of Minesium tardigradum (Phylum Tardigrata). When this animal is exposed to environmental conditions that are not good for their activity, they are transferred to a special shape called 'tun'. We have investigated the resistibility of the tun against super high pressure. Twenty specimens of M. tardigradum were transferred to tun in dry conditions, and were kept in desiccator for a week. Tuns were placed in 7.5 GPa for 20 min, 3 hrs, 6 hrs, 12 hrs, and 24 hrs, respectively. While almost of tuns exposed up to 6 hrs recovered, but all of the no specimens exposed for 24 hrs did recover. Twenty-five percent of the specimens exposed to 12 hrs were alive, but they couldn't walk and were died within a week. We supposed that resistibility of M. tardigradum should be further enhanced if their tun is formed in complete vacuum and low temperature., 資料番号: AA0063349115

Microbial cells were irradiated with high-dose X-ray (0.2 nm, 500 R/s) for 0 to 5 min to examine their survivability based on the biological 'energy currency', i.e., Adenosine 5'-Triphosphate (ATP), and the Colony-Forming Units (CFU). The well-known radiation-resistant bacterium, Deinococcus radiodurans, and the normal and mini cells of Escherichia coli X-1488 were used for the irradiation tests. Minicells are known to lack genomic DNA, and were thus used to examine the effect of X-ray on non-DNA damages, while X-ray causes indirect (e.g., via OH-radical formation) damages to DNA. The results were: (1) ATP showed highest survivability in the D. radiodurans cells, followed by the normal E. coli cells; (2) CFU of D. radiodurans showed highest survivability, too; and, (3) ATP and CFU of minicells showed rapid decrease despite absence of DNA to-be-damaged by X-ray irradiation. These results suggest that non-DNA damages (probably damages against proteins and/or membrane) affect the viability of minicells. Direct effects of X-ray irradiation against non-cellular ATP and other biomolecules should be assessed in future studies., 資料番号: AA0063349116

第27回宇宙利用シンポジウム (2011年1月24日-25日, 宇宙航空研究開発機構宇宙科学研究所相模原キャンパス), 相模原市, 神奈川県, The Twenty-seventh Space Utilization Symposium (January 24-25, 2011. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan, Mosses have high tolerance to desiccation and freezing. It is known that sugar accumulation enhance freezing tolerance. This study investigated the relation of sugar concentration to the desiccation tolerance. For this purpose, we used each 2 species from dry habitats (Hedwigia ciliata and Eurohypnum leptothallum) and wet habitats (Rhynchostegium riparioides and Plagiomnium vesicatum). Desiccation tolerance was represented as survival ratio after slow or fast desiccation. The survival ratio was determined by the method of using electrolyte leakage. After slow desiccation and under wet condition (control experiment), the sugar content of mosses was analyzed by HPLC. The mosses from dry habitats maintained high survival ratio after either slow or fast desiccation, whereas mosses from wet habitats showed relative low ratio after fast desiccation. The survival ratio of the mosses after fast desiccation corresponded not to one kind of sugar amount but also to the total sugar amount. Sucrose was the major sugar in all mosses. We have previously thought the large amount of one trisaccharide protect against desiccation in Bryum argenteum. However, the present data suggest the possibility that both sucrose and trisaccharide play the role of protectant., 資料番号: AA0065129064

第27回宇宙利用シンポジウム (2011年1月24日-25日, 宇宙航空研究開発機構宇宙科学研究所相模原キャンパス), 相模原市, 神奈川県, The Twenty-seventh Space Utilization Symposium (January 24-25, 2011. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan, The seeds of plants represent a dormant stage of plant life cycle and show strong resistance to environmental stresses such as desiccation and low temperature. In this study, we examined resistance and sensitivity of seeds to tremendous level of pressure. Seeds of Arabidopsis thaliana were exposed to ultrahigh pressure (7.5GPa) and seed germination and post-germination were investigated. We found that ultrahigh pressure treatment of seeds for 30 minutes to 2 hours inhibited seed germination and suppressed the growth of shoots and roots after germination. The ultrahigh pressure treatment for 5 hours and 24 hours completely inhibited seed germination. Morphological analysis of non-germinated seeds demonstrated that cells of embryos treated with ultrahigh pressure were almost identical to that of non-treated embryos. In addition, a germination-promoting hormone gibberellic acid did not overcome the inhibition of seed germination by the ultrahigh pressure treatment. To investigate the effect of ultrahigh pressure on cell division, we used transgenic Arabidopsis expressing Beta-glucronidase (GUS) reporter gene under the control of CYCLIN B1;1 promoter (CYCB1;1-GUS). The CYCB1;1-GUS seedlings germinated after ultrahigh pressure treatment did not show any GUS activity in root meristem and shoot meristem. Taken together, our results suggest that ultrahigh pressure strongly suppresses cell division in meristems and inhibit seed germination and post-germination growth in A. thaliana., 資料番号: AA0065129063

著者人数: 12名, Accepted: 2011-11-13, 資料番号: SA1004244000

第26回宇宙利用シンポジウム(2010年1月25日-26日, 宇宙航空研究開発機構宇宙科学研究本部相模原キャンパス), The Twenty-sixth Space Utilization Symposium (January 25-26, 2010: ISAS/JAXA Sagamihara, Japan), Mosses are tolerant to excess environmental conditions such as desiccation and freezing. Tolerance may be generated by increase of sugar concentration. A moss, Bryum argenteum is widely distributed on stones and concrete walls all over the world, and is tolerant to desiccation for a long time. Several kinds of sugar are synthesized by this species. We have investigated whether some of these sugars increased upon desiccation. The moss was collected from the field, and was kept in three conditions; i.e., 80 % relative humidity, low temperature (4C), and ABA (abscisic acid) for 1, 3 and 6 days, respectively, and the sugar content was analyzed using HPLC. For control experiment, B. argenteum was kept in moist condition at 25C as control experiment. Sucrose content (mg/g dry weight) increased in low temperature and ABA treatment as well as control experiment. This suggests that sugars are synthesized without exposure to excess stresses., 共催: 日本学術会議, joint hosting: The Science Council of Japan, 資料番号: AA0064730061

第26回宇宙利用シンポジウム(2010年1月25日-26日, 宇宙航空研究開発機構宇宙科学研究本部相模原キャンパス), The Twenty-sixth Space Utilization Symposium (January 25-26, 2010: ISAS/JAXA Sagamihara, Japan), One of major problems in astrobiology is intense radiation, theoretical and experimental studies on biological protection and tolerance to radiation are needed. Wet and freeze-dried microbial cells were irradiated with high-dose X-ray for 0 to 10,000 Gy and high-energy Fe ions for 0 to 4,850 Gy to examine their survivability based on the most probably number (MPN), the biological "energy currency", i.e., adenosine 5'-triphosphate (ATP) and genomic DNA fragmentation. The well known radiation-resistant bacteria such as genus Deinococcus radiodurans, highly stress-resistant spore former Bacillus subtilis spore and radiation-sensitive Escherichia coli were used for this experiment. Irradiation of synchrotron X-ray (0.2 nm) at a high dose rate of 4.4 Gy/s (500 R/s) was done at KEK Photon Factory. Freeze dried D. raduidurans and E. coli cells showed higher survivability than their wet cells. But B. subtilis spores have not changed their survivability wet or freeze-dried. Freeze-dried celluar ATP showed no decrease against to the dose. In addition, genomic DNA fragmentation was not easy to generated in freeze-dried cells. Irradiation of 500 MeV Fe ion at a dose rate of 0.172 Gy/s (2.5×10(exp8) particles/s) was done at NIRS HIMAC. Generally similar results to X-ray irradiation were observed, but ATP showed exponential decrease in wet cells against to the dose., 形態: カラー図版あり, 共催: 日本学術会議, 著者人数: 25人, Physical characteristics: Original contains color illustrations, joint hosting: The Science Council of Japan, 資料番号: AA0064730053

第25回宇宙利用シンポジウム(2009年1月14日-15日, 宇宙航空研究開発機構宇宙科学研究本部相模原キャンパス), The Twenty-fifth Space Utilization Symposium (January 14-15, 2009: ISAS/JAXA Sagamihara, Japan), One of major problems in astrobiology is intense radiation, theoretical and experimental studies on biological protection and tolerance to radiation are needed. Air dried-microbial cells were irradiated with high-dose X-ray for 0 to 66,500 Gy and high-energy Fe ions for 0 to 2,000 Gy to examine their survivability based on the biological "energy currency", i.e., adenosine 5'-triphosphate(ATP), and the Most probably number (MPN). The well known radiation-resistant bacteria such as genus Deinococcus and Rubrobacter radiotolerans, highly stress-resistant spore former family Bacillaceae and radiation-sensitive Escherichia coli strains were used for this experiment. Irradiation of synchrotron X-ray (0.2 nm) at a high dose rate of 4.4 Gy/s (500 R/s) was done at KEK Photon Factory. All species showed exponential decrease in MPN against total dose. However, celluar ATP showed little decrease at low dose and linear (or exponential) decrease at high dose. Genus Deinococcus and Rubrobacter radiotolerans showing survival at 67 kGy, was more than 60 times resistant compared with normal E. coli. Irradiation of 500 MeV Fe ion at a dose rate of 0.172 Gy/s (2.5 x 10(exp 8) particles/s) was done at NIRS HIMAC. Generally similar results to X-ray irradiation were observed, but some genus Deinococcus and Rubrobacter radiotolerans showed no decrease at total dose 2000 Gy. And celluar ATP showed no decrease against to the dose. More biomacromolecule should be used in future study., 形態: カラー図版あり, 資料番号: AA0064297069

第22回宇宙利用シンポジウム(2006年1月17日-19日, 日本学術会議6階会議室 六本木、東京), The Twenty-second Space Utilization Symposium (January 17-19, 2006: Science Council of Japan, Roppongi, Tokyo, Japan), Recent findings in planetary science have increased anticipations for extraterrestrial lives, which are also relevant to the origin of the terrestrial life. Comets and meteorites may serve as life-carrying "arks" to seed potentially habitable planets such as prebiotic Earth. Success of exogenous transfer depends on survivability of life or seed life (panspermia) encrusted in comets and meteorites. Likelihood of survival may be estimated on the basis of (i) hit rates and intensities of cosmic rays during transfer, and (ii) heat and mechanical damages caused by entry and landing impact. The latter could be evaluated by experiments and calculations, despite uncertainties such as velocity and angle of entry, presence of atmosphere/ocean, and size of a carrier, namely a panspermian ark. In contrast, influences of high-energy heavy (HZE) particles have been conceptually considered. A major concern in the consideration was the hit of high-energy but low-frequency rays that react with comet/meteorite-building materials to generate secondary or sequential radiations, or hadron shower. The energy of hadron shower radiations may be high enough to damage life in shallow interior, and could be lowered to non-lethal levels in deep interior. Thus the occurrence of internal habitable zones, or protectable bodies, depends on the frequency and energy of hit rays and the size of life carriers. This idea would be tested by simulating hadron showers with the algorithm GEANT4 and by blistering artificial "bacterial arks" with high-energy proton of >10 GeV or heavier particles of GeV levels. In the light of availability of and accessibility to such high-energy particles, the use of accelerator beam dumps is comparable and complement to space in situ experiments. Improved dosimetry for artificial hadron shower is needed to simulate natural hadron showers that panspermia would encounter during interplanetary and interstellar transmigration., 共催: 日本学術会議, 著者人数: 18人, Meeting sponsors: The Science Council of Japan, The Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (ISAS)(JAXA), 資料番号: AA0064113107

第22回宇宙利用シンポジウム(2006年1月17日-19日, 日本学術会議6階会議室 六本木、東京), The Twenty-second Space Utilization Symposium (January 17-19, 2006: Science Council of Japan, Roppongi, Tokyo, Japan), Several animals show resistance to excess environmental stresses such as desiccation for a long time, tremendous level of pressure and temperature, in cryptobiotic stages. Milnesium tardigradum (Phylum Tardigrada) is one of these animals. When the specimens encounters desiccation, their body soon changes into a criptobiotic condition called 'tun'. The body weight of 'tun' decreases to 3% in comparison with normal condition, and the metabolism decreases to 0.01%. The criptobiotic stage of this animals shows a tremendous resistance to excess environmental conditions. For example, it is tolerant to -253C to 50C, vacuum to 600 MP, up to 5700 gray, and a number of chemicals. We have focused on phyciological and molecular mechanisms of the criptobiotic stage of M. tardigradum. We have reported life cycle of this species in this symposium, and proposed a research project on this phenomenon. Furthermore, we have discussed utilization of this animal for investigation of space research. We are organizing a joint study between Japan and Russia. The outline of this project has also been explained., 共催: 日本学術会議, Meeting sponsors: The Science Council of Japan, The Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (ISAS)(JAXA), 資料番号: AA0064113108