Sancho Leopoldo G, de la Torre Rosa, Horneck Gerda, Ascaso Carmen, de Los Rios Asunción, Pintado Ana, Wierzchos J, Schuster M
Departamento de Biología Vegetal II, Universidad Complutense, Madrid, Spain.
Astrobiology. 2007 Jun;7(3):443-54. doi: 10.1089/ast.2006.0046.
This experiment was aimed at establishing, for the first time, the survival capability of lichens exposed to space conditions. In particular, the damaging effect of various wavelengths of extraterrestrial solar UV radiation was studied. The lichens used were the bipolar species Rhizocarpon geographicum and Xanthoria elegans, which were collected above 2000 m in the mountains of central Spain and as endolithic communities inhabiting granites in the Antarctic Dry Valleys. Lichens were exposed to space in the BIOPAN-5 facility of the European Space Agency; BIOPAN-5 is located on the outer shell of the Earth-orbiting FOTON-M2 Russian satellite. The lichen samples were launched from Baikonur by a Soyuz rocket on May 31, 2005, and were returned to Earth after 16 days in space, at which time they were tested for survival. Chlorophyll fluorescence was used for the measurement of photosynthetic parameters. Scanning electron microscopy in back-scattered mode, low temperature scanning electron microscopy, and transmission electron microscopy were used to study the organization and composition of both symbionts. Confocal laser scanning microscopy, in combination with the use of specific fluorescent probes, allowed for the assessment of the physiological state of the cells. All exposed lichens, regardless of the optical filters used, showed nearly the same photosynthetic activity after the flight as measured before the flight. Likewise, the multimicroscopy approach revealed no detectable ultrastructural changes in most of the algal and fungal cells of the lichen thalli, though a greater proportion of cells in the flight samples had compromised membranes, as revealed by the LIVE/DEAD BacLight Bacterial Viability Kit. These findings indicate that most lichenized fungal and algal cells can survive in space after full exposure to massive UV and cosmic radiation, conditions proven to be lethal to bacteria and other microorganisms. The lichen upper cortex seems to provide adequate protection against solar radiation. Moreover, after extreme dehydration induced by high vacuum, the lichens proved to be able to recover, in full, their metabolic activity within 24 hours.
本实验旨在首次确定地衣在太空环境中的生存能力。具体而言，研究了外星太阳紫外线辐射不同波长的破坏作用。所用地衣为两极物种石果衣和优美黄衣，它们采集于西班牙中部山区海拔2000米以上地区，以及南极干谷中栖息在花岗岩内的石内群落。地衣在欧洲航天局的BIOPAN - 5设施中被暴露于太空；BIOPAN - 5位于绕地球轨道运行的俄罗斯FOTON - M2卫星的外壳上。地衣样本于2005年5月31日由联盟号火箭从拜科努尔发射，在太空飞行16天后返回地球，届时对其进行生存测试。叶绿素荧光用于测量光合参数。背散射模式扫描电子显微镜、低温扫描电子显微镜和透射电子显微镜用于研究两种共生体的组织结构和组成。共聚焦激光扫描显微镜结合使用特定荧光探针，可评估细胞的生理状态。所有暴露的地衣，无论使用何种光学滤光片，飞行后测得的光合活性与飞行前几乎相同。同样，多显微镜方法显示地衣叶状体的大多数藻类和真菌细胞没有可检测到的超微结构变化，尽管如LIVE/DEAD BacLight细菌活力试剂盒所显示，飞行样本中更大比例的细胞膜已受损。这些发现表明，大多数地衣化真菌和藻类细胞在完全暴露于大量紫外线和宇宙辐射后能够在太空中存活，而这些条件已被证明对细菌和其他微生物是致命的。地衣的上表皮似乎能提供足够的防晒保护。此外，在高真空导致的极端脱水后，地衣被证明能够在24小时内完全恢复其代谢活性。
