Tepfer David, Leach Sydney
1 PESAC, Institut National de la Recherche Agronomique , Versailles, France .
2 LERMA, Observatoire de Paris, PSL Research University , CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Meudon, France .
Astrobiology. 2017 Mar;17(3):205-215. doi: 10.1089/ast.2015.1457. Epub 2017 Mar 6.
For life to survive outside the biosphere, it must be protected from UV light and other radiation by exterior shielding or through sufficient inherent resistance to survive without protection. We tested the plausibility of inherent resistance in plant seeds, reporting in a previous paper that Arabidopsis thaliana and tobacco (Nicotiana tabacum) seeds exposed for 558 days outside the International Space Station (ISS) germinated and developed into fertile plants after return to Earth. We have now measured structural genetic damage in tobacco seeds from this EXPOSE-E experiment by quantitatively amplifying a segment of an antibiotic resistance gene, nptII, inserted into the chloroplast genome. We also assessed the survival of the antibiotic resistance encoded by nptII, using marker rescue in a soil bacterium. Chloroplast DNA damage occurred, but morphological mutants were not detected among the survivors. In a second, longer mission (EXPOSE-R), a nearly lethal exposure was received by Arabidopsis seeds. Comparison between a ground simulation, lacking UV, and fully exposed seeds in space indicated severe damage from these short wavelengths and again suggested that DNA degradation was not limiting seed survival. To test UV resistance in long-lived, larger seeds, we exposed Arabidopsis, tobacco, and morning glory seeds in the laboratory to doses of UV, ranging as high as 2420 MJ m. Morning glory seeds resisted this maximum dose, which killed tobacco and Arabidopsis. We thus confirm that a naked plant seed could survive UV exposures during direct transfer from Mars to Earth and suggest that seeds with a more protective seed coat (e.g., morning glory) should survive much longer space travel. Key Words: UV light-Flavonoids-Sinapate-DNA degradation-Arabidopsis-Tobacco-Seeds-Space-International Space Station-EXPOSE-E-EXPOSE-R. Astrobiology 17, 205-215.
为了使生命在生物圈之外存活，必须通过外部屏蔽或具备足够的内在抗性来保护其免受紫外线和其他辐射，以便在没有保护的情况下也能存活。我们测试了植物种子内在抗性的合理性，在之前的一篇论文中报告称，在国际空间站（ISS）外暴露558天的拟南芥和烟草（Nicotiana tabacum）种子在返回地球后发芽并发育成可育植株。我们现在通过定量扩增插入叶绿体基因组的一段抗生素抗性基因nptII，来测量此次EXPOSE-E实验中烟草种子的结构遗传损伤。我们还利用土壤细菌中的标记拯救来评估nptII编码的抗生素抗性的存活率。叶绿体DNA发生了损伤，但在存活植株中未检测到形态突变体。在第二次更长时间的任务（EXPOSE-R）中，拟南芥种子受到了近乎致命的照射。地面模拟（缺乏紫外线）与太空中完全暴露的种子之间的比较表明，这些短波长造成了严重损伤，再次表明DNA降解并不限制种子存活。为了测试长寿、较大种子的抗紫外线能力，我们在实验室中将拟南芥、烟草和牵牛花种子暴露于高达2420 MJ m的紫外线剂量下。牵牛花种子能抵抗这一最大剂量，而该剂量杀死了烟草和拟南芥。因此，我们证实裸植物种子在从火星直接转移到地球的过程中能够经受紫外线照射，并表明具有更具保护作用种皮的种子（如牵牛花）应该能够在更长的太空旅行中存活。关键词：紫外线-黄酮类化合物-芥子酸酯-DNA降解-拟南芥-烟草-种子-太空-国际空间站-EXPOSE-E-EXPOSE-R。天体生物学17，205 - 215。
