EXPERIMENT RECORD N° 9146
EXPOSE-E SEEDS (Testing plant seed as a terrestrial model for panspermia vehicle and as a source for universal UV screens)
  1. 2007 • ISS Increment 16
  2. 2008 • EXPOSE-E
  3. 2008 • ISS Increment 17
  4. 2008 • ISS Increment 18
  5. 2009 • ISS Increments 19-20
Life Sciences:
  • Exobiology
EXPOSE-E
Rene Demets
rene.demets@esa.int
D. Tepfer (1), S. Leach (2), S. Vrønning-Hoffmann (3), P.H. Ducrot (1), F. Corbineau (4), A. Zalar (1)
(1)  
Institut National de la Recherche Agronomique (INRA)
PESSAC, Laboratoire de Biologie de la Rhizosphere
Route de St. Cyr
78026 Versailles, CEDEX
FRANCE
e-mail:  
david.tepfer@gmail.com
andreja.zalar@versailles.inra.fr
paul-henri.ducrot@versailles.inra.fr
(2)  
LERMA, Meudon Observatory
Place Jules Janssen
92195 Meudon, Cedex
FRANCE
e-mail:  
sydney.leach@obspm.fr
(3)  
Institute for Storage Ring Facilities (ISA)
University of Aarhus
Ny Munkegade 120
bygning 1525, lokale 327
8000, Aarhus C
DENMARK
Tel:  
+45(0)8942.3781
Fax:  
+45(0)2338.2344
e-mail:  
vronning@phys.au.dk
(4)  
Université Pierre et Marie Curie
Equipe
4, place Jussieu
75252 Paris, Cedex 05
FRANCE
Tel:  
+33(0)1.30.83.30.40
e-mail:  
francoise.corbineau@upmc.fr
Terrestrial models for panspermia and lithopanspermia have been for now focused on bacterial spores. Another candidate to be considered that could endure the deleterious conditions of space travel is plant seeds. Indeed, seeds have evolved to conserve the species and its genome under extreme stress conditions (cold, vacuum, desiccation…).

The main objective of the SEEDS experiment is therefore to determine the resistance of plant seeds and their components to the space environment, including solar UV, vacuum, cosmic radiation and extreme temperature variations. After the flight, the germination rate of the seeds is determined. The resulting seedlings and plants are tested for morphology and integrity of the genome.

The DNA molecule absorbs UV light with maximums under UV-B and C wavelengths (<300 nm). However, these energetic radiations are blocked by Earth’s ozone layer and only UV-A reach the surface. Therefore, unprotected by Earth’s atmosphere, DNA is highly subjected to damages caused by these UV radiations but also by electrons and cosmic radiations.

Seeds have previously shown resistance to space-like conditions such as vacuum, extreme temperatures, UV exposure. Their direct exposure to space can improve our knowledge on the resistance of multi-cellular, higher organism with complex genetics, biochemistry and development.

Moreover, a class of plant secondary metabolites called "flavonoids" and present in the plant seeds are known to protect it from UV, oxidation, dehydration. Their role will be assessed in the SEEDS experiment on the EXPOSE-E facility onboard the ISS using several mutants with different levels of flavonoids.

The EXPOSE Facility
The EXPOSE facility is part of ESA’s research in astrobiology - the study of the origin, evolution and distribution of life in the universe. EXPOSE was built to allow exposure of small biological organisms and biochemical compounds to space conditions in LEO. The first EXPOSE mission was called EXPOSE-E.

EXPOSE-E was in space for 1.5 years.
Upload: 7 February 2008, Space Shuttle STS-122
Download: 12 September 2009, Space Shuttle STS-128

Arabidopsis seeds (wild type and two UV screen mutants) and tobacco seeds (wild type and transgenic) were exposed to space conditions on the outside of the ISS for 18 months. Upon return to Earth, germination kinetics were established by sowing the seeds in vitro and scoring germination as the emergence of the root through the seed coat. 1500 to 2000 seeds were tested in each experiment.

Environmental Conditions

Pressure                        
          10-7 - 10-4 Pa

Total solar dose, full spectrum         
          7.1x106 – 10.2x106 kJ/cm2  (Beuselinck & van Bavinchove, 2011).

Solar wavelength range  
           λ > 110 nm (behind MgF2 windows)

Temperature                  
         Oscillating within a band of -12 °C and +40 °C.
         Approx. 200 transitions through zero-Celsius over the full mission.  

Ionizing radiation (sun-exposed seeds)           
        Total mission dose (behind 0.4 g/cm2)   295.6 mGy (Dachev at al., 2012)
        Particle composition:
               GCR (Galactic Cosmic Rays)          53.1 mGy  (583 days of exposure) 18%       
               SAA protons                                      237.7 mGy  (558 days of exposure) 80%
               ORB electrons                                  4.8 mGy  (558 days of exposure)   2%
Ionizing radiation (sun-shielded seeds)           
        Total mission dose                                ~200  mGy (Berger et al., 2012)

REFERENCE EXPERIMENTS
A ground experiment was carried out comprising simulated solar exposure (λ >200 nm), temperature history and pressure drop, but lacking cosmic radiation and microgravity.
In space the seeds were tested in two ways: exposed to the sun and in darkness for reference.

SOLAR IRRADIATION SIMULATION
To complement the on-board solar recordings (Schuster et al., 2012) a 3D solar simulation model was developed for EXPOSE-E to quantify the solar dose per individual experiment position (Beuselinck & van Bavinchove, 2011). Final dose was calculated from attitude with respect to the sun and shadow maps generated by the 3D model.

From this EXPOSE-E experiment, structural genetic damage in tobacco seeds were measured 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.

Of the 2100 wild-type Arabidopsis thaliana and Nicotiana tabacum (tobacco) seeds 23% produced viable plants after exposure for 1.5 years to full space conditions including solar UV. The highest survival occurred in tobacco (44%). These results indicate that an unprotected, seed-like entity could survive exposure to solar UV radiation during a hypothetical transfer between Mars and Earth.
Full survival was attained in seeds shielded from solar light, indicating that a longer space travel would be possible for seeds embedded in an opaque matrix.
Survival was lower in the Arabidopsis Wassilewskija ecotype and in mutants (tt4-8 and fah1-2) lacking UV screens.
Chemical samples of seed flavonoid UV screens were degraded by UV but their overall capacity to absorb UV was retained. Naked DNA encoding the nptII gene (kanamycin resistance) was also degraded by UV. A fragment however was detected by the polymerase chain reaction, and the gene survived in space when protected from UV. Even if seeds do not survive, components (e.g., their DNA) might survive transfer over cosmic distances.

For more details on the experiment and the results, please, consult the reference document (see "Attachments" section):
David Tepfer, Sydney Leach
Survival and DNA Damage in Plant Seeds Exposed for 558 and 682 Days outside the International Space Station
Astrobiology, 17, 3, 2017, DOI: 10.1089/ast.2015.1457

[1]  
E. Rabbow, G. Horneck, P. Rettberg, J.U. Schott, C. Panitz, A. L Afflitto, R. von Heise-Rotenburg, R. Willnecker, P. Baglioni, J. Hatton, J. Dettmann, R. Demets, G. Reitz, (2009), "EXPOSE, an Astrobiological Exposure Facility on the International Space Station - from Proposal to Flight", Origins of Life and Evolution of Biospheres, 39, 581-598.
[2]  
T. Beuselinck, C. van Bavinchove, (2011), "EXPOSE: Environmental history by calculation - EXPOSE-E Simulation Results", ESA Contract No 4000102520, EXP-RP-017-RS, Issue A, Revision 2, ESA.
[3]  
G. Horneck, M. Zell, (2012), "Introduction to the EXPOSE-E Mission", Astrobiology - Special Collection: The EXPOSE-E Mission, 12, 5, pp. 373.
[4]  
E. Rabbow, P. Rettberg, S. Barczyk, M. Bohmeier, A. Parpart, C. Panitz, G. Horneck, R. von Heise-Rotenburg, T. Hoppenbrouwers, R. Willnecker, P. Baglioni, R. Demets, J. Dettmann, G. Reitz, (2012), "EXPOSE-E: An ESA Astrobiology Mission 1.5 Years in Space", Astrobiology - Special Collection: The EXPOSE-E Mission, 12, 5, pp. 374-386.
[5]  
D. Tepfer, A. Zalar, S. Leach, (2012), "Survival of Plant Seeds, Their UV Screens, and nptII DNA for 18 Months Outside the International Space Station", Astrobiology - Special Collection: The EXPOSE-E Mission, 12, 5, pp. 517-528.
[6]  
D. Tepfer, (2008), "The origin of life, panspermia and a proposal to seed the universe", Plant Science, 175, 6, pp. 756-760.
[7]  
A. Zalar, D. Tepfer, S.V. Hoffmann, J.M. Kenney, S. Leach, (2007), "Directed exospermia: I. biological modes of resistance to uv light are implied through absorption spectroscopy of dna and potential uv screens", International Journal of Astrobiology, 6, 3, pp. 229-240.
[8]  
A. Zalar, D. Tepfer, S.V. Hoffmann, A. Kollmann, S. Leach, (2007), "Directed exospermia: II. vuv-uv spectroscopy of specialized uv screens, including plant flavonoids, suggests using metabolic engineering to improve survival in space", International Journal of Astrobiology, 6, 4, pp. 291-301.
[9]  
D. Tepfer, S. Leach, (2017), "Survival and DNA Damage in Plant Seeds Exposed for 558 and 682 Days outside the International Space Station", Astrobiology, 17, 3, DOI: 10.1089/ast.2015.1457.
click on items to display

portrait picture of David Tepfer and Sydney Leach

Seeds deposited in a monolayer behind magnesium fluoride windows.

Figure 1: Expose-E in the Space Shuttle cargo bay (see red circle).

Figure 2: Expose-E (far right) mounted on the EuTEF platform outside Columbus.

Figure 3: Expose-E close-up.

Figure 4: Expose-E sketch.

Figure 5: Expose-E sample container with 2 levels of cells (exposed and not exposed).

Figure 6: Expose-E sample tray.

Figure 7: Photograph of Expose-E payload with lids closed.
http://www.esa.int/Our_Ac
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Figure 8: Photograph of Expose-E payload with lids open and samples integrated.

Figure 9: Expose-E experiment arrangement.

ESA webstory from 1 February 2010 on astrobiology research on the ISS with EXPOSE-E
http://www.dlr.de/me/en/d
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1752/2384_read-21011
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EXPOSE-E, return of a long term external ISS experiment

E. Rabbow, G. Horneck, P. Rettberg, J.U. Schott, C. Panitz, A. L Afflitto, R. von Heise-Rotenburg, R. Willnecker, P. Baglioni, J. Hatton, J. Dettmann, R. Demets, G. Reitz, (2009), "EXPOSE, an Astrobiological Exposure Facility on the International Space Station - from Proposal to Flight", Orig. Life Evol. Biosph., 39, 581-598.

T. Beuselinck, C. van Bavinchove, 2011, EXPOSE: Environmental history by calculation - EXPOSE-E Simulation Results; EXP-RP-017-RS, Issue A, Revision 2; ESA Contract No 4000102520
http://eea.spaceflight.es
a.int/attachments/spacest
ations/ID5017fe50018da.pd
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http://eea.spaceflight.es
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G. Horneck, M. Zell, (2012), "Introduction to the EXPOSE-E Mission", Astrobiology - Special Collection: The EXPOSE-E Mission, 12, 5, pp. 373

E. Rabbow, P. Rettberg, S. Barczyk, M. Bohmeier, A. Parpart, C. Panitz, G. Horneck, R. von Heise-Rotenburg, T. Hoppenbrouwers, R. Willnecker, P. Baglioni, R. Demets, J. Dettmann, G. Reitz, (2012), "EXPOSE-E: An ESA Astrobiology Mission 1.5 Years in Space", Astrobiology - Special Collection: The EXPOSE-E Mission, 12, 5, pp. 374-386

M. Schuster, T. Dachev, P. Richter, D-P. Häder, (2012), "R3DE:Radiation Risk Radiometer-Dosimeter on the International Space Station - Optical Radiation Data Recorded During 18Months of EXPOSE-E Exposure to Open Space", Astrobiology - Special Collection: The EXPOSE-E Mission, 12, 5, pp. 393-402
http://eea.spaceflight.es
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http://eea.spaceflight.es
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D. Tepfer, A. Zalar, S. Leach, (2012), "Survival of Plant Seeds, Their UV Screens, and nptII DNA for 18 Months Outside the International Space Station", Astrobiology - Special Collection: The EXPOSE-E Mission, 12, 5, pp. 517-528

T. Dachev, G. Horneck, D-P. Häder, M. Schuster, P. Richter, M. Lebert, R. Demets, (2012), "Time Profile of Cosmic Radiation Exposure During the EXPOSE-E Mission: The R3DE Instrument", Astrobiology - Special Collection: The EXPOSE-E Mission, 12, 5, pp. 403-411

T. Berger, M. Hajek, P. Bilski, C. Körner, F. Vanhavere, G. Reitz, (2012) "Cosmic Radiation Exposure of Biological Test Systems During the EXPOSE-E Mission", Astrobiology - Special Collection: The EXPOSE-E Mission, 12, 5, pp. 387-392
http://eea.spaceflight.es
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David Tepfer, Sydney Leach
Survival and DNA Damage in Plant Seeds Exposed for 558 and 682 Days outside the International Space Station; Astrobiology, 17, 3, 2017, DOI: 10.1089/ast.2015.1457
 
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