title: Ionizing radiation impacts photochemical quantum yield and oxygen evolution activity of Photosystem II in photosynthetic microorganisms.
abstract: OBJECTIVE
  Long-term space exploration requires biological life support systems capable of coping with the deleterious space environment. The use of oxygenic photosynthetic microorganisms represents an intriguing topic in this context, mainly from the point of view of food and O2 production. The aim of the present study was to assess the effects of space ionizing radiation exposure on the photosynthetic activity of various microorganisms.
  
  
  METHODS
  Ground-based irradiation experiments were performed using fast neutrons and gamma rays on microorganisms maintained at various light conditions. A stratospheric balloon and a European Space Agency (ESA) flight facility were used to deliver organisms to space at the altitude of 38 and 300 km, respectively. During the balloon flight, the fluorescence activity of the organisms was real-time monitored by means of a special biosensor.
  
  
  RESULTS
  The quantum yield of Photosystem II (PSII), measured directly in flight, varied among the microorganisms depending on the light conditions. Darkness and irradiation of cells at 120 and 180 micromol m(-2) s(-1) enhanced the radiation-induced inhibition of photosynthetic activity, while exposure to weaker light irradiance of 20 and 70 micromol m(-2) s(-1) protected the cells against damage. Cell permanence in space reduced the photosynthetic growth while the oxygen evolution capacity of the cells after the flight was enhanced.
  
  
  CONCLUSIONS
  A potential role of PSII in capturing and utilizing ionizing radiation energy is postulated.
authors.affiliation: IC-CNR, Area of Research of Rome, Department of Agrofood, National Research Council, Rome, Italy.
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Rea
authors.forename: Dania
authors.initials: D
authors.lastname: Esposito
authors.forename: Mario
authors.initials: M
authors.lastname: Damasso
authors.forename: Agnese
authors.initials: A
authors.lastname: Serafini
authors.forename: Andrea
authors.initials: A
authors.lastname: Margonelli
authors.forename: Cecilia
authors.initials: C
authors.lastname: Faraloni
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Torzillo
authors.forename: Alba
authors.initials: A
authors.lastname: Zanini
authors.forename: Ivo
authors.initials: I
authors.lastname: Bertalan
authors.forename: Udo
authors.initials: U
authors.lastname: Johanningmeier
authors.forename: Maria T
authors.initials: MT
authors.lastname: Giardi
mesh_terms: D002470:Cell Survival / Q000528:radiation effects; D004579:Electron Transport / Q000528:radiation effects; D056890:Eukaryota / Q000166:cytology / Q000378:metabolism* / Q000528:radiation effects*; D005720:Gamma Rays; D009502:Neutrons; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism* / Q000528:radiation effects*; D013026:Space Flight
chemical_list: D045332:Photosystem II Protein Complex; D010100:Oxygen