title: Estimation of radiation tolerance to high LET heavy ions in an anhydrobiotic insect, Polypedilum vanderplanki.
abstract: OBJECTIVE
  Anhydrobiotic larvae of Polypedilum vanderplanki are known to show an extremely high tolerance against a range of stresses. We have recently reported that this insect withstands exposure to high doses of gamma-rays (linear energy transfer [LET] 0.2 keV/microm). However, its tolerance against high LET radiation remains unknown. The aim of this study is to characterize the tolerance to high-LET radiations of P. vanderplanki.
  
  
  METHODS
  Larval survival and subsequent metamorphoses were compared between anhydrobiotic (dry) and non-anhydrobiotic (wet) samples after exposure to 1 - 7000 Gy of three types of heavy ions delivered from the azimuthally varying field (AVF) cyclotron with LET values ranging from 16.2 - 321 keV/microm. The tolerance against 4He ions was also compared among three chironomid species.
  
  
  RESULTS
  At all LET values measured, dry larvae consistently showed greater radiation tolerance than hydrated larvae, perhaps due to the presence of high concentrations of the disaccharide trehalose in anhydrobiotic animals, and the radiation-induced damage became evident at lower doses as development progressed. Relative biological effectiveness (RBE) values based on the median inhibitory doses reached a maximum at 116 keV/microm (12C), and the maximum RBE clearly increased as development progressed. Lower D0 (dose to reduce survival from relative value 1.00 - 0.37 on the exponential part of the survival curve), and higher Dq (quasi-threshold dose) were found in individuals exposed to 4He ions, compared to gamma-rays, and in P. vanderplanki larvae compared to non-anhydrobiotic chironomids.
  
  
  CONCLUSIONS
  Anhydrobiosis potentiates radiation tolerance in terms of larval survival, pupation and adult emergence of P. vanderplanki exposed to high-LET radiations as well as to low-LET radiation. P. vanderplanki larvae might have more efficient DNA damage repair after radiation than other chironomid species.
authors.affiliation: Anhydrobiosis Research Unit, National Institute of Agrobiological Sciences, Ohwashi, Tsukuba, Ibaraki, Japan.
authors.forename: Masahiko
authors.initials: M
authors.lastname: Watanabe
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Sakashita
authors.forename: Akihiko
authors.initials: A
authors.lastname: Fujita
authors.forename: Takahiro
authors.initials: T
authors.lastname: Kikawada
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Nakahara
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Hamada
authors.forename: Daiki D
authors.initials: DD
authors.lastname: Horikawa
authors.forename: Seiichi
authors.initials: S
authors.lastname: Wada
authors.forename: Tomoo
authors.initials: T
authors.lastname: Funayama
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Takashi
authors.initials: T
authors.lastname: Okuda
mesh_terms: D000818:Animals; D001822:Body Burden; D002683:Chironomidae / Q000502:physiology* / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D020450:Heavy Ions / Q000009:adverse effects*; D007814:Larva / Q000502:physiology / Q000528:radiation effects; D007928:Lethal Dose 50; D018499:Linear Energy Transfer / Q000502:physiology* / Q000528:radiation effects; D011829:Radiation Dosage; D011836:Radiation Tolerance / Q000502:physiology* / Q000528:radiation effects; D012062:Relative Biological Effectiveness; D015996:Survival Rate