Estimation of radiation tolerance to high LET heavy ions in an anhydrobiotic insect, Polypedilum vanderplanki.
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.
Watanabe
Masahiko
M
Anhydrobiosis Research Unit, National Institute of Agrobiological Sciences, Ohwashi, Tsukuba, Ibaraki, Japan.
Sakashita
Tetsuya
T
Fujita
Akihiko
A
Kikawada
Takahiro
T
Nakahara
Yuichi
Y
Hamada
Nobuyuki
N
Horikawa
Daiki D
DD
Wada
Seiichi
S
Funayama
Tomoo
T
Kobayashi
Yasuhiko
Y
Okuda
Takashi
T
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