Ⅲ-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 51 (2018)

Eﬀects of heavy-ion-beam irradiation on survival in Eisenia arborea
H. Yamada,∗1 Y. Hayashi,∗2 and T. Abe∗2∗1∗2Shizuoka Prefectural Research Institute of Fishery
RIKEN Nishina CenterFig. 1. Eisenia arborea.
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'RVH *\Fig. 2. Survival rates of male and female gametophytes andsporophytes 3 and 4 weeks after irradiation with an Arion beam, respectively.
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Along the coast of Hainan on the west coast of Suruga Bay in Shizuoka prefecture, there once existed akelp forest of species such as Eisenia arborea (Fig. 1).
This kelp forest was a good ﬁshing ground for shellﬁshsuch as abalone. In addition, E. arborea was caught asedible seaweed. However, the kelp forest disappeared,
along with shellﬁsh, and ﬁshery suﬀered serious economic damage. Although measures to restore the kelpforest have been taken subsequently, E. arborea has notrecovered. Therefore, we investigated survival in E. arborea after irradiation with a heavy-ion beam and examined the optimum dose for creating useful properties
in E. arborea such as high growth and to contribute to
the recovery of the kelp forest.
Gametophytes of E. arborea were irradiated with an
Ar-ion beam (184 keVµm) at a dose range of 0.625–
20 Gy and with a C-ion beam (23 keVµm) at a dose
range of 5–100 Gy. After the irradiation, batches of
48 female and 48 male gametophytes (approximately100 µm in length) were incubated at 20◦ C with 12-h
photoperiods and a light intensity of 30 µmol m−2 s−1 .
After 3 weeks of culture, they were measured with a microscope, and gametophytes not growing were deemed
to have died. Furthermore, to conﬁrm the survival
again, gametophytes visually conﬁrmed to be alive after 8–9 months of culture were regarded as surviving
individuals, and the survival rates were obtained.
Sporophytes of E. arborea (approximately 3 mm inlength) were irradiated with an Ar-ion beam at a doserange of 1.25–10 Gy and with a C-ion beam at a dose
range of 10–100 Gy. After the irradiation, batches of
50 sporophytes were incubated at 20◦ C with 12-h photoperiods and a light intensity of 80 µmol m−2 s−1 . The
survival rates were measured after 4 weeks of culture.
The survival rates after 3 weeks of gametophytes irradiated with the Ar-ion beam showed a tendency todecrease beyond a dose of 10 Gy in both male and female samples (Fig. 2). The survival rates after 3 weeksof gametophytes irradiated with the C-ion beam decreased from 80 Gy in male samples and 100 Gy infemale samples (Fig. 3). The survival rates after 8–9
months of culture decreased and abruptly decreased for
Ar-ion-beam irradiation at 10 Gy and C-ion-beam irradiation at 80 Gy, respectively (Table 1), which almostagreed with the results after 3 weeks of culture. The
survival rates of the sporophytes sharply decreased for
Ar-ion-beam irradiation at 7.5 Gy and C-ion-beam irradiation at 20 Gy, respectively (Fig. 2, 3). Susceptibility
to heavy-ion beams was higher in sporophytes than ingametophytes.
Based on the above results, the optimum doses were*DPHWRSK\WH0DOH*DPHWRSK\WH)HPDOH
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'RVH *\Fig. 3. Survival rates of male and female gametophytes andsporophytes 3 and 4 weeks after irradiation with a C-ionbeam, respectively.
Table 1. Survival rates of male and female gametophytes
8–9 months after irradiation with Ar and C-ion beams.

ArCcontrol

10Gycontrol

80GyMale

100%71%100%

17%

Female

50%

29%

94%

8%

estimated as 2.5 and 5 Gy for gametophytes and sporophytes irradiated with an Ar-ion beam, respectively;
20 and 40 Gy for gametophytes irradiated with a Cion beam; and 10 and 20 Gy for sporophytes irradiatedwith C-ion beam. In the future, we will perform mutant
screening of the sporophytes in the M2 generations.

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