I��

Ⅲ-4. Radiation Chemistry & Biology

RIKEN Accel. Prog. Rep. 51 (2018)

��Comparison of LET eﬀect of heavy-ion beam irradiation in rice
Y. Hayashi,∗1 K. Ichinose,∗1 Y. Shirakawa,∗1 S. Ohbu,∗1 H. Tokairin,∗1 T. Sato,∗1,∗2 and T. Abe∗1∗1∗2

RIKEN Nishina Center
Graduate School of Agricultural Science, Tohoku University

��




Survival(rate((%)

Linear energy transfer (LET) is a contributing factor
in heavy-ion mutagenesis. Our previous study revealed
a LET-dependent eﬀect in Arabidopsis thaliana. A LETof 30 keV/µm is the most eﬀective for inducing mutation.1) Although a high LET of heavier ions such as Ar
and Fe resulted in a lower mutation frequency, they caneasily cause larger deletions and complex mutations.2–5)
In 2015, a new high-energy beam line called the WACAME line was constructed, which enables the irradiation of heavier ions with a longer range.6) The choice ofLET values for biological samples was extended by using this beam line. Knowledge about the LET eﬀect inmodel plants can be applied for other plants and is useful for eﬃcient mutagenesis. In this study, we examinedthe eﬀect of a higher LET of heavy-ion beam irradiationin rice as another model plant.
Dry seeds of rice (Oryza sativa L. cv. Nipponbare)with a water content of 13% were used for the experiment. The seeds were placed into a plastic bag without
overlapping and vacuum-packed for irradiation treatment. The seeds were irradiated with Ar (184 keV/µm,289 keV/µm) and Fe (650 keV/µm). Ar (184 keV/µm)
is a high-energy beam produced using the WACAME
line. The doses of Ar ions and Fe ion were 10 to 50 Gy,
7.5 to 40 Gy, and 10 to 50 Gy, respectively. Survival
rates were estimated by counting plants surviving fourweeks after sowing. Figure 1 shows the survival curve after irradiation. A decrease of survival rate was observed
for a dose greater than 20 Gy with Ar (289 keV/µm)
irradiation. On the other hand, a decrease of survival
rate was observed for a dose greater than 30 Gy withAr (184 keV/µm) and Fe (650 keV/µm) irradiation. M1plants from the irradiation with a high survival rate weregrown in a paddy ﬁeld. M2 seeds were obtained individually from each M1 plant. The fertility was evaluatedusing the number of fertile spikelets in the main panicleof the M1 plant. Figure 2 shows the percentage of fertility in M1 plants. The mean value of the number of fertile
spikelets per panicle in control Nipponbare was 105.7 ±16.24. The percentage of low-fertility plants increased
with the increase of dose at any LET value.
Chlorophyll-deﬁcient mutants (CDM) were observedin two-weeks-old M2 seedlings grown in a greenhouse.
Mutation rates were calculated based on the numbers of
M1 lines, which showed CDM in M2 generation. The
highest frequency of CDM was observed at 20–30 Gy of
Ar (184 keV/µm) irradiation (Table 1). Furthermore,
there was no severe decrease of fertility at a dose of
20 Gy. This result suggests the possibility of high eﬃciency of the Ar-ion beam produced using the WACAME
line. We will conduct the genome sequencing of isolated
mutants to characterize the mutations irradiated at 184,���




Dose((Gy)

1 EffectLETon
on survival
survival rate
Fig. Fig.
1. EﬀectofofLET
rateininrice
rice.
＊Dose (Gy)
＊
10Ar
184

20
30

0
1-910 - 49
50 and more

7.5

Ar
289

101510

Fe
650

15
200%

50%
Percentage of fertile spikelet number

100%Fig. 2. Comparison of the number of fertile spikelets per panicle.
Table 1. Eﬀect of High-LET ion-beam irradiation on mutation induction.
���������������������� ������������������������� �� ������������������������������������������������������������������������������������������������������������������������������������������������������������

�

289, and 650 keV/µm and compare the mutagenic eﬀects
of higher-LET irradiation in rice.
References
1) Y. Kazama et al., Plant Biotech. 25, 113 (2008).
2) T. Hirano et al., Mutat. Res. 735, 19 (2012).
3) Y. Kazama et al., Genes Genet. Syst. 88, 189 (2013).
4) T. Hirano et al., Plant J. 82, 93 (2015).
5) Y. Kazama et al., Plant J. 92, 1020 (2017).
6) N. Fukunishi et al., Proc. 13th Int. Conf. on Heavy Ion
Accel. Tech. (2015), p. 42.

- 238 -