Research Activities 1991–2016

RIKEN Accel. Prog. Rep. 50 (2017)

Ion beam breeding – An eﬃcient synergic link between agriculturalscience and accelerator physics –T. Abe ∗1 and S. Yoshida ∗2
pollination was 18%.1) Morphological (e.g., variegatedstrains, albinos, and ﬂower color mutants) and physiological (e.g., heavy metal, salt, and herbicide tolerance)
mutants were successfully selected, suggesting the effectiveness of heavy-ion beams as a mutagen.

We have developed a unique technology for mutation induction using energetic heavy-ion beams at theRI Beam Factory. This development was achieved
through an eﬃcient synergic link between agriculturalscience and accelerator physics. At relatively lowdoses, ion beams induce mutations at a high rate without severely inhibiting growth. The irradiation treatment can be given to various plant materials and quick,
lasting between seconds and a few minutes are enoughto induce mutation. The ion beam is thus a highly eﬃcient tool for improving crops through mutation breeding. This technology has developed in three stages.

Trial use for ﬂower plant breeding
We have collaborated with ﬂower companies andpublic agricultural experiment stations since 1996 on
the potential of practical breeding using heavy-ion
beams. As a result, two new cultivars of plants weregenerated from irradiated materials in 1998. Specifically, dahlias “World” with large ﬂowers and a newcolor was successfully generated, and have been marketed in Hiroshima City since the autumn of 2001. We
successfully bred sterile verbena “Temari Bright Pink”,
which generates no seeds with a prolonged lifespanof the ﬂower. It has been marketed since the springof 2002. The similar successful cases were demonstrated by the new color ﬂowers, Petunia “Saﬁnia RoseVeined” (2003), “Saﬁnia Pure White” (2012), Torenia“Summer Wave Pink” (2007), Dianthous “Olivea purewhite” (2008), Cherry blossom “Nishina Zao” (2008)
and many new cultivars.

Demonstration as a mutagen in a model plant
In 1993, we started with the seed embryos at a particular stage during fertilization in tobacco (Nicotianatabacum L.) plant, which generates a large number ofseeds per ovary, as a model to investigate mutagenesis by heavy-ion beams. When irradiated by heavyion beam immediately after fertilization, an embryoshould produce a plant composed of mutant cells. The
highest percentage of morphologically abnormal plants
geminated seeds at 30–48 hrs of treatment stage after

Discovery of LETmax in a model plant
The eﬀect of LET on mutation frequencies is important to determine the most eﬀective irradiation condition in mutagenesis. We investigated the eﬀect of LET
on mutation induction using the model plant Arabidopsis thaliana. The most eﬀective LET (LETmax ) formutation induction was 30 keV/μm.2) Subsequently,
we have reported detailed analyses on the molecularnature of DNA alterations induced by heavy-ion irradiation with LETmax using morphological mutants.
The most mutations were deletions ranging from several to several tens of bp.3) Irradiation at LETmax iseﬀective for breeding because of its very high mutation rate. Since most mutations are small deletion,these are suﬃcient to disrupt a single gene.
Perspective
Fig. 1. A ﬂower bed in front of RIBF building. These ﬂowers were created by ion beam breeding. “Saﬁnia RoseVeind”, “Temari Sakura”, and “Temari Momo” fromfront.
∗1∗2

Recently, beneﬁcial variants have been grown forvarious plant species, such as salt resistant rice, low
polyphenol oxidase lettuce, low allergen peanut, highyield wakame (edible seaweed), and high oil contentalgae. We have found that high LET ions such as ironare eﬀective for breeding microbes. And we worked

Director of Accelerator Applications Research Group,RIKEN Nishina Center (2010–present)
Chief Scientist of Plant Functions Laboratory (1994–2004)

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RIKEN Accel. Prog. Rep. 50 (2017)

Research Activities 1991–2016

with SAITC to create “Saitama F yeast”, that is usedby 20 breweries in Saitama Pref. to ferment ﬂavoredrice wine. One brand of them is collectively known
as “Nishina-Homare” (in honor of Nishina), named after Yoshio Nishina. We built a new beam line, called
WACAME to increase available ion species with higher
LET and longer range. The beams are accelerated bythe AVF, RRC, and IRC to 160 MeV/nucleon andsent to E5 biological experiment room. We would
like to contribute to advances in these ﬁelds, examine
the eﬀects of physical factors (e.g., ion species, LET,and dose) on DNA-mutated regions, and elucidate themechanism of mutagenesis with heavy-ion beams. And
the discovery of genes using the combination of mutants and genome sequencing technology may lead to
new ﬁeld in biology, “mutagenomics”.
References
1) T. Abe et al., Gamma Field Symposia 39, 45 (2000).
2) Y. Kazama et al., Plant Biotech. 25, 113 (2008).
3) Y. Kazama et al., BMC Plant Bio. 11, 161 (2011).

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