JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

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Effect of Different LET Radiations on Root Growth of
Arabidopsis thaliana
R. Yoshihara a) , S. Nozawa a) , H. Saika b) , M. Teranishi c) ,
S. Toki b,d) , J. Hidema c) and A. N. Sakamoto a)
a) Radiation-Applied Biology Division, QuBS, JAEA, b) Plant Genetic Engineering Research Unit,
National Institute of Agrobiological Sciences, c) Graduate School of Life Sciences, Tohoku University,
d) Kihara Institute for Biological Research, Yokohama City University
Biological effects of ion beams have been mainly studied
in animal or bacterial systems because of the need of
ion-beam application in medical treatments. Concurrently,
ion beams have been used as a remarkable mutagen in the
mutation breeding for useful agricultural or garden products.
Although many valuable cultivars have been produced in the
ion-beam breeding, little is known about the mechanism of
ion-beam mutagenesis in higher plants. In this study, we
aim to elucidate the effects of ion beams on higher plants.
We focus on two points: i) what kinds of damage are
produced by ion beams, and ii) what kinds of cellular
processes are involved to turn the damage into mutations.
Such information will lead to great advancement of
ion-beam breeding techniques.
To analyze the effects of ion beams on higher plants, we
first quantified the growth inhibitory effects by ion-beam
irradiation. We irradiated the model plant Arabidopsis
thaliana with 220 MeV carbon ion beams (220 MeV C,
LET: 112 keV/μm), 50 MeV helium ion beams (50 MeV He,
LET: 16.8 keV/μm) or -rays (LET: 0.2 keV/μm), and root
growth was measured after each treatment.
Arabidopsis seeds were sown on Murashige and Skoog
(MS) ager plates aseptically. The plates were held
vertically in the 23 °C growth chamber for three days so that
roots grew along the surface of plates, ensuring of accurate
irradiation. The plants were exposed to ion-beam or -ray
radiations. After grown for another 3 days, the root length
was measured. Root elongation rate is shown as the rate of
root length of irradiated plant to that of non-irradiated plant.
Root elongation rates of wild-type Arabidopsis exposed to
50 MeV He were indistinguishable with those exposed to
-rays. This result let us speculate that the both radiations
induce comparable quantity and/or quality of DNA lesions
that inhibit the root growth (Fig. 1 [A]).
[A] [B]
1.0
0.9
-rays/wild
-rays/wild
50 MeV He/wild
1.0
0.9
-rays/wild -rays/wild type
-rays/NHEJ-
-rays/NHEJ-
0.8
220 MeV C/wild
0.8
0.7
0.7
0.6
0.6
0.5
0.5
0.4
0.4
0.3
0 100
Dose (Gy)
200
0.3
0 100
Dose (Gy)
200
Root elongation rate
Root elongation rate
JAEA-Review 2010-065
However, root elongation rates of plants exposed to
220 MeV C were significantly lower (Fig. 1 [A]). This
result suggests that 220 MeV C may induce more numbers
of DNA lesions or more severe types of DNA lesions than
-rays and 50 MeV He.
In prior studies, it was suggested that ion beams induce
DNA double-strand breaks (DSBs) in plant. The DSBs are
known as one of the most severe DNA lesions and repaired
by non-homologous end-joining (NHEJ) or homologous
recombination (HR) pathways in many organisms.
Arabidopsis also posses a series of genes involved in the
NHEJ and HR pathways. Therefore, we prepared a mutant
Arabidopsis that is deficient in NHEJ and exposed it to ion
beams to examine whether the ion-beam induced DNA
lesions are repaired by the NHEJ pathway.
When the wild-type and NHEJ deficient plants were
exposed to -rays or 50 MeV He, the root elongation rate of
NHEJ deficient mutant was more severely inhibited than the
wild type (Fig. 1 [B], [C]). However, the root elongation
rate of the mutant exposed to 220 MeV C was almost the
same as that of the wild type (Fig. 1 [D]). These results
suggest that the considerable amount of DNA lesions
induced by -rays or 50 MeV He are repaired by NHEJ, but
the majority of DNA lesions induced by 220 MeV C are not
repaired by NHEJ. From this observation, we propose a
hypothesis that the types of DNA lesions induced by
relatively low LET radiations such as -rays or 50 MeV He
and those by extremely high LET radiations such as
220 MeV C are inherently different. The difference in
types of DNA lesions could affect the variety of mutation
induced. We will next analyze the mutation spectrum in
various repair-deficient plants to elucidate the mechanism of
ion beam mutagenesis in higher plants.
[C]
[D]
1.0
0.9
50 MeV He/wild type
50 MeV He/NHEJ-
1.0
0.9
220 MeV C/wild type
220 MeV C/NHEJ-
0.8
0.8
0.7
0.7
0.6
0.6
0.5
0.5
0.4
0.4
0.3
0 100 200
0.3
0 20 40 60
Dose (Gy) Dose (Gy)
Root elongation rate
Fig. 1 Root elongation rate of wild type and mutant Arabidopsis.
[A] Root elongation rate of wild type plants exposed to -rays, 50 MeV He and 220 MeV C,
[B], [C], [D] Inhibitory effect on root elongation in mutant plants by -rays [B], 50 MeV He [C] and 220 MeV C [D].
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Root elongation rate