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

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Quantitative Evaluation of Rice Varieties
in Cadmium Uptake Activities
for Remediation of Cadmium-contaminated Soil
S. Ishikawa b) , N. Suzui a) , S. Ito a) , S. Ishii a) , H. Yamazaki a), c) N. Kawachi a) ,
N. S. Ishioka a) and S. Fujimaki a)
a) Radiation-Applied Biology Division, QuBS, JAEA,
b) Soil Environment Division, National Institute for Agro-Environmental Sciences,
c) Faculty of Science and Technology, Tokyo University of Science.
Introduction
Contamination of arable soil with cadmium (Cd) is one
of the most serious problems in Japan. Rice is the most
major source of Cd intake for Japanese people, therefore, a
lot of efforts have been taken and many future plans are
discussed to reduce Cd content in rice grain. The idea
called “phytoremediation” is considered one of the most
feasible and effective plans to reduce the contamination of
soil with Cd in Japan. The project employs rice plants
which are NOT edible but intensively absorb Cd from the
soil and accumulate it in their aerial part to be harvested.
To drive this approach forward, National Institute for
Agro-Environmental Sciences (NIAES) has been selecting
rice varieties with good potentials for intensive
accumulation of Cd. However, two subjects should be
completed to establish the practical rice cultivar for
phytoremediation. First, physiological activities on Cd
translocation of the test plants should be evaluated
quantitatively to find best candidates. Second, the
biological mechanisms which provide differences of such
activities among the varieties should be elucidated.
On the other hand, the movement of Cd in intact rice
plants was first visualized by JAEA in 2005 using a
positron-emitting tracer imaging system (PETIS).
Recently, the translocation of Cd in the whole rice plant
body, for instance, absorption by roots, transport towards the
aerial parts, transfer from the xylem (route to the leaves) to
the phloem (to the grains) and accumulation to the spikelets,
1)
was described quantitatively using PETIS . In this study,
we evaluated the activities on Cd translocation of a few
candidate varieties and analyzed the biological mechanisms
using PETIS.
Results and Discussion
Positron-emitting cadmium tracer, 107 Cd, was produced
and purified as described previously 2) . In this study, three
common rice cultivars, Nipponbare, Koshihikari and
Sasanishiki and three candidate varieties were subjected.
We equally fed the hydroponic culture solution including
107
Cd to the six test plants and obtained the serial images of
the Cd distribution in the aerial parts every 4 min for 36 h
1)
using PETIS, as described previously .
Figure 1 shows the result as an integrated image. It was
found that the three candidate plants accumulated Cd in their
aerial parts approximately two times as common cultivars.
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It was also found that almost all Cd in the culture solution
was absorbed by all the tested plants (data not shown).
Therefore, this result indicates that the difference was due to
greater activities of the candidates in the process to export
Cd from the root tissue to the aerial parts, but not in the
process of absorption from the culture. This strongly
supports the previous report by Uraguchi et al., NIAES 3) .
It should also be stressed that the candidates tested in this
study are foreign varieties and NOT suitable for cultivation
in Japan. Practical cultivar for phytoremediation must be
established by crossing these candidates with cultivars
adequate for cultivation in Japan. Each physiological
process of Cd translocation is considered to be executed by
molecular machinery programmed by specific genes, and
thus our result leads to the conclusion that the genes of the
candidates related to the Cd export process from the root
should be introduced into the progeny in order to realize the
desired rice cultivar. We will continue the evaluation of
the crossed progeny, which are genetically suggested to
have the related genes derived from the candidates, with the
PETIS-based method established in this study.
References
1) S. Fujimaki et al., Plant Physiol. 152 (2010) 1796-1806.
2) N. S. Ishioka et al., TIARA Ann. Rep. 2004 (2006)
277-279.
3) S. Uraguchi et al., J. Exp. Bot. 60 (2009) 2677-2688.
Fig. 1 Photograph of the tested plants (left) and the
integrated PETIS image of Cd translocation in the same
area (right). From the left, Nipponbare, Koshihikari,
Sasanishiki, and three varieties of candidates were set.