Plant Physiol, November 2000, Vol. 124, pp. 1019-1026
Identification of Rice Varieties with High Tolerance or
Sensitivity to Lead and Characterization of the Mechanism of
Tolerance1
Young-Yell
Yang,
Ji-Young
Jung,
Won-Yong
Song,
Hak-Soo
Suh, and
Youngsook
Lee*
Department of Life Science, Pohang University of Science and
Technology, Pohang, 790-784 Korea (Y.-Y.Y., J.-Y.J., W.-Y.S.,
Y.L.); and Department of Agronomy, Yeungnam University, Kyongsan
712-749, Korea (H.-S.S.)
Pb inhibits plant growth. To study Pb tolerance in rice
(Oryza sativa), we screened 229 varieties for Pb
tolerance or sensitivity. Three-day-old seedlings were treated for
12 d with 20 µM Pb solution. Based on the dry weight
of the root, three Pb-tolerant (var CH-55, var KH-2J, var Kumnung) and
three Pb-sensitive (var Aixueru, var C-9491, var Milyang23) rice
varieties were selected. The root biomasses of the tolerant varieties
were approximately 10-fold higher than those of the sensitive ones. The
greatest morphological difference between the two groups was in the
growth of the adventitious roots, as tolerant lines were able to
develop adventitious roots after 6 d of Pb treatment, whereas
sensitive ones did not develop any even after 15 d. The growth of
adventitious roots in the tolerant varieties was dependent on a
mechanism, whereby Pb was altered to a form that cannot be taken up by
the tissue, because (a) the solution in which the tolerant varieties of
rice had grown still contained Pb but nevertheless did not affect the
root growth of new rice seedlings, and (b) the adventitious roots of
tolerant seedlings developed in Pb solution contained little Pb. The
oxalate content in the root and root exudate increased upon Pb
treatment in the tolerant varieties, whereas the opposite was observed
for the sensitive ones. Oxalate added to the growth solution
ameliorated the inhibition of root growth by Pb. These results suggest
that compounds such as oxalate secreted from the root may reduce the bio-availability of Pb, and that this may constitute an important Pb
tolerance mechanism in the tolerant rice varieties studied here.
1
This work was supported by the Korea Institute
of Science and Technology Evaluation and Planning (no.
98-N1-03-02-A-05) and Pohang Iron and Steel Co., Ltd. Experiments
at Pohang Light Source were supported in part by the Ministry of
Science and Technology of Korea.
*
Corresponding author; e-mail ylee{at}postech.ac.kr; fax
82-54-279-2199.
© 2000 American Society of Plant Physiologists
