First published online January 9, 2003; 10.1104/pp.014118
Plant Physiol, February 2003, Vol. 131, pp. 656-663
Overexpression of Arabidopsis Phytochelatin Synthase
Paradoxically Leads to Hypersensitivity to Cadmium
Stress1
Sangman
Lee,
Jae S.
Moon,
Tae-Seok
Ko,
David
Petros,
Peter B.
Goldsbrough, and
Schuyler S.
Korban*
Department of Natural Resources and Environmental Sciences,
University of Illinois, Urbana, Illinois 61801 (S.L., T.-S.K., S.S.K.);
and Biopotency Evaluation Laboratory, Korea Research Institute of
Bioscience and Biotechnology, Yusong-Gu, Taejon 305-333, Korea
(J.S.M.); and Department of Horticulture and Landscape
Architecture, Purdue University, West Lafayette, Indiana 47907 (D.P.,
P.B.G.)
Phytochelatin (PC) plays an important role in heavy metal
detoxification in plants and other living organisms.
Therefore, we overexpressed an Arabidopsis PC synthase
(AtPCS1) in transgenic Arabidopsis with the goal of
increasing PC synthesis, metal accumulation, and metal tolerance in
these plants. Transgenic Arabidopsis plants were selected, designated
pcs lines, and analyzed for tolerance to cadmium (Cd). Transgenic pcs
lines showed 12- to 25-fold higher accumulation of
AtPCS1 mRNA, and production of PCs increased by 1.3- to
2.1-fold under 85 µM CdCl2 stress for 3 d when compared with wild-type plants. Cd tolerance was assessed by
measuring root length of plants grown on agar medium containing 50 or
85 µM CdCl2. Pcs lines paradoxically showed
hypersensitivity to Cd stress. This hypersensitivity was also observed
for zinc (Zn) but not for copper (Cu). The overexpressed AtPCS1 protein
itself was not responsible for Cd hypersensitivity as transgenic
cad1-3 mutants overexpressing AtPCS1 to similar levels
as those of pcs lines were not hypersensitive to Cd. Pcs lines were
more sensitive to Cd than a PC-deficient Arabidopsis mutant,
cad1-3, grown under low glutathione (GSH) levels. Cd
hypersensitivity of pcs lines disappeared under increased GSH levels
supplemented in the medium. Therefore, Cd hypersensitivity in pcs lines
seems due to the toxicity of PCs as they existed at supraoptimal levels
when compared with GSH levels.
1
This work was supported by the Illinois
Department of Natural Resources.
*
Corresponding author; e-mail s-korban{at}uiuc.edu; fax
217- 333-8298.
© 2003 American Society of Plant Biologists
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