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Plant Physiol, July 2001, Vol. 126, pp. 1001-1011
Increased Cysteine Biosynthesis Capacity of Transgenic Tobacco
Overexpressing an O-Acetylserine(thiol) Lyase Modifies
Plant Responses to Oxidative Stress1
Shohab
Youssefian,*
Michimi
Nakamura,2
Emin
Orudgev,3 and
Noriaki
Kondo4
Laboratory of Molecular Genetics, Biotechnology Institute, Faculty
of Bioresource Sciences, Akita Prefectural University, Ohgata-mura
010-0444, Akita, Japan (S.Y., M.N., E.O.); and Regional Environment
Division, National Institute for Environmental Studies, Tsukuba 305, Japan (N.K.)
O-Acetylserine(thiol) lyase (OASTL), a key enzyme of
plant sulfur metabolism, catalyzes the formation of Cys from sulfide and O-acetylserine. The biosynthesis of Cys is regarded as
the exclusive function of sulfur reduction in plants, and a key
limiting step in the production of glutathione (GSH), a thiol
implicated in various cellular functions, including sulfur transport,
gene expression, scavenging of reactive oxygen species (ROS), and
resistance to biotic and abiotic stresses. To examine whether an
increased capacity for cysteine (Cys) biosynthesis alters cellular
responses to such stresses, we studied the differential changes in
thiol levels and ROS scavenging of transgenic tobacco (Nicotiana
tabacum) plants expressing the wheat (Triticum
aestivum) OASTL gene, cys1, to
SO2 and to the ROS generator, methyl viologen.
Intracellular Cys and GSH contents were generally higher in
cys1 transgenics than in controls under normal growth
conditions, but became especially elevated in transgenic plants after
SO2 exposure. An examination of differences in the ROS
scavenging system of the transgenic plants also demonstrated the
specific accumulation of Cu/Zn superoxide dismutase transcripts, known
to be induced by Cys or GSH, and elevated cellular superoxide dismutase
activities. The transgenic plants accordingly showed dramatic
reductions in the extent of both foliar and photooxidative damage in
response to acute SO2, as well as reduced levels of
chlorosis and membrane damage following methyl viologen treatment.
Overall, our results imply that OASTL plays a pivotal role in the
synthesis of Cys and GSH that are required for regulation of plant
responses to oxidative stress.
1
This work was supported in part by the Nissan
Science Foundation (grant to S.Y.) and by the Sasagawa Science
Foundation (grant to S.Y.).
2
Present address: Faculty of Pharmaceutical Sciences,
Chiba University, Chiba 263-8522, Japan.
3
Present address: Department of Physics, University of
California, Santa Barbara, CA 93106.
4
Present address: Department of Biological Sciences,
Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan.
*
Corresponding author; e-mail shohab{at}agri.akita-pu.ac.jp; fax
81-185-45-2678.
© 2001 American Society of Plant Physiologists
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