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West Lafayette, Indiana
December 12, 2001
High salt levels found in
one-third of the world's cropland causes reduced yields and poor
growing conditions.
Now, a team of Purdue University scientists have discovered the
protein and the gene responsible for allowing salt to enter
plants. The breakthrough is expected to lead to plants that are
resistant to the salt found in saline soils and groundwater.
Ray Bressan, professor of horticulture, says, "As long as people
have been working on salinity toxicity ‹ over many decades and
in thousands of scientific papers written on the subject ‹ no
one knew the most fundamental thing about it, which is how
sodium gets into plants. We didn't know the beginning of the
story.
"So this is the first piece of work that shows what protein is
responsible. There have been biochemical experiments that showed
that this protein had the potential to be a sodium transporter,
but there was no evidence that it was actually involved in
tolerance to sodium toxicity in plants."
Salt toxicity in crops is a problem in areas where irrigation is
used extensively, such as on high-value crops in California.
According to the U.S. Department of Agriculture's George E.
Brown Jr. Salinity Laboratory, up to 25 million acres of land
are lost because of salinity caused by irrigation each year.
Salinity also is a problem in areas with saline groundwater,
such as is found in Egypt and Israel. In some areas, soil
salinity is so high that crops can't be grown. Despite decades
of plant breeding efforts, researchers have not been able to
develop more than a few salt-resistant plants.
"A second reason that this research is important is that we also
discovered more about how the protein functions," Bressan says.
"We discovered another entry system for sodium. This explains
why controlling this entry system didn't allow us to make
completely salt-tolerant plants. They're more tolerant, but not
completely. But now we have important clues about how this
works.
"When we've identified all of the salt-tolerance genes of
plants, we'll be able to control them, and we'll be able to
create salt-tolerant crops. Now we see the light at the end of
the tunnel."
Mike Hasegawa, professor of horticulture and the principal
investigator on the research, says this information fills in
holes in scientists' understanding of how plants work.
"This is a significant discovery that answers one of the major
questions in this field," Hasegawa says. "It is now clear that
despite the fact that salt is toxic to plants, they have a
specific transport system for the uptake of salt. This means
that in saline environments, plants have developed a way to cope
with high salt levels instead of avoiding them."
The protein, which has the unwieldy scientific name of AtHKT1,
is thought to act as a transporter in plant tissue, binding with
the salt ion and ferrying it into the plant cells.
Genes are the blueprints for proteins in living things. When a
gene is activated, or expressed, proteins are manufactured. To
confirm that the protein AtHKT1 was involved in salt transport
in plants, postdoctoral researcher Ana Rus used Arabidopsis
thaliana, a type of wild mustard
commonly used in plant experiments.
Rus searched for disabled genes in the plant that would cause a
special salt-sensitive strain of Arabidopsis to become as
resistant as regular Arabidopsis plants. After screening more
than 65,000 plant lines, she found a double mutant plant that
took up less salt and grew as quickly as normal plants. She then
isolated the gene responsible for this action, and discovered
that in the double mutant plant the gene that produces AtHKT1
had been disabled, or, in the jargon of scientists, knocked-out.
Further research found that at high salt concentrations plant
growth still declined, indicating that salt uptake is a complex
system with multiple genes involved.
"What makes study of salt uptake so difficult is it depends on
many genes, but we will continue our experiments to find these
other genes," Rus says. "Another question we have is why is this
gene responsible for sodium uptake when sodium has no value to
the plant. What other functions it has aren't known. But now
that we have these plants with the knocked-out genes we can work
on that, too."
The findings were announced in a paper in the Nov. 20 issue of
the Proceedings of the National Academy of Science. The research
also won the top research presentation award at an October
international conference on salinity sponsored by the Juan March
Institute for Study and Research in Madrid, Spain. The
proceedings of that meeting will be published next spring by the
scientific journal European Molecular Biology Organizations
Reports.
The National Science Foundation funded the research. The Purdue
Research Foundation has filed a provisional patent on the gene.
Writer: Steve Tally, (765) 494-9809;
tally@aes.purdue.edu
Sources:
Ray Bressan, (765) 494-1336;
bressan@hort.purdue.edu
Ana Rus, (765) 494-1315;
rus@hort.purdue.edu
Paul M. Hasegawa, (765) 494-1315;
paul.m.hasegawa@purdue.edu
Related Web sites:
Bressan's Web page:
http://www.hort.purdue.edu/hort/people/faculty/bressan.html
Hasegawa's Web page:
http://www.hort.purdue.edu/hort/people/faculty/hasegawa.html
Research activities of Bressan and Hasegawa:
http://www.hort.purdue.edu/CFPESP/Hasegawa/HASEGAWA.HTM
Juan March Institute for Study and Research salinity conference:
http://www.march.es/nuevo/ijm/crib/PROGRAMAS/CARTELES/MOLECULAR_BASIS_OF_ION
IC_HOMEOSTASIS_AND_SALT_TOLERANCE_IN_PLANTS.HTML
USDA George E. Brown Jr. Salinity Laboratory:
http://www.ussl.ars.usda.gov/
University of Arizona site on salt tolerance in plants:
http://www.nsf.gov/od/lpa/nsf50/nsfoutreach/htm/n50_z2/pages_z3/36_pg.htm#answer3
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Jeanne Norberg, Director, Purdue News Service
(765) 494-2084;
jnorberg@purdue.edu
Pager: 423-8662; Home: 449-4986
Fax: (765) 494-0401
http://news.uns.purdue.edu
--
Beth Forbes, Ag News Coordinator
Ag Communications Service
(765) 494-2722
bforbes@aes.purdue.edu
Fax: (765) 496-1117
http://persephone.agcom.purdue.edu/AgCom/news/
Purdue University news release
N4040
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