First published online March 6, 2003; 10.1104/pp.102.003616
Plant Physiol, April 2003, Vol. 131, pp. 1748-1755
Tolerance of Mannitol-Accumulating Transgenic Wheat to Water
Stress and Salinity1
Tilahun
Abebe,2
Arron C.
Guenzi,*
Bjorn
Martin, and
John C.
Cushman3
Department of Plant and Soil Sciences (T.A., A.C.G., B.M.) and
Department of Biochemistry and Molecular Biology (J.C.C.), Oklahoma
State University, Stillwater, Oklahoma 74078
Previous work with model transgenic plants has demonstrated that
cellular accumulation of mannitol can alleviate abiotic stress. Here,
we show that ectopic expression of the mtlD gene for the biosynthesis of mannitol in wheat improves tolerance to water stress
and salinity. Wheat (Triticum aestivum L. cv Bobwhite) was transformed with the mtlD gene of Escherichia
coli. Tolerance to water stress and salinity was evaluated
using calli and T2 plants transformed with (+mtlD) or
without ( mtlD) mtlD. Calli were exposed to 1.0 MPa
of polyethylene glycol 8,000 or 100 mM NaCl. T2
plants were stressed by withholding water or by adding 150 mM NaCl to the nutrient medium. Fresh weight of mtlD
calli was reduced by 40% in the presence of polyethylene glycol and 37% under NaCl stress. Growth of +mtlD calli was not affected by
stress. In mtlD plants, fresh weight, dry weight, plant height, and
flag leaf length were reduced by 70%, 56%, 40%, and 45% compared with 40%, 8%, 18%, and 29%, respectively, in +mtlD plants. Salt stress reduced shoot fresh weight, dry weight, plant height, and flag
leaf length by 77%, 73%, 25%, and 36% in mtlD plants,
respectively, compared with 50%, 30%, 12%, and 20% in +mtlD plants.
However, the amount of mannitol accumulated in the callus and mature
fifth leaf (1.7-3.7 µmol g 1 fresh weight in the callus
and 0.6-2.0 µmol g1 fresh weight in the leaf) was too
small to protect against stress through osmotic adjustment. We conclude
that the improved growth performance of mannitol-accumulating calli and
mature leaves was due to other stress-protective functions of mannitol,
although this study cannot rule out possible osmotic effects in growing regions of the plant.
1
This work was supported by the Oklahoma
Agricultural Experiment Station, by the Oklahoma Wheat Research
Foundation, by the National Science Foundation (grant no.
EPS-9550478), by a scholarship from the Fulbright Foundation (to
T.A.), and in part by the Nevada Agricultural Experiment Station
(article no. 03031230).
2
Present address: Department of Agronomy, University of
Wisconsin, Madison, WI 53706.
3
Present address: Department of Biochemistry/MS200,
University of Nevada, Reno, NV 89557.
*
Corresponding author; e-mail acg{at}okstate.edu;
fax 405-744-6039.
© 2003 American Society of Plant Biologists
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