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Plant Physiol, April 2000, Vol. 122, pp. 1427-1438
Iron-Superoxide Dismutase Expression in Transgenic Alfalfa
Increases Winter Survival without a Detectable Increase in
Photosynthetic Oxidative Stress Tolerance1
Bryan D.
McKersie,2*
Julia
Murnaghan,
Kim S.
Jones,3 and
Stephen R.
Bowley
Plant Biotechnology Division, Department of Plant Agriculture,
University of Guelph, Guelph, Ontario, Canada N1G 2W1
To
determine whether overexpression of Fe-superoxide (SOD) dismutase would
increase superoxide-scavenging capacity and thereby improve the winter
survival of transgenic alfalfa (Medicago sativa L.)
plants, two genotypes were transformed with the vector pEXSOD10, which
contains a cDNA for Arabidopsis Fe-SOD with a chloroplast transit
peptide and cauliflower mosaic virus 35S promoter. A novel Fe-SOD was
detected by native PAGE in both greenhouse- and field-grown transgenic
plants, but activity varied among independent transgenic plants. The
increased Fe-SOD activity was associated with increased winter survival
over 2 years in field trials, but not with oxidative stress tolerance
as measured by resistance of leaves to methyl viologen, a superoxide
generator. Total shoot dry matter production over 2 harvest years was
not associated with Fe-SOD activity. There was no detectable difference
in the pattern of primary freezing injury, as shown by vital staining,
nor was there additional accumulation of carbohydrates in
field-acclimated roots of the transgenic alfalfa plants. We did not
detect any difference in growth of one transgenic plant with high
Fe-SOD activity compared with a non-transgenic control. Therefore, the
improvement in winter survival did not appear to be a consequence of
improved oxidative stress tolerance associated with photosynthesis, nor
was it a consequence of a change in primary freezing injury. We suggest
that Fe-SOD overexpression reduced secondary injury symptoms and
thereby enhanced recovery from stresses experienced during winter.
1
Financial support for this research was provided
by a research grant from the Natural Sciences and Engineering Research
Council of Canada and by the Ontario Ministry of Agriculture Food and Rural Affairs.
2
Present Address: BASF Plant Science, 26 Davis Drive, Research Triangle Park, NC 27509.
3
Present Address: Department of Chemical
Engineering, University of Toronto, Toronto, Ontario, Canada M5S 3E5.
*
Corresponding author; e-mail mckersb{at}basf.com; fax
919-547-2423.
© 2000 American Society of Plant Physiologists
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