Winter Survival of Transgenic Alfalfa Overexpressing Superoxide
Dismutase1
Bryan D. McKersie*,
Stephen R. Bowley, and
Kim S. Jones
Plant Biotechnology Division, Department of Plant Agriculture,
University of Guelph, Guelph, Ontario, Canada N1G 2W1
To test the hypothesis that enhanced
tolerance of oxidative stress would improve winter survival, two clones
of alfalfa (Medicago sativa) were transformed with a
Mn-superoxide dismutase (Mn-SOD) targeted to the mitochondria or to the
chloroplast. Although Mn-SOD activity increased in most primary
transgenic plants, both cytosolic and chloroplastic forms of Cu/Zn-SOD
had lower activity in the chloroplast SOD transgenic plants than in the
nontransgenic plants. In a field trial at Elora, Ontario, Canada, the
survival and yield of 33 primary transgenic and control plants were
compared. After one winter most transgenic plants had higher survival
rates than control plants, with some at 100%. Similarly, some
independent transgenic plants had twice the herbage yield of the
control plants. Prescreening the transgenic plants for SOD activity,
vigor, or freezing tolerance in the greenhouse was not effective in
identifying individual transgenic plants with improved field
performance. Freezing injury to leaf blades and fibrous roots, measured
by electrolyte leakage from greenhouse-grown acclimated plants,
indicated that the most tolerant were only 1°C more freezing-tolerant
than alfalfa clone N4. There were no differences among transgenic and control plants for tetrazolium staining of field-grown plants at any
freezing temperature. Therefore, although many of the transgenic plants
had higher winter survival rates and herbage yield, there was no
apparent difference in primary freezing injury, and therefore, the
trait is not associated with a change in the primary site of freezing
injury.
1
Financial support for this research was provided
by the Natural Sciences and Engineering Research Council of Canada and
the Ontario Ministry of Agriculture Food and Rural Affairs.
*
Corresponding author; e-mail: mckersie{at}plant.uoguelph.ca; fax
1-519-763-8933.
Plant Physiol. (1999) 119: 839-848
Copyright Clearance Center: 0032-0889/99/119//10
© 1999 American Society of Plant Physiologists
