Iron-superoxide dismutase expression in transgenic alfalfa increases winter survival without a detectable increase in photosynthetic oxidative stress tolerance.
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.
McKersie
B D
BD
Plant Biotechnology Division, Department of Plant Agriculture, University of Guelph, Guelph, Ontario, Canada N1G 2W1. mckersb@basf.com
Murnaghan
J
J
Jones
K S
KS
Bowley
S R
SR
D000222:Adaptation, Physiological; D001483:Base Sequence; D017931:DNA Primers; D000455:Medicago sativa / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D018384:Oxidative Stress; D010788:Photosynthesis; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D013482:Superoxide Dismutase / Q000235:genetics*
D017931:DNA Primers; D013482:Superoxide Dismutase