Cloning of cDNAs encoding SODs from lettuce plants which show differentialregulation by arbuscular mycorrhizal symbiosis and by drought stress

In the present study three cDNA fragments were cloned using degenerate prim ers for Mn-sod genes and PCR: two showed a high degree of identity with Mn- sods from plants and the third with Fe-sod. Arbuscular mycorrhizal (AM) sym biosis down-regulated their expression pattern under well-watered condition s. In contrast, AM symbiosis in combination with drought stress considerabl y increased the expression of the Mn-sod II gene and this correlated well w ith plant tolerance to drought. These results would suggest that mycorrhiza l protection against oxidative stress caused by drought may be an important mechanism by which AM fungi protect the host plant against drought.