Isolation, chromosomal localization, and differential expression of mitochondrial manganese superoxide dismutase and chloroplastic copper zinc superoxide dismutase genes in wheat

Superoxide dismutase (SOD) gene expression was investigated to elucidate it s role in drought and freezing tolerance in spring and winter wheat (Tritic um aestivum). cDNAs encoding chloroplastic Cu/ZnSODs and mitochondrial MnSO Ds were isolated from wheat. MnSOD and Cu/ZnSOD genes were mapped to the lo ng arms of the homologous group-2 and -7 chromosomes, respectively. Norther n blots indicated that MnSOD genes were drought inducible and decreased aft er rehydration. In contrast, Cu/ZnSOD mRNA was not drought inducible but in creased after rehydration. In both spring and winter wheat seedlings expose d to 2 degrees C, MnSOD transcripts attained maximum levels between 7 and 4 9 d. Transcripts of Cu/ZnSOD mRNA were detected sooner in winter than in sp ring wheat; however, they disappeared after 21 d of acclimation. Transcript s of both classes of SOD genes increased during natural acclimation in both spring and winter types. Exposure of fully hardened plants to three nonlet hal freeze-thaw cycles resulted in Cu/Zn mRNA accumulation; however, MnSOD mRNA levels declined in spring wheat but remained unchanged in winter wheat . The results of the dehydration and freeze-thaw-cycle experiments suggest that winter wheat has evolved a more effective stress-repair mechanism than spring wheat.