DIFFERENTIAL EXPRESSION OF CUZN-SUPEROXIDE AND FE-SUPEROXIDE DISMUTASE GENES OF TOBACCO DURING DEVELOPMENT, OXIDATIVE STRESS, AND HORMONAL TREATMENTS

Chloroplasts of Nicotiana tabacum have two superoxide dismutases: a Fe - and a CuZn-containing enzyme, encoded by the nuclear genes sodB and sodCp, respectively, As a first step in studying the physiological fun ction of these two enzymes, we compared the expression of sodB and sod Cp in different plant organs, in response to hormonal treatments, and upon treatment with paraquat and Norflurazon. The sodCp transcript and active enzyme were detected only in young leaves of mature plants. Th e sodB transcript was more abundant in young compared to old leaves, b ut the enzymatic activity was higher in mature and senescent leaves. s odCp and sodB exhibited a different expression pattern upon treatment with abscisic acid, indole-3-acetic acid, kinetin, gibberellin, and 1- aminocyclopropane-1-carboxylate. Paraquat treatment caused a decrease in abundance of both transcripts, although the dose dependency of this decrease differed, Norflurazon-induced photooxidation resulted in a 1 0-fold increase of sodCp mRNA whereas the sodB transcript level was 25 % higher than the control, These differences in expression might expla in why both plastid-located superoxide dismutase enzymes are needed, p articularly under stress conditions.