EXPRESSION OF SODCP AND SODB GENES IN NICOTIANA-TABACUM - EFFECTS OF LIGHT AND COPPER EXCESS

Light and copper are necessary for the biogenesis and normal function of chloroplasts, but are also known to initiate the production of acti ve oxygen species. Tobacco (Nicotiana tabacum L.) contains two plastid -located superoxide dismutases, Cu/Zn-SOD and Fe-SOD, encoded by the n uclear genes sodCp and sodB, respectively, The expression of both gene s is developmentally regulated and influenced by oxidative stress, Her e, the effects of light and copper excess on the expression of these t wo genes were analysed in seedlings and in leaves of non-flowering tob acco plants, The accumulation of both transcripts was induced by light in seedlings and in young leaves of mature plants, but changes in enz ymatic activities were only observed in seedlings, Copper excess was i nduced in two experimental systems, In the first, axenically-grown pla nts were transferred to the medium containing excess copper and grown for 10 d. Excess copper induced an increase of sodCp mRNA level, but n ot of enzymatic activity, whereas Fe-SOD activity and sodB transcript level decreased. In contrast, after transfer of hydroponically grown p lants to a copper excess medium and growth for an additional 3 d, sodB mRNA and enzyme levels increased, whereas the sodCp transcript level was reduced, Changes in the expression levels of both genes were more pronounced in young leaves, The effects of light and copper on the exp ression of plastid-located SODs are discussed.