Expression of sodCp and sodB genes in Nicotiana tabacum: Effects of light and copper excess

Abstract

Light and copper are necessary for the biogenesis and normal function of chloroplasts, but are also known to initiate the production of active oxygen species. Tobacco (Nicotiana tabacum L.) contains two plastid-located superoxide dismutases, Cu/Zn-SOD and Fe-SOD, encoded by the nuclear genes sodCp and sodB, respectively. The expression of both genes is developmentally regulated and influenced by oxidative stress. Here, the effects of light and copper excess on the expression of these two genes were analysed in seedlings and in leaves of non-flowering tobacco plants. The accumulation of both transcripts was induced by light in seedlings and in young leaves of mature plants, but changes in enzymatic activities were only observed in seedlings. Copper excess was induced in two experimental systems. In the first, axenically-grown plants were transferred to the medium containing excess copper and grown for 10 d. Excess copper induced an increase of sodCp mRNA level, but not of enzymatic activity, whereas Fe-SOD activity and sodB transcript level decreased. In contrast, after transfer of hydroponically grown plants 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 expression of plastid-located SODs are discussed.