Molecular characterization and response to salt stress of mRNAs encoding cytosolic Cu/Zn superoxide dismutase and catalase from Bruguiera gymnorrhiza

To analyze the potential of the active oxygen-scavenging system of the cytosol in leaves of salt-stressed Bruguiera gymnorrhiza, we isolated a full-length cDNA encoding a 153-amino-acid sequence of cytosolic Cu/Zn superoxide dismutase (SOD) and a partial cDNA encoding catalase. Northern blot analyses showed that the transcript level of cytosolic Cu/Zn-SOD increased after 1 and 5 days NaCl treatment, but no significant change occurred in the expression of the catalase gene. The transcript of cytosolic Cu/Zn-SOD was also induced by mannitol treatment. This suggests that the increase in cytosolic Cu/Zn-SOD 1 day after NaCl treatment is a response to osmotic stress. After 5 days treatment with NaCl, the transcript level of cytosolic Cu/Zn-SOD increased in young and mature leaves rather than in old leaves. Expression of the cytosolic Cu/Zn-SOD gene was induced by exogenous abscisic acid, while the catalase gene was induced by application of 2-chloroethyl-phosphonic acid, which is a generator of ethylene. The results from this study suggest that salt stress leads to the generation of superoxide in the cytosol and that the oxygen-scavenging system in the cytosol contributes to the salt tolerance capacity of B. gymnorrhiza.