ASCORBATE PEROXIDASE-ACTIVITY, NOT THE MESSENGER-RNA LEVEL, IS ENHANCED IN SALT-STRESSED RAPHANUS-SATIVUS PLANTS

The effect of salt on ascorbate peroxidase (EC 1.11.1.11) activity and mRNA level in radish (Raphanus sativus L. cv. Fakir) was investigated . cDNA encoding a radish ascorbate peroxidase was obtained and sequenc ed. Sequence data analysis showed that the coding region was well cons erved among higher plants. The radish cDNA was used as a probe to meas ure the steady-state level of ascorbate peroxidase mRNA in plants subj ected to salt stress (100 mM NaCl). The levels of transcripts encoding ascorbate peroxidase were almost identical in control or salt-grown r adish plants in both leaves and roots. The activity of soluble ascorba te peroxidase was enhanced by the salt treatment in both leaves and ro ots. The salt-induced increase in ascorbate peroxidase activity requir es days to become significant and can be considered as a late response . The increase in activity, but not in mRNA level, suggests that the s alt-induced ascorbate peroxidase expression is probably the consequenc e of post-transcriptional events.