When callus tissue derived from Coker 312 is exposed to salt treatment an increase in the activity of antioxidant enzymes including ascorbate peroxidase and glutathione reductase is observed. In order to address the question of whether the increase in activity is due to an increase in the transcription of the genes encoding these enzymes or whether it is due to the translation of existing transcripts or possibly to the mobilization of existing enzyme pools, a series of experiments was undertaken using a-amanitin, a specific inhibitor of RNA polymerase II. Callus tissue from a salt-tolerant cell line was transferred to aerated culture tubes containing either 150 mM NaCl (NaCl-tolerant control) or media containing 150 mM NaCl + 100 ng ml^-1 a-amanitin. Following a 2-hour pre-incubation, the tubes containing 150 mM NaCl and the tubes containing 150 mM NaCl + 100ng ml^-1 a-amanitin were adjusted to a final concentration of 250 mM NaCl. In a parallel series of experiments, callus tissue from a control cell line (NaCl-sensitive control) was transferred to aerated culture tubes containing either 0 mM NaCl or media containing 0 mM NaCl + 100ng ml^-1 a-amanitin. Following a 2-hour pre-incubation period, the tubes containing 0 mM NaCl and the tubes containing 0 mM NaCl + 100ng ml^-1 a-amanitin were adjusted to a final concentration of 75 mM NaCl. The callus tissue from both experiments was harvested at 30 min, 1 hr, 2 hr, 4 hr, and 8 hr intervals and analyzed for ascorbate reductase (AP) and glutathione reductase (GR) activity. In both sets of experiments a complete suppression of the salt induced increase in the activity of ascorbate peroxidase and glutathione reductase was observed in replicates to which a-amanitin was added. These results suggest that the upregulation of the activity of AP and GR in response to salt stress is due to a de novo transcription of the genes encoding these two enzymes and is not due to the translation of existing transcripts or mobilization of existing enzyme pools.