Figure 3. Responses of wild-type and ZmSO over-expression tobacco plants to toxic levels of sulfite.

(A) Toxic effect of Na₂SO₃ (5 and 10 mM) on leaf discs from 8-week old wild-type and OE lines. After 16 h treatment, Leaf discs of wild-type plants showed higher chlorosis and damage than OE lines (OE-3 and OE-7). (B) Sulfite concentration in Na₂SO₃ treated leaves from wild-type and OE plants. (C) Sulfate concentration in Na₂SO₃ treated leaves from wild-type and OE plants. In both (B) and (C), leaf discs were separately sampled and washed three times with distilled water after exposure of the plants to 0, 5 and 10 mM Na₂SO₃ for 16 h. The leaves were then used for sulfite and sulfate contents analysis. Data are the means of three replicates (±SE). Means denoted by the same letter did not significantly differ at P<0.05. The data are from one of three different experiments that yielded essentially identical results.