Enhanced tolerance to methyl viologen (MV)-mediated oxidative stress in SA transgenic leaves. (a) 100 μM MV-treated leaves showing senescence phenotype of WT and transgenic plants. Scale bar = 0.5 cm. (b) and (c) The chlorophyll and malondialdehyde (MDA) contents in the first leaf of MV-treated and untreated plants (d) and (e) Changes in SOD and APX activities between WT and transgenic cassava during MV treatment. WT, wild-type control; SA1, SA2 and SA4, independent transgenic plant lines. Data presented as mean ± SD from triplicate independent measurements. **Significant at 1% level from WT by t-test.