Enhanced tolerance to methyl viologen-induced oxidative stress and high temperature in transgenic potato plants overexpressing the CuZnSOD, APX and NDPK2 genes

Oxidative stress is a major threat for plants exposed to various environmental stresses. Previous studies found that transgenic potato plants expressing both copper zinc superoxide dismutase (CuZnSOD) and ascorbate peroxidase (APX) (referred to as SSA plants), or nucleoside diphosphate kinase 2 (NDPK2) (SN plants), showed enhanced tolerance to methyl viologen (MV)-induced oxidative stress and high temperature. This study aimed to develop transgenic plants that were more tolerant of oxidative stress by introducing the NDPK2 gene into SSA potato plants under the control of an oxidative stress-inducible peroxidase (SWPA2) promoter to create SSAN plants. SSAN leaf discs and whole plants showed enhanced tolerance to MV, as compared to SSA, SN or non-transgenic (NT) plants. SSAN plants sprayed with 400 mu M MV exhibited about 53 and 83% less visible damage than did SSA and SN plants, respectively. The expression levels of the CuZnSOD, APX and NDPK2 genes in SSAN plants following MV treatment correlated well with MV tolerance. SOD, APX, NDPK and catalase antioxidant enzyme activities were also increased in MV-treated SSAN plants. In addition, SSAN plants were more tolerant to high temperature stress at 42 degrees C, exhibiting a 6.2% reduction in photosynthetic activity as compared to plants grown at 25 degrees C. In contrast, the photosynthetic activities of SN and SSA plants decreased by 50 and 18%, respectively. These results indicate that the simultaneous overexpression of CuZnSOD, APX and NDPK2 is more effective than single or double transgene expression for developing plants with enhanced tolerance to various environmental stresses.