Antioxidative Responses of Transgenic Tobacco Plants Expressing both Superoxide Dismutase and Ascorbate Peroxidase in Chloroplasts to Several Herbicides

Antioxidative responses of transgenic tobacco plants expressing both superoxide dismutase (SOD) and ascorbate peroxidase (APX) in chloroplasts was investigated with several herbicides. In greenhouse test, tolerance of SOD/APX-overexpressed tobacco (CA) to photosystem (PS) I inhibitor paraquat was increased by about 40%. However, any response differences between CA and wild type (WT) tobacco was not observed in a treatment with PS II inhibitors (bromoxynil, diuron and bromacil), chlorophyll biosynthesis inhibitor(oxyfluorfen), carotenoid biosynthesis inhibitor (fluridone) and 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase inhibitor (glyphosate). This tendency was also similar in the growth chamber test of low light intensity, using paraquat and diuron. That is, increased antioxidant activity of CA was shown only in paraquat treatment. When paraquat was foliar-treated to 6 to 9-leaf stage plant, the third to fourth placed leaf from shoot tip showed relatively higher antioxidant activity. Ascorbate supplemented to paraquat solution alleviated the phytotoxicity with a similar range in both CA and WT. In conclusion, CA specifically responded to oxidative stress induced by paraquat among tested herbicides in a whole plant assay.