Level of protoporphyrinogen oxidase activity tightly correlates with photodynamic and defense responses in oxyfluorfen-treated transgenic rice

Transgenic rice systems involving the plastidal expression of Arabidopsis protoporphyrinogen oxidase (Protox) (AP line) and the dual expression of Myxococcus xanthus Protox in chloroplasts and mitochondria (TTS line) were used to investigate the effect of Protox levels on photodynamic stress and defense responses imposed by peroxidizing herbicide oxyfluorfen. The oxyfluorfen-treated TTS line showed less photodynamic stress and antioxidant responses than AP and wild-type lines, indicating that sustained Protox activity in the TTS line during oxyfluorfen action prevented the accumulation of photodynamic protoporphyrin IX. This study suggests evidence of a tight correlation of Protox activity with herbicidal resistance in rice plants.