Enhancement of NADP-malic enzyme in transgenic rice induced the accumulation of reactive oxygen species

It had been demonstrated that the photosynthetic photodamage, such as photoinhibition and photooxidation, was enhanced in transgenic rice plants overexpressing NADP-malic enzyme (ME). However, its physiological base has not been investigated. In order to elucidate the physiological elements contributed to the enhancement of photodamage in NADP-ME transgenic rice plants, some physiological indices related to reactive oxygen species (ROS) accumulation were studied using the T1 progeny of transgenic rice plants. The results showed that more ROS such as O2−. and H2O2 were accumulated in transgenic rice plants, which enhanced photooxidation, while the accumulation of malondialdehyde in transgenic rice plants was not evident as compared with the wild-type plants. The measurement of NADPH/NADP ratios in leaves showed that transgenic rice plants had a higher ratio than untransformed rice plants. Based on these data, we speculated that overexpression of NADP-ME led to the deficiency of NADP and overreduction of photosystem I, which induced the accumulation of ROS in the transgenic rice plants, and just ROS were accounted for plant sensitivity to photooxidation.