Abstract
This study assessed the responses of wild-type (WT) and transgenic Arabidopsis expressing seven combinations of maize (Zea mays) genes phosphoenolpyruvate carboxylase (pepc), pyruvate phosphate dikinase (ppdk), and NADP-malic enzyme (nadp-me) to high light. Our results showed that the net CO(2) assimilation rate (P(n)) and shoot dry weight of four of the transgenic Arabidopsis genotypes were significantly different from those of WT under high-light treatment, being in the order of Zmpepc+Zmppdk+Zmnadp-me (PC-K-M) > Zmpepc+Zmppdk (PC-K) > Zmpepc (PC), Zmpepc+Zmnadp-me (PC-M) > WT. The other genotypes did not differ from WT. This indicated that Zmpepc was essential for maintaining high photosynthetic performance under high light, Zmppdk had a positive synergistic effect on Zmpepc, and the combination of all three genes had the greatest synergistic effect. These four genotypes also maintained higher photosystem II (PSII) activity (K-phase, J-phase, RC/CSm), electron transfer capacity (J-phase), and photochemical efficiency (TRo/ABS), and accumulated less reactive oxygen species (O(2)·(-), H(2)O(2)) and suffered less damage to the membrane system (MDA) than WT under high light. Collectively, PC, PC-K, PC-M, and PC-K-M used most of the absorbed energy for CO(2) assimilation through a significantly higher P(n), which reduced the generation of excess electrons in the photosynthetic apparatus, thereby reducing damage to the membrane system and PSII. This ultimately resulted in improved high-light tolerance. P(n) was the main reason for the significant difference in the high-light tolerance of the four genotypes. Joint expression of the three maize genes may be of great value in the genetic improvement of high-light tolerance in C(3) crops.