Characterization of transgenic rice plants overproducing four different enzymes related to C4 photosynthesis

Abstract

PEPC, PPDK, NADP-MDH, and NADP-malic enzyme (ME) were overproduced in the mesophyll cell of rice plants. Overproduction of PEPC alone stimulates respiration in the light and slightly reduces the carboxylation efficiency, thereby suppressing the photosynthetic CO₂ assimilation. The stimulated respiration remained unaffected by overproduction of all the four enzymes, but the carboxylation efficiency was restored. The apparent CO₂ assimilation rate was also restored to reach levels comparable to or slightly higher than that of non-transformants. The extent of the restoration, however, was more marked at higher CO₂ concentrations, indicating that overproduction of the four enzymes did not act to concentrate CO₂ inside the chloroplast. The δ¹³C value was unaffected by overproduction of any of four enzymes but slightly increased by overproduction of all the four. Since a similar increase was observed in other transformants overproducing PEPC and ME, it likely reflected some metabolic path constituted of foreign PEPC and ME.