Abstract
Ammonia (NH4+) is assimilated in roots. This general understanding fails because excess NH4+ is transported to the aerial parts and is probably assimilated when plants are transferred from low N to high N condition (fertilization, etc.) in rice. Phosphoenolpyruvate carboxylase (PEPC) has a role of carbon skeleton provisions for the nitrogen assimilation. For clarifying the functions of chloroplastic PEPC (Osppc4) and cytosolic PEPC (Osppc2a), both knockdown lines (4i and 2i, respectively) and non-transgenic plants (NT) were grown in hydro culture (1 mM NH4Cl). NH4+ content in xylem sap increased at 6 h after when transferring to high N (2 mM) and there was no change among the lines. Area-based NH4+ content of uppermost fully expanded leaves in 4i was about twice higher than NT at high N, which was canceled out by imposing dark on the plants. Leaf NH4+ content of 2i was always higher than NT irrespective of the dark treatment, but its difference was smaller than between 4i and NT. These results suggest that the cytosolic PEPC functions in the dark whereas the chloroplastic PEPC mainly functions under light for carbon skeleton supply in assimilating NH4+ of the rice leaf blade.
