Abstract
In transgenic rice plats with an enhancement of Rubisco protein content to 120% of wild-type level, photosynthetic rates under the present ambient [CO2] and high irradiance conditions were not enhanced. To investigate this reason, the amounts of photosynthetic and other primary metabolites were determined with CE-TOFMS. Leaves were immediately frozen in liquid nitrogen and sampled after their photosynthetic rate reached steady-state. In transgenic plants, the amount of 3-phosphoglycerate as well as fructose-1,6-bisphosphate and sedoheptulose 7-phosphate increased to 1.4-fold of wild-type plants. On the other hand, the amounts of other photosynthetic metabolites including ribulose 1,5-bisphosphate did not differ between these genotypes. The amounts of ATP, ADP, NADPH and NADP+ and their ratios were also similar. These results suggest that although the increase in Rubisco protein contents leads to an enhancement of its catalytic reaction in the transgenic rice plants, enzymatic step(s) in RuBP regeneration become bottleneck for photosynthetic rates. Additionally, changes in other carbon and nitrogen metabolism are also discussed.
