Effects of elevated CO2 concentration on photosynthetic carbon metabolism in flag-leaf blades of rice before and after heading

We monitored the effects of elevated atmospheric CO2 concentrations on the photosynthetic carbon metabolism in the flag leaves of rice plant (Oryza sativa L. cv. Akitakomachi) before and after heading. The plants were grown under ambient (350 ppm : control) or elevated (650 ppm) CO2 conditions. Flag-leaf blades grown under high CO2 accumulated more starch than control leaf blades before heading, but the level of starch declined to almost zero under both CO2 concentrations as soon as the development of ears began. Before heading, the transcript level of sucrose-phosphate synthase (SPS) (EC 2.4.1.14), a key enzyme in the sucrose synthesis in flag-leaf blades was significantly higher under elevated CO2 conditions than under elevated CO2 (P<0.01). The difference in the expression of SPS decreased after heading, coinciding with a change in starch contents in both groups. These results showed that the effects of elevated CO2 concentration on rice plants might vary with the growth stage of the leaf blades. We also discussed the influence of the changes in the carbohydrate metabolism of rice plants caused by elevated CO2 concentration on yield.