Changes in Photosynthetic Activity and Export of Carbon by Overexpressing a Maize Sucrose-Phosphate Synthase Gene under Elevated CO2 in Transgenic Rice

AbstractTo investigate whether increased sucrose-phosphate synthase (SPS) activity alters photosynthetic activity and/or the export of carbon from leaves under elevated C02 partial pressure ([C02]), we raised two lines of transgenic rice (H54-9 and H69-7), each overexpressing a maize SPS gene, and wild-type rice under ambient [C02] (35 Pa) and elevated [0O2] (100 Pa). Under ambient [C02], no significant difference was observed between the transgenic and wild-type plants in the levels of sucrose or starch in leaves or the photosynthetic activity; but the carbon export rate was higher in H69-7 than in the wild-type. Under elevated [C02], photosynthetic activity increased in all plants, but the accumulation of starch was significantly repressed in H54-9, whose SPS activity was about 12.5 times higher than that of the wild-type. The carbon export rate was higher in both transgenic lines than the wild-type. We considered that increased SPS activity in rice plants would promote the export of carbon from leaves ...