Physiological characteristics of the primitive CO(2) concentrating mechanism in PEPC transgenic rice

The relationship between carbon assimilation and high-level expression of the maize PEPC in PEPC transgenic rice was studied by comparison to that in the untransformed rice,japonica kitaake. Stomatal conductance and photosynthetic rates in PEPC transgenic rice were higher than those of untransformed rice, but the increase of stomatal conductance had no statistical correlation with that of photosynthetic rate. Under high levels of light intensity, the protein contents of PEPC and CA were increased significantly. Therefore the photosynthetic capacity was increased greatly (50%) with atmospheric CO(2) supply. While CO(2) release in leaf was reduced and the compensation point was lowered correspondingly under CO(2) free conditions. Treatment of the rice with the PEPC-specific inhibitor DCDP showed that overexpression of PEPC and enhancement of carbon assimilation were related to the stability of Fv/Fm. Labeling with(14)CO(2) for 20 s showed more(14)C was distributed to C(4) primary photosynthate asperate in PEPC transgenic rice, suggesting that there exists a limiting C(4) photosynthetic mechanism in leaves. These results suggest that the primitive CO(2) concentrating mechanism found in rice could be reproduced through metabolic engineering, and shed light on the physiological basis for transgenic breeding with high photosynthetic efficiency.