With untransformed rice cv. Kitaake as control, the characteristics of carbon assimilation and photoprotection of a transgenic rice line over-expressing maize phosphoenolpyruvate carboxylase (PEPC) were investigated. The PEPC activity in untransformed rice was low, but the activity was stimulated under high irradiance or photoinhibitory condition. PEPC in untransformed rice contributed by about 5-10 % to photosynthesis, as shown by the application of the specific inhibitor 3,3-dichloro-2-(dihydroxyphosphinoylmethyl)propenoate (DCDP). When maize PEPC gene was introduced into rice, transgenic rice expressed high amount of maize PEPC protein and had high PEPC activity. Simultaneously, the activity of carbonic anhydrase (CA) transporting CO2 increased significantly. Thus the photosynthetic capacity increased greatly (50 %) under high CO2 supply. In CO2-free air, CO2 release in the leaf was less. In addition, PEPC transgenic rice was more tolerant to photoinhibition. Treating by NaF, an inhibitor of phosphatase, showed that in transgenic rice more phosphorylated light-harvesting chlorophyll a/b-binding complexes (LHC) moved to photosystem 1 (PS1) protecting thus PS2 from photo-damage. Simultaneously, the introduction of maize PEPC gene could activate or induce activities of the key enzymes scavenging active oxygen, such as superoxide dismutase (SOD) and peroxidase (POD). Hence higher PS2 photochemical efficiency and lower superoxygen anion (O2.-) generation and malonyldiadehyde (MDA) content under photoinhibition could improve protection from photo-oxidation. and D. M. Jiao, X. Li, B. H. Ji.
In the untransformed rice (WT) and transgenic rice with the PEPC and PPDK genes (CK) we determined activities of C4 photosynthetic enzymes, photosynthetic response to irradiance and temperature, the metabolic index of active oxygen, and the yield component factors. The activities of C4 photosynthetic enzymes in WT were very low, while those of corresponding enzymes in CK were highly observable. Moreover, after adenosine triphosphate (ATP) treatment, and under high irradiance and high temperature, the net photosynthetic rate of CK increased by 17 and 12 %, respectively, as compared to that achieved without ATP treatment. The resistance of CK against photo-oxidation was enhanced under these conditions, and CK yield increased by 15 %. ATP treatment enhanced the photosynthetic productivity of CK, thereby proving that ATP is the key factor in enhancing the photosynthetic capacity of transgenic rice with C4 gene. Our new technical approach can be used in breeding rice with high photosynthetic efficiency and high grain yield. and B. J. Zhang ... [et al.].
High level of phosphoenolpyruvate carboxylase (PEPC) gene was stably inherited and transferred from the male parent, PEPC transgenic rice, into a female parent, japonica rice cv. 9516. Relative to the female parent, the produced JAAS45 pollen lines exhibited high PEPC activity (17-fold increase) and also higher photosynthetic rates (about 36 %-fold increase). The JAAS45 pollen lines were more tolerant to photoinhibition and to photo-oxidative stress. Furthermore, JAAS45 pollen lines, as well as their male parent, were tested to exhibit a limiting C4 cycle by feeding with exogenous C4 primary products such as oxaloacetate (OAA). Thus the PEPC gene and photosynthetic characteristics of PEPC transgenic rice could be stably transferred to the hybrid progenies, which might open a new breeding approach to the integration of conventional hybridization and biological technology. and L. Ling, B. J. Zhang, D. M. Jiao.