Alleviation of Drought Stress Inhibition on Photosynthesis by Overexpression of PEPC in Rice

Introducing enzymes involved in photosynthesis of C₄ plants into rice (Oryza sativa L.) is supposed to enhance the photosynthesis and crop productivity. However, only a few researches showed that the photosynthesis and crop productivity have been improved by introducing phosphoenolpyruvate carboxylase (PEPC) gene into rice. In the present study, the photosynthetic rates (P_n) in 42 rice lines overexpressing PEPC gene were investigated. The average P_n value of transgenic lines was almost the same as that of the wild type (control) in paddy field, but was much higher than that of the control in upland field. Only a few transgenic lines showed higher P_n in paddy field and most of them showed higher P_n in upland field. Similar results were found in the water controlled experiment. Two transgenic lines with different relative activities of PEPC (10 and 25 folds) were selected to study their photosynthesis under different water potentials (0, −20, and −40 kPa). In both lines, the P_n values were similar to that in the wild type under normal condition (0 kPa) and higher under drought conditions (−20 kPa and −40 kPa). In both experiments, the transgenic lines had higher P_n under drought conditions, with a slower decreasing rate than the wild type. Therefore, the present results suggested that the overexpressed PEPC could not improve the photosynthetic rate of transgenic rice plants. But the photosynthetic rate of transgenic rices declined slowly under drought condition. It is supposed that PEPC might be involved in drought resistance to decrease the inhibition of drought stress on photosynthesis in rice.