| Improve the crop photosynthesis and break the yield barrier is the main research topic in the recent years. It was supposed that enhance the crop photosynthesis is the key method to increase the crop yield after the"Green Revolution"and using of heterosis. It was suggested by the scientists from IRRI that creating the C4 rice then increase the rice photosynthesis is the only way to meet the food demand in Asian. So, introduce the C4 enzymes into C3 crop to improve the photosynthesis and crop yield has been becoming the hot research field.Several attempts have been made to transfer phosphoenolpyruvate carboxylase (PEPC) gene from maize into rice, however, there is still a controversy in whether the transgenic plants advanced in photosynthesis and productivity. Photosynthesis is easy affected by environmental stress, especially the drought stress decrease the photosynthetic rate severely. At present, research focus on PEPC regulation under stress conditions, several reports showed that the PEPC transgenic rice maintain high photosynthetic rate under intense light and high temperature conditions. In addition, drought, salt and cold stress induce the expression of PEPC, thus, PEPC was supposed to participate in the stress tolerance in plants response to environmental stress. In the present research, the T4 offspring of PEPC transgenic rice was investigated to analyze the relation of photosynthetic capacity, productivity and stress tolerance under drought stress conditions. The main results were:(1). Drought stress induces the expression of PEPC gene in rice plants, and plays an important role in transgenic rice response to stress condition. The data showed that the activity of PEPC was increased with the drought stress level, especially in PEPC transgenic rice. It is suggested that the maize PEPC gene contribute to the increase of PEPC activity.(2). The PEPC transgenic rice plants maintain higher photosynthesis than wild type under drought stress. There was no significant difference in photosynthetic rate (A) between transgenic rice (T1 and T2) and wild type (WT) under normal irrigation condition; but measurements under drought stress and upland cultivation, the PEPC transgenic rice maintain higher photosynthetic rate (A), stomatal conductance (Gs), chl content and water use efficiency (WUE). Therefore, the transgenic rice plants exhibited higher photosynthesis under drought stress condition.(3). The PEPC transgenic rice plants maintain higher photoprotective ability than wild type under drought stress. In the present research, the PSâ…¡system was not affected severely and there was also no significant difference between transgenic rice and wild type under drought stress. It is suggested that the higher photosynthetic rate in transgenic rice plants was not related to the function of PSâ…¡system. The transgenic rice plants showed higher non-photochemical quenching (NPQ) and electron transfer rate (ETR) under drought stress. So, it is suggested that the activation of photoprotective mechanism in transgenic rice plants enhance the photosynthesis response to drought stress.(4). The transgenic rice plants shower higher drought resistance, as advanced in anti-oxidate and osmotic regulation ability under drought stress. The present research showed that the transgenic rice plants exhibited higher higher superoxide dismutase (SOD) activity, lower malondialdehyde (MDA) content, higher proline content and lower increase of osmotic potential than the wild type under drought stress. So, the anti-oxidate and osmotic regulation ability of transgenic rice plants contribute to avoid membrane damage, higher stomatal conductance maintain and higher photosynthetic rate under drought stress.(5). The transgenic rice plants shower higher yield under upland cultivation. There was no significant difference between transgenic rice plants and wild type under normal irrigation. The results indicated that the yield increased by 28% and 42%, and the number of tillers increased by 27% and 40%, respectively, in two transgenic lines T1 and T2 compared with those of the wild type under upland cultivation. So, the present results suggested that, the PEPC gene overexpressed rice confers higher photosynthesis and drought tolerance under drought stress, which is helpful to increase the number of tillers, then contribute to enhance the rice yield.
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