Response of Gas Exchange and Water Use Efficiency to Light Intensity and Temperature in Transgenic Rice Expressing PEPC and PPDK Genes

Aiming to controvert whether the photosynthetic capacity of transgenic rice expressing C4 genes is enhanced, with the C3-type untransformed rice (WT) and maize (a C4 plant) as controls, the activity of C4 photosynthetic enzymes, gas exchange parameters and water use efficiency (WUE) under different light intensities and temperatures, the stable carbon isotope ratio (δ13C) value and the metabolic index of active oxygen as well as plant yield parameters were determined in transgenic rice carrying the PEPC and PPDK genes (CK) in this study. The results showed that the light-saturated photosynthetic rate of CK was intermediate between that of WT and maize, with a slight bias towards that of maize. Under a high light intensity (1 200 μmol m−2 s−1) and high temperature (35°C), CK still exhibited higher photosynthetic capacity, while the Gs decreased. The WUE of CK was only slightly increased, and was similar to that of WT. The δ13C value indicated that CK functioned as a C3 plant. In addition, the tolerance to photo-oxidation and grain yield of CK was enhanced by sprayed with NaHSO3. In conclusion, CK possesses higher photosynthetic productivity under the conditions of high photon flux density (PFD), high temperature and spraying with NaHSO3 solution, thereby providing a new technical approach and physiological basis for constructing C4-like rice.