During the grain-filling period, photosynthesis in rice plants contributes 60%–100% of the final grain carbohydrate, but in the mean time, photo-oxidation caused by low temperature and high light is always suffered by top leaves. So it is same importance to increase the resisting photo-oxidation, as well as to improve net photosynthetic rate (Pn) in this period. In previous works, the progenies (SHPF6) which had high net photosynthetic rate were obtained from the hybrids Oryza sativa Azucena × Oryza rufipogon Ramper 6. Photosynthetic structures of them have been transformed so that a high Gs can be seen. But it is not known whether these progenies also have a high net photosynthetic rate in the grain-filling period and whether they can resist the photo-oxidation under the high light circumstance after the MV treatment. Thus, in this paper, a MV treatment was applied, photosynthetic parameters and chlorophyll fluorescence were measured to identify the extent of photo-oxidation. The results showed that SHPF6 had a high Pn under high light in the filling-grain period and the Pn increased with the further increment of light intensity. There was a significant correlation with between and Pn Ci (r = －0.767, P<0.01). After MV treatment, the value of F0, Fv/Fm and Fv/F0 changed significantly in Zhonghua 10 (P < 0.05), but not in SHPF6. All of this results suggested that the method of distant crossing can not only improve the net photosynthetic rate, increase stomatal conductance and promote the efficiency of CO2 assimilation in the filling-grain period, but also increase the resistance to photo-oxidation.
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