Abstract: 【Objective】The chlorophyll content of a chlorophyll-deficit rice mutant (YL) is significantly lower than its wild type (WT), but its photosynthetic electron transport rate and net photosynthetic rate are significantly higher than its WT. The aim of this study is to understand the physiological basis, and its potential use in high photosynthetic efficiency breeding was prospected.【Method】A pot experiment in the climate chamber at high light intensity (HL) and low light intensities (LL), and a field experiment were conducted. Chlorophyll fluorescence, the concentration of super oxygen anion and malodialdehyde, superoxide dismutase activity, light fluorescent and electron micrographs, canopy temperature were investigated. 【Result】 The results show that the chlorophyll content was significantly lower in the mutant than its WT, and the light treatment had different effects on chlorophyll content in the mutant and its WT. When compared the HL and LL treatments, the chlorophyll content was increased by 60% in the mutant, but decreased by 20% in the WT. The light response curves showed that the mutant has a higher photosynthetic capacity than its WT. At the irradiance of 1 000 µmol·m^-2·s^-1, the photosynthetic rate was 46.5% and 9.4% higher in the mutant than its WT, in HL and LL treatments, respectively. The chlorophyll fluorescence measurements indicate that the photosynthetic electron transport rate (ETR), photosystem Ⅱ efficiency (Φ_PSⅡ), photosynthetic quenching (qP), and maximum efficiency of open photosystem Ⅱ in the light (F′v/F′m) were significantly higher in mutant than its WT. The content of oxygen anion and malondialdehyde were higher in WT than the mutant, especially in HL treatment, indicating photoinhibition in WT. The electron micrographs and light fluorescent micrographs of the mutant and its WT indicated that the chloroplast was to some extent harmed. The inter-vein distance was also found larger in WT than in the mutant, and the area of vascular bundle is smaller in WT than in the mutant, indicating a better water status in mutant than in its WT. The thermal image indicated that the canopy temperature was significantly lower in mutant than in its WT at noon with high irradiance. All the results suggested that the high chlorophyll content in the WT excessively absorbed light energy, causing photoinhibition (high oxygen anion and malondialdehyde content, reduced photosystem Ⅱefficiency and decreased SOD activity), and had a lower photosynthetic rate than the mutant. The excessively absorbed light energy also contributed the higher canopy temperature in WT than in mutant, which is adverse for canopy photosynthesis.【Conclusion】All these results implicate that selecting for moderate chlorophyll content in breeding would help avoiding the generation of reactive oxygen species and alleviating the photoinhibition, improving photosynthesis, especially at noon under high solar radiation.

Key words: rice, photosynthetic rate, chlorophyll, chlorophyll fluorescence, photoinhibition