Effects of Photooxidation on Photosynthetic Characteristics of Different Super Japonica Rice Varieties

Purpose To investigate the photochemical response characteristics of super japonica rice varieties Nanjing44 and Nanjing5055 to photooxidation treatment and their tolerance mechanism, and to compare the differences in photooxidation resistance characteristics, providing theoretical reference for the cultivation of high quality super rice.

Methods Nanjing44 and Nanjing5055 were used as test materials. After 10 days of flowering, the leaves were photooxidized for seven days to analyze and compare the chlorophyll fluorescence kinetic parameters of two japonica rice varieties before and after treatment.

Results  There was no significant difference in chlorophyll fluorescence kinetic parameters between Nanjing44 and Nanjing5055 before photooxidation treatment. After photooxidation treatment, the photosystem Ⅱ (PSⅡ) of the two cultivars were suppressed to varying degrees, the structure and physiological state of PSⅡ were damaged, the photosynthetic performance of PSⅡ was decreased, the initial fluorescence (F_o) was increased, the maximum photochemical efficiency (F_v/F_m) and leaf photosynthetic performance index (PI_abs) were decreased, and the photochemical activity of PSⅡ was decreased. However, the photochemical activity of Nanjing44 was significantly higher than that of Nanjing5055. Absorption flux per RC (ABS/RC), trapped energy flux per RC (TR_o/RC) and dissipated energy flux per RC (DI_o/RC) of Nanjing44 were not significantly higher than those of the control after photooxidation treatment, but were significantly lower than those of Nanjing5055, indicating that the number of active reaction centers per unit area of Nanjing44 was relatively high. The donor side parameters relative variable fluorescence at 300 μs (V_K) and relative variable fluorescence at 150 μs (V_L) of Nanjing44 leaf PSⅡ were 0.50 times and 0.45 times of Nanjing5055, and the receptor side parameters relative variable fluorescence at 2 ms (V_J), relative variable fluorescence at 30 ms (V_I), approximated initial slope (in ms⁻¹) of the fluorescence transient (M_o) and size of PSⅡ receptor side library (S_m) ware 0.60 times, 0.91 times, 0.50 times and 1.74 times times of Nanjing5055, respectively. After photooxidation, the supply capacity of PSⅡ donor electron and the electron transfer capacity from Q_A to Q_B on the acceptor side of Nanjing44 were significantly better than that of Nanjing5055. The F_v/F_m and PI_abs of Nanjing44 were significantly higher than Nanjing5055 by 28.24% and 776.82%, respectively.

Conclusion Nanjing44 has better photooxidation resistance than Nanjing5055 due to its strong PSⅡ photosynthetic performance and reduced photoinhibition through self-regulation.