Disentangling the photosynthesis performance in japonica rice during natural leaf senescence using OJIP fluorescence transient analysis

Rice undergoes leaf senescence accompanied with grain filling when the plants reach the end of their temporal niche, and a delay in leaf senescence ultimately improves the yield and quality of grain. To estimate the decline in photosynthesis during leaf senescence and to find an efficient and useful tool to identify rice genotypes with a longer duration of active photosynthesis, we examined PSII photosynthetic activity in the flag leaves of japonica rice Shennong265 (SN265) and Beigeng3 (BG3) during leaf senescence using chlorophyll a fluorescence kinetics. The results show that inhibition occurred in the electron transport chains, but the energetic connectivity of PSII units was not affected as dramatically during leaf senescence. PSII reaction centres (RCs) were transformed into ‘silent RCs,’ and the chlorophyll content decreased during leaf senescence. However the size of the ‘economic’ antennae increased. Further, the percentage of variation of the specific energy flux parameters can rationally be used to indicate leaf senescence from the perspective of energy balance. Although the performance indices were more sensitive than other functional and structural JIP-test parameters, they still did not serve as an indicator of crop yield.