Physiological features and thylakoid membrane proteomic analysis of rice NG46 during natural leaf senescence

As the last step of leaf development, premature senescence often causes the damage of photosynthetic apparatus and the reduction of active photosynthesis, which leads to a decrease in crop yield. In this study, we investigated the early response of rice NG46 leaves to senescence by following changes in physiological attributes and thylakoid membrane proteins. We found that photosynthetic pigment contents, net photosynthetic rate (PN), stomatal conductance (gs) and transpiration rate (E) decreased significantly, while the contents of superoxide anion (O2·−), malondialdehyde concentration (MDA) and the antioxidant enzyme activities were substantially increased. Analysis of OJIP transients and parameters showed that part of photosystem II (PSII) reaction center (RC) was damaged and electron transport chain was impaired. Blue native page investigations revealed that the amount of supercomplexes increased at the filling stage, while a significant decrease in PSII monomer and cytochrome b6/f (Cyt b6/f) complex was observed. Further analysis of the thylakoid protein complex by 2-D BN/SDS-PAGE showed that the differential proteins were involved in light harvesting, stability and function of photosystems, electron transport, CO2 assimilation rate, and breakdown and repair of thylakoid membranes. Our results suggest that PSII and Cyt b6/f of rice NG46 are extremely susceptible to senescence, which affects the stability of the photosynthetic apparatus and exhibits a low photosynthetic capacity.