Effects of Nitrogen Management on Protein Expression of Flag Leaves at Grain-Filling Stage in Large Panicle Rice

To explain the metabolic mechanism of leaf during grain filling of rice (Oryza sativa L.) in response to nitrogen application, the differential expression patterns of leaf proteins were investigated at different time points of grain filling using two-dimensional electrophoresis (2-DE) technique. Thirty-two differentially expressed proteins were detected including 27 up-regulated and 5 down-regulated proteins in response to increased nitrogen application at grain-filling stage. These proteins were classified into 5 main categories according to their deduced functions, which were involved in photosynthesis (12), response to adversity resistance (5), hormone synthesis and signal transduction (5), cell growth and differentiation (5), and unknown functions (5). The photosynthesis-related features, together with adversity-defense-related indicators, were then determined to reveal the regulation of nitrogen to rice leaf. As appropriate increase of nitrogen application at late growth stage, the adversity-defense ability of leaf was strengthened during grain filling by delaying degradation of chlorophyll and soluble protein, prolonging photosynthesis, activating superoxide dismutase, peroxidase, and catalase, and depressing lipid peroxidation. These physiological changes verified the result of proteomics. Therefore, appropriate increased nitrogen supply at late growth stage is favorable to leaf metabolisms during grain filling in rice.