Differential proteomic expressions between superior and inferior spikelets of rice in response to varied nitrogen treatments

Grain-filling and molecular mechanisms of Indica rice jinhui No.809 (large-panicle type) were investigated. By keeping the total N supply constant and varying the early and late growth stage fertilizer application ratios, changes in the protein expressions of the rice superior and inferior spikelets were determined. The two N fertilization treatments were traditional and modern nitrogen applications (TNA and MNA). Using 2-DE and MALDI-TOF/MS, 38 proteins were identified to show differential expressions in response to the different N treatments. MNA appeared to promote protein up-regulation in the inferior spikelets, including cell respiration related proteins (e.g. fructose-bisphosphate aldolase, phosphoglycerate mutase, glyceraldehyde-3-phosphate dehydrogenase, malic oxidoreductase, succinate dehydrogenase, transketolase, phosphoglucomutase, and some starch synthesis related proteins (e.g., phosphoglucomutase, WRKY, glycolipid transfer and fatty acid hydroxylase) clearly indicating that the increased N supply at the late growth stage was favorable for the grain-filling of inferior spikelets. Moreover, the up-regulated auxin-responsive protein IAA22 and gibberellin response modulator implied that the MNA treatment could increase the content of phytohormones in inferior spikelets. In addition, the proteomic analysis and physiological observations in the present study also elucidated the mechanism underlying the asynchronous grain-fillings between the superior and inferior spikelets of rice.