Effects of nitrogen management on protein expression of rice (Oryza sativa L.) root in the late growth stage

Application of nitrogen fertilizer is the most important agricultural measures in increasing paddy rice production. Recently, the postponed nitrogen application has developed as a modern cultivation measure, which not only is beneficial to the high yield formation, but also increases utilization efficiency of nitrogen fertilizer. However, the molecular basis of such adaptation remains unclear. In present study, the molecular mechanisms of rice ‘jinhui No.809’ (large-panicle type) root in response to the postponed nitrogen application were investigated. By keeping the total nitrogen supply constant and varying the early and late growth stage fertilizer application ratios, changes in the protein expressions of the rice root in late growth stage were determined. The two nitrogen fertilization treatments were traditional (NT) and postponed nitrogen application (NP). Using 2-DE and MALDI-TOF/MS, 57 proteins with 40 up-regulated and 17 down-regulated in response to NP treatment were successfully identified. According to the protein function, the identified proteins were classified into 12 categories, mainly including signal transduction, ammonia assimilation, stress and defense, glycolysis, tricarboxylic acid cycle, protein synthesis and folding, and amino acid metabolism. The results indicated that the signal proteins of GDP dissociation inhibitor protein and GTP-binding nuclear protein Ran-2 in rice root were responsive to the NP treatment, then transfer signal to the membrane protein, including voltage dependent anion selective channel protein, annexin p35 and vacuolar ATP synthase subunit C, leading to the changes of intercellular material transport and message transference. The protein abundance of glycolysis and tricarboxylic acid cycle related protein, including phosphoglycerate kinase, phosphoglucomutase, 6-phosphofructokinase, UDP-glucose pyrophosphorylase, NADP-isocitrate dehydrogenase and aconitate hydratase were increased by the NP treatment, in turn, induced more ATP were generated for the root growth. The up-regulated antioxidative enzymes and defence related protein delayed the root senescence in the late growth stage. Moreover, glutamate dehydrogenase, glutamines synthetase root isozyme and aspartate minotransferase, three of which were involved in the plant nitrogen metabolism, increased in abundance in the NP treatment, which were favorable for the nitrogen uptake and translocation. This study added new significant insights to our current understanding of the molecular ecology characteristic of rice root in response to nitrogen management.