Comparative proteomic analysis provides new insights into the regulation of carbon metabolism during leaf senescence of rice grown under field conditions.

In rice (Oryza sativa), approximately 60-100% of the carbon in mature grains originates from CO(2) assimilation during the grain-filling period, with the flag leaf as the most important contributor to the dry weight accumulation in grains. It is therefore important to understand molecular mechanisms of flag leaf senescence. To investigate the regulation of the metabolic network during leaf senescence, changes in protein expression were analyzed using a comparative proteomic approach during senescence of flag leaves in rice grown under field conditions. A total of 170 differentially expressed proteins during senescence of flag leaves were identified by mass spectrometry. Of these, there were 48 down-regulated proteins and 122 up-regulated proteins, corresponding to total 124 unique proteins. These identified proteins are involved in different cellular responses and metabolic processes, including photosynthesis, photorespiration, glycolysis, cell defense, redox homeostasis, signal transduction, protein synthesis, folding and assembly. Based on the abundance changes of these proteins, together with their putative functions and participation in physiological processes, we propose protein networks of carbon metabolism at the protein level during leaf senescence. These networks illustrate, for the first time, an overview of the regulations of carbon metabolic reactions occurring during leaf senescence.