Proteome analysis of maize seeds: the effect of artificial ageing

Previous understanding of the mechanism of seed ageing is largely based on observations on imbibed seeds rather than dry seeds. The present research was conducted to investigate whether seed ageing has effects on the dry seeds through proteome analysis. Maize (Zea mays cv. Dabaitou) seeds were artificially aged at 50°C (13.58% moisture content) for 5 or 13 days, and the total protein was extracted from embryos of the dry seeds. Two-dimensional electrophoresis was performed and the differentially expressed proteins were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry. A total of 40 proteins were identified, in which 16 proteins were upregulated, indicating that artificial ageing affected the proteome of the dry seeds. Proteomic studies revealed that the signal transduction and transcription were disturbed by artificial ageing, which might lead to reduced protection against ageing. Artificial ageing also increased proteases and broke down stored proteins, impaired metabolism and energy supply, and ultimately resulted in seed deterioration. Proteins involved in metabolism and energy were the largest downregulated protein group, with regard to glycolysis, tricarboxylic acid cycle, the electron transport chain and oxidative phosphorylation. The downregulation of these proteins, together with reduction in the specific activity of glucose-6-phosphate dehydrogenase, and the content of glucose 6-phosphate, pyruvic acid and ATP in aged seeds, suggested the important roles of the mobilization of stored carbohydrates and energy supply in seed ageing and seed vigor. The present work provides new information about the proteomic changes during seed ageing and provides a possible mechanism for seed deterioration.