| Seeds enters aging phase after maturation. Seed viability keeps on decrease along with the extended storage time, even when being stored at genebanks with low temperature and relative humidty. It is essential to get a better understand of the character of seed aging in order to asure safe long-term storage. In this work, the loss of seed viability under different storage conditions, the changes of genetic integrity brought by regeneration carried ou at various viability levels, and the proteomic changes brought by seed aging were studied by seed viability monitoring, agronomic traits, gliadin SDS-PAGE,2-DE and MALDI-TOF/MS in order to further our understanding of seed aging mechanism, and to provide theoretical basis for the establishment of a germination standard for seed aging and germplasm regeneration. The main results are as follows:(1) Viability monitoring of seeds being stored at low temperature genebank:The viability of14706seed accessions, belonging to34crops, was detected after being stored at the National Genebank (-18℃) for20to23years. Results showed that the viability of92.9%accessions was above85%, which indicated that most of the collections in the National Genenbank can be safely conserved for more than20years. But the viability of1.1%of the monitored accessions was lower than70%, which suggested that seed still loss their viability even at-18℃storage.(2) Seed viability loss under different storage conditions:The viability monitoring data of wheat and soybean seeds from a midterm genebank (10～4℃), ambient storage, as well as an accelerated aging experiment were quantified, and results showed that seed longevity of all accessions followed normal distribution, and that seed survival curves showed inverse-S shape, which received no obvious effects from storage condition. The point between the plateau phase and viability sharp decline phase was recorded as the turning point (Pt). Results showed that the Pt under different storage conditions were quite close, which varied between82.2%and83.6%, indicating the possible role of Pt as indicators for seed viability loss during germplasm storage.(3) Changes of the proteome of aged seeds:The proteomic changes in the dry embryos of maize (Zea mays L. cv. Dabaitou) seeds being artificially aged at50℃were studied using2-DE and MALDI-TOF/MS. A total of40differentially expressed proteins were identified, in which16proteins were up-regulated, indicating that artificial aging affected the proteome of the dry seeds. Identification of these proteins revealed that the signal transduction and transcription was disturbed by artificial aging, which might lead to reduced protection against aging. Artificial aging 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 down-regulated protein group, which concerning glycolysis, TCA cycle, the electron transport chain, and oxidative phosphorylation. The down-regulation of these proteins, together with reduction in the specific activity of G6PDHase, and the content of Glc-6-P, pyruvic acid and ATP in aged seeds, suggested the important roles of the mobilization of stored carbohydrates and energy supply in seed aging and seed vigour. Proteins that dissapered or showed only in aged seeds, could be used as warning indicators for seed aging.(4) Changes of genetic integrity brought by seed aging:Ten wheat accessions that had been stored at a medium-term genebank (10～4℃) for16to17years were regenerated and16agronomic traits and the gliadin spectrum were compared with seeds stored at a long-term genebank. The results provided evidence that some agronomic traits, such as length and width or the flag leaf, plant height, and the frequency of the gliadin band-type, and/or some of the genetic parameters, such as I, He, of4accessions changed significantly after only one generation. The original germination percentages of these four accessions were equal to and lower than66%. As for those accessions, which were regenerated at viability equal to and higher than75%germination, no significant changes were detected. Therefore,75%germination percentage is recommended as the safe lower limit of regeneration standard for wheat seeds.
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