The Study On Mitochondrial Metabolic Shift During The Critical Node Of Seed Ageing In Rice

Crop germplasm is an important national strategic resource. Collection and preservation are the key basis for crop breeding, science research and agricultural production. In addition, it is the important for the food security, ecological security and agricultural sustainable development. In worldwide, In the conservation of plant resources, more than 740,0000 accessions have been collected and preserved, of which the National Genbank of China currently holds more than 390,000 accessions at-18?, which are represented by base collections of crops and their wild relatives. Monitoring of 14,000 accessions over a 20-year storage period showed that seed vigor noticeably decreases, of which 1.1% decreased to below 70%, entering the rapid decreasing stage during Phase ? Currently, the National Genbank of China holds more than 72,000 rice accessions; yet, part of their vigor has decreased to the critical node. The first transformation from Phase I to Phase II is a critical node, which is extremely important for seed conservation and maintaining genetic integrity. In previous studies, the critical node (Phase I-II) of seed ageing is 80% more or less. The Phase I of rice seeds is when the germination percentage exceeds 88%. In this study, we provide novel insights about the regulatory effect of mitochondria on seed ageing, which would facilitate the comprehensive conservation of germplasm resources.Rice(Oryza sativa L. japonica. nipponbare) seeds were obtained from Jiangxi Academy of Agricultural Sciences. Seed was artificially aged at 40? and 75% relative humidity for various times. In this study, we characterized the mitochondrial physiology, ultrastracture, gene expression and proteome after the aged rice seed imbibition for 48 h. The results were presented as follows:The aged rice seeds were subject to significant alteration in ultrastructure. Changes included the loss of cristae and membrane in mitochondria, an irregular cytoplasmic layer, and an undeveloped nuclear structure. The mitochondrial enzyme activity and oxygen consumption are paralleled by the damage to the mitochondrial ultrastructure in aged seeds.Plant mitochondria contain multiple energy dissipating components in the respiratory chain, including the cytochrome pathway (cytochrome oxidase, COX) and alternative pathways. During the critical node of seed ageing, the transcript of the alternative pathway of the respiratory chain was significantly induced, whereas the transcript of the cytochrome oxidase pathway was inhibited.During the critical node of seed ageing, these changes were concomitant with the down-regulation of mitochondrial protein levels related to carbon and nitrogen metabolism, ATP synthase complex, TCA cycle, mitochondrial oxidative enzymes, heat shock proteins, and a variety of other proteins.In conclusion, the present study indicates that the respiratory capacity of aged seeds is restricted in the critical node. This response is due to the inhibition of ATP production and signals from mitochondria activated stress responses, such as cytochrome c and ROS accumulation, which may induce oxidative damage and cell death, triggering the acceleration of the ageing process in Phase ?.