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Abstract
Seed aging is a process that results in a delayed germination, a decreased germination percentage, and finally a total loss of seed viability. However, the mechanism of seed aging is poorly understood. In the present study, Yliangyou 2 hybrid rice (Oryza sativa L.) seeds were artificially aged at 100% relative humidity and 40°C, and the effect of artificial aging on germination, germination time course and the change in protein profiles of embryo and endosperm was studied to understand the molecular mechanism behind seed aging. With an increasing duration of artificial aging, the germination percentage and germination rate of hybrid rice seeds decreased. By comparing the protein profiles from the seeds aged for 0, 10 and 25 days, a total of 91 and 100 protein spots were found to show a significant change of more than 2-fold (P < 0.05) in abundance, and 71 and 79 protein spots were identified, in embryos and endosperms, respectively. The great majority of these proteins increased in abundance in embryos (95%) and decreased in abundance in endosperms (99%). In embryos, most of the identified proteins were associated with energy (30%), with cell defense and rescue (28%), and with storage protein (18%). In endosperms, most of the identified proteins were involved in metabolism (37%), in energy (27%), and in protein synthesis and destination (11%). The most marked change was the increased abundance of many glycolytic enzymes together with the two fermentation enzymes pyruvate decarboxylase and alcohol dehydrogenase in the embryos during aging. We hypothesize that the decreased viability of hybrid rice seeds during artificial aging is caused by the development of hypoxic conditions in the embryos followed by ethanol accumulation.
Highlights
There are currently more than 7.4 million accessions of seed germplasm conserved in 1750 genebanks around the world, and more than 130 genebanks have 10,000 or more accessions (FAO, 2010)
By comparing the protein profiles of different seed samples, 1109 ± 103 and 1093 ± 93 protein spots were detected in embryo and endosperm, respectively, during aging of Yliangyou 2 hybrid rice seeds (Supplementary Figures S1, S2)
By monitoring changes in proteome of embryo and endosperm from seeds aged for different duration, it is possible to form a picture of the events that lead to the loss of germinability: A general observation was that many endosperm proteins decreased in abundance during aging
Summary
There are currently more than 7.4 million accessions of seed germplasm conserved in 1750 genebanks around the world, and more than 130 genebanks have 10,000 or more accessions (FAO, 2010). One of the earliest symptoms of seed aging is a delay in radical emergence, followed by a progressive loss of capacity for normal germination (Priestley, 1986; Bewley et al, 2013). This seriously influences the maintenance of seed vigor and the long-term conservation of plant germplasm resource and has led to serious economic losses for agriculture, forestry and horticulture. Seed aging is affected by genetic components and by storage conditions. Reactive oxygen species (ROS) and lipid peroxidation are thought to be the major contributors to seed aging (decrease in vigor), which include loss of membrane integrity, reduction in energy metabolism, decrease in antioxidant system activity, impairment of RNA and protein synthesis, and DNA degradation (Hendry, 1993; Bailly et al, 1996; Bailly, 2004; Bewley et al, 2013; Yin et al, 2014; Xia et al, 2015)
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