| In the present study, the different seed species were chosen to investigate the effect of ultradrying on seed germplasm preservation. The prominent storage substances, soluble sugars, heat-stable proteins and the metabolism of active oxygen in different seed species were evaluated for dry-tolerance and prolonging storage longevity of ultradried seeds. The aim of this study is to provide theory and to develop the technology of ultradried seed storage for germplasm preservation. The results are summarized as follows:1. Peanut, rape, sesame, cucumber, onion, soybean, mungbean, rice, corn and wheat seeds were dehydrated at 25 ℃, and the moisture content was measured at stated time intervals. Desiccation tolerance we, re observed in all of the above seeds, and The vigor indexes and germination percents of seeds with 5-4.5% moisture content did not visibly changed. However, when further dehydrated, different seed species showed dissimilar of desiccation tolerance capabilities. The vigor indexes and germination rate of peanut, rape, sesame and cucumber seeds did not changed within 2.0% moisture content, whereas onion, soybean, mungbean, rice, corn and wheat seeds showed great changes in their vigor indexes and germination rate.Higher lipid contents showed 'significantly higher speeds of dehydrating and greater ultradry-tolerant abilities than seeds of high protein or starch contents, while seeds of different starches showed parallel speeds of dehydrating, although with distinct ultradry-tolerant abilities. The germination rate and vigor index of Japonica rice seeds (Chunjiang15 and Chunjiang683) decreased rapidly when their moisture content fell to 4.5%. On the contrary, the germination rate and vigor index of Indica rice (J174 and J106) seeds changed little even when their moisture content fell to 3.5%, which indicated that Indica rice had strong ultra-drying tolerance. While the seeds' tolerance of Waxy rice and Hybrid rice (Shanyou 63) were intervened in Japonica rice's and Indica rice's.2. The rehumidification treatment and a measuration of conductance of seeds with low moisture content before germination suggested that the rehumidification treatment was necessary to effectively reduce the water absorption rate and the membrane restoration during rehydration, thus maintaining the seeds' vigor.3. The relationship between ultradry-tolerant ability and soluble sugars, heat-stable proteins or metabolism of active oxygen were investigated after ultradrying. The results showed that: (1) The ratio of non-reducing sugars/reducing sugars in embryo and cotyledons of moderately ultradried peanut seeds(MC2.0%), soybean seeds(MC4.0%), and mungbean seeds(MC4.5%) has been increased, while no significant changes in the ratio of sucrose /oligosaccarides was observed, which indicates a positive correlation between ultradry-tolerance capabilities and the ratio of non-reducing sugars/reducing sugars of seeds. Ultradrying treatments reduced the activity of invertase and a -galactosidase in embryo of peanut seeds, soybean seeds, and mungbean seeds, thus decreasing the wastage of sucrose, oligosaccarides and other protective substances. (2) Ultradrying treatments did not induce new heat-stable proteins in embryo and cotyledons of peanut seeds, soybean seeds, and mungbean seeds, although heat-stable proteins was changed. Moderate ultradrying treatments could induce to accumulate heat-stable proteins in embryo of peanut seeds and mungbean seeds, but not in soybean seeds, in the embryo of which even a decrease of heat-stable proteins was observed when excessively ultradried. This suggested that the heat-stability of some proteins was improved. The content of heat-stable proteins in peanut seeds was significantly greater than that of soybean and mungbean seeds, which cauld be one of the possible reasons of different ultradry-tolerance abilities in different seeds. (3) After ultradrying treatments, the superoxide-producing rate significantly increased, the content of MDA and the rigor of LOX did...
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