Changes Of Detoxifying Systems Of Rice Seed After Rtificial Aging

This study, based on the free radical hypothesis of aging, is to reveal the relationship of seed agingand antioxidant system and to determine the effect of major antioxidant enzyme in the elimination offree radicals through the study of antioxidant system especially the antioxidant enzyme involved in theartificially accelerated aging process. It is believed that the unbalance between ROS producing anddetoxifying is the primary cause of seed aging, so the antioxidant system is vital to maintain viability ofseed. Different vigour seeds of "Wanhua11xuan" were chose as the experimental materials. Weanalyzed the changes of the antioxidant system of rice seed in the items of the content of active oxygenand antioxidant, the activity of antioxidant enzymes, isozymes and dynamic expression of isozymegenes during seed artificial aging and germination to reveal the mechanism of seed aging at themolecular level and to provide theoretical basis for the safe preservation of the germplasm resources.The main research results are as follows：1. The content of ROS in rice seeds was not significantly increased after aging but increased duringearly stage of germination. Only the O.-2production rate of52%seeds is higher than CK seed, andcontent of H2O2in rice seeds was not significantly increased. It is assumed that the content of ROSmaintained at a stable level due to the limited production and the role of the antioxidant system. Duringgermination process, the O.-2production rate and content of H2O2increased due to the state of seed, inwhich metabolism recovery is done and the cells recovery undone. There is some effect of aging on seedand the effect appears during seed germination.2. The content of DHA and GSSG increased after aging, ASC remained stable and GSH decreased, sothe ratio of ASC/DHA and GSH/GSSG decreased. Ascorbic acid ASC and GSH is essential for seedgermination and aging process have effect on the role of them. DHAR activity is relatively high in dryseed, while a decline in the germination process, supposing that DHA reduction is a resource of ASC atthe early stage of germination and biosynthesis of ASC provides ASC more effectively than DHAreduction.3. The activity of CAT and DHAR decreased due to Aging in the rice seeds, while other enzymesactivity did not change significantly. The activity of CAT, APX, MDHAR and DHAR were closelyrelated to seed vigor during germination and that high-vigor seed corresponds to the high enzymeactivity. The activity of CAT, APX and MDHAR increase and DHAR reduce in germination process.4. Isozymes of each antioxidant enzyme expression are consistent with enzyme activity, in the processof rice seed germination, SOD, CAT, APX and GR all have new bands and isozymes of CAT and APXare agreed with seed vigor highly.5. The mRNA abundance of most of antioxidant enzyme gene was lower because of aging，while APX1expression increased and the abundance of APX6,APX7,DHAR and GR2mRNA remained unchanged.In the germination process of rice seeds imbibition，mRNA abundance of most of the genes increase inthe early stage of germination，and the higher of the degree of aging，the more obvious of increase ofmRNA expression，however，the reason is still unknown. Also，the changes of the genes of the low-vigor seeds is generally lags behind that of the high-vigor seeds in the germination process，speculating that aging affects mRNA synthesis and the synthesis mechanism of low-vigor seed isrelatively weak. Change laws of genes of CAT1, APX1, APX2,APX5,APX6, CuZnSOD1, DHAR andMDHAR1are consistent with that of seed vigor, high-vigor seeds show a high abundance of mRNA,speculating that the expression of these genes are connected with seed vigor combining the analysis ofantioxidant enzyme activity6. In summary, gene CuZnSOD1, CAT enzyme and its gene CAT1, APX enzyme and its gene APX1,APX2, APX5, APX6, DHAR enzyme and its genes DHAR, MDHAR enzyme and its gene MDHAR1,as well as ASC and GSH, are closely related to seed aging and viability.