Study On Methods And Mechanisms Of Improving Vigor In Cabbage (Brassica Oleracea L.var.capitata) Seed

Medium, mediumlow and low vigor cabbage seeds were obtained respectively by accelerated aging of 3 cabbage varieties (xiyuan NO.4, xiyuan NO8, yufeng NO.3 ).Different methods,including imbibition/dryback treatment, polythyleneglycol (PEG),mannitol gibberellin(GA),CaCl2,KH2PO4, ascorbic acid(AsA),were used to enhance the seed vigor by Ly(3 ) orthogonal experiments.Then the probe into the changes of cabbage seeds at physiology and biochemical level,cell level and ultrastructure of cell were conducted.The results indicated that:On the condition of 40℃ and RH100% ,vigor index(VI) and germination percentage came down gradually as aging time increased,and the change rate of VI was related to varieties (genotypes).Medium, mediumlow and low vigor seeds could be acquired after different aging time (For xiyuan N0.4,aging time was respectively 3 days,4 days and 5 days,for xiyuan NO.8, aging time was respectively 3 days,4 days and 5 days,for yufeng NO.3, aging time was respectively 1 days,2 days and 3 days).All the seven methods, including imbibition/dryback treatment, polythyleneglycol (PEG),mannitol,gibberellin(GA),CaCl2,KH2PO4,ascorbic acid(AsA),could improve the vigor of cabbage seeds.The analysis showed that improving degree of vigor was affected by different temperature, time, density (or times) etc. As to the seeds of different varieties and different vigor, the order and the best combination of these factors weren't the same.In general,the improving degree of vigor for low vigor seed was higher. The seed vigor treated by all the best combination was significantly higher than CK, and the treatments of PEG and GA were the best, moreover, the difference between PEG, GA and other methods was significant.Some physiological and biochemical changes, such as relative elelctive conductivity (REC) and the content of malondialdehyde (MDA) in seed, activities of protease, dehydrogenase, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), were investigated before and after improving the seed vigor. The result showed that protease, dehydrogenase, SOD, CAT and POD were reduced signficantly. Moreover, the changing degree was related to different varieties or primary vigor degrees. Principal Component Analysis indicted that activities of protease, dehydrogenase, SOD, CAT and POD werecorrelated significantly and positively with VI, REC and the content of MDA were correlated significantly and negatively with VI.As a result, these parameters were the main reasons for the change of seed vigor (at physiological and biochemical level), and-they were reliable indexes for measuring seed vigor.Karyotypes of root tip chromosome showed that the arm volume ratio, the mean relative volume (as a percentage) and idiogram were identical before and after improving seed vigor, so the pattern of chromosome did not change. But we couldn't confirm whether the pattern of other separation dates and the inner structure varied in this experiment, such as gene mutation.Observation on the ultrastructure of the radicle cell of cabbage seeds indicated that the ultrastructure changed with the seed vigor reduced, such as the segregation of cytoplasm from the cell wall, the fragmentation of cell membrane, the vesiculation of protoplasm, the homogenization of chromation, the disintegration of cytoplasm, the distinguishing of nuclear membrane and nucleous ,and so on.The lower the seed vigor ,the clearer the change .When the seed vigor was improved,the ultrastructure of cell would be resumed at different degrees.