Effects of Seed-Soaking with Spermidine on Seed Germination and Starch Metabolism of White Clover(Trifolium repens L.) under Osmotic Stress

The effects of seed-soaking with spermidine(Spd) on seed germination and starch metabolism were investigated under osmotic stress induced by 0,10%,15%and 20%aqueous solutions of polyethylene glycol6000(PEG-6000) in white clover(Trifolium repens cv.'Ladino').The results showed that germination rate,germination vigor,germination index,fresh weight of plumule and radicle,and radicle length of white clover seeds were significantly(P0.05) reduced,as well as the transformation rate of starch into reducing sugar and glucose were suppressed in the process of seed germination under osmotic stress.Compared with seed-soaking with distilled water,seed-soaking with 0.05 mmol·L~(-1) Spd significantly(P0.05) improved seed germination rate,germination vigor,germination index,fresh and dry weight of radicle and plumule,and radicle length under the same osmotic stress.At the same time,seed-soaking with Spd showed significantly higher activities of a-amylase,β-amylase and(a+P)-total amylase,and higher contents of reducing sugar and glucose,but lower content of starch than those in seed-soaking with distilled water.In conclusion,the above results indicated that the ability of seed germination and environmental adaptability of white clover seedlings was improved by seedsoaking with Spd under osmotic stress,which could be related to timely supply of sufficient energy resulted from accelerating transformation starch into sugars by Spd activating amylase activities during seed germination and early growth of seedlings.