Effect of Spermidine on Seed Germination and Physiological Characteristics of Cassia obtusifolia L. Seedlings Under Drought Stress

To explore the possible method for alleviating drought stress of Cassia obtusifolia,PEG-6000 at the concentration of 15% was used to create a simulated drought stress,and C.obtusifolia seeds were treated with spermidine(Spd) at different concentrations.Germination rate(Gr),germination index(Gi) and vigor index(Vi),and the contents of chlorophyll,O-2·,malondialdehyde(MDA),soluble protein and proline and the activities of superoxide(SOD),peroxidase(POD) and catalase(CAT) of C.obtusifolia were determined.15% PEG-6000 stress had an obvious inhibition to seed germination of C.obtusifolia and treatments of Spd at different concentrations significantly improved all germination indices studied.The Spd treatment at 0.5 mmol/L gave the greatest improvement,Gr,Gi and Vi being 84.67,95.10 and 7.30,or a 1.84-,1.19-and 1.96-fold improvement over the control(drought stress).The Spd treatments significantly improved the chlorophyll content and the activities of SOD and POD of C.obtusifolia seedlings and decreased,to different extents,the contents of soluble protein,free proline,O-2· and MDA and CAT activity.Of all Spd treatments made,the treatment of 0.5 mmol/L had the most prominent effect.These results showed that Spd with an appropriate concentration(0.5 mmol/L in this experiment) could significantly improve the germination ability of C.obtusifolia under drought stress,effectively reduce the damages caused by drought stress to its seedlings,alleviate the over-accumulation of osmotic regulation substances and promote the drought resistance of the seeds and seedlings by adjusting their protective enzyme activity.