The effects of spermidine (Spd) pretreatment on relative water content (RWC), H2O2 content, malonyldialdehyde (MDA) level, electrolyte leakage and activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidese (APX) in wheat seedlings (Triticum aestivum L. cv. Miannong 4) were investigated under osmotic dehydration by －0.6 MPa polyethylene glycol 6000 (PEG-6000). Half of eight-day-old seedlings (control) were daily sprayed with distilled water + 0.02% (V/V) Tween-80 and irrigated with half-strength Hoagland’s nutrient solution, and the other half seedlings (Spd pretreatment) were daily sprayed with 0.2 mmol/L Spd + 0.02 % (V/V) Tween-80 and irrigated with 0.2 mmol/L Spd + half-strength Hoagland’s nutrient solution for 2 days before osmotic stress. The results showed that the RWC decreased, lipid peroxidated, as well as H2O2 content and electrolyte leakage increased in seedling leaves of control under osmotic stress, while these changes deferred in Spd pretreatment. Under osmotic stress, the activities of SOD, POD and APX increased, but CAT activity decreased in control. Spd pretreatment increased the activities of SOD and POD. Moreover, the activities of POD, CAT and APX, especially SOD in seedling leaves of Spd pretreated were higher than those of control during the throughout osmotic stress period. It suggested that Spd could induce and maintain the higher level of antioxidant enzyme activities, and decrease the concentration of H2O2, therefore alleviate oxidative damages by osmotic stress, and promote antioxidant capacity of wheat seedlings under osmotic stress.
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