Chilling stress is a major limiting factor for rice production in many parts of the world. The study was carried out in the Seed Research Laboratory of the Department of Crop Science, Ferdowsi University of Mashhad in summer 2011. Rice (cv. Khazar) seeds were soaked in 50, 150 and 300 mg l-1 spermidine aerated solutions for 48 h and then dried back to the original moisture content and were sown in three temperatures (28°C as normal, 12°C and 8°C as chilling stress). Chilling stress (8°C) reduced the root (39%) and shoot (52%) growth in untreated seeds while the reduction of 11% root growth and 20% shoot growth was observed when the seeds were primed with 300 mg l-1 spermidine solution. The electrolyte leakage of the seedling leaves significantly increased in low temperatures as it was 67 percent in 8°C in compared with normal condition. Chilling stress significantly increased superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activity in rice seedlings leaves though this increase was not significant for glutathione reductase (GR). Seed priming with spermidine had a positive effect on seedlings leaves antioxidant activity in every temperature conditions. As in 8°C, the sharp increase (73%) in SOD activity was occurred at 300 mg l-1 spermidine solution and it was 23 and 46 percent for CAT and APX, respectively. In general, seed priming with spermidine alleviated the chilling effect, probably as a result of activating antioxidants production processes and membrane stabilizing in cellular structures.

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