Chilling injury caused by low temperature happens frequently during seed imbibition in maize (Zea mays L.). Polyamines (PAs) such as putrescine (Put), spermindine (Spd), and spermine (Spm) are accumulated in plants, maintaining the stability and integrality of membrane under low temperature stress and eliminating free radicals in cells. They have been used by presoaking and leaf spray in barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.) respectively to improve the tolerance to abiotic stresses. In the present study, Spd and Spm were used as an inducer to investigate chilling tolerance during seed imbibition and seed germination in maize. Seeds of maize inbred lines ‘Hung C’ (chilling-tolerant) and ‘Mo17’ (chilling-sensitive) were soaked with 0.25 mmol L-1 of Spd and Spm, respectively for 72 h under dark at 15℃, and the control was not treated with PAs. Part of the seeds were germinated for 7 d under 25℃ after imbibition for 48 h under 5℃ in dark. The germination rates were tested every day with 4 replicates (25 seeds per replicate) each. Other part of seeds were imbibed for 0, 12, 24, 36, and 48 h, respectively at 5℃ in dark. The embryos were separated from the seeds for testing the activities of peroxidase (POD), catalase (CAT), superoxide dismutase (SOD) and ascorbate peroxidese (APX) as well as the contents of proline (Pro), soluble protein, and nucleic acid in embryo leakage. All measurements repeated 3 times with 15 seeds each time. Under chilling stress, both Spd and Spm treatments increased the activities of POD, CAT, SOD, and APX, raised soluble protein and Pro contents, and reduced nucleic acid content in embryo leakage. The treatments also increased seed germination percentage and shortened the mean germination time (MGT) which increased by 18.5% and 14.0%, and decreased by 1.21 d and 1.14 d for Spd and Spm treatments, respectively as compared with those of control. During the imbibition under chilling stress, the activities of POD, CAT, SOD and APX, Pro and soluble protein contents in embryos and germination percentage were higher, whereas the content of nucleic acid and MGT were lower in untreated Huang C seeds than in untreated Mo17 seeds. The results suggested that Spd and Spm treatments can improve the chilling tolerance during seed imbibition, and enhance the germination of maize seeds.
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