| Supersweet corn with sh2 gene is popularly planted all over the world, however, low seed quality induces low germination percentage, poor emergence and field. Seed quality is sum of genetic quality and sowing quality. Seed quality is formed during seed development, and it can be improved by seed treatment. Polyamines (PAs) are small aliphatic polycationic nitrogenous compounds and are ubiquitous in higher plants. They are important modulators of biological processes and suggested to play an important role in plant growth and development. Two supersweet corn varieties, Supersweet 17 and Jinyintian 5 were chosen as materials to study the modulation and treating effects of endogenous and exogenous PAs on seed quality during seed development in supersweet corn. The main results are as follows:The changes of free putrescine (Put), spermidine (Spd) and spermine (Spm) concentrations in supersweet 17 were determined to investigate the relationship between PAs and seed quality during seed development. Concentrations of Put, Spd and Spm increased from 14 to 30 days after pollination (DAP). After 30 DAP Put concentration declined with an opposite trend to that of Spd and Spm. The regression analysis between PAs and seed quality described by physiological and biochemical parameters including germination percentage, germination energy, germination index, seed size, seed fresh and dry weight, total soluble sugar, total soluble protein, Malondialdehyde (MDA) concentration, electrolyte leakage, peroxidase (POD) and catalase (CAT) activity were conducted. Spd was observed to have a closer relation with the comprehensive physiological changes of seeds during their development than that of Put and Spm. Moreover, the Spm concentration might be more suitable to forecast seed germinability during seed maturation period than Spd and Put. It indicated that endogenous Spd and Spm in dissociated form had more effect than Put during seed development progress of sweet corn.In present study, seed quality parameters in supersweet corn seeds at different seed developmental stages were determined after exogenous spermidine (Spd) was sprinkled on the top three functional leaves of the female parent plants before and after pollination. The effect of exgonous Spd on seed quality was studied then. The higher concentration (1 mM) Spd treatment significantly decreased germination percentage, germination energy and germination index, however lower concentration (0.1 mM) Spd treatment enhanced the germination percentage and germination energy at the latter period of seed maturation and germination index at all stages from 18 d to 42 d after pollination (DAP).0.1 mM Spd significantly enhanced seed fresh and dry weight, seed volume, embryo fresh weight and total soluble sugar concentration at seed maturation stage (42 DAP) as compared with the control. But 0.1 mM Spd treatment significantly declined the concentrations of total soluble protein and nucleic acid leakage at seed maturation (42 DAP) compared with the control. It seems that seed development and seed quality are obviously improved by treating with appropriate exogenous Spd during maturation in supersweet corn seeds.Response surface analysis (RSA) experiment with two factors (Spd concentration and seed soaking time) of 14 combinations was performed to investigate the effects on improving seed vigor in supersweet corn, cv. Supersweet 17 and Jinyintian 5. After soaking treatment, treated seeds were germinated according to the international rules of seed testing. Then, the germination parameters, vigor index, the length and weight of roots and shoots, and the nucleic acid concentration of seedlings were analyzed by RSA. For Supersweet 17, the optimum combinations of Spd concentration and soaking time for improving germination percentage, germination energy, germination index, vigor index, length of shoot and root, fresh and dry weight of shoot and nucleic acid leakage concentration in seedlings were obtained. According to these combinations, the suitable range for Spd soaking was 0.54-0.73 mM concentration and 8.2-13.2 h, respectively. For Jinyintian 5, the optimum combinations of Spd concentration and soaking time for improving germination percentage, germination energy, vigor index, fresh and dry weight of shoot and dry weight of root were obtained. According to these combinations, the suitable range for Spd soaking was 0.47-0.74 mM concentration and 8.87-12.47 h, respectively. It suggests that seed soaking in Spd can improve the seed germination and seedling growth of supersweet corn.D-Arg and difluoromethylornithine (DFMO) as two inhibitors were used in present study to investigate whether the physiological functions of supersweet corn seeds were influenced by the PAs inhibitor which baffled PAs synthesis. The result showed that 0.1 mM D-Arg treatment affected seed germination significantly, also, germination index and vigor index were reduced significantly by 0.1 mM DFMO. On POD and SOD, D-Arg had a significant negative role but DFMO only affected SOD. However, the inhibitors had no significant negative role on CAT. Both D-Arg and DFMO decreased the concentrations of total soluble sugar and total soluble protein. Except 0.01 mM D-Arg, all the treatments increased the nucleic acid leakage concentration of single seed. The result also showed that DFMO had more significant effect on Put concentration restraining than D-Arg, it indicated that PAs synthesis by both ADC and ODC pathways, and ODC was dominant during early seed development in supersweet corn.Spd and Spm with two concentrations (0.1 mM and 0.5 mM) were used as primers to treat supersweet corn seeds at different maturation levels. Both Spd and Spm improved seed germination ability significantly, while Spm showed much effective than Spd on germination percentage. Between two concentrations,0.5 mM treatment showed more improvement effect than 0.1 mM treatment. About seedling quality, such as length, fresh and dry weight were improved by priming. Chlorophyll a and chlorophyll b concentrations were increased by Spd treatments much more significantly than Spm. Spd and Spm priming increased CAT and SOD activity more obviously than POD, and Spd significantly reduced the nucleic acid leakage concentration in seeds. DNA replication levels, determined by flow cytometric determination, in primed seeds were improved demonstrated by the 2C:4C ratio in embryonic root tip cells was significantly reduced by Spm priming. It indicated that priming with Spd and Spm could improve seed germination, peroxidase activity and quality of seedling.
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