| Stored reserves are mobilized to provide energy during seed germination. Carbohydrate is the main energy source during starchy seed germination. Our previous study showed the down-regulation of phosphoglucomutase, 3-phosphoglycerate, malate dehydrogenase and ATP synthase in aged maize seeds, so we speculated that aging impair energy required to accomplish germination. Therefore, a study of the relationship between seed aging and energy supply is conducted to get a better understanding of the mechanism of seed aging and to provide theoretical basis for the safe preservation of the germplasm resources. Maize seeds were artificially aged at 50°C for 0d(control), 3.5d, 5.5d, 7.5d, 9.5d and 15 d, and seeds were imbibied for 0h, 24 h, 48 h and 72 h, respectively. Then the changes of imbibition curve, starch mobilization, the content of soluble sugar and ATP, and the activities of key enzymes of glycolysis and pentose phosphate pathway were analyzed. The main results are as follows:1. Artif ical aging treatment resulted in decreased germinability. The germination percentage of control seeds was 97.3±4.6%, but after being aged for 3.5d, 5.5d, 7.5d, 9.5d, and 15 d, the germination percentage decreased to 96.0±2.6%, 86.0±6.4%, 64.0±4.0%, 35.0±6.3%, 0.0±0.0%, espectively.2. Artifical aging reduced the speed of seed germination and the growth rate of seedlings. The time taken for the first seed germination of the control seeds was 20 HAI, and for 50% maximum germination was 30 HAI. With aging time increasing, the time for seed to break the seed coat gradually extended and, accordingly, the time to reach 50% maximum germination was also delayed. Seed germination index, germination potential, vigor index and dry weight of seedling were also signif icantly decreased by artifical aging.3. Artifical aging treatment impeded seed water absorption. The water uptake of the control follows the three-stage pattern, with the phase I ends at 16 h after imbibition(HAI), and phase II ends at 48 HAI. The water uptake of the 3.5d-aged seeds was similiar to that of the control, but the imbibition speed was signif icantly slowed down, with phase I and II ends at 20 and 56 HAI, respectively. For seeds aged for longer time, the imbibition curve could not be aacomplish by the three-stage pattern, and the ends of phase I was postponed to longer than 24 HAI.4. The mobilization of stored starch was hindered by artificial aging. The activity of amylases in control seeds were signif icantly increased at 48 HAI, accompanied by the increase in small starch grains, which declared the mobilization of stored starch. The activity of amylase was inhibited by aging, leading to disruption of starch mobilization.5. The supply of soluble sugar during seed germination was obstructed by aging. Sucrose is the major soluble sugar in dry maize seed. Seed firstly mobilized the storage soluble sugar to provide energy for seed early germination. Starch began to mobilize to synthetic sucrose, maltose after 48 HAI. Then they were transfered to embryo provided energy for seed germination. The mobilization of sugar and starch was hindered by aging, resulting in insufficient energy supply during germination, thereby blocked seed germination.6. Glycolysis and pentose phosphate pathway were inhibited by aging, leading to limited ATP and NADP H synthesis. The content of ATP was very low in dry seed. The activities of hexokinase and G6 PDH was signif icantly increased to promote ATP production after seed imbibition. But aging hindered the increase in activities of hexokinase and G6 PDH upon imbibition, resulting in blocked glycolytic and pentose phosphate pathway and limited ATP synthesis.Take all the results together, we found that artifical aging treatment impeded the mobilization of sucrose and stored starch, affected the supply of sucrose, maltose, glucose and fructose and activities of hexokinase and G6 PDH, blocked glycolytic and pentose phosphate pathway and limited ATP synthesis. So artifical aging caused loss of seed vigor. |
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