Studies On Desiccation Tolerance And Storage Behavior And The Relative Physiological Mechanism Of Oryza Sativa L. Seeds

This thesis mainly investigated seeds of conventional rice ZR02 and hybrid rice Zhu1S/ZR02 and Jin23A/ZR02 of the changes of biological characteristics during development, and with dehydration by silica gel in a closed glass container (rapid dehydration, RD) and natural air on the indoor platform (slow dehydration, SD), the germination percentage, simplified vigor index, electrolytic conductivity of seed-soaked solution, content of soluble sugars and soluble proteins and the activity of SOD etc of seeds were measured to evaluate the formation of desiccation tolerance of rice seeds and compare the difference of the desiccation tolerance between seeds of conventional rice and hybrid rice, the difference of anti-aging ability of seeds which were stored at different condition (with dry silica or indoor open condition), and investigated the relative physiological mechanism.The results showed that the whole growth time of seeds of three varieties conventional rice ZR02, hybrid rice Zhu1S/ZR02 and Jin23A/ZR02 was all about 17 d. The caryopsis color changed from green to yellowish green then to yellow with ongoing development. The moisture content of seeds showed a similar downward tendency during development, but it rapidly declined at 5 DAA-9 DAA (days after anthesis), and then slowly declined down, the fresh and dry weight of seed of the three varieties during development showed a consistent changing mode:5 DAA-13 DAA was the rapid growth period, and went to a constant level at 17 DAA, therefore seed harvesting should not be earlier than 17 DAA.At 7 DAA, seeds of all three rice varieties began to have the ability to germinate when they were placed in suitable germination condition. The germination percentage of fresh seeds was relatively lower, either rapid or slow dehydration was obviously able to enhance the germination of seeds when dehydrated to moisture content of 0.11 g H2O·g-1DW. When the seeds with the identical developing stage dehydrated to the same moisture content with SD and RD separately, those with SD treatment improved the germination percentage and simplified vigor index by a greater extent, especially the ones having not developed to maturity yet.Dehydrated to the equilibrium moisture content 0.04 g H2O·g-1DW and 0.11 g H2O·g-1DW by RD and SD separately, the germination percentage and simplified vigor index of the mature seeds (21 DAA) of all three rice varieties were higher than the initial value of fresh seeds. Meanwhile, when the seeds dehydrated to the identical moisture content, no matter conventional rice or hybrid rice, those ones with SD showed the higher germination percentage than that with RD. These results demonstrated that rice seeds are orthodox which are able to tolerate extreme dehydration. On the other hand, there exists difference of the desiccation tolerance between conventional and hybrid rice seeds:firstly, the initial gentle dehydration with RD (to 0.25 g H2O·g-1DW) had only slight influence on the germination of conventional seeds, but reduced the germination percentage of seeds of two hybrid rice by a distinct extent, although it would go up again as the moisture content went down with the continuing dehydration; secondly, dehydrated to the equilibrium moisture content by RD and SD separately, seeds of the conventional rice had almost the same germination percentage, while the germination percentage of seeds of two hybrid rice with RD was obviously lower than that of ones with SD.To analyze the physiological mechanism to seed desiccation tolerance, some relative physiological indices such as the content of soluble sugar, soluble protein and MDA, as well as the SOD activity were measured. Compared with RD, SD was more conducive for seed to accumulate soluble protein and soluble sugar, and remain the SOD activity at a high level. Moreover, SD was able to increase the SOD activity of mature seeds. The electrolytic conductivity of seed-soaked solution of the seeds after dehydration treatment was significantly higher than that of fresh ones before 11 DAA. However, to the seeds after 11 DAA, the identical dehydration made the electrolytic conductivity of seed-soaked solution to get increased very slightly. So the seeds before 11 DAA should be at the initial phase of the formation of seed desiccation tolerance, dehydration on seeds more easily injured cell membrane which resulted in the membrane permeability ascending. In addition, dehydration led to MDA content in seeds to increase significantly, and the upgrade degree was negative to seed development level, but the seeds of the identical development stage at SD produced lower content of MDA than the ones at RD. These results demonstrated that the desiccation tolerance of rice seeds gradually formed as seed developed.After 3 months of preservation in indoor open condition or in dry silica gel in closed condition, followed by artificial aging for 15 days, seeds of conventional rice ZR02 were more anti-aging than those of two hybrid rice Zhu1S/ZR02 and Jin23A/ZR02 did. While comparing to the anti-aging capacity of seeds of two hybrid rice with different degree of development, after the same preservation and artificial aging as above,17 DAA ones showed the highest. Analyses of physiological indices to 15 DAA seeds before and after aging treatment indicated that aging led to rice seeds to reduce the content of soluble sugar and soluble protein and the activity of SOD significantly, and the reduce degree in hybrid rice seeds was greater than that in conventional rice ones.