Abstract: Objective This study aims to investigate the desiccation sensitivity as well as the critical moisture content of the seed and embryonic axis of Quercus acutissim and explore low-temperature preservation techniques for Q. acutissima seeds and ultra-low temperature preservation techniques for the embryonic axis, in order to provide technical guidance for the preservation of recalcitrant seeds such as Q. acutissima. Method Wild Q. acutissim seeds were used as experimental materials, the silica gel weight reduction method was used to rapidly dehydrate the seeds to the target moisture content, and then the germination indexes of seeds and embryonic axes with different moisture contents were determined. The differential scanning calorimetry (DSC) was employed to determine the thermodynamic parameters of embryonic axes and cotyledons with different moisture contents, and the critical moisture content of crystallization in the embryonic axis was evaluated according to the relationship between moisture content and corresponding enthalpy. The low-temperature sealed storage method was used to preserve seeds with different moisture contents, and the vitrification method was used for cryopreservation of the embryonic axis. Result 1) When the initial moisture content of the seeds and embryonic axes decreased from 34.90% and 44.14% to 10.00%, their germination percentage decreased from 93.00% and 90.00% to 5.00% and 52.00%, respectively. 2) The DSC results of Q. acutissim embryonic axis and cotyledon with different moisture contents showed that with the decrease of moisture content of embryonic axis and cotyledon, the crystallization initiation temperature, peak temperature and enthalpy value showed a regular downward trend, which were significantly positively correlated with moisture content. The average enthalpy value of the embryonic axis was higher than that of the cotyledon, and the free moisture content of the embryonic axis was higher than that of the cotyledon. It was preliminarily determined that the theoretical critical moisture content of crystallization in this batch of the embryonic axes was 11.72%. 3) The effects of dehydration on the physiological and biochemical characteristics of Q. acutissima seeds showed that as dehydration progressed, the activities of superoxide dismutase (SOD) and peroxidase (POD), as well as the contents of proline (PRO) and malondialdehyde (MDA) in seeds initially increased and then decreased. 4) Q. acutissim seeds with initial moisture content stored at 4 ℃ for 21 days showed no change in the germination vitality, and the seeds with severe dehydration (10%–20%) were still able to tolerate a certain degree of low temperature damage. The results of cryopreservation of embryonic axis with different moisture contents showed that moisture content had a significant impact on the results of cryopreservation. When pretreated with PVS2 for 30 min before cryopreservation, the embryonic axis with 10.00% and 15.00% moisture content had a 5.00% and 3.00% survival rate, respectively, and the thermodynamic characteristics of the embryonic axis with different moisture content changed. The embryonic axis with 15.00% moisture content regained free moisture. Conclusion The germination rate of Q. acutissim seeds and embryonic axes decreases with the decrease of moisture content, which is a typical characteristics of recalcitrant seeds with the dehydration sensitivity. Dehydration has a significant effect on the physiological and biochemical characteristics of the seeds. The theoretical critical moisture content of crystallization in Q. acutissim embryonic axis is 11.72%. Cryopreservation of Q. acutissimembryonic axis is possible, but the method still needs adjustment to increase the recovery of germination rate, and then is applied to the long-term preservation of the recalcitrant seed.

Key words: Quercus acutissim, desiccation sensitivity, cryopreservation, recalcitrant seeds, differential scanning calorimetry (DSC).