Effects of oxidative stress on the changes of viability of Paeonia lactiflora seeds with different water content before and after cryopreservation.

Cryopreservation in liquid nitrogen (LN) is an efficient long - term seed preservation strategy and water content is one of the main factors affecting seed viability after cryopreservation. In this study, Paeonia lactiflora seeds with varying water content were used as materials to determine changes in the antioxidant system before and after cryopreservation. When the water content of P. lactiflora seeds was 15.96 %-10.12 %, the viability of P. lactiflora seeds decreased significantly compared with that of the seeds without cryopreservation, but at the water content of 8.14 %-7.56 % there were no significant differences. However, when the water content of P. lactiflora seeds decreased to 6.01 %-5.19 % the viability was slightly increased compared to the seeds without cryopreservation. The content of superoxide anion (O₂^-), hydroxyl radical (·OH), hydrogen peroxide (H₂O₂), malondialdehyde (MDA) and protein carbonyl group (PCO) of seeds with high water content (15.96 %-10.12 %) were significantly increased after cryopreservation. However, superoxide anion (O₂^-), hydroxyl radical (·OH) and hydrogen peroxide (H₂O₂) did not change significantly in seeds with low water content (6.01 %-5.19 %) after cryopreservation, while oxidative stress indexes MDA and PCO decreased. These three substances were significantly negatively correlated with seed viability. In terms of antioxidant substances, the contents of catalase (CAT), ascorbic acid (AsA) and glutathione (GSH) decreased and the activities of glutathione reductase (GR) and dehydroascorbate reductase (DHAR) increased during the cryopreserved process of seeds with varying water content. These changes were significantly correlated with ROS content and the changes of MDA and PCO, among which AsA content, GSH content and CAT activity were positively correlated with seed viability. The changes of GR and DHAR activity were negatively correlated with seed viability. In summary, when the water content of the seeds ranged from 8.14 % to 5.19 %, ROS content did not increase significantly after cryopreservation compared with that of before preservation. The changes of MDA and PCO contents before and after cryopreservation, it was inferred that no obvious oxidative damage occurred in seeds, so the viability of seeds did not decrease compared with that of before cryopreservation. Therefore, the optimum water content of P. lactiflora seeds for cryopreservation is 8.14 %-5.19 %.