Impacts of Rapid Desiccation on Oxidative Status, Ultrastructure and Physiological Functions of Syzygium maire (Myrtaceae) Zygotic Embryos in Preparation for Cryopreservation

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 %.

Variation of sugar compounds in Phoebe chekiangensis seeds during natural desiccation

To investigate the role of sugar metabolism in desiccation-sensitive seeds, we performed a natural desiccation treatment on Phoebe chekiangensis seeds in a room and systematically analyzed the changes in seed germination, sugar compounds, malondialdehyde, and relative electrical conductivity during the seed desiccation. The results revealed that the initial moisture content of P. chekiangensis seed was very high (37.06%) and the seed was sensitive to desiccation, the germination percentage of the seed decreased to 5.33% when the seed was desiccated to 22.04% of moisture content, therefore, the seeds were considered recalcitrant. Based on the logistic model, we know that the moisture content of the seeds is 29.05% when the germination percentage drops to 50% and that it is desirable to keep the seed moisture content above 31.74% during ambient transportation. During seed desiccation, sucrose and trehalose contents exhibited increasing trends, and raffinose also increased during the late stage of desiccation, however, low levels of the non-reducing sugar accumulations may not prevent the loss of seed viability caused by desiccation. Glucose and fructose predominated among sugar compounds, and they showed a slight increase followed by a significant decrease. Their depletion may have contributed to the accumulation of sucrose and raffinose family oligosaccharides. Correlation analysis revealed a significant relationship between the accumulation of sucrose, trehalose, and soluble sugars, and the reduction in seed viability. Sucrose showed a significant negative correlation with glucose and fructose. Trehalose also exhibited the same pattern of correlation. These results provided additional data and theoretical support for understanding the mechanism of sugar metabolism in seed desiccation sensitivity.