Optimized cryopreservation of embryogenic tissue of Picea abies based on differential scanning calorimetry

Cryopreservation is the most economically, viable, and reliable method for long-term preservation of plant germplasm resources. Given the application of somatic embryogenesis techniques in conifer vegetative propagation, cryopreservation of Norway spruce (Picea abies (L.) Karst.) is highly necessary. Here, an optimal concentration of embryogenic tissue (ET) suspensions (0.1 g mL^-1) was achieved according to the regrowth rates of various Norway spruce lines and different solutions concentrations. On this basis, the Norway spruce ETs were cryopreserved using eight cryoprotectant pretreatments (CPTs). The enthalpy values of different CPTs were evaluated by differential scanning calorimetry (DSC). Subsequently, the relationship between the regrowth and the enthalpy was investigated. DSC showed that the enthalpy values of Norway spruce ETs treated with various CPTs significantly decreased during the warming. Moreover, the T6 (0.3 M sorbitol for 48 h, 10 %DMSO as the cryoprotectant) exhibited superior solution stability, as the regrowth rate of T6 was 2.94 times higher than that of T3. By comprehensive comparison, T6 might be considered an optimized CPT method for Norway spruce ETs. Notably, correlation analysis demonstrated that the enthalpy of warming stage and cooling stage was negatively correlated with the regrowth rate. Thus, the enthalpy of warming melting stage and cooling crystallization stage could serve as potential indicators of the regrowth rate. Our study provides an optimized CPT for Norway spruce ETs, which may offer a reference for the development of a novel rapid detection method to assess plant cryopreservation efficiency. KEY MESSAGE: Optimized cryopreservation protocol based on differential scanning calorimetry.