Dehydration status of ABA-treated and cold-acclimated Hypericum perforatum L. shoot tips subjected to cryopreservation

To improve the vitrification protocol for Hypericum perforatum shoot tips, calorimetric measurements of the intensity of thermal transitions in the samples during warming using differential scanning calorimetry were assessed. Comparison of ABA treatment and cold-acclimation revealed higher content of crystallizable water in the latter. Regeneration capacity of cryopreserved H. perforatum shoot tips increased progressively with the exposure time in PVS3 cryoprotection mixture reaching the maximum between 59.3 and 71.3% after 180 min when the proportion of freezable water ranged between 0.0 and 0.4% of total water content respectively. Glass transitions were observed in all samples dehydrated with PVS3 when freezable water was present. However, the decreasing recovery of H. perforatum shoot tips after prolonged PVS3 dehydration (without LN storage) indicated some injuries of meristematic tissue induced by PVS3 dehydration rather than ice nucleation and resulted from genotype-dependent tolerance to abiotic stresses accompanying the entire process.