Abstract
Shoot tips excised from in vitro grown Chinese leek “Nakamidori” were successfully cryopreserved by vitrification. After 2 weeks cold-hardening, the excised shoot tips (1mm × 1.5mm) were precultured on Murashige and Skoog medium with 0.3M sucrose for 1 day at 5°C. The shoot tips were then osmoprotected with loading solution (LS) for 20 min at 25°C, dehydrated with plant vitrification solution 2 (PVS2) for 40 min at 25°C and immersed into liquid nitrogen (LN). The survival rate of cryoperserved shoot tips was about 80%. Shoot tips were also successfully cryopreserved by the encapsulation-vitrification method. The cold-hardened, precultured shoot tips were encapsulated with alginate-gel and simultaneously osmoprotected by LS solution for 90 min at 25°C. Then they were dehydrated with PVS2 for 120 min at 25°C and immersed in LN. The survival rate after cryopreservation amounted to about 80%. The optimal exposure time by PVS2 varied among specimens, especially depending upon whether meristem domes were covered with young leaves and the base of a leaf sheath. For the vitrification-based method, an appropriate unit of specimen for cryopreservation and an appropriate dehydration time using PVS2 were essential factors in achieving high survival rate.
