Cryopreservation of in vitro Shoot Tips of Ulluco (Ullucus tuberosus Cal.) Using D Cryo-Plate Method

　　BACKGROUND: Maintenance of in vitro collections of ulluco (Ullucus tuberosus Cal.) is cumbersome and costly in an ex-situ genebank. An alternative method for long term preservation which is safe and cost-effective is required.

OBJECTIVE

To apply a novel cryopreservation procedure using the cryo-plate system to improve the long-term conservation of ulluco.

MATERIALS AND METHODS

Initially V and D cryo-plate methods were tested, subsequently the D cryo-plate method was selected for ulluco cryopreservation. The D cryo-plate procedures were optimized for post-LN regrowth procedures including cold-hardening, sucrose addition in alginate gel, and duration of LS treatment. Optimized procedures were tested with 11 ulluco lines.

RESULTS

Shoot tips were isolated from cold-hardened shoots for 3-4 weeks at 5 degree C were excised to 1.0-1.5 mm long and 0.5 mm wide and precultured for 16h at 25 degree C on MS with 0.3 M sucrose. The shoot tips were attached on the cryo-plates by alginate gel with 0.4M sucrose. The cryo-plates with attached shoot tips were treated with 2.0 M glycerol and 1.0 M sucrose solution for 90 min at 25 degree C and dehydrated on filter paper in a Petri dish by air current flow at 25 degree C for 45 min before direct immersion in LN. This optimized procedure was applied to shoot tips of 11 ulluco lines, resulting regrowth ranging from 73 % to 97 %, with an average of 90 % post-LN regrowth.

CONCLUSION

D cryo-plate is a practical and simple procedure for cryo-storage of in vitro grown ulluco shoot tips in an ex situ genebank.

Dehydration improves cryopreservation of mat rush (Juncus decipiens Nakai) basal stem buds on cryo-plates

Two cryopreservation procedures using aluminium cryo-plates, termed V-Cryo-plate and D-Cryo-plate, were successfully developed for in vitro mat rush (Juncus decipiens Nakai) basal stem buds. Multiple stems induced in liquid MS medium containing 8.9 μM BA by roller culture were cut into small clumps, plated on solid MS medium and cultured for 1 week at 25 degree C. Clumps that had produced many buds were cold-hardened at 5 degree C for 1-2 months. The buds with basal stems were dissected from small clumps and precultured overnight at 25 degree C on solid MS medium containing 0.3 M sucrose. Precultured buds were placed on aluminium cryo-plates and embedded in calcium alginate gel. Osmoprotection was performed by immersing the cryo-plates for 30 min at 25 degree C in loading solution (2 M glycerol + 1.0 M sucrose). In the D-Cryo-plate procedure, the buds were dehydrated to 27-25% moisture content (fresh weight) by placing the cryo-plates in the air current of a laminar flow cabinet for 2 to 3 h. In the V-Cryo-plate procedure, buds were dehydrated by immersing the cryo-plates in PVS2 vitrification solution for 40 min at 25 degree C. In both procedures, cooling was performed by placing the cryo-plates in uncapped cryotubes, which were immersed in liquid nitrogen. For rewarming, cryo-plates were immersed in medium with 1.0 M sucrose for 20 min at room temperature. Regrowth of cryopreserved buds of line 'Kitakei 2' using D-Cryo-plate and V-Cryo-plate procedures, was 90% and 80%, respectively. The two procedures were applied to 20 additional mat rush lines. Using the V-Cryo-plate procedure resulted in regrowth ranging between 13.3 and 86.7%, with an average of 52.5%. The D-Cryo-plate led to regrowth ranging between 73.3 and 96.7%, with an average of 86.3%. The D-Cryo-plate procedure will facilitate cryostorage of mat rush germplasm.