Cryopreservation of embryogenic cell suspensions by encapsulation-vitrification.

Encapsulation-vitrification, which is a combination of encapsulation-dehydration and vitrification procedures, is a newly developed technique for cryopreservation of plant germoplasm. Here, we describe the protocol of this methodology, using grapevine (Vitis) as a model plant. Cell suspensions at the exponential growth stage were encapsulated with 2.5% sodium alginate solution in 0.1 M calcium chloride solution for 20 min to form beads of about 4 mm in diameter containing 25% cells. The beads were stepwise precultured in increasing sucrose concentrations of 0.25, 0.5, and 0.75 M for 3 yr, with 1 d for each step. Precultured beads were treated with a loading solution for 60 min at room temperature and then dehydrated with PVS2 at 0 degrees C for 270 min, followed by direct immersion in liquid nitrogen for 1 h. The beads were rapidly rewarmed at 40 degrees C in a water bath for 3 min and then diluted with 1 M sucorse solution at room temperature for 30 min. Rewarmed, washed beads were post-cultured on a recovery medium for 3 d at 25 degrees C in the dark for survival. Surviving cells were transferred to a regrowth medium to induce cell proliferation. Embryogenic cell suspensions were re-established by suspending the cells in a cell suspension maintenance medium maintained on a gyratory shaker at 25 degrees C in the dark. For plant regeneration, surviving cells were transferred from the recovery medium to an embryo maturation medium and maintained at 25 degrees C under light conditions. Embryos at the torpedo stage were cultured on rooting medium until whole plantlet was developed.