Cryopreservation of Kalopanax septemlobus embryogenic callus using vitrification and droplet-vitrification

A cryopreservation protocol has been developed for embryogenic callus cultures of castor aralia (Kalopanax septemlobus), a deciduous tree which is widely used in oriental medicine and in landscape design. Three preculture treatments, four loading and six vitrification solutions were tested in a vitrification procedure. Preculture of embryogenic callus (EC) with high sucrose concentrations (up to 0.7 M) showed no effect on regrowth after cryopreservation. Loading for 20 min at ambient temperature improved regrowth of cryopreserved EC by 70-75 percent compared with non-loaded samples, regardless of the composition of the loading solution. Among vitrification solutions, the highest regrowth of 95-100 percent after cryopreservation was obtained after incubation of EC in a vitrification solution A3-80 percent comprising (w/v) 33.3 percent glycerol + 13.3 percent DMSO + 13.3 percent EG + 20.1 percent sucrose for 40 min at 0°C. Profiling of crystallization and recrystallization events using differential scanning calorimetry (DSC) confirmed that freezing injury was minimized in samples after loading and cryoprotection with this vitrification solution. Unlike many other papers, the droplet-vitrification protocol did not produce higher post-cryopreservation regrowth of Kalopanax EC, compared with the vitrification procedure. When samples are sufficiently cryoprotected during VS treatment, vitrification using cryovials may be preferred, since droplet-vitrification is more complex and requires skilled personnel. Cryopreserved callus grew rapidly and produced numerous somatic embryos, which developed similarly to embryos obtained from non-cryopreserved samples.