Abstract
Shoot apices of asparagus (Asparagus officinalis L.) can be successfully cryopreserved (by freezing at a rate of 0.5℃/min in the presence of 8% DMSO and 0.2 M sorbitol) after pretreatments either by precultufe in media containing 0.5 M glucose for 2 days or by cold acclimation at 0℃ for 20 days. In the present study, we examined the effects of pretreatments for subsequent successful cryopreservation of the shoot apices. Freezing tolerance, as revealed by LT_<50> under equilibrium-freezing, was -20℃ in both specimens with pretreatment by 0.5 M glucose and by cold acclimation, while LT_<50> was -7℃ in control specimens. Both pretreatments produced distinct cellular ultrastructural changes as observed with ultra-thin section electron microscopy. Number of plastids rich in starch granules increased in precultured specimens, whereas those poor in the starch granules increased in cold acclimated specimens. Occurrence of freezing injury by equilibrium-freezing, as observed with a freeze-fracture replica technique, was associated with formation of aparticulate domains with accompanying fracture-jump lesions in the plasma membranes, not only in precultured specimens with 0.5 M glucose and in cold acclimated specimens, but also in control specimens.
