Ultrastructural effects of early imbibition and cryostorage on Zea mays L-root meristems

In order to achieve successful cryopreservation of a hybrid maize variety it was necessary to isolate the embryonic axes from the caryopses. To facilitate the isolation of the axes without physical injury, the seeds were first imbibed thereby softening the testa. The effects of imbibition and subsequent cryostorage on vigour, viability and on the root meristem ultrastructure were followed for a range of imbibition periods. Imbibition for more than 4.5 h resulted in extensive subcellular damage post cryostorage and this was associated with a loss in vigour and quality of regenerative growth. Material imbibed for shorter periods prior to cryostorage exhibited less damage to the cells of the meristem and this was linked to the low level of cellular metabolism as indicated by the ultrastructure.