VITRIFICATION OF CRYOPRESERVED MINT SHOOT TIPS AS FOLLOWED BY CRYO-SEM AND DSC

摘要

Plant germplasm cryopreservation aims to store specimens stopping as much as possible both chemical reactions and physical processes. However, cryopreservation can give rise to the formation of ice crystals, damaging tissues. Several of the methods currently applied with success make use of vitrification to achieve stoppage of processes while avoiding ice formation. These procedures involve a series of steps leading to natural defense induction, water content reduction and overall cytoplasm molecular mobility impairment. A quick cooling step by immersion in liquid nitrogen follows. Mint shoot tips, in different stages of the "droplet" cryopreservation protocol, were studied both by cold-stage scanning electron microscopy (cryo-SEM) and differential scanning calorimetry (DSC). Results show how cells at intermediate treatment steps develop ice crystals during liquid nitrogen cooling, while specimens whose treatment was completed become vitrified, with no evidence of ice formation. These results agree with the generally observed plant recuperation after cryopreservation and allow some preliminary conclusions to be drawn, concerning the cryopreservation protocol followed.