Cold acclimation and thermal transitions in the cryopreservation of hop shoot tips

The effect of cold acclimation on the shoot recovery rate from encapsulated Humulus lupulus L. cv Nugget shoot tips after cryopreservation was studied . A 7 to 45 d-periods of cold acclimation of the in vitro cultures increase d the shoot recovery percentages respect non-acclimated plant material. Col d acclimation improved the resistance of the encapsulated plant material to cryopreservation through an increase in tolerance to both sucrose precultu re conditions and dehydration duration. Only marginal differences were note d between slow and rapid freezing;. Differential scanning calorimetry analy sis performed on encapsulated shoot tips dehydrated to different moisture c ontents showed a correlation between partial desiccation, the formation of a glassy state, and survival after cryopreservation. By contrast, ice nucle ation was always associated with insufficient dehydration and mortality of the plant material during cryopreservation.