Revisiting crucial steps of an encapsulation/desiccation based cryopreservation process:: importance of thawing method in the case of Pelargonium meristems

This study questioned (1) the need for progressive osmotic desiccation (2) the efficiency of a new thawing method using 0.75 M sucrose liquid medium (3) the effect of various evaporative desiccation rates, in an encapsulation/desiccation cryopreservation process established for Pelargonium meristems. Whether progressive or not, osmotic desiccation in presence of high sucrose concentrations (up to 1 M) was equally efficient in the induction of meristem tolerance to further evaporative desiccation. The latter step was necessary for meristems to reach a water content window compatible with cryopreservation. This window was dependent on the thawing regime. Indeed, when frozen at relatively high water content (0.56 g g(-1) DW), high meristem survival rates (30-54%) were recorded only after sucrose-thawing. Moreover, at relatively lower water content (0.30 g g(-1) DW or lower), sucrose-thawing resulted in significantly higher survival rates than the traditional ambient- and 40 degreesC water bath-thawing. Irrespective of evaporative desiccation rates, meristem viability after dehydration to an approximate water content of 0.30 g g(-1) DW, was similar. Additional cryopreservation of such dehydrated meristems did not affect their survival. The beneficial effect of, sucrose-thawing on residual freezable water behaviour (detected via differential scanning calorimetry (DSC)) is discussed. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.