The encapsulation-
dehydration cryopreservation protocol is critically dependent upon the evaporative desiccation step, which must optimise survival with the retention of glass stability on sample cooling and
rewarming. Desiccation is usually achieved evaporatively by drying in a sterile airflow. However, chemical desiccation using
silica gel has advantages for laboratories that do not have environmental control and/or which are exposed to high relative humidities and risks of microbial contamination. This study characterised thermal profiles of
silica gel-desiccated encapsulated shoot-
tips of two Ribes species using Differential Scanning Calorimetry. For both species
silica gel-desiccation at 16 degrees C for 5 h decreased bead water content from ca. 75 to 28% fresh weight (3.8 to 0.4 g x g(-1) dry weight); further desiccation (for 6 and 7 h) reduced the bead water content to 21% (0.3 g x g(-1) dry weight). These changes in water status altered the thermal properties of beads for both species. After 7 h desiccation over
silica gel stable glass transitions were observed on both cooling and
rewarming of beads containing meristems. Tg mid-point temperatures ranged from -78 to -51 degrees C (cooling) and from -88 to -54 degrees C (warming) [at cooling and warming rates of 10 and 5 degrees C min(-1), respectively] after 5 to 7 h
silica gel-desiccation. Post-cryopreservation viability of both species was ca. 63%. Thermal analysis studies revealed that an encapsulation/
dehydration protocol using
silica gel as a
desiccant should comprise a minimum 5 h drying (at 16 degrees C). This reduces bead moisture content to a critical point (ca. 0.4 g x g(-1) dry weight) at which stable glasses are formed on cooling and
rewarming. It is concluded that
silica gel has advantages for use as a
desiccant for
alginate-encapsulated plant meristems by promoting stable vitrification and is useful in laboratories and/or geographical locations where environmental conditions are not under stringent control.