Glass transition and heat capacitybehaviors of plant vitrification solutions

Abstract

Differential scanning calorimetry (DSC) was employed to investigate the vitrification and annealing behaviors of the most commonly used plant vitrification solutions (PVS). These solutions are employed to protect plant tissues towards ice formation and freeze injury, and help to the vitrification of these tissues, by globally reducing the intracellular fluids mobility. Glass transition temperatures (T_g) and heat capacity increments (∆Cp) were determined for five solutions PVS1, PVS2, PVS2 mod, PVS3 and PVS3 mod, with different composition, and a range of cooling and warming rates was employed. Glass transitions showed clear and consistent temperature differences within vitrification solutions, which could be related to composition and water content. Roughly, two sets of T_G values were obtained, those for PVS1 and 2, at -112 ºC and -114 ºC, respectively, and those for PSV3, at -90 ºC. The observed Tg and ∆Cp, unexpectedly, did not significantly change within a wide range of cooling rates (from 5 ºC min^-1 to liquid nitrogen quenching) and warming rates (from 5 to 20 ºC). Garlic shoot tips cryopreserved after the droplet method produced a similar result to that of the vitrification solutions employed. After quench cooling to temperatures below T_g, repeated excursions to higher temperatures were made and the cooling and warming Tg were recorded. These treatments had little or no effect over the PVS solutions T_g, which remained practically constant. A direct practical consequence is that the plant vitrification solutions glass transition temperature does not significantly change with cryopreservation methods based on either direct plunging of samples into liquid nitrogen or employing closed cryovials.