State and phase transition behaviors of Quercus rubra seed axes and cotyledonary tissues: Relevance to the desiccation sensitivity and cryopreservation of recalcitrant seeds

Abstract

Freezing and melting transitions of cellular water in embryonic axes and cotyledonary tissues of recalcitrant Quercus rubra (red oak) seeds were compared under slow and rapid cooling conditions. The relevance of desiccation sensitivity (critical water content) and state/phase transition behaviors to cryopteservation was examined. Under a slow to intermediate cooling condition (≤10°C min-1), unfrozen water content in the tissues decreased to less than the critical water content, resulting in a dehydration damage. Under a rapid cooling condition (>100°C min-1) using liquid nitrogen (LN2 freeze-induced dehydration damage could be avoided if the initial water content was >0.50 g g-1 dry wt. However, at water content >0.50 g g-1 dry wt, the vitrified cellular matrix was highly unstable upon warming at 10°C min-1. These results offered a theoretical explanation on the difficulty for successful cryopreservation of recalcitrant red oak embryonic axes. A complete state/phase transition diagram for red oak axes was constructed, and a vitrification-based cryopreservation protocol that employed predehydration and rapid cooling was examined. State/phase transition behaviors of cellular water are important parameters for cryopreservation; however, vitrification alone was not sufficient for seed tissues to survive the cryopreservation condition.