Assessment of desiccation sensitivity of tea embryos for cryopreservation

Tea (Camellia sinensis (L.) O. Kuntze) has been reported as a species with recalcitrant seeds. The seeds can be stored for less than one year under high humidity conditions in a refrigerator at 5-7 degrees C. An efficient cryopreservation protocol for tea embryos using embryonic axes with portions of cotyledons still attached as drying material was established, which led to survival percentages around 92%. However, understanding the pattern of desiccation sensitivity, which is the key-limiting factor for cryopreservation, is of importance for implementation of cryopreservation using this protocol. In this study, the degree of desiccation sensitivity of tea seeds and cotyledonary embryonic axes (CEAs) was studied as a function of dehydration velocity, repeated dehydration-rehydration cycles, storage temperature, duration of storage of dried CEAs at room temperature, and seed harvesting date. This study suggests that there are no less than two mechanisms involved in desiccation sensitivity of tea seeds and embryos. Firstly, desiccation sensitivity of tea embryos occurs predominantly in a quantitative manner with continuous variation under intermediate dehydrated status rather than because of desiccation itself to a critical moisture content (MC). Secondly, desiccation sensitivity is due to the removal of the structural water at MCs of lower than 11.5%, when the EAs are flash-dried.