Acquisition and loss of cryotolerance in Livistona chinensis embryos during seed development

Changes in desiccation tolerance and cryotolerance of chinese fan palm (Livistona chinensis [Jacq.] R. Br.) Embryos were studied during seed development from 15 to 45 weeks after flowering (WAF). Acquisition and then progressive loss in both desiccation tolerance and cryotolerance was observed within this period. Survival (apparent elongation of embryos) and emergence (formation of root and/or shoot) of embryos following dehydration increased progressively with development of seeds until 33 WAF, and then decreased up to 45 WAF. Similar changes occurred in the minimum moisture content at which 90% of embryos survived or emerged. Cryotolerance of embryos was nil at the early stages of seed development, until 21 WAF. Embryos acquired slight cryotolerance at 23 WAF and cryotolerance increased gradually from 27 to 36 WAF, then decreased by 45 WAF. Survival and emergence of post-thaw embryos were closely related to their moisture contents prior to freezing. However, this correlation between cryopreservation and moisture content was notably influenced by the embryos' developmental stage. Embryos at stages with greater cryotolerance gave higher post-thaw survival and emergence at a given moisture content, and the moisture content range allowing embryos to avoid cryo-damage was widened at both the lower and upper limits. Greater than 50% post-thaw emergence was observed only in embryos with moisture contents below 20% (fresh weight) at developmental stages between 27 and 36 WAF, although more than 90% of embryos could be dehydrated to < 20% moisture contents without loss in survival and emergence as early as 21WAF. Nearly 80% embryos could be dehydrated safely to 20% moisture content as late as 45 WAF.