Desiccation tolerance and cryopreservation of embryonic axes of recalcitrant species

Because recalcitrant seeds are generally large and show very curtailed longevity even if stored hydrated, cryopreservation of their embryonic axes seems to be the most obvious way to create a gene bank. The aim of this investigation was to determine the minimal water content tolerated by embryos of five recalcitrant species and their subsequent survival after cryopreservation. As sucrose is known to improve desiccation- and cryopreservation-tolerance of many plant tissues, experiments were performed with both non-pre-treated and sucrose pre-treated embryonic axes. Embryonic axes of Camellia sinensis and Azadirachta indica tolerated dehydration to very low water contents, 0.14 and 0.23 g water per g of dry weight (g.g(-1)), respectively. In such dry states most of the axes survived cryopreservation. Below 0.29, 0.42 and 0.34 g.g(-1) no survival after desiccation was recorded for Trichilia dregeana Artocarpus heterophyllus and Landolphia kirkii embryos, respectively. Survival at lower water contents, 0.16 and 0.21 g.g(-1), respectively for Trichilia dregeana and Artocarpus heterophyllus could be obtained after a high sucrose pre-treatment. In contrast, viability was lost below 0.42 g.g(-1) in the case of pre-treated axes of Landolphia kirkii. Concerning the last three species, survival after cryopreservation was recorded only for sucrose pre-treated, desiccated axes of Trichilia dregeana.