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Title: Factors affecting stress tolerance in recalcitrant embryonic axes from four Quercus (Fagaceae) species native to the US or China

item XIA, KE - Chinese Academy Of Sciences
item Hill, Lisa
item LI, DE-ZHU - Chinese Academy Of Sciences
item Walters, Christina

Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2014
Publication Date: 12/1/2014
Citation: Xia, K., Hill, L.M., Li, D., Walters, C.T. 2014. Factors affecting stress tolerance in recalcitrant embryonic axes from four Quercus (Fagaceae) species native to the US or China. Annals Of Botany. 114(8):1747-1759. DOI: 10.1093/aob/mcu193.

Interpretive Summary: Several species of agronomic or ecological interest produce “recalcitrant” seeds, meaning that the seeds do not survive drying and so are killed using conventional storage protocols used for plant genebanks. Cryopreservation methods have been established for these types of seeds for species growing in temperate climates. However, attempts to cryopreserve recalcitrant seeds from species growing in tropical climates are usually unsuccessful. What explains the difference in response to cryopreservation treatments in embryonic tissues from two environments? In this paper, we explore the relationship between environmental conditions for growth and tolerance of embryonic tissues to drying and low temperature in acorns. We showed that there was no relationship between adaptation for the whole plant to dry environments and tolerance of the embryo to desiccation. We also show that acorns from oak trees having subfreezing winters are more amenable to desiccation and cryopreservation. This study suggests a link between freezing tolerance and desiccation tolerance that may provide additional understanding of the recalcitrant seed condition.

Technical Abstract: Recalcitrant-seeded Quercus species are often considered “keystone” components of the ecosystems. However, their populations are declining and there is a considerable urgency to develop ex situ conservation strategies. The storage physiology of seeds within Quercus was explored in order to determine factors that affected survival during cryopreservation. Water relations and survival of excised axes in response to water loss and cryo-exposure were compared for 4 Quercus species from subtropic China and temperate USA. Seed tissues had initially high water contents and water potentials, but survived to different water contents. Desiccation tolerance of embryonic axes was not correlated with the rainfall patterns where samples originated. Instead, higher desiccation tolerance was observed in samples growing in areas with colder winters. Survival following cryo-exposure correlated with desiccation tolerance. Among species, plumule tissues were more sensitive to excision, desiccation and cryoexposure, and this led to a higher proportion of abnormally developing embryos during recovery following stress. Quercus species adapted to the desert still produce recalcitrant seeds. Ability to avoid freezing rather than drought may be a more important selection factor to increase desiccation tolerance. Cryopreservation of recalcitrant germplasm from temperate species is currently feasible and additional protective treatments are needed for ex situ conservation of Quercus from tropical and semitropical areas.