title: Factors affecting stress tolerance in recalcitrant embryonic axes from seeds of four Quercus (Fagaceae) species native to the USA or China.
abstract: OBJECTIVE
  Quercus species are often considered 'foundation' components of several temperate and/or subtropical forest ecosystems. However, the populations of some species are declining and there is considerable urgency to develop ex situ conservation strategies. In this study, the storage physiology of seeds within Quercus was explored in order to determine factors that affect survival during cryopreservation and to provide a quantitative assessment of seed recalcitrance to support future studies of this complex trait.
  
  
  METHODS
  Water relations and survival of excised axes in response to water loss and cryo-exposure were compared for four Quercus species from subtropical China (Q. franchetii, Q. schottkyana) and temperate USA (Q. gambelii, Q. rubra).
  
  
  RESULTS
  Seed tissues initially had high water contents and water potentials. Desiccation tolerance of the embryonic axis was not correlated with the post-shedding rainfall patterns where the 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 than radicles to excision, desiccation and cryo-exposure, and this led to a higher proportion of abnormally developing embryos during recovery following stress.
  
  
  CONCLUSIONS
  Quercus species adapted to arid and semi-humid climates still produce recalcitrant seeds. The 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, whilst additional protective treatments are needed for ex situ conservation of Quercus from tropical and subtropical areas.
authors.affiliation: Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China USDA-ARS National Center for Genetic Resources Preservation, Fort Collins, CO 80524, USA.
authors.forename: Ke
authors.initials: K
authors.lastname: Xia
authors.affiliation: USDA-ARS National Center for Genetic Resources Preservation, Fort Collins, CO 80524, USA.
authors.forename: Lisa M
authors.initials: LM
authors.lastname: Hill
authors.affiliation: Germplasm Bank of Wild Species, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming 650201, China Key Laboratory of Biodiversity and Biogeography, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, China.
authors.forename: De-Zhu
authors.initials: DZ
authors.lastname: Li
authors.affiliation: USDA-ARS National Center for Genetic Resources Preservation, Fort Collins, CO 80524, USA christina.walters@ars.usda.gov.
authors.forename: Christina
authors.initials: C
authors.lastname: Walters
mesh_terms: D000222:Adaptation, Physiological; D018533:Biomass; D002681:China; D002980:Climate; D003681:Dehydration; D004573:Electrolytes / Q000378:metabolism; D005615:Freezing; D018517:Plant Roots / Q000502:physiology; D011312:Pressure; D029963:Quercus / Q000196:embryology* / Q000254:growth & development / Q000502:physiology*; D012044:Regression Analysis; D012639:Seeds / Q000502:physiology*; D013312:Stress, Physiological; D013997:Time Factors; D014481:United States; D014867:Water
chemical_list: D004573:Electrolytes; D014867:Water
keywords: Cyclobalanopsis; Quercus franchetii; Quercus gambelii; Quercus rubra; Quercus schottkyana; Seed desiccation tolerance; critical moisture content; cryopreservation; embryonic axis; oak; plumule; recalcitrance; subtropical