title: Effect of root length on epicotyl dormancy release in seeds of Paeonia ludlowii, Tibetan peony.
abstract: OBJECTIVE
  Epicotyl dormancy break in seeds that have deep simple epicotyl morphophysiological dormancy (MPD) requires radicle emergence and even a certain root length in some species. However, the mechanisms by which root length affects epicotyl dormancy break are not clear at present. This study aims to explore the relationship between root length and epicotyl dormancy release in radicle-emerged seeds of Tibetan peony, Paeonia ludlowii, with discussion of the possible mechanisms.
  
  
  METHODS
  Radicle-emerged seeds (radicle length 1.5, 3.0, 4.5 and 6.0 cm) were incubated at 5, 10 and 15 °C. During the stratification, some seeds were transferred to 15 °C and monitored for epicotyl-plumule growth. Hormone content was determined by ELISA, and the role of hormones in epicotyl dormancy release was tested by exogenous hormone and embryo culture.
  
  
  RESULTS
  Cold stratification did not break the epicotyl dormancy until the root length was ≥6 cm. The indole-3-actic acid (IAA) and GA3 contents of seeds having 6 cm roots were significantly higher than those of seeds with other root lengths, but the abscisic acid (ABA) content was lowest among radicle-emerged seeds. GA3 (400 mg L(-1)) could break epicotyl dormancy of all radicle-emerged seeds, while IAA (200 mg L(-1)) had little or no effect. When grown on MS medium, radicles of naked embryos grew and cotyledons turned green, but epicotyls did not elongate. Naked embryos developed into seedlings on a mixed medium of MS + 100 mg L(-1) GA3.
  
  
  CONCLUSIONS
  A root length of ≥6.0 cm is necessary for epicotyl dormancy release by cold stratification. The underlying reason for root length affecting epicotyl dormancy release is a difference in the GA3/ABA ratio in the epicotyl within radicle-emerged seeds, which is mainly as a result of a difference in ABA accumulation before cold stratification.
authors.affiliation: Institute of Botany, Chinese Academy of Sciences, Beijing, China.
authors.forename: Hai-ping
authors.initials: HP
authors.lastname: Hao
authors.forename: Zhi
authors.initials: Z
authors.lastname: He
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.forename: Lei
authors.initials: L
authors.lastname: Shi
authors.forename: Yu-Dan
authors.initials: YD
authors.lastname: Tang
mesh_terms: D000040:Abscisic Acid / Q000032:analysis / Q000378:metabolism; D018548:Cotyledon / Q000254:growth & development / Q000502:physiology; D018525:Germination / Q000502:physiology*; D005875:Gibberellins / Q000032:analysis / Q000378:metabolism; D018546:Hypocotyl / Q000254:growth & development / Q000502:physiology; D007210:Indoleacetic Acids / Q000032:analysis / Q000378:metabolism; D029596:Paeonia / Q000254:growth & development / Q000502:physiology*; D057445:Plant Dormancy / Q000502:physiology*; D010937:Plant Growth Regulators / Q000032:analysis / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development / Q000502:physiology; D018520:Plant Shoots / Q000254:growth & development / Q000502:physiology; D036226:Seedlings / Q000254:growth & development / Q000502:physiology; D012639:Seeds / Q000254:growth & development / Q000502:physiology; D013696:Temperature; D013997:Time Factors
chemical_list: D005875:Gibberellins; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; C030737:indoleacetic acid; D000040:Abscisic Acid; C007842:gibberellic acid
keywords: Paeonia ludlowii; Seed; Tibetan peony; epicotyl dormancy release; hormone; root length