title: Deep simple epicotyl morphophysiological dormancy in seeds of two Viburnum species, with special reference to shoot growth and development inside the seed.
abstract: OBJECTIVE
  In seeds with deep simple epicotyl morphophysiological dormancy, warm and cold stratification are required to break dormancy of the radicle and shoot, respectively. Although the shoot remains inside the seed all winter, little is known about its growth and morphological development prior to emergence in spring. The aims of the present study were to determine the temperature requirements for radicle and shoot emergence in seeds of Viburnum betulifolium and V. parvifolium and to monitor growth of the epicotyl, plumule and cotyledons in root-emerged seeds.
  
  
  METHODS
  Fresh and pre-treated seeds of V. betulifolium and V. parvifolium were incubated under various temperature regimes and monitored for radicle and shoot emergence. Growth of the epicotyl and cotyledons at different stages was observed with dissecting and scanning electron microscopes.
  
  
  RESULTS
  The optimum temperature for radicle emergence of seeds of both species, either kept continuously at a single regime or exposed to a sequence of regimes, was 20/10 °C. GA(3) had no effect on radicle emergence. Cold stratification (5 °C) was required for shoot emergence. The shoot apical meristem in fresh seeds did not form a bulge until the embryo had grown to the critical length for radicle emergence. After radicle emergence, the epicotyl--plumule and cotyledons grew slowly at 5 and 20/10 °C, and the first pair of true leaves was initiated. However, the shoot emerged only from seeds that received cold stratification.
  
  
  CONCLUSIONS
  Seeds of V. betulifolium and V. parvifolium have deep simple epicotyl morphophysiological dormancy, C(1b)B (root)-C(3) (epicotyl). Warm stratification was required to break the first part of physiological dormancy (PD), thereby allowing embryo growth and subsequently radicle emergence. Although cold stratification was not required for differentiation of the epicotyl--plumule, it was required to break the second part of PD, thereby allowing the shoot to emerge in spring.
authors.affiliation: Division of Silviculture, Taiwan Forestry Research Institute, Taipei 10066, Taiwan.
authors.forename: Ching-Te
authors.initials: CT
authors.lastname: Chien
authors.forename: Shun-Ying
authors.initials: SY
authors.lastname: Chen
authors.forename: Ching-Chu
authors.initials: CC
authors.lastname: Tsai
authors.forename: Jerry M
authors.initials: JM
authors.lastname: Baskin
authors.forename: Carol C
authors.initials: CC
authors.lastname: Baskin
authors.forename: Ling-Long
authors.initials: LL
authors.lastname: Kuo-Huang
mesh_terms: D057445:Plant Dormancy / Q000502:physiology*; D018515:Plant Leaves / Q000254:growth & development; D018520:Plant Shoots / Q000254:growth & development*; D012621:Seasons; D012639:Seeds / Q000254:growth & development / Q000502:physiology*; D013696:Temperature; D013997:Time Factors; D027925:Viburnum / Q000196:embryology / Q000254:growth & development / Q000502:physiology*