title: Identification and characterization of ten new water gaps in seeds and fruits with physical dormancy and classification of water-gap complexes.
abstract: OBJECTIVE
  Physical dormancy (PY) occurs in seeds or fruits of 18 angiosperm families and is caused by a water-impermeable palisade cell layer(s) in seed or fruit coats. Prior to germination, the seed or fruit coat of species with PY must become permeable in order to imbibe water. Breaking of PY involves formation of a small opening(s) (water gap) in a morpho-anatomically specialized area in seeds or fruits known as the water-gap complex. Twelve different water-gap regions in seven families have previously been characterized. However, the water-gap regions had not been characterized in Cucurbitaceae; clade Cladrastis of Fabaceae; subfamilies Bombacoideae, Brownlowioideae and Bythnerioideae of Malvaceae; Nelumbonaceae; subfamily Sapindoideae of Sapindaceae; Rhamnaceae; or Surianaceae. The primary aims of this study were to identify and describe the water gaps of these taxa and to classify all the known water-gap regions based on their morpho-anatomical features.
  
  
  METHODS
  Physical dormancy in 15 species was broken by exposing seeds or fruits to wet or dry heat under laboratory conditions. Water-gap regions of fruits and seeds were identified and characterized by use of microtome sectioning, light microscopy, scanning electron microscopy, dye tracking and blocking experiments.
  
  
  RESULTS
  Ten new water-gap regions were identified in seven different families, and two previously hypothesized regions were confirmed. Water-gap complexes consist of (1) an opening that forms after PY is broken; (2) a specialized structure that occludes the gap; and (3) associated specialized tissues. In some species, more than one opening is involved in the initial imbibition of water.
  
  
  CONCLUSIONS
  Based on morpho-anatomical features, three basic water-gap complexes (Types-I, -II and -III) were identified in species with PY in 16 families. Depending on the number of openings involved in initial imbibition, the water-gap complexes were sub-divided into simple and compound. The proposed classification system enables understanding of the relationships between the water-gap complexes of taxonomically unrelated species with PY.
authors: Department of Biology, University of Kentucky, Lexington, KY 40506, USA. nalinsuranjith@uky.edu
authors: N S
authors: NS
authors: Gama-Arachchige
authors: J M
authors: JM
authors: Baskin
authors: R L
authors: RL
authors: Geneve
authors: C C
authors: CC
authors: Baskin
mesh_terms: D004396:Coloring Agents / Q000032:analysis; D019662:Cucurbitaceae / Q000033:anatomy & histology / Q000166:cytology / Q000502:physiology; D007887:Fabaceae / Q000033:anatomy & histology / Q000166:cytology / Q000502:physiology; D005638:Fruit / Q000033:anatomy & histology* / Q000166:cytology / Q000502:physiology*; D019684:Magnoliopsida / Q000033:anatomy & histology* / Q000166:cytology / Q000502:physiology*; D019660:Malvaceae; D008855:Microscopy, Electron, Scanning; D057445:Plant Dormancy / Q000502:physiology*; D012394:Rosaniline Dyes / Q000032:analysis; D029631:Sapindaceae / Q000033:anatomy & histology / Q000166:cytology / Q000502:physiology; D012639:Seeds / Q000033:anatomy & histology* / Q000166:cytology / Q000502:physiology*; D014867:Water
chemical_list: D004396:Coloring Agents; D012394:Rosaniline Dyes; D014867:Water
keywords: Chalaza; PY breaking; dye tracking; fruit coat; hilum; micropyle; palisade cells; physical dormancy; seed coat; water-gap complex
references: Am J Bot. 2004 Nov;91(11):1846-62
references: 21652332
references: Ann Bot. 2010 Jun;105(6):977-90
references: 20400757
references: Ann Bot. 2007 Jul;100(1):13-22
references: 17513869
references: Ann Bot. 2008 Jul;102(1):39-48
references: 18453546
references: Ann Bot. 2009 Oct;104(5):833-44
references: 19620135
references: Ann Bot. 2012 Aug;110(3):637-51
references: 22684684
references: Ann Bot. 2008 Feb;101(3):341-52
references: 18032427
references: Ann Bot. 2013 May;111(5):849-58
references: 23456728
references: Ann Bot. 2011 Jul;108(1):51-64
references: 21546433
references: Am J Bot. 1999 Nov;86(11):1505-11
references: 10562242
references: Philos Trans R Soc Lond B Biol Sci. 2004 Oct 29;359(1450):1495-508
references: 15519968
references: Am J Bot. 1999 Oct;86(10):1474-86
references: 10523287
references: Ann Bot. 2009 Jan;103(1):45-63
references: 19074450
references: Mol Phylogenet Evol. 2004 Dec;33(3):861-79
references: 15522809