title: ULTRASTRUCTURAL RESPONSE OF EMBRYONIC AXES OF Fortunella polyandra TO DEHYDRATION AND CRYOPRESERVATION.
abstract: BACKGROUND
  To further understand the survival characteristics of desiccation-sensitive excised embryonic axes of Fortunella polyandra to desiccation and cryopreservation it is necessary to study the impact of drying rates on both the ultrastructure and electrolyte leakage.
  
  
  OBJECTIVE
  To examine the effects of two different drying regimes (silica gel and ultra-rapid) on the survival, ultrastructure and membrane leakage characteristics of excised embryonic axes of F. polyandra before and after cryopreservation.
  
  
  METHODS
  The effects of the drying regimes on the survival, ultrastructure and membrane integrity of the excised embryonic axes of F. polyandra was determined. Survival was assessed in vitro, and the integrity of membranes following drying was estimated by electrolyte leakage and observation under the transmission electron microscope (TEM). Survival and ultrastructural changes were also observed after cryopreservation.
  
  
  RESULTS
  Electrolyte leakage increased with decreasing water content of the embryonic axes, indicative of substantial subcellular damage, after both ultra-rapid dehydration (to water contents of <0.16 g H2O g(-1) dw) and silica gel dehydration (to <0.28 g H2O g(-1) dw water content). Ultrastructurally, axes showed increasing cytoplasm and vacuole shrinkage and disruption of cell membranes with longer dehydration periods. Normal seedling recovery of 50 to 47% for cryopreserved embryonic axes of F. polyandra was observed after ultra-rapid and silica gel drying respectively. Extreme cell injury was observed after exposure to liquid nitrogen at high moisture content. Although cells of dehydrated axes encountered stress during cryopreservation, the main damage occurred during the dehydration step.
  
  
  CONCLUSIONS
  For surviving axes, the damage was less severe and the axes grew to become normal seedlings. Ultrastructural studies reveal the damage of the cells at different rates of dehydration and during cryopreservation.
authors.affiliation: School of Biosciences and Biotechnology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Selangor, Malaysia. omaralzoubi73@yahoo.com.
authors.forename: Omar M
authors.initials: OM
authors.lastname: Al Zoubi
authors.affiliation: Institute of Systems Biology, Universiti Kebangsaan Malaysia, Selangor, Malaysia.
authors.forename: M N
authors.initials: MN
authors.lastname: Normah
mesh_terms: D015925:Cryopreservation; D003890:Desiccation / Q000295:instrumentation / Q000379:methods*; D046529:Microscopy, Electron, Transmission; D027821:Rutaceae / Q000196:embryology* / Q000502:physiology / Q000648:ultrastructure*; D012639:Seeds