title: Measurement of the distribution of non-structural carbohydrate composition in onion populations by a high-throughput microplate enzymatic assay.
abstract: BACKGROUND
  Non-structural carbohydrate (NSC; glucose, fructose, sucrose and fructan) composition of onions (Allium cepa L.) varies widely and is a key determinant of market usage. To analyse the physiology and genetics of onion carbohydrate metabolism and to enable selective breeding, an inexpensive, reliable and practicable sugar assay is required to phenotype large numbers of samples.
  
  
  RESULTS
  A rapid, reliable and cost-effective microplate-based assay was developed for NSC analysis in onions and used to characterise variation in tissue hexose, sucrose and fructan content in open-pollinated breeding populations and in mapping populations developed from a wide onion cross. Sucrose measured in microplates employing maltase as a hydrolytic enzyme was in agreement with HPLC-PAD results. The method revealed significant variation in bulb fructan content within open-pollinated 'Pukekohe Longkeeper' breeding populations over a threefold range. Very wide segregation from 80 to 600 g kg(-1) in fructan content was observed in bulbs of F2 genetic mapping populations from the wide onion cross 'Nasik Red × CUDH2150'.
  
  
  CONCLUSIONS
  The microplate enzymatic assay is a reliable and practicable method for onion sugar analysis for genetics, breeding and food technology. Open-pollinated onion populations may harbour extensive within-population variability in carbohydrate content, which may be quantified and exploited using this method. The phenotypic data obtained from genetic mapping populations show that the method is well suited to detailed genetic and physiological analysis.
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Christchurch, New Zealand.
authors.forename: Roopashree
authors.initials: R
authors.lastname: Revanna
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Turnbull
authors.forename: Martin L
authors.initials: ML
authors.lastname: Shaw
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Wright
authors.forename: Ruth C
authors.initials: RC
authors.lastname: Butler
authors.forename: Paula E
authors.initials: PE
authors.lastname: Jameson
authors.forename: John A
authors.initials: JA
authors.lastname: McCallum
mesh_terms: D001947:Breeding; D002874:Chromosome Mapping; D003433:Crosses, Genetic; D019422:Dietary Sucrose / Q000032:analysis*; D057075:Enzyme Assays / Q000379:methods*; D005630:Fructans / Q000032:analysis* / Q000235:genetics; D014644:Genetic Variation; D019697:Onions / Q000737:chemistry* / Q000235:genetics; D010641:Phenotype; D018517:Plant Roots / Q000737:chemistry*; D015203:Reproducibility of Results; D013395:Sucrose / Q000032:analysis; D000520:alpha-Glucosidases / Q000378:metabolism
chemical_list: D019422:Dietary Sucrose; D005630:Fructans; D013395:Sucrose; D000520:alpha-Glucosidases