title: Distribution of calcium (Ca) and magnesium (Mg) in the leaves of Brassica rapa under varying exogenous Ca and Mg supply.
abstract: OBJECTIVE
  Leafy vegetable Brassica crops are an important source of dietary calcium (Ca) and magnesium (Mg) and represent potential targets for increasing leaf Ca and Mg concentrations through agronomy or breeding. Although the internal distribution of Ca and Mg within leaves affects the accumulation of these elements, such data are not available for Brassica. The aim of this study was to characterize the internal distribution of Ca and Mg in the leaves of a vegetable Brassica and to determine the effects of altered exogenous Ca and Mg supply on this distribution.
  
  
  METHODS
  Brassica rapa ssp. trilocularis 'R-o-18' was grown at four different Ca:Mg treatments for 21 d in a controlled environment. Concentrations of Ca and Mg were determined in fully expanded leaves using inductively coupled plasma-mass spectrometry (ICP-MS). Internal distributions of Ca and Mg were determined in transverse leaf sections at the base and apex of leaves using energy-dispersive X-ray spectroscopy (EDS) with cryo-scanning electron microscopy (cryo-SEM).
  
  
  RESULTS
  Leaf Ca and Mg concentrations were greatest in palisade and spongy mesophyll cells, respectively, although this was dependent on exogenous supply. Calcium accumulation in palisade mesophyll cells was enhanced slightly under high Mg supply; in contrast, Mg accumulation in spongy mesophyll cells was not affected by Ca supply.
  
  
  CONCLUSIONS
  The results are consistent with Arabidopsis thaliana and other Brassicaceae, providing phenotypic evidence that conserved mechanisms regulate leaf Ca and Mg distribution at a cellular scale. The future study of Arabidopsis gene orthologues in mutants of this reference B. rapa genotype will improve our understanding of Ca and Mg homeostasis in plants and may provide a model-to-crop translation pathway for targeted breeding.
authors.affiliation: Plant and Crop Sciences Division, School of Biosciences, Sutton Bonington Campus, University of Nottingham, Loughborough LE12 5RD, UK.
authors.forename: Juan Jose
authors.initials: JJ
authors.lastname: Rios
authors.forename: Seosamh O
authors.initials: SO
authors.lastname: Lochlainn
authors.forename: Jean
authors.initials: J
authors.lastname: Devonshire
authors.forename: Neil S
authors.initials: NS
authors.lastname: Graham
authors.forename: John P
authors.initials: JP
authors.lastname: Hammond
authors.forename: Graham J
authors.initials: GJ
authors.lastname: King
authors.forename: Philip J
authors.initials: PJ
authors.lastname: White
authors.forename: Smita
authors.initials: S
authors.lastname: Kurup
authors.forename: Martin R
authors.initials: MR
authors.lastname: Broadley
mesh_terms: D001693:Biological Transport, Active / Q000187:drug effects*; D029741:Brassica rapa / Q000187:drug effects* / Q000378:metabolism*; D002118:Calcium / Q000008:administration & dosage / Q000493:pharmacokinetics*; D008274:Magnesium / Q000008:administration & dosage / Q000493:pharmacokinetics*; D018515:Plant Leaves / Q000187:drug effects* / Q000378:metabolism*; D014018:Tissue Distribution; D014675:Vegetables / Q000187:drug effects / Q000378:metabolism
chemical_list: D008274:Magnesium; D002118:Calcium