Characterisation of lead precipitate following uptake by roots of Brassica juncea.
Seedlings of Brassica juncea (L.) Czern. were grown in solution culture for 14 d prior to exposure to Pb₂+ at an activity of 31 microM for 72 h. Electron dense deposits found within the apoplast and symplast were analysed using scanning transmission electron microscopy-energy dispersive spectroscopy (STEM-EDS) to determine the chemical identity of the deposits and potential toxicity resistance mechanisms. Irrespective of the cellular compartment in which they were found, the deposits contained Pb, O, P and Cl. For the extracellular deposits, the average Pb: P : O atomic ratio was 1 : 0.54 : 3.0, which together with the hexagonal crystal system suggests that Pb is present as chloropyromorphite (Pb₅(PO₄)₃Cl). A weak Ca signal was also detected in about half of the spectra, possibly indicating the presence of small concentrations of phosphohedyphane (Pb₃Ca₂(PO₄)₃Cl). The evidence suggests that B. juncea resists Pb toxicity by storing precipitated Pb in the vacuole.
Meyers
Donald E R
DE
Willow Environmental, Palmwoods, Queensland 4555, Australia. donald.meyers@bigpond.com
Kopittke
Peter M
PM
Auchterlonie
Graeme J
GJ
Webb
Richard I
RI
D001692:Biological Transport; D007854:Lead / Q000032:analysis*; D017348:Microscopy, Electron, Scanning Transmission; D008903:Minerals / Q000032:analysis*; D009149:Mustard Plant / Q000737:chemistry / Q000378:metabolism*; D010710:Phosphates / Q000032:analysis*; D018517:Plant Roots / Q000737:chemistry / Q000378:metabolism*; D036226:Seedlings / Q000254:growth & development / Q000378:metabolism; D013052:Spectrometry, X-Ray Emission
D008903:Minerals; D010710:Phosphates; C469846:chloropyromorphite; D007854:Lead