title: Efficient xylem transport and phloem remobilization of Zn in the hyperaccumulator plant species Sedum alfredii.
abstract: Sedum alfredii is one of a few species known to hyperaccumulate zinc (Zn) and cadmium (Cd). Xylem transport and phloem remobilization of Zn in hyperaccumulating (HP) and nonhyperaccumulating (NHP) populations of S. alfredii were compared. Micro-X-ray fluorescence (μ-XRF) images of Zn in the roots of the two S. alfredii populations suggested an efficient xylem loading of Zn in HP S. alfredii, confirmed by the seven-fold higher Zn concentrations detected in the xylem sap collected from HP, when compared with NHP, populations. Zn was predominantly transported as aqueous Zn (> 55.9%), with the remaining proportion (36.7-42.3%) associated with the predominant organic acid, citric acid, in the xylem sap of HP S. alfredii. The stable isotope (68)Zn was used to trace Zn remobilization from mature leaves to new growing leaves for both populations. Remobilization of (68)Zn was seven-fold higher in HP than in NHP S. alfredii. Subsequent analysis by μ-XRF, combined with LA-ICPMS (laser ablation-inductively coupled plasma mass spectrometry), confirmed the enhanced ability of HP S. alfredii to remobilize Zn and to preferentially distribute the metal to mesophyll cells surrounding phloem in the new leaves. The results suggest that Zn hyperaccumulation by HP S. alfredii is largely associated with enhanced xylem transport and phloem remobilization of the metal. To our knowledge, this report is the first to reveal enhanced remobilization of metal by phloem transport in hyperaccumulators.
authors: MOE Key Laboratory of Environment Remediation and Ecological Health, College of Environmental & Resource Science, Zhejiang University, Hangzhou, 310058, China.
authors: Lingli
authors: L
authors: Lu
authors: MOE Key Laboratory of Environment Remediation and Ecological Health, College of Environmental & Resource Science, Zhejiang University, Hangzhou, 310058, China.|Department of Plant Sciences, University of California, Davis, CA, 95616, USA.
authors: Shengke
authors: S
authors: Tian
authors: MOE Key Laboratory of Environment Remediation and Ecological Health, College of Environmental & Resource Science, Zhejiang University, Hangzhou, 310058, China.
authors: Jie
authors: J
authors: Zhang
authors: MOE Key Laboratory of Environment Remediation and Ecological Health, College of Environmental & Resource Science, Zhejiang University, Hangzhou, 310058, China.
authors: Xiaoe
authors: X
authors: Yang
authors: Department of Plant Sciences, University of California, Davis, CA, 95616, USA.
authors: John M
authors: JM
authors: Labavitch
authors: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.
authors: Samuel M
authors: SM
authors: Webb
authors: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, 94025, USA.
authors: Matthew
authors: M
authors: Latimer
authors: Department of Plant Sciences, University of California, Davis, CA, 95616, USA.
authors: Patrick H
authors: PH
authors: Brown
mesh_terms: D001692:Biological Transport; D060146:Ecotype; D013058:Mass Spectrometry / Q000379:methods; D052585:Phloem / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D031963:Sedum / Q000378:metabolism*; D013052:Spectrometry, X-Ray Emission / Q000379:methods; D052584:Xylem / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism / Q000493:pharmacokinetics*; D015033:Zinc Isotopes
chemical_list: D015033:Zinc Isotopes; D015032:Zinc