title: Speciation and localization of Zn in the hyperaccumulator Sedum alfredii by extended X-ray absorption fine structure and micro-X-ray fluorescence.
abstract: Differences in metal homeostasis among related plant species can give important information of metal hyperaccumulation mechanisms. Speciation and distribution of Zn were investigated in a hyperaccumulating population of Sedum alfredii by using extended X-ray absorption fine structure and micro-synchrotron X-ray fluorescence (μ-XRF), respectively. The hyperaccumulator uses complexation with oxygen donor ligands for Zn storage in leaves and stems, and variations in the Zn speciation was noted in different tissues. The dominant chemical form of Zn in leaves was most probably a complex with malate, the most prevalent organic acid in S. alfredii leaves. In stems, Zn was mainly associated with malate and cell walls, while Zn-citrate and Zn-cell wall complexes dominated in the roots. Two-dimensional μ-XRF images revealed age-dependent differences in Zn localization in S. alfredii stems and leaves. In old leaves of S. alfredii, Zn was high in the midrib, margin regions and the petiole, whereas distribution of Zn was essentially uniform in young leaves. Zinc was preferentially sequestered by cells near vascular bundles in young stems, but was highly localized to vascular bundles and the outer cortex layer of old stems. The results suggest that tissue- and age-dependent variations of Zn speciation and distribution occurred in the hyperaccumulator S. alfredii, with most of the Zn complexed with malate in the leaves, but a shift to cell wall- and citric acid-Zn complexes during transportation and storage in stems and roots. This implies that biotransformation in Zn complexation occurred during transportation and storage processes in the plants of S. alfredii.
authors.affiliation: MOE Key Laboratory of Environment Remediation and Ecological Health, College of Environmental & Resource Science, Zhejiang University, Hangzhou 310058, China. Electronic address: lulingli@zju.edu.cn.
authors.forename: Lingli
authors.initials: L
authors.lastname: Lu
authors.affiliation: MOE Key Laboratory of Environment Remediation and Ecological Health, College of Environmental & Resource Science, Zhejiang University, Hangzhou 310058, China.
authors.forename: Xingcheng
authors.initials: X
authors.lastname: Liao
authors.affiliation: Department of Plant Sciences, University of California, Davis, CA 95616, USA.
authors.forename: John
authors.initials: J
authors.lastname: Labavitch
authors.affiliation: MOE Key Laboratory of Environment Remediation and Ecological Health, College of Environmental & Resource Science, Zhejiang University, Hangzhou 310058, China.
authors.forename: Xiaoe
authors.initials: X
authors.lastname: Yang
authors.affiliation: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
authors.forename: Erik
authors.initials: E
authors.lastname: Nelson
authors.affiliation: Institute of Chemical & Engineering Sciences, Agency for Science, Technology and Research (ASTAR), Jurong Island, Singapore 627833, Singapore.
authors.forename: Yonghua
authors.initials: Y
authors.lastname: Du
authors.affiliation: Department of Plant Sciences, University of California, Davis, CA 95616, USA.
authors.forename: Patrick H
authors.initials: PH
authors.lastname: Brown
authors.affiliation: 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. Electronic address: tiansk@zju.edu.cn.
authors.forename: Shengke
authors.initials: S
authors.lastname: Tian
mesh_terms: D005453:Fluorescence; D031963:Sedum / Q000378:metabolism*; D013052:Spectrometry, X-Ray Emission / Q000379:methods*; D015032:Zinc / Q000378:metabolism*
chemical_list: D015032:Zinc
keywords: Cellular distribution; Hyperaccumulation; Sedum alfredii; Speciation; Zinc