Cellular Sequestration of Cadmium in the Hyperaccumulator Plant Species Sedum alfredii

• Published in: Plant physiology (Bethesda) 2011-12, Vol.157 (4), p.1914-1925
• Main Authors: Tian, Shengke, Lu, Lingli, Labavitch, John, Yang, Xiaoe, He, Zhenli, Hu, Hening, Sarangi, Ritimukta, Newville, Matt, Commisso, Joel, Brown, Patrick
• Format: Article
• Language: English
• Subjects: Cadmium; Cadmium - analysis; Cadmium - metabolism; Cadmium - pharmacology; Calcium - metabolism; Carboxylic Acids - metabolism; ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS; Epidermis; Fluorescence; Hyperaccumulators; Image Interpretation, Computer-Assisted; Lasers; Leaves; Ligands; Malates - metabolism; Mass Spectrometry - methods; Organic acids; Plant Epidermis - cytology; Plant Epidermis - drug effects; Plant Epidermis - metabolism; Plant Leaves - cytology; Plant Leaves - drug effects; Plant Leaves - metabolism; Plant roots; Plant Roots - cytology; Plant Roots - drug effects; Plant Roots - metabolism; Plant Stems - cytology; Plant Stems - drug effects; Plant Stems - metabolism; Plants; Sedum - cytology; Sedum - drug effects; Sedum - metabolism; Seedlings - cytology; Seedlings - drug effects; Seedlings - metabolism; Spectrometry, X-Ray Emission; Stems; Synchrotrons; Vascular bundles; X-Ray Absorption Spectroscopy
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.111.183947

Spatial imaging of cadmium (Cd) in the hyperaccumulator Sedum alfredii was investigated in vivo by laser ablation inductively coupled plasma mass spectrometry and x-ray microfluorescence imaging. Preferential Cd accumulation in the pith and cortex was observed in stems of the Cd hyperaccumulating ecotype (HE), whereas Cd was restricted to the vascular bundles in its contrasting nonhyperaccumulating ecotype. Cd concentrations of up to 15,000 µg g⁻¹ were measured in the pith cells, which was many fold higher than the concentrations in the stem epidermis and vascular bundles in the HE plants. In the leaves of the HE, Cd was mainly localized to the mesophyll and vascular cells rather than the epidermis. The distribution pattern of Cd in both stems and leaves of the HE was very similar to calcium but not zinc, irrespective of Cd exposure levels. Extended x-ray absorption fine structure spectroscopy analysis showed that Cd in the stems and leaves of the HE was mainly associated with oxygen ligands, and a larger proportion (about 70% in leaves and 47% in stems) of Cd was bound with malic acid, which was the major organic acid in the shoots of the plants. These results indicate that a majority of Cd in HE accumulates in the parenchyma cells, especially in stems, and is likely associated with calcium pathways and bound with organic acid (malate), which is indicative of a critical role of vacuolar sequestration of Cd in the HE S. alfredii.