Localization and chemical forms of cadmium in plant samples by combining analytical electron microscopy and X-ray spectromicroscopy
详细信息 查看全文
- 作者：Marie-Pierre Isaure ; Barbara Fayard ; Gé ; raldine Sarret ; Sé ; bastien Pairis ; Jacques Bourguignon
- 关键词：Cadmium ; Plant ; SEM-EDX ; Micro-XRF ; Micro-XANES
- 刊名：Spectrochimica Acta Part B: Atomic Spectroscopy
- 出版年：2006
- 出版时间：December 2006
- 年：2006
- 卷：61
- 期：12
- 页码：1242-1252
- 全文大小：1695 K
文摘
Cadmium (Cd) is a metal of high toxicity for plants. Resolving its distribution and speciation in plants is essential for understanding the mechanisms involved in Cd tolerance, trafficking and accumulation. The model plant Arabidopsis thaliana was exposed to cadmium under controlled conditions. Elemental distributions in the roots and in the leaves were determined using scanning electron microscopy coupled with energy dispersive X-ray microanalysis (SEM-EDX), and synchrotron-based micro X-ray fluorescence (μ-XRF), which offers a better sensitivity. The chemical form(s) of cadmium was investigated using Cd LIII-edge (3538 eV) micro X-ray absorption near edge structure (μ-XANES) spectroscopy. Plant μ-XANES spectra were fitted by linear combination of Cd reference spectra. Biological sample preparation and conditioning is a critical point because of possible artifacts. In this work we compared freeze-dried samples analyzed at ambient temperature and frozen hydrated samples analyzed at −170 °C. Our results suggest that in the roots Cd is localized in vascular bundles, and coordinated to S ligands. In the leaves, trichomes (epidermal hairs) represent the main compartment of Cd accumulation. In these specialized cells, μ-XANES results show that the majority of Cd is bound to O/N ligands likely provided by the cell wall, and a minor fraction could be bound to S-containing ligands. No significant difference in Cd speciation was observed between freeze-dried and frozen hydrated samples. This work illustrates the interest and the sensitivity of Cd LIII-edge XANES spectroscopy, which is applied here for the first time to plant samples. Combining μ-XRF and Cd LIII-edge μ-XANES spectroscopy offers promising tools to study Cd storage and trafficking mechanisms in plants and other biological samples.