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- Title
Chemical forms of calcium in Ca,Zn- and Ca,Cd-containing grains excreted by tobacco trichomes.
- Authors
Sarret, Géraldine; Isaure, Marie-Pierre; Marcus, Matthew A.; Harada, Emiko; Yong-Eui Choi; Pairis, Sébastien; Fakra, Sirine; Manceau, Alain
- Abstract
Tobacco (Nicotiana tabacum L. cv. Xanthi) plants exposed to toxic levels of zinc and cadmium excrete metals through their leaf trichomes (epidermal hairs) as Zn,Ca- and Cd,Ca-containing grains. Little is known about the nature and formation mechanism of these precipitates. The chemical, crystalline, and noncrystalline compositions of individual grains produced by tobacco were studied by scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM-EDX), micro-X-ray diffraction (µXRD), and calcium K-edge micro X-ray absorption near edge structure (µXANES) spectroscopy. Zinc is predominantly incorporated in calcite and cadmium in calcite and vaterite. Aragonite, which occurs occasionally, does not seem to contain trace metals. In addition to being precipitated in its three possible polymorphic forms, calcite, aragonite, and vaterite, calcium is also speciated as amorphous CaCO3 and possibly organic Ca in some grains. Most often, a particular grain consists of two or more crystalline and noncrystalline phases. The observed variability of intra- and inter-grain elemental and phase composition suggests that this biomineralization process is not constrained by biological factors but instead results from thermodynamically and kinetically controlled reactions. This study illustrates the potential of laterally resolved X-ray synchrotron radiation techniques (µXRD and µXANES) to study biomineralization and metal immobilization processes in plants.
- Subjects
TOBACCO; ZINC; CADMIUM; TRICHOMES; X-ray diffraction
- Publication
Canadian Journal of Chemistry, 2007, Vol 85, Issue 10, p738
- ISSN
0008-4042
- Publication type
Article
- DOI
10.1139/V07-076