Chemical forms of calcium in Ca,Zn- and Ca,Cd-containing grains excreted by tobacco trichomes
Chemical forms of calcium in Ca,Zn- and Ca,Cd-containing grains excreted by tobacco trichomes
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烟草毛状体分泌的含钙、锌和钙、镉颗粒中钙的化学形态
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
A. Manceau
中科院分区：
文献类型：
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作者：
G. Sarret;M. Isaure;M. Marcus;E. Harada;Yong‐Eui Choi;S. Pairis;S. Fakra;A. Manceau
烟草（Nicotiana tabacum L.）CV. Xanthi）植物暴露于有毒水平的锌和镉通过它们的叶毛（表皮毛）以含Zn、Ca和Cd、Ca的颗粒的形式排泄金属。这些沉淀物的性质和形成机理目前还不清楚。通过扫描电子显微镜结合能量色散X射线分析（SEM-EDX）、微X射线衍射（µXRD）和钙K边微X射线吸收近边结构（µXANES）光谱，研究了烟草产生的单个颗粒的化学、结晶和非结晶成分。锌主要结合在方解石中，镉主要结合在方解石和球霰石中。文石偶尔出现，似乎不含微量金属。除了以其三种可能的多晶型形式（方解石、文石和球文石）沉淀外，钙还以无定形CaCO 3和某些颗粒中可能的有机Ca的形式形成。最常见的是，一个特定的晶粒由两个或多个结晶和非结晶相组成。所观察到的内和粒间元素和相组成的变化表明，这种生物矿化过程不受生物因素的约束，而是从化学和动力学控制的反应结果。这项研究说明了横向分辨X射线同步辐射技术（µXRD和µXANES）在研究植物生物矿化和金属固定过程中的潜力。
Tobacco (Nicotiana tabacum L. cv. Xanthi) plants exposed to toxic levels of zinc and cadmium excrete met- als through their leaf trichomes (epidermal hairs) as Zn,Ca- and Cd,Ca-containing grains. Little is known about the na- ture 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.