Isaure M-P, Fraysse A, Devès G, Le Lay P, Fayard B, Susini J, Bourguignon J, Ortega R
CEA, DRT, LITEN, section d'application des traceurs, CEA-Grenoble, 17, rue des Martyrs, 38054 Grenoble, cedex 09, France.
Biochimie. 2006 Nov;88(11):1583-90. doi: 10.1016/j.biochi.2006.08.006. Epub 2006 Sep 7.
Cesium as an alkali element exhibits a chemical reactivity similar to that of potassium, an essential element for plants. It has been suggested that Cs phytotoxicity might be due either to its competition with potassium to enter the plant, resulting in K starvation, or to its intracellular competition with K binding sites in cells. Such elemental interactions can be evidenced by chemical imaging, which determines the elemental distributions. In this study, the model plant Arabidopsis thaliana was exposed to 1 mM cesium in the presence (20 mM) or not of potassium. The quantitative imaging of Cs and endogenous elements (P, S, Cl, K, Ca, Mn, Fe, and Zn) was carried out using ion beam micro-chemical imaging with 5 microm spatial resolution. Chemical imaging was also evidenced by microfocused synchrotron-based X-ray fluorescence (microXRF) which presents a better lateral resolution (<1 microm) but is not quantitative. Cesium distribution was similar to potassium which suggests that Cs can compete with K binding sites in cells. Cesium and potassium were mainly concentrated in the vascular system of stems and leaves. Cs was also found in lower concentration in leaves mesophyll/epidermis. This late representing the larger proportion in mass, mesophyll/epidermis can be considered as the major storage site for cesium in A. thaliana. Trichomes were not found to accumulate cesium. Interestingly, increased Mn, Fe, and Zn concentrations were observed in leaves at high chlorosis. Mn and Fe increased more in the mesophyll than in veins, whereas zinc increased more in veins than in the mesophyll suggesting a tissue specific interaction of Cs with these trace elements homeostasis. This study illustrates the sensitivity of ion beam microprobe and microfocused synchrotron-based X-ray fluorescence to investigate concentrations and distributions of major and trace elements in plants. It also shows the suitability of these analytical imaging techniques to complement biochemical investigations of metallic stress in plants.
铯作为一种碱金属元素，其化学反应性与钾相似，而钾是植物必需的元素。有人认为，铯对植物的毒性可能是由于它与钾竞争进入植物体内，导致钾缺乏，或者是它在细胞内与钾结合位点竞争。这种元素间的相互作用可以通过化学成像来证明，化学成像可确定元素分布。在本研究中，模式植物拟南芥在有（20 mM）或无钾的情况下暴露于1 mM铯中。使用具有5微米空间分辨率的离子束微化学成像对铯和内源元素（磷、硫、氯、钾、钙、锰、铁和锌）进行定量成像。基于微聚焦同步加速器的X射线荧光（microXRF）也证明了化学成像，其横向分辨率更好（<1微米）但不具有定量性。铯的分布与钾相似，这表明铯可以与细胞内的钾结合位点竞争。铯和钾主要集中在茎和叶的维管系统中。在叶肉/表皮中也发现铯的浓度较低。叶肉/表皮占质量的比例较大，可以被认为是拟南芥中铯的主要储存部位。未发现毛状体积累铯。有趣的是，在高度黄化的叶片中观察到锰、铁和锌的浓度增加。锰和铁在叶肉中的增加比在叶脉中更多，而锌在叶脉中的增加比在叶肉中更多，这表明铯与这些微量元素稳态存在组织特异性相互作用。本研究说明了离子束微探针和基于微聚焦同步加速器的X射线荧光在研究植物中大量元素和微量元素的浓度及分布方面的敏感性。它还表明了这些分析成像技术适用于补充植物金属胁迫的生化研究。
