Al localization in plant roots using EDXA and EELS techniques

Abstract

Aluminum, which is soluble at pH 5.0 is toxic to plants and frequently the most important yield limiting factor of crop production, on acid soils. Moreover, Al has been associated with human mental diseases (e.G. Alzheimer).Phytotoxicity of Al primarily results in adecline of mitotic activity of the root meristem, an evident reduction of root growth and subsequently affects mineral nutrition and water supply. Several authors assume a shifting of Alin to the nucleus and a direct influence on DNA-synthesis to be the reason for this growth reduction. However, Al in nucleus has only been demonstrated after preparations allowing Al to shift during this preparation. Using SEM and microprobe-analysis, it was only possible to demonstrate Al in roots mainly to be absorbed (as Al-phosphate) in cell walls. A quantification in cytoplasma or even a localisation in distinct organelles (e.g. the nucleus) fails due to the low tracability and the in sufficient resolution.Therefore, in addition to EDX-analysis we try to localize Al by using electron spectroscopic imaging (ESI) and electron energy loss spectroscopy (EELS) techniques, which are distinguished by an excellent spatial resolution and a high sensitivity. So element scan be analyzed and localized in small cell compartments. For those observations the plant material has to be fixed, embedded and cutin ultrathin sections. During chemical fixation procedure, however, the membranes lose their semipermeability and substances may be extracted or shifted inside the tissue or the cells. There fore elemental analysis must be done only under special conditions.