Evaluation of micro-energy dispersive X-ray fluorescence and histochemical tests for aluminium detection in plants from High Altitude Rocky Complexes, Southeast Brazil

The soils developed under High Altitude Rocky Complexes in Brazil are generally of very low chemical fertility, with low base saturation and high exchangeable aluminium concentration. This stressful condition imposes evolutionary pressures that lead to ecological success of plant species that are able to tolerate or accumulate high amounts of aluminium. Several analytical methods are currently available for elemental mapping of biological structures, such as micro-X-ray fluorescence (μ-EDX) and histochemical tests. The aim of this study was to combine μ-EDX analysis and histochemical tests to quantify aluminium in plants from High Altitude Rocky Complexes, identifying the main sites for Al-accumulation. Among the studied species, five showed total Al concentration higher than 1000 mg kg−1. The main Al-hyperaccumulator plants, Lavoisiera pectinata, Lycopodium clavatum and Trembleya parviflora presented positive reactions in the histochemical tests using Chrome Azurol and Aluminon. Strong positive correlations were observed between the total Al concentrations and data obtained by μ-EDX analysis. The μ-EDX analysis is a potential tool to map and quantify Al in hyperaccumulator species, and a valuable technique due to its non-destructive capacity. Histochemical tests can be helpful to indicate the accumulation pattern of samples before they are submitted for further μ-EDX scrutiny

Tools for the discovery of hyperaccumulator plant species and understanding their ecophysiology

Globally the discovery of hyperaccumulator plants has been hindered by systematic screening of plant species, and is highly biased towards Ni hyperaccumulators. This is mainly due to the existence of a reagent paper test that is only specific to nickel (based on dimethylglyoxime) such that more than 400 of the approximately 500 known hyperaccumulators species are for Ni. New technical advances now permit massive screening of herbarium specimens using non-destructive, portable X-Ray Fluorescence Spectroscopy (XRF), an approach that has already led to the discovery of numerous hyperaccumulator species new to science. The elemental distribution in selected hyperaccumulator plant tissues can then be further studied using techniques such as desktop or synchrotron micro-XRF, nuclear microprobe (PIXE), scanning/transmission electron microscopy with energy-dispersive spectroscopy (SEM/TEM-EDS), secondary ion mass spectrometry (SIMS) or laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS). The use of histochemical dyes combined with light microscopy further aids in the identification of anatomical and structural features of the studied plant tissues