Abstract
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.
Highlights
IntroductionHigh soil acidity increases aluminium avail ability, which, in turn, can affect Al-sensitive plants causing both root growth inhibition and thickening of root epidermis (Ciamporová 2002, Vitorello et al 2005)
The soils of tropical and subtropical regions commonly exhibit acidic properties due to intense leaching, which results in removal of negative soils derived from granitic and gneiss rocky outcrops of the Serra da Mantiqueira are associated with high Al3+ contents (Benites et al 2007).High soil acidity increases aluminium avail ability, which, in turn, can affect Al-sensitive plants causing both root growth inhibition and thickening of root epidermis (Ciamporová 2002, Vitorello et al 2005)
The positive reaction to Chrome Azurol was noted in primary walls, epidermal cells, parenchyma and phloem
Summary
High soil acidity increases aluminium avail ability, which, in turn, can affect Al-sensitive plants causing both root growth inhibition and thickening of root epidermis (Ciamporová 2002, Vitorello et al 2005). Low nutrient availability combined with high aluminium concentrations in soil solution act as an important environmental stress agent (Larcher 2000, Grime 2001). The tolerance to high Al3+ concentrations is an ecological attribute that permits the occupation of a site qualified as inappropriate for Al-sensitive species (Jansen et al 2002a). Hyperaccumulator plants have mechanisms of aluminium resistance, such as synthesis of chelator agents and turnover of roots and leaves which have already reached high levels of aluminium (Cuenca and Herrera 1987, Cuenca and Medina 1990)
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