Aluminium-induced changes in the profiles of both organic acids and phenolic substances underlie Al tolerance in Rumex acetosa L.

The common sorrel, Rumex acetosa L. is well adapted to acid mineral soils with high availability of phytotoxic Al species. The mechanisms of Al resistance in this species are not established. Our goal was to assess the possible implications of organic acids and phenolic substances in Al detoxification in roots and shoots of this plant. R. acetosa plants were exposed in nutrient solution (pH 4.3) to a non-growth reducing Al concentration of 50 μM Al for 5 days. Exclusion of Al from root tips was visualized by haematoxylin staining. Tissue Al and Ca concentrations were analysed by ICP ES. Root and shoot concentrations of organic acids and phenolic substances were analysed by HPLC. A time-dependent (model II type) Al exclusion pattern in root tips was observed. Nonetheless, high Al concentrations accumulated in roots (1170 μg/g) and shoots (275 μg/g). Aluminium supply enhanced root citrate concentrations but decreased shoot organic acid levels. Aluminium induced high levels of anthraquinone in roots and of catechol, catechin and rutin in shoots. Aluminium resistance in R. acetosa implies both exclusion of Al from root tips and tolerance to high Al tissue concentrations. Citrate in roots and phenolics in shoots may bind Al in non-toxic form. Anthraquinones, as strong antioxidants, may play a role in a general defence response to the root stress.