Aluminium toxicity is one of the major factors that limit plant growth and development in many acid soils. Root cells plasma membrane, particularly of the root apex, seems to be a major target of A1 toxicity. However, strong interaction of A13+ , the main A1 toxic form, with oxygen donor ligands (proteins, nucleic acids, polysaccharides) results in the inhibition of cell division, cell extension, and transport. Although the identification of A1 tolerance genes is under way, the mechanism of their expression remains obscure.