† Background and Aims: Aluminium is toxic in acid soils because the soluble Al3+ inhibits root growth.Amechanism of Al3+ tolerance discovered in many plant species involves the release of organic anions fromroot apices. The Al3+ - activated release of citrate from the root apices of Al3+ -tolerant genotypes of barley is controlled by a MATE gene named HvAACT1 that encodes a citrate transpor…