The outer layer of living cells of the endosperm of wheat and other cereal species. It is a single layer of cells that during germination synthesizes α‎-amylase and proteases. These enzymes are secreted into the starch-filled endosperm to break down the starch into maltose and glucose, and to hydrolyse proteins into amino acids, making them available for the developing embryo. The embryo secretes gibberellins that diffuse into the aleurone layer, where they trigger the synthesis of the enzymes by switching on their respective genes.