Aleurone

Aleurone (from Greek "aleuron", flour) is a protein found in protein granules of maturing seeds and tubers. The term is also used for the outermost cell layer of the seed coat, the aleurone layer.

Aleurone protein

Aleurones can have two different morphological features, homogenous and heterogeneous. The homogenous aleurone consists of similar protein bodies (e.g. "Phaseolus vulgaris") while the heterogeneous aleurone consists of granules of different shapes and types of proteins covered with a membrane (e.g. "Ricinus communis").

Aleurone tissue

The aleurone layer surrounds the endosperm tissue of grass seeds. In the cultivated cereals it is usually single-layered (except in barley). In cereals with starchy endosperm, the aleurone contains about 30% of the kernel's proteins. In multicolored corn, anthocyanin pigments in the aleurone layer give the kernels a dark, bluish-black color.

During seed germination, the plant embryo produces the hormone gibberellin that triggers the aleurone cells to release enzymes for the hydrolysis of starch and storage proteins into the endosperm. The breakdown of the starchy endosperm supplies sugars to drive the growth of roots and the acrospire. This effect is inhibited by the plant hormone abscisic acid, which keeps the seed dormant.

The gibberellin effect on the aleurone is used in brewing, specifically in the production of barley malt where treatment ensures that a batch of barley seeds will germinate evenly.