The Structure and Composition of the Wheat Grain

The wheat grain (caryopsis) is a single seeded fruit in which the embryo and endosperm are surrounded by fused outer layers: the pericarp, testa, and nucellar epidermis (accounting for about 8% of the grain). The embryo and endosperm are derived from a double fertilisation event and are diploid and triploid tissues, respectively. The embryo accounts for about 3% of the mature grain and comprises the embryonic axis, which forms the seeding during germination, and a single cotyledon (modified leaf, called the scutellum), which is a storage tissue. The endosperm accounts for up to 90% of the grain and is differentiated to form two tissues: the central starchy endosperm, which accumulates starch and gluten storage proteins, and a single outer layer of aleurone cells, which are rich in fibre, oil, protein, and minerals. The amounts, structures, and properties of the major groups of components in the mature grain, notably carbohydrates (including starch) and proteins, and their distributions within the mature grain are discussed in detail.