The Biochemistry and Molecular Biology of Seed Storage Proteins

Most plants synthesise proteins in their organs of reproduction and propagation, such as seeds of gymnosperms and angiosperms. Storage proteins are usually located in two tissues. In dicotyledonous plants they may be located in the diploid cotyledons (exalbuminous}, in the triploid endosperm (albuminous) or, occasionally, in both tissues. In monocotyledonous cereals they are primarily located in the triploid endosperm tissue. They are deposited in high amounts in the seed, in discrete deposits (protein bodies) and survive desiccation for long periods of time. In most cases, storage proteins lack any other biological activity and simply provide a source of nitrogen, sulphur and carbon skeletons for the developing seedling (Shotwell and Larkins 1989; Shewry 1995 ). From the human point of view, seeds represent the most important plant tissue that is harvested and consumed, consequently, the economic 'importance of seed proteins is considerable. Seed storage proteins form the most important source of dietary proteins for humans as about 70% of the total intake comes directly from this source. In addition, seed proteins provide the major component of the diet of nonruminant farm animals. Although proteins make up a relatively small proportion of the cereal grain (usually 7-15%, compared with up to 40% in legumes), cereals are the dominant world crops in terms of both dry matter production and protein pro-