Functions of Endosperm
The tissue of young endosperm is rich in food materials and various growth hormones. It regulates the precise mode of embryo development and nourishes the developing embryo. During seed germination, the reserve food materials stored in mature endosperm are digested and utilized for the growth of the seedling until the later develops chlorophyll and is able to manufacture its own food. In some plants, the seed coat and the fruit wall are consumed by the endosperm, which ultimately becomes exposed to sunlight and develops chlorophyll for photosynthesis. Rarely the outermost layer of such exposed endosperm takes on a protective function. In the absence of endosperm, the embryo usually aborts.
Endosperm development is a characteristic feature of all the families of angiosperms with the exceptions of Podostemaceae and Trapaceae. In the Orchidaceae endosperm degenerates quite early. Endosperm may be used up by the embryo as such the mature seed has no traces of it (exalbuminous seed). In most monocotyledons it persists (albuminous conditions). In the main food plants such as wheat, rice, maize and sorghum it is the starchy endosperm that forms the bulk of the grain. In many legumes the mature seed has food reserves in the cotyledons rather than in the endosperm. In the castor seed endosperm is laden with fatty substances. The cereal endosperm is made of very different tissues at maturity. The outer aleurone layer consists of living cells. The endosperm usually occupies the bulk (87%) of the grain and about 10% of the endosperm dry weight is aleurone. The aleurone layer stores lipid (about 90% of total endosperm lipid) and also contain 20% of protein. During germination, hydrolytic enzymes are produced in the aleurone layer and these are released into starchy endosperm where the reserves are hydrolysed. When the barley grains are soaked in water gibberellins (GA3 and GA1) are released from scutellum of embryo and diffuse into the endosperm.
The largest tissue for this hormone is the aleurone, which responds by breaking down its own protein reserves and by secreting enzymes (mostly hydrolytic) into the starchy endosperm. Some of these enzymes are newly synthesized (e.g. α-amylase) and some are (e.g. β-glucanase) pre-existent probably all cereals except sorghum, have aleurone that responds similarly. Thus endosperm has a very important role in the development of the embryo. In most of inter varietal and interspecific crosses, embryos fail to form because of failure of endosperm formation.