Structure and Fate of Endosperm
The cells of endosperm are usually thin-walled, large isodiametric and devoid of pits and store large amount of food materials. The starch along with other food substances like oils and proteins are gradually accumulated in these cells. On account of heavy deposition of food materials, the nuclei become disorganised and deformed. In mature dry seeds, the endosperm represents a physiologically inactive tissue. In any plant such endosperm constitutes the edible part of seed fruit (cereals, coconut) and source of commercial oils (castor, coconut). Usually the endosperm is non- chlorophyll. However, in some members of the Amaryllidaceae such as Crinum seed coats as well as fruit wall are absorbed during seed development and the endosperm which becomes exposed to sunlight turns green. In some cases the outermost layer of such naked endosperm becomes suberized and protective in function.
In the Gramineae, one or a few outer layers of the endosperm become highly specialized and constitute the aleurone tissue. To begin with, the cells of these layers are meristematic which contribute thin-walled cells towards inside. These newly-cut cells later become deposited with starch. During maturation of seed, the cells of the outer most peripheral layer lose their meristematic activity, become enlarged and develop thick walls. The seeds become gorged with aleurone grains. Each aleurone grain is surrounded by a single membrane which is closely associated with spherosomes.