Question

Name the following:
The layer of the endosperm of maize, rich in protein.

Answer 1

The endosperm plays an important role in embryonic growth by supplying nutrients, protecting the embryo and controlling embryo growth by acting as a mechanical barrier during seed development and germination. The endosperm of maize is basically a large storage organ that constitutes 80–$90\%$ of the mature kernel dry weight.

Complete Answer:
Maize has a larger endosperm with more cytologically identifiable cell types than smaller grain cereals, such as barley, wheat, and rice. Aleurone is a protein found in the protein granules of maturing seeds and tubers. It is one of the two major cell types of the endosperm and is its outermost layer, followed by the inner starchy endosperm. This layer of cells is also referred to as the peripheral endosperm. The aleurone layer lies between the pericarp and the hyaline layer of the endosperm. Unlike the cells of the starchy endosperm, aleurone cells remain alive at maturity. The ploidy of the aleurone is (3n) due to double fertilization. The aleurone layer in maize is single layered. The aleurone tissue contains many protein-storing vacuoles termed as protein bodies. In cereals with starchy endosperm, the aleurone contains about $30\%$ of the kernel's proteins. In multi-coloured maize, anthocyanin pigments in the aleurone layer give the kernels a dark, bluish-black colour.

Note:
In cereals, the aleurone layer releases organic and phosphoric acids to keep the pH of the endosperm between 3.5 and 4. In barley, the aleurone layer releases nitrite into the starchy endosperm and apoplast under anaerobic conditions. In addition (although the function is unclear), a certain class of haemoglobin is present in the outer layer of living cells including the aleurone tissue in barley and rice seeds.