Nitrogen Storage in Crops: Case Study of Zeins in Maize

Crop grains accumulate significant amounts of nitrogen in the form of storage proteins. Grain storage proteins are not only important in the aspects of germination but also, storage proteins are a valuable food source in human and animal nutrition. This chapter will give insight into genotype and growing conditions influencing the quantity and quality of storage proteins, primarily maize storage proteins the leading cereal by world production. Main storage proteins in cereals are prolamins, and in maize prolamins are called zeins located within the endosperm in protein agglomerations called protein bodies. Four main classes of zein proteins are: alpha, beta, gamma and delta zein. Each of four zein classes has a distinctive position and role within protein bodies. Prolamin proteins define nutritional value of maize grain not only via amino acid quality but also via starch availability. Starch, the most important energy component of maize grain, is located within starch-protein matrix. Within this matrix, starch granules are surrounded by protein bodies that limit starch availability. In this chapter, we will describe how zein proteins influence characteristics of maize grain and nutritional value of maize.