14 - Products of nitrate assimilation are deposited in plants as storage proteins

Abstract

Whereas the products of CO2 assimilation are deposited in plants in the form of oligo- and polysaccharides, the amino acids formed as products of nitrate assimilation are stored as proteins. These are mostly special storage proteins, which have no enzymatic activity and are often deposited in the cell within protein bodies. Protein bodies are enclosed by a single membrane and are derived from the endomembrane system of the endoplasmic reticulum and the Golgi apparatus or the vacuoles. In potato tubers, storage proteins are also stored in the vacuole. Storage proteins can be deposited in various plant organs, such as leaves, stems, and roots. They are stored in seeds and tubers, and also in the cambium of tree trunks during winter to enable the rapid formation of leaves during seed germination and sprouting. Storage proteins are located in the endosperm in cereal seeds and in the cotyledons of most of the legume seeds. Whereas in cereals the protein content amounts to 10% to 15% of the dry weight, in some legumes (e.g., soybean) it is as high as 40% to 50%. About 85% of these proteins are storage proteins.