Plant Physiology - Musienko M. M. 2001

Root Nutrition of Plants
Nitrogen Transport and Storage: Amino Acids and Amides in Plants. Seed Proteins

The main transport forms of nitrogen in most plants are asparagine, aspartate, glutamine, glutamate, and Arginine (in woody species). Depending on the plant species, some other forms may also occur. The storage pool of nitrogen in plant stems is often similar in composition to the transport pool, whereas in leaves it differs. Both in nitrogen storage and transport, an important criterion for a storage or transport form is the N:C ratio; the higher this value, the better (for instance, it is 1:2 in asparagine). All storage or transport Amino Acids are metabolically closely linked to ketoglutaric or oxaloacetic acid, whose carbon Skeleton is easily incorporated into or exits from The Tricarboxylic Acid Cycle.

In addition to ketoglutaric acid, which primarily binds ammonia, other keto acids and aldehyde acids also act as ammonia acceptors, yielding so-called primary amino acids. Subsequently, Transamination processes take place with the participation of aminotransferases. In The ROOT System, more than 25 types of nitrogen compounds are synthesized As a result of transamination, amination, and amidation processes.

In green plants, the main nitrogenous fraction is protein nitrogen (80–95%), the share of nucleic acid nitrogen is about 10%, and Amino Acids and amides account for 5% of the total in plant material. In vegetative Organs, it is part of Enzymes, while in seeds, it forms storage Proteins:

Enzymes, structural proteins, and storage proteins have been identified in seeds. In cereal crops, 70% of the grain protein is accounted for by gluten, which is formed by approximately equal amounts of prolamins and glutelins. The remainder of the protein fraction consists of albumins and globulins. These protein fractions differ in their solubility.

It is interesting to note that in barley, the main protein group is globulin. In legume seeds, the albumin and globulin fractions predominate. In many oilseed plants, globulins also constitute the main protein group. Nitrogen is likewise a component of Phospholipids, Coenzymes, chlorophyll, phytohormones, and other essential Organic compounds.