Review: Nitrogen assimilation in crop plants and its affecting factors

Mokhele, B., Zhan, X., Yang, G. and Zhang, X. 2012. Review: Nitrogen assimilation in crop plants and its affecting factors. Can. J. Plant Sci. 92: 399-405. In this review we discuss mainly nitrogen assimilation in crop plants and factors affecting the related process. Nitrogen is a major macro-element limiting the growth and development of plants in agriculture. Both organic and inorganic forms of nitrogen are metabolized in plants; nitrate and ammonia in soil are common forms of inorganic nitrogen that can be metabolized in all plants. There are other nitrogen forms, which include amino acids, nitrite and urea, that are metabolized in plants. Metabolism normally starts with reduction of nitrate to nitrite, and the latter further reduces to form ammonium with the presence of relevant enzymes. This reaction occurs more rapidly in leaves in the presence of light. After ammonia is formed, it enters into the biosynthetic pathways of plant cells, such as reductive amination and transpiration, to produce different amino acids. Amino acids in cells take part in the synthesis of protein and other nitrogenous compounds that help in body building. Radiation, gaseous factors, the presence of metals, soil pH and amount of nitrate are some of the environmental factors affecting absorption and reduction of nitrogen in plants. This review presents a comprehensive understanding of the assimilation process by crop plants of nitrogen and recommends that favorable surrounding conditions are the prerequisites for plants to absorb and utilize nitrogen efficiently.