ABSTRACT
Nitrogen is an essential nutrient in plant growth. The main constituent of chlorophyll, it is the most central pigment required for photosynthesis process in the plants, in addition to amino acids, the fundamental building blocks of proteins. Even though it comprises 78% of atmospheric gases, molecular nitrogen (N2) is metabolically not useful directly to plants. To be so, N2 should be initially reduced to ammonium or nitrate through the chemical fixation of nitrogen. Alternatively, atmospheric N2 is reduced to ammonium by microbial nitrogenase enzyme through a process known as biological nitrogen fixation (BNF). In this chapter we focus on: (i) the importance of biological nitrogen fixation; (ii) symbiotic nitrogen fixation in cereals; (iii) the association of diazotrophs with non-leguminous plants; and (iv) engineering symbiotic nitrogen fixation in cereals.
