Nitrate assimilation: cross talk between plants and soil

Plants can acquire most of their nutrients from air, water, or soil for their growth and development. The availability of nitrogen and phosphorus is the most important limiting factor. Nitrogen can be obtained in several forms from the soil, primarily nitrate and ammonium. However most of the plants prefer nitrate as a source of nitrogen and they acquire it through a sophisticated nitrate transport system. The nitrate transporters are classified on the basis of their affinity toward nitrate as either high-affinity and low-affinity, and also on the basis of gene expression, constitutive and inducible. These nitrate transporters are regulated by various factors like concentration of nitrate in the soil, pH, energy, etc. Signaling molecules in the roots play a crucial role in maintaining the supply of nitrate to plants from soil. Nitrate can be stored in the root vacuoles, converted to ammonia or transported to leaves for further assimilation. Nitrate reductase and nitrite reductase enzymes are responsible for facilitating the conversion of nitrate to ammonia. NR is one of the most studied and highly regulated enzymes in plants. This book chapter deals with the recent advances in our understanding of nitrate uptake and the assimilation process by plants. The role of various signaling pathways in the communication between roots and soils will also be discussed in the chapter.