Nitrogen Nutrition, Its Regulation and Biotechnological Approaches to Improve Crop Productivity

Abstract

Nitrogen is the most important macronutrient needed for plant growth and development. The availability of nitrogen in the soil fluctuates greatly in both time and space. Crop plants, except leguminous plants, depend on supply of nitrogen as fertilizers. Large quantities of nitrogen fertilizers are applied to crop plants, but only 33% of it is utilized by the plant. Plants have developed efficient mechanisms to sense the varying levels of nitrogen forms and uptake them. They also have well developed mechanisms to assimilate the incoming nitrogen immediately or translocate to different parts of the plant wherever it is needed. Maintenance of nitrogen homeostasis is essential to avoid toxicity. Apart from translocation and assimilation, plants have developed different mechanisms, nitrogen efflux; vacuolar nitrogen storage and downward transport of nitrogen from aerial parts to roots, for maintaining nitrogen homeostasis. In crop plants the “grain yield per unit of available nitrogen in the soil” is referred as the nitrogen use efficiency (NUE) for which remobilization of nitrogen, mediated by various transporters plays a crucial role. All these processes are tightly regulated by proteins and microRNA in response to both external and internal nitrogen levels, carbon status of the plant and hormones. As most crop plants are non-leguminous and depend on soil nitrogen, more production could be achieved if crop plants can be made to utilize the available nitrogen efficiently. The recent explosion of research information and the mechanisms behind nitrogen sensing, signaling, transport and utilization enables biotechnological interventions for better nitrogen nutrition of crop plants. This review discusses such possibilities in the context of recent understanding of nitrogen nutrition and the genomic revolution sweeping the crop science.