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.
Highlights
Plants require many mineral elements for their growth and development
Extensive research data is available on the genes/proteins associated with nitrogen nutrition of crop plants and their regulation and these data can be used for generating inter plant species/crop variations which have little practical significance for biotechnological interventions as differences are known to exist between plant species which are totally different genetic entities
Though more than 57.5 million tons of nitrogen fertilizer is applied each year for cereals alone, only 33 percent of it is utilized by the plant and the rest is lost
Summary
Plants require many mineral elements for their growth and development. Elements like nitrogen, potassium, calcium, magnesium, phosphorus, and sulphur are required in large quantities (macronutrients), while boron, chlorine, copper, iron, manganese, molybdenum and nickel are required in smaller quantities (micro nutrients) [1] [2]. Soil is the source of mineral nutrients for plants and for crop plants mineral nutrients are supplied in the form of fertilizers to increase the yield. By supplying nitrogen as fertilizers along with genetic improvement of crop plants, green revolution achieved substantial increase in crop productivity [6] [7]. Nitrogen fertilizer application is the major factor responsible for huge increase in yield of crop plants, 2/3rds of the applied nitrogen is not utilized by the plants and is lost in the soil due to leaching, surface run-off, volatilization and de nitrification by microorganisms [9]-[16]. As most crop plants are non-leguminous and depend on soil nitrogen, more production can be achieved if crop plants can be made to utilize the available nitrogen efficiently [23]-[25]. This paper aims at discussing such possibilities taking into consideration the voluminous information generated recently and the genomic revolution that is sweeping crop science
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