Plant Nitrogen Nutrition and Transport


Nitrogen (N) is a major plant nutrient and is available in soil chiefly as nitrate (NO3), ammonium and amino acids. N is acquired through roots and then transported around the plant or it can be combined with carbon to produce amino acids (assimilation) before being redistributed. Most plant cells can assimilate N and any not required for growth is stored as protein. Reserve N can be accumulated as the photosynthetic enzyme Rubisco and species‐specific storage proteins in vegetative tissue or seed endosperm. Cellular storage of NO3 occurs in the vacuole, where it is important for driving osmotic expansion growth. The amount of these stored forms defines a plant's N status. Some structural materials like lignin contain a high proportion of N, but this is not stored and is not remobilised. Some plants form a symbiotic relationship with bacteria in specialised nodules to enable the direct assimilation of gaseous N.

Key Concepts:

  • Nitrogen supply limits plant growth in almost all natural environments.

  • The soil available form of N depends on factors like soil type, weather and temperature with NO3 dominating temperate climates.

  • Some plants form a specialised symbiosis with bacteria to fix atmospheric N.

  • Agriculture includes the addition of N fertiliser to optimise yield.

  • Regulation of plant carbon and N metabolism is carefully coordinated for normal growth and development.

  • Changes in plant N supply trigger alterations in a huge number of genes resulting in changes in morphology, growth rate and development.

  • A change in the phosphorylation status of some plasma membrane NO3 and ammonium transporter proteins provides a receptor mechanism that links uptake to external availability.

Keywords: amino acids; ammonium uptake; nitrogen assimilation; nitrate uptake; nitrogen use efficiency; nitrogen sensor; root morphology; roots

Figure 1.

An overview of N uptake and assimilation in a generalised plant cell.

Figure 2.

Arabidopsis wild‐type (WS) and atnar2.1–1 mutant growing at different NO3 supplies on soil and in hydroponics. The missing HATS in the atnar2.1–1 plant (right) produces a dwarf phenotype when compared with wild‐type plants (left) grown on an unfertilised soil (a) but the phenotype is less obvious on diluted compost (b) and lost on full nutrient compost (c). The dwarf phenotype of the mutant is seen when plants were grown hydroponically on a full nutrient solution containing 0.5 mM NO3 (d) but not on 6 mM NO3 (e). Four wild‐type plants are shown in image (d) each labelled W. Alternative WT and mutant plants are shown in image (e). All plants were grown for 40d under the same short‐day environmental conditions (see Orsel et al., ). Scale bar of 1 cm is shown. Reproduced from Miller et al. . With permission from Oxford University Press.

Figure 3.

Regulatory control systems in N metabolite sensing and signalling. Alterations in N supply result in huge changes in gene expression that can lead to morphological adaptation. These changes not only directly affect growth (biomass production) including root/shoot ratio, but can also trigger developmental adjustments such as delayed flowering. In the central box some putative sensing mechanisms are shown, but little is known about these signals. Dashed arrows indicate where negative feedback can operate.



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Further Reading

Garnett T, Conn V and Kaiser B (2009) Root based approaches to improving nitrogen use efficiency in plants. Plant Cell and Environment 32: 1272–1283.

Hirel B, Le Gouis J, Ney B and Gallais A (2007) The challenge of improving nitrogen use efficiency in crop plants: towards a more central role for genetic variability and quantitative genetics within integrated approaches. Journal of Experimental Botany 58: 2369–2387.

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Sellick CA and Reece RJ (2005) Eukaryotic transcription factors as direct nutrient sensors. Trends in Biochemical Sciences 30: 405–412.

Tsay YF, Chiu CC, Tsai CB, Ho CH and Hsu PK (2007) Nitrate transporters and peptide transporters. FEBS Letters 581: 2290–2300.

Walch‐Liu P, Ivanov II, Filleur S et al. (2006) Nitrogen regulation of root branching. Annals of Botany 97: 875–881.

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Miller, Anthony J(May 2010) Plant Nitrogen Nutrition and Transport. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0021257]