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AOBPreview originally published online on November 16, 2005
Annals of Botany 2006 97(1):121-131; doi:10.1093/aob/mcj007
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© The Author 2005. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Changes in Growth and Nutrient Uptake in Brassica oleracea Exposed to Atmospheric Ammonia

ANA CASTRO, INEKE STULEN, FREEK S. POSTHUMUS and LUIT J. DE KOK*

Laboratory of Plant Physiology, University of Groningen, PO Box 14, 9750 AA Haren, The Netherlands

* For correspondence. E-mail l.j.de.kok{at}rug.nl

Received: 24 June 2005    Returned for revision: 10 August 2005    Accepted: 27 September 2005    Published electronically: 16 November 2005

• Background and Aims Plant shoots form a sink for NH3, and are able to utilize it as a source of N. NH3 was used as a tool to investigate the interaction between foliar N uptake and root N uptake. To what extent NH3 can contribute to the N budget of the plant or can be regarded as a toxin, was investigated in relation to its concentration and the N supply in the root environment.

• Methods Brassica oleracea was exposed to 0, 4 and 8 µL L–1 NH3, with and without nitrate in the nutrient solution. Growth, N compounds, nitrate uptake rate, soluble sugars and cations were measured.

• Key Results In nitrate-sufficient plants, biomass production was not affected at 4 µL L–1 NH3, but was reduced at 8 µL L–1 NH3. In nitrate-deprived plants, shoot biomass was increased at both concentrations, but root biomass decreased at 8 µL L–1 NH3. The measured nitrate uptake rates agreed well with the plant's N requirement for growth. In nitrate-sufficient plants nitrate uptake at 4 and 8 µL L–1 NH3 was reduced by 50 and 66 %, respectively.

• Conclusions The present data do not support the hypothesis that NH3 toxicity is caused by a shortage of sugars or a lack of capacity to detoxify NH3. It is unlikely that amino acids, translocated from the shoot to root, are the signal metabolites involved in the down-regulation of nitrate uptake, since no relationship was found between changes in nitrate uptake and root soluble N content of NH3-exposed plants.

Key words: Atmospheric ammonia, Brassica oleracea, cations, nitrate requirement, nitrate uptake, nutrient, relative growth rate, shoot : root ratio, soluble sugars, sulfate uptake, toxin


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