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AOBPreview published online on November 16, 2005
Annals of Botany, 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
Received June 24, 2005
Revised August 10, 2005
Accepted September 27, 2005

Article

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

ANA CASTRO 1, INEKE STULEN 1, FREEK S. POSTHUMUS 1, and LUIT J. DE KOK 1 *

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

* To whom correspondence should be addressed.
LUIT J. DE KOK, E-mail: l.j.de.kok{at}rug.nl


  Abstract

• 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.

Keywords: 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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