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JXB Advance Access published online on July 5, 2007
Journal of Experimental Botany, doi:10.1093/jxb/erm135
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© The Author [2007]. Published by Oxford University Press [on behalf of the Society for Experimental Biology]. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

RESEARCH PAPER

Ammonium transport and CitAMT1 expression are regulated by light and sucrose in Citrus plants

Gemma Camañes1, Miguel Cerezo1,*, Eduardo Primo-Millo2, Alain Gojon3 and Pilar García-Agustín1,*

1Área de Fisiología Vegetal, Departamento de Ciencias Agrarias y del Medio Natural, Escuela Superior de Tecnología y Ciencias Experimentales, Universitat Jaume I, E-12071 Castellón de la Plana. Spain
2Departamento de Citricultura, Instituto Valenciano de Investigaciones Agrarias, Apartado oficial, E46113 Moncada, Valencia, Spain
3Biochimie et Physiologie Moléculaire des plantes, UMR 5004, Agro-M, CNRS, UM2, Place Viala, F34060 Montpellier, Cedex 1, France

* To whom correspondence should be addressed. E-mail: garciap{at}uji.es or cerezo{at}uji.es

Here the isolation and characterization of CitAMT1 cDNA from citrange Troyer (Citrus sinensis L. OsbeckxPoncirus trifoliata Blanco) is reported, suggesting that this belongs to the AMT gene family, which is involved in the high-affinity transport system (HATS). Results show that in Citrus plants, the HATS is much more dependent on the light conditions and C status of the roots than the low-affinity transport system. Most importantly, a strong correlation was found between the regulation of both HATS activity and CitAMT1 expression. CitAMT1 expression is sucrose-stimulated and may account for the regulation of NH4+ HATS. Furthermore, a similar link was also recorded with photosynthetic activity in the shoots, suggesting that the variations in production and transport of photosynthates to the roots are responsible for the diurnal changes of both CitAMT1 expression and NH4+ HATS activity. On the other hand, results indicate that the effect of stimulating light on CitAMT1 expression and NH4+ HATS activity is independent of the circadian rhythm. Finally, CitAMT1 expression seems to be specifically stimulated by sucrose, suggesting that sucrose is a pivotal signal governing both assimilate partitioning from source organs and assimilate utilization in sink organs.

Key words: AMT, Citrus, HATS, LATS, NH4+ uptake, sucrose

Received 27 February 2007; Revised 23 May 2007 Accepted 23 May 2007


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