Ammonium transport and CitAMT1 expression are regulated by N in Citrus plants
2009
Camañes, Gemma | Cerezo, Miguel | Primo-Millo, Eduardo | Gojon, Alain | García-Agustín, Pilar
Citrus seedlings (Citrus sinensis L. Osbeck x Poncirus trifoliata Blanco) were used to describe the effects of different N treatments on the NH₄ ⁺ influx mediated by high- and low-affinity transport systems (HATS and LATS, respectively) and CitAMT1 gene expression. Results show that Citrus plants favor NH₄ ⁺ over NO₃ ⁻ influx mediated by HATS and LATS when both N sources are present in the nutrient solution and Citrus plants display a much higher capacity to take up NH₄ ⁺ than NO₃ ⁻. Furthermore, NH₄ ⁺ exerts a regulatory effect on NH₄ ⁺ HATS activity and CitAMT1 expression, both are down-regulated by high N status of the plant, but specifically stimulated by NH₄ ⁺ and the balance between these two opposite effects depends on the prior nutrition regime of the plant. On the other hand, supply of NO₃ ⁻ inhibits CitAMT1 expression but doesn't affect NH₄ ⁺ HATS activity on the roots. To explain this discrepancy, it is possible that other CitAMT1 transporters, up-regulated by N limitation, but not repressed by NO₃ ⁻ could be involved in the stimulation of NH₄ ⁺ HATS activity under pure NO₃ ⁻ nutrition or CitAMT1 transporter could be regulated at the post-transcriptional level.
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