Physiological and Transcriptomic Aspects of Urea Uptake and Assimilation in Arabidopsis Plants  

Abstract

Urea is the major nitrogen (N) form supplied as fertilizer in agriculture, but it is also an important N metabolite in plants. Urea transport and assimilation were investigated in Arabidopsis (Arabidopsis thaliana). Uptake studies using 15 N-labeled urea demonstrated the capacity of Arabidopsis to absorb urea and that the urea uptake was regulated by the initial N status of the plants. Urea uptake was stimulated by urea but was reduced by the presence of ammonium nitrate in the growth medium. N deficiency in plants did not affect urea uptake. Urea exerted a repressive effect on nitrate influx, whereas urea enhanced ammonium uptake. The use of [ N]urea and [15 N]ammonium tracers allowed us to show that urea and ammonium assimilation pathways were similar. Finally, urea uptake was less efficient than nitrate uptake, and urea grown-plants presented signs of N starvation. We also report the first analysis, to our knowledge, of Arabidopsis gene expression profiling in response to urea. Our transcriptomic approach revealed that nitrate and ammonium transporters were transcriptionally regulated by urea as well as key enzymes of the glutamine synthetase-glutamate synthase pathway. AtDUR3, a high-affinity urea transporter in Arabidopsis, was strongly up-regulated by urea. Moreover, our transcriptomic data suggest that other genes are also involved in urea influx.

Molecular and physiological interactions of urea and nitrate uptake in plants

“…12,37,38 Data reported in Arabidopsis and maize have revealed that the urea acquisition is induced by the presence in the external solution of the substrate itself. 8,39 In particular in maize roots, the high affinity transport system of urea appeared to be inducible by urea itself, retro-regulated and dependent on the external urea concentration and on the duration of root exposure to the N source. 8 Despite this physiological response to urea, transcriptional changes in plants are rather limited in this condition.…”

Nitrogen Uptake by Native and Invasive Temperate Coastal Macrophytes: Importance of Dissolved Organic Nitrogen

“…It is possible that even though 13 C concentrations were not increased significantly in the urea treatment that the urea molecule was assimilated intact. Merigout et al (2008) showed for the plant Arabidopsis that the urea molecule was hydrolyzed in the root tissue by cytosolic ureases into two amino groups and the resulting 13 CO 2 gas would dissipate and therefore be undetectable in the root biomass.…”

Assessing the Metabolic Impact of Nitrogen Availability Using a Compartmentalized Maize Leaf Genome-Scale Model

“…The methylerythritol phosphate pathway and farnesyl diphosphate biosynthesis lead to a reactant required for the production of chlorophyll a from chlorophyllide a (Lange and Ghassemian, 2003). In both of the GS mutant conditions, the flux through chorismate biosynthesis (Tzin and Galili, 2010), Ser biosynthesis (Ho and Saito, 2001), and the urea cycle (Mérigout et al, 2008) must decrease compared with the N + WT condition. Choline biosynthesis (McNeil et al, 2001) is decreased in the N 2 WT condition, increased in the gln1-3 mutant, and decreased in the gln1-4 mutant condition.…”