title: In low transpiring conditions, uncoupling the BnNrt2.1 and BnNrt1.1 NO 3(-) transporters by glutamate treatment reveals the essential role of BnNRT2.1 for nitrate uptake and the nitrate-signaling cascade during growth.
abstract: In plants, the nitrate transporters, NRT1.1 and NRT2.1, are mainly responsible for nitrate uptake. Intriguingly, both nitrate transporters are located in a complementary manner in different cells layers of the mature root suggesting that their coordination should occur during nitrate uptake and plant growth. This hypothesis was examined on 5-d-old rape seedlings grown on agar medium supplemented with 1 or 5mM nitrate. Seedlings were treated with increasing potassium glutamate concentrations in order to uncouple the two nitrate transporters by inhibiting BnNRT2.1 expression and activity specifically. In both nitrate treatments, increasing the glutamate concentrations from 0.5 to 10mM induced a reduction in (15)NO 3(-) uptake and an inhibition of N assimilation. The decrease in (15)NO 3(-) uptake was caused by downregulation of BnNRT2.1 expression but surprisingly it was not compensated by the upregulation of BnNRT1.1. This created an unprecedented physiological situation where the effects of the nitrate signal on shoot growth were solely modulated by nitrate absorption. In these conditions, the osmotic water flow for volumetric shoot growth was mainly dependent on active nitrate transport and nitrate signaling. This behavior was confirmed by the allometric relationships found between changes in the root length with (15)N and water accumulation in the shoot. These findings demonstrate that the BnNRT2.1 transporter is essential for nitrate uptake and growth, and renew the question of the respective roles of the NRT2.1 and NRT1.1 transporters in nitrate uptake and sensing at the whole plant level.
authors.affiliation: Université Caen; IBFA; UMR INRA 950 EVA; Caen France.
authors.forename: Antonin
authors.initials: A
authors.lastname: Leblanc
authors.affiliation: Université Caen; IBFA; UMR INRA 950 EVA; Caen France.
authors.forename: Raphaël
authors.initials: R
authors.lastname: Segura
authors.affiliation: Université Rennes 1; UMR INRA 1349 IGEPP; Rennes, France.
authors.forename: Carole
authors.initials: C
authors.lastname: Deleu
authors.affiliation: Université Caen; IBFA; UMR INRA 950 EVA; Caen France.
authors.forename: Erwan
authors.initials: E
authors.lastname: Le Deunff
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D029688:Brassica napus / Q000187:drug effects / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D018698:Glutamic Acid / Q000494:pharmacology*; D009566:Nitrates / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D018520:Plant Shoots / Q000187:drug effects / Q000378:metabolism
chemical_list: D009566:Nitrates; D010940:Plant Proteins; D018698:Glutamic Acid
keywords: Brassica napus; NRT2.1 and NRT1.1 nitrate transporters; cell expansion; nitrate signaling; nitrate uptake; organ growth; water uptake