Combined allosteric responses explain the bifurcation in non-linear dynamics of 15 N root fluxes under nutritional steady-state conditions for nitrate

Erwan Le Deunff (1) , Patrick Beauclair (2) , Julien Lecourt (3) , Carole Deleu (4) , Philippe Malagoli (5)

1 IPS2 (UMR_9213 / UMR_1403) - Institut des Sciences des Plantes de Paris-Saclay
2 FERLUS - Fourrages, ruminants et environnement
3 NIAB EMR
4 IGEPP - Institut de Génétique, Environnement et Protection des Plantes
5 PIAF - Laboratoire de Physique et Physiologie Intégratives de l’Arbre en environnement Fluctuant

With regard to thermodynamics out of equilibrium, seedlings are open systems that dissipate energy towards their environment. Accordingly, under nutritional steady-state conditions, changes in external concentrations of one single ion provokes instability and reorganization in the metabolic and structure/architecture of the seedling that is more favorable to the fluxes of energy and matter. This reorganization is called a bifurcation and is described in mathematics as a non-linear dynamic system. In this study, we investigate the non-linear dynamics of 15 N fluxes among cellular compartments of B. napus seedlings in response to a wide range of external 15 NO − 3 concentrations (from 0.05 to 20 mM): this allows to determine whether any stationary states and bifurcations could be found. The biphasic behavior of the root 15 NO − 3 uptake rate (v in) was explained by the combined cooperative properties between the v app (N uptake, storage and assimilation rate) and v out (N translocation rate) 15 N fluxes that revealed a unique and stable stationary state around 0.28 mM nitrate. The disappearance of this stationary state around 0.5 mM external nitrate concentrations provokes a dramatic bifurcation in 15 N flux pattern. This bifurcation in the v in and v out 15 N fluxes fits better with the increase of BnNPF6.3/NRT1.1 expression than BnNRT2.1 nitrate transporter genes, confirming the allosteric property of the BnNPF6/ NRT1.1 transporter, as reported in the literature between low and high nitrate concentrations. Moreover, several statistically significant power-law equations were found between variations in the shoots tryptophan concentrations (i.e., IAA precursor) with changes in the v app and v out 15 N fluxes as well as a synthetic parameter of plant N status estimated from the root/shoot ratio of total free amino acids concentrations. These relationships designate IAA as one of the major biological parameters related to metabolic and structural-morphological reorganization coupled with the N and water fluxes induced

Keywords: ion transport kinetics; nitrate uptake; N translocation; analysis of non linear dynamic systems; irreversible thermodynamics

Domains: Vegetal Biology

Erwan Le Deunff, Patrick Beauclair, Julien Lecourt, Carole Deleu, Philippe Malagoli. Combined allosteric responses explain the bifurcation in non-linear dynamics of 15 N root fluxes under nutritional steady-state conditions for nitrate. Frontiers in Plant Science, 2020, 11, ⟨10.3389/fpls.2020.01253⟩. ⟨hal-02964841⟩