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

Abstract : 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
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Submitted on : Monday, October 12, 2020 - 5:16:28 PM
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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⟩



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