A Multi Compartments Model of Nitrate Metabolism Regulation in Plant Roots

Abstract

A new concept illustrated by a corresponding mathematical model of nitrate metabolism regulation is proposed. The model is based on the root nitrate compartmentation in several functional pools: storage, metabolic and mobile (MobP) intended for translocation to shoots. Data on nitrate uptake, compartmentation, reduction in intact roots and translocation to shoots were obtained on steady state wheat seedlings grown at 25° and 12°C in the root zone. The net uptake, influx/efflux ratio, MobP size and translocation changed depending on the medium temperature. The oscillations of the net uptake rate, nitrate tissue concentration and its temperature modification were revealed. The scheme of regulation is based on the idea that net uptake through nitrate influx/efflux is under the control of the nitrate of MobP which size was dependent on the nitrate translocation into shoots. The mathematical model is represented by a system of ordinary differential equations simplified according to the time hierarchy of reactions. It has a limit cycle at definite values of parameters. The model postulates the mechanism of a positive feed-back regulation of newly absorbed nitrate transfer into translocated pool formed in the root cortex. Theoretical results are verified experimentally.

Combined Allosteric Responses Explain the Bifurcation in Non-Linear Dynamics of 15N Root Fluxes Under Nutritional Steady-State Conditions for Nitrate

“…In addition, the wide range of substrates (K + , Cl - , , peptides, amino acids, auxin, ABA,…) for the NPF6.3 -like transport proteins of the NPF family highlights the variability of their functional capabilities and questions their major importance for ion fluxes and plant growth in response to nitrate ( Wen et al., 2017 ; Wen and Kaiser, 2018 ). In fact, these top-down (from isotherm to transporter) and bottom-up (from transporter to isotherm) approaches are often discordant because molecular physiologists have to cope with emergent functional and morphological behaviors to nitrate that cannot be deduced uniquely by the sum of corresponding sub-systems or gene regulation identified from transcriptomic studies or approaches of system biology ( Gallagher and Appenzeller, 1999 ; Alekhina et al., 2000 ; Ricard, 2006 ; Horaruang et al., 2020 ). Likewise, ion isotherms represent an integrated view of ion uptake which does not reflect the underlying dynamic fluxes of nitrate that depends on ion transporter activity throughout the root symplastic pathway ( Figure 1A ).…”

“…From a dynamic point of view, nitrate uptake cannot be reduced to the mere acquisition by the root’s epidermis ( Alekhina et al, 2000 ; Horaruang et al., 2020 ). Indeed, this represents an over-simplification of the symplastic pathway of root nitrate transport ( Figure 1A ) which also involves the nitrate assimilation and accumulation rates into the vacuole and plasts as well as nitrate loading rate into the xylem ( Scheible et al., 1997 ; Britto and Kronzucker, 2001b ; Britto and Kronzucker, 2003 ; Le Deunff et al., 2016a ).…”