Le Deunff Erwan, Beauclair Patrick, Lecourt Julien, Deleu Carole, Malagoli Philippe
Normandie Université, UNICAEN, Caen, France.
Institute of Plant Sciences Paris Saclay (IPS2), CNRS, INRA, Université Paris-Sud, Université d'Evry, Université Paris-Saclay, Gif-sur-Yvette, France.
Front Plant Sci. 2020 Aug 28;11:1253. doi: 10.3389/fpls.2020.01253. eCollection 2020.
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 N fluxes among cellular compartments of seedlings in response to a wide range of external 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 uptake rate ( ) was explained by the combined cooperative properties between the (N uptake, storage and assimilation rate) and (N translocation rate) 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 N flux pattern. This bifurcation in the and N fluxes fits better with the increase of expression than nitrate transporter genes, confirming the allosteric property of the 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 and 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 by nitrate. The results seriously challenge the scientific grounds of the concept of high- and low-affinity of nitrate transporters and are therefore discussed in terms of the ecological significance and physiological implications on the basis of recent agronomic, physiological and molecular data of the literature.
关于非平衡态热力学，幼苗是向其环境耗散能量的开放系统。因此，在营养稳态条件下，单一离子外部浓度的变化会引发幼苗代谢和结构/架构的不稳定与重组，这更有利于能量和物质的通量。这种重组被称为分岔，在数学上被描述为非线性动力系统。在本研究中，我们研究了幼苗细胞区室间氮通量的非线性动力学，以响应广泛的外部浓度范围（从0.05到20 mM）：这使得能够确定是否能找到任何稳态和分岔。根系吸收速率（ ）的双相行为是由 （氮吸收、储存和同化速率）和 （氮转运速率）氮通量之间的联合协同特性所解释的，这揭示了在约0.28 mM硝酸盐浓度附近存在一个独特且稳定的稳态。在约0.5 mM外部硝酸盐浓度时该稳态的消失引发了氮通量模式的剧烈分岔。 和 氮通量的这种分岔与 表达的增加比与硝酸盐转运蛋白基因的增加更契合，证实了 转运蛋白的变构特性，正如文献中在低和高硝酸盐浓度之间所报道的那样。此外，在地上部色氨酸浓度（即吲哚 - 3 - 乙酸前体）的变化与 和 氮通量的变化以及根据总游离氨基酸浓度的根/茎比估算的植物氮状态综合参数之间，发现了几个具有统计学意义的幂律方程。这些关系表明吲哚 - 3 - 乙酸是与由硝酸盐诱导的氮和水流通量相关的代谢及结构 - 形态重组的主要生物学参数之一。这些结果严重挑战了硝酸盐转运蛋白高亲和力和低亲和力概念的科学依据，因此基于文献中最近的农艺、生理和分子数据，从生态意义和生理影响方面进行了讨论。
