Foster Kylie J, Miklavcic Stanley J
Phenomics and Bioinformatics Research Centre, School of Information Technology and Mathematical Sciences, University of South AustraliaMawson Lakes, SA, Australia.
Front Plant Sci. 2017 Jul 28;8:1326. doi: 10.3389/fpls.2017.01326. eCollection 2017.
In this paper, we present a detailed and comprehensive mathematical model of active and passive ion and water transport in plant roots. Two key features are the explicit consideration of the separate, but interconnected, apoplastic, and symplastic transport pathways for ions and water, and the inclusion of both active and passive ion transport mechanisms. The model is used to investigate the respective roles of the endodermal Casparian strip and suberin lamellae in the salt stress response of plant roots. While it is thought that these barriers influence different transport pathways, it has proven difficult to distinguish their separate functions experimentally. In particular, the specific role of the suberin lamellae has been unclear. A key finding based on our simulations was that the Casparian strip is essential in preventing excessive uptake of Na into the plant via apoplastic bypass, with a barrier efficiency that is reflected by a sharp gradient in the steady-state radial distribution of apoplastic Na across the barrier. Even more significantly, this function cannot be replaced by the action of membrane transporters. The simulations also demonstrated that the positive effect of the Casparian strip of controlling Na uptake, was somewhat offset by its contribution to the osmotic stress component: a more effective barrier increased the detrimental osmotic stress effect. In contrast, the suberin lamellae were found to play a relatively minor, even non-essential, role in the overall response to salt stress, with the presence of the suberin lamellae resulting in only a slight reduction in Na uptake. However, perhaps more significantly, the simulations identified a possible role of suberin lamellae in reducing plant energy requirements by acting as a physical barrier to preventing the passive leakage of Na into endodermal cells. The model results suggest that more and particular experimental attention should be paid to the properties of the Casparian strip when assessing the salt tolerance of different plant varieties and species. Indeed, the Casparian strip appears to be a more promising target for plant breeding and plant genetic engineering efforts than the suberin lamellae for the goal of improving salt tolerance.
在本文中，我们提出了一个详细且全面的植物根系中主动和被动离子及水分运输的数学模型。两个关键特征是明确考虑了离子和水分在质外体和共质体中各自独立但相互关联的运输途径，以及纳入了主动和被动离子运输机制。该模型用于研究内皮层凯氏带和木栓质层在植物根系盐胁迫响应中的各自作用。虽然人们认为这些屏障会影响不同的运输途径，但通过实验区分它们各自的功能却很困难。特别是，木栓质层的具体作用一直不清楚。基于我们模拟的一个关键发现是，凯氏带对于防止通过质外体旁路过度吸收Na进入植物至关重要，其屏障效率由质外体Na在屏障处稳态径向分布的急剧梯度反映出来。更重要的是，这种功能不能被膜转运蛋白的作用所替代。模拟还表明，凯氏带控制Na吸收的积极作用，在一定程度上被其对渗透胁迫成分的贡献所抵消：一个更有效的屏障增加了有害的渗透胁迫效应。相比之下，发现木栓质层在对盐胁迫的整体响应中发挥的作用相对较小，甚至非必需，木栓质层的存在仅导致Na吸收略有减少。然而，也许更重要的是，模拟确定了木栓质层在通过作为防止Na被动泄漏到内皮层细胞的物理屏障来降低植物能量需求方面可能发挥的作用。模型结果表明，在评估不同植物品种和物种的耐盐性时，应更多且特别关注凯氏带的特性。事实上，对于提高耐盐性的目标而言，凯氏带似乎比木栓质层更有希望成为植物育种和植物基因工程努力的目标。
