Upscaling from Rhizosphere to Whole Root System: Modelling the Effects of Phospholipid Surfactants on Water and Nutrient Uptake

While the rhizosphere presents a different chemical, physical and biological environment to bulk soil, most experimental and modelling investigations of plant growth and productivity are based on bulk soil parameters. In this study, water and nutrient acquisition by wheat (Triticum aestivum L.) roots was investigated using rhizosphere- and root-system-scale modelling. The physical and chemical properties of rhizosphere soil could be influenced by phospholipid surfactants in the root mucilage. Two models were compared: a 2-dimensional (2D) Finite Element Method rhizosphere model, and a 3-dimensional (3D) root architecture model, ROOTMAP. ROOTMAP was parameterised to reproduce the results of the detailed 2D model, and was modified to include a rhizosphere soil volume. Lecithin (a phospholipid surfactant) could be exuded into the rhizosphere soil volume, decreasing soil water content and hydraulic conductivity at any given soil water potential, and decreasing phosphate adsorption to soil particles. The rhizosphere-scale modelling (5 × 5 mm² soil area, 10 mm root length, uptake over 12 h) predicted a reduction in water uptake (up to 16% at 30 kPa) and an increase in phosphate uptake (up to 4%) with lecithin exudation into the rhizosphere, but little effect on nitrate uptake, with only a small reduction in dry soil (1.6% at 200 kPa). The 3D root model reproduced the water (y = 1.013x, R² = 0.996), nitrate (y = 1x, R² = 1) and phosphate (y = 0.978x, R² = 0.998) uptake predictions of the rhizosphere model, providing confidence that a whole root system model could reproduce the dynamics simulated by a Finite Element Method rhizosphere model. The 3D root architecture model was then used to scale-up the rhizosphere dynamics, simulating the effect of lecithin exudation on water, nitrate and phosphate acquisition by a wheat root system, growing over 41 d. When applied to growing and responsive roots, lecithin exudation increased P acquisition by up to 13% in nutrient-rich, and 49% in relatively nutrient-poor soil. A comparison of wheat (Triticum aestivum L.) and lupin (Lupinus angustifolius L.) root architectures, suggested an interaction between the P acquisition benefit of rhizosphere lecithin and root architecture, with the more highly-branched wheat root structure acquiring relatively more P in the presence of lecithin than the sparsely-branched lupin root system.     

Ion channels and transporters regulate nutrient absorption in health and disease

Ion channels and transporters are ubiquitously expressed on cell membrane, which involve in a plethora of physiological process such as contraction, neurotransmission, secretion and so on. Ion channels and transporters is of great importance to maintaining membrane potential homeostasis, which is essential to absorption of nutrients in gastrointestinal tract. Most of nutrients are electrogenic and require ion channels and transporters to absorb. This review summarizes the latest research on the role of ion channels and transporters in regulating nutrient uptake such as K+ channels, Ca2+ channels and ion exchangers. Revealing the mechanism of ion channels and transporters associated with nutrient uptake will be helpful to provide new methods to diagnosis and find potential targets for diseases like diabetes, inflammatory bowel diseases, etc. Even though some of study still remain ambiguous and in early stage, we believe that ion channels and transporters will be novel therapeutic targets in the future.     

Supply and demand: Cellular nutrient uptake and exchange in cancer

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General Mechanisms for Solute Transport Across the Tonoplast of Plant Vacuoles: a Patch-Clamp Survey of Ion Channels and Proton Pumps

The electrical properties of the tonoplast from a large variety of plant materials such as mesophyll cells, storage cells, tumor cells, suspension cultured cells, guard cells, coleoptile cells, and liverwort cells have been investigated using the patch-clamp technique. Whole-vacuole recordings were employed to study the dynamics of an ATP-dependent proton pump by directly measuring the electrogenic currents. The addition of Mg-ATP induced an inwardly directed current which depolarized the tonoplast (the vacuole becoming positive inside). Furthermore, voltage-dependent passive ion fluxes were analyzed using whole vacuoles and isolated membrane patches. Whole-vacuolar currents and single-channel currents were induced at hyperpolarizing potentials, whereas currents decreased at positive trans-tonoplast potentials. The electrical properties of the tonoplast of vacuoles from various plant tissues were similar and it was concluded that ion fluxes across the tonoplast follow the same general mechanisms.     

植物根毛的发生、发育及养分吸收

根毛是植物吸收养分的重要器官,认识根毛的发生、发育规律及其与养分吸收的关系,可为植物养分吸收效率的遗传改良提供依据。介绍了植物根毛的形态特性、发生和发育过程及其调控机制,并结合本实验室的工作,讨论了根毛对养分吸收的贡献、根毛受养分有效性的调节及其与其他根系形态构型性状间的关系,阐述了根毛中养分转运等植物营养过程及其生理和分子生物学基础。最后提出了关于根毛研究中的一些问题和研究前景。     

植物根毛的发生、发育及养分吸收

根毛是植物吸收养分的重要器官,认识根毛的发生、发育规律及其与养分吸收的关系,可为植物养分吸收效率的遗传改良提供依据.介绍了植物根毛的形态特性、发生和发育过程及其调控机制,并结合本实验室的工作,讨论了根毛对养分吸收的贡献、根毛受养分有效性的调节及其与其他根系形态构型性状间的关系,阐述了根毛中养分转运等植物营养过程及其生理和分子生物学基础.最后提出了关于根毛研究中的一些问题和研究前景.     

异质养分环境中一年生分蘖草本黍根系的生长特征

为揭示黍（Panicum miliaceum L.)根系对异质养分环境的生长反应,作研究了黍根系从起始斑块向目标斑块水平生长时,时始斑块和目标斑块养分水平根生长的影响,就低养分起始珏块而言,粗根生物量,粗根长度,粗根表面积和细极长度在高养分目标斑块中的分配比例均小于其在低养分目标斑块中的分配比例,而细根长度及其密度,细根表面积指及其密度的变化恰好相反,就高养分起始斑块而言,高养分目标斑块的细根长度,细根长度密度,细根表面积指数和细根表面积密均不于低养分目标斑块,而粗根对目标斑块中养分状的反应不明显。当黍根系从桢的起始斑块进入不同的目标斑块后,目标斑块的养分状况对细根生物量及其分配无影响,而显影响细根长度和表现积,这指示细根是通过长度和表面积可塑性而不是生物量变化响应目标斑块中的养分差异。     

Logistics of water and salt transport through the plant: structure and functioning of the xylem

The xylem is a long‐distance transport system that is unique to higher plants. It evolved into a very sophisticated plumbing system ensuring controlled loading/unloading of ions and water and their effective translocation to the required sinks. The focus of this overview will be the intrinsic inter‐relations between structural and functional features of the xylem. Taken together the xylem is designed to prevent cavitation (entry of air bubbles), induced by negative pressures under transpiration and to repair the cavitated vessels. Half‐bordered pits between xylem parenchyma cells and xylem vessels are on the one hand the gates to the vessels but on the other hand a serious ‘bottle‐neck’ for transport. Hence it becomes evident that special transport systems exist at the interface between the cells and vessels, which allow intensive fluxes of ions and water to and out of the xylem. The molecular identification and biophysical/biochemical characterization of these transporters has just started. Paradigms for the sophisticated mechanism of controlled xylem transport under changing environmental conditions are SKOR, a Shaker‐like channel involved in K⁺‐loading and SOS1, a Na⁺/H⁺ antiporter with a proposed dual function in Na⁺ transport. In view of the importance of plant water relations it is not surprising to find that water channels dominate the gate of access to xylem. Future studies will focus on the mechanism(s) that regulate water channels and ion transporters and on their physiological role in, for example, the repair of embolism. Clearly, progress in this specific field of research will greatly benefit from an integration of molecular and biophysical techniques aimed to understand ‘whole‐plant’ behaviour under the ever‐changing environmental conditions in the daily life of all plants.     

Effect of potassium status on K+ (Rb)+ uptake and transport in sunflower roots

Young sunflower plants ( Helianthus annuus L. cv. Halcón), grown in nutrient solution at two K⁺ levels (0.25 and 2.5 m M ) were used to study the effect of K⁺ content in the root on uptake and transport of K⁺ to the exuding stream of decapitated plants. Roots of plants grown in low K⁺ gave higher exudation flux, higher K⁺ concentration in exudate and higher K⁺ flux than high K⁺ roots. After 6 h of uptake the K⁺ flux in low K⁺ roots was about three times that in high K⁺ roots. When the roots were kept in a nutrient solution in which Rb⁺ replaced K⁺, low K⁺ roots exuded much more Rb⁺ than K⁺ after the first 2 h, whereas high K⁺ roots exuded about similar amounts of K⁺ and Rb⁺. In intact plants grown at three different K⁺ levels (0.1, 1.0 and 10.0 m M ), there was an inverse relationship between the K⁺ level in the nutrient solution and the Rb⁺ accumulated in the roots or transported to the shoot. The results suggest that the transport of ions from xylem parenchyma to stele apoplast may be controlled by ions coming down from the shoot in sieve tubes.     

Root Growth of the Annual Tillering Grass Panicum miliaceum in Heterogeneous Nutrient Environments (in English)

To study growth responses of the roots of Panicum miliaceum L. to heterogeneous supply of nutrients. The authors analyzed the effects of the nutrient levels in both original patches (O) and destination patches (D) on the root growth of P. miliaceum when its roots were allowed to extend from original patch into destination patch. When the nutrient levels in the original patches were low, coarse root biomass ratio (coarse root biomass in the D/total coarse root biomass), coarse root length ratio (coarse root length in the D/total coarse root length), coarse root surface area ratio (coarse root surface area in the D/total coarse root surface area) and fine root length ratio (fine root length in the D/total fine root length) were greater in the destination patches with lower nutrient levels than in the destination patches with higher nutrient levels, while fine root length, fine root length density, fine root surface index, and fine root surface area density were smaller in the former than in the latter. When the nutrient levels in the original patches were high, fine root length, fine root length density, fine root surface area index and fine root surface density were greater in the destination patches with lower nutrient levels than in the destination patches with higher nutrient levels, coarse roots did not respond to the nutrient levels in the destination patches significantly. When the roots extended from the original patches with the same nutrient level into the destination patches with contrasting nutrient levels, fine root biomass and its percentage allocation did not respond to the nutrient levels in the destination patches significantly, whereas both root length and root surface area did. This indicates that the fine roots of P. miliaceum responded to difference in nutrient supply by plasticity in their length and surface area, rather than in their root biomass.     

Effects of Local Nitrogen Supply on Water Uptake of Bean Plants in a Split Root System

To study the effects of local nitrogen supply on water and nutrient absorption, French bean （Phaseolus vulgaris L.） plants were grown in a split root system. Five treatments supplied with different nitrogen forms were compared： homogeneous nitrate （NN） and homogenous ammonium （AA） supply, spatially separated supply of nitrate and ammonium （NA）, half of the root system supplied with N-free nutrient solution, the other half with either nitrate （NO） or ammonium （AO）. The results showed that 10 d after onset of treatments, root dry matter （DM） in the nitratesupplied vessels treated with NA was more than two times higher than that in the ammonium-supplied vessels. Water uptake from the nitrate-supplied vessels treated with NA was 281% higher than under ammonium supply. In treatments NO and AO, the local supply of N resulted in clearly higher root DM, and water uptake from the nitratesupplied vessels was 82% higher than in the -N vessels. However, in AO plants, water uptake from the -N nutrient solution was 129% higher than from the ammonium-supplied vessels. This indicates a compensatory effect, which resulted in almost identical rates of total water uptake of treatments AA and AO, which had comparable shoot DM and leaf area. Ammonium supply reduced potassium and magnesium absorption. Water uptake was positively correlated with N, Mg and K uptake.     

Arabidopsis Lateral Root Development 3 is essential for early phloem development and function, and hence for normal root system development

We have identified a gene, Lateral Root Development 3 (LRD3), that is important for maintaining a balance between primary and lateral root growth. The lrd3 mutant has decreased primary root growth and increased lateral root growth. We determined that the LRD3 gene encodes a LIM-domain protein of unknown function. LRD3 is expressed only in the phloem companion cells, which suggested a role in phloem function. Indeed, while phloem loading and export from the shoot appear to be normal, delivery of phloem to the primary root tip is limited severely in young seedlings. Abnormalities in phloem morphology in these seedlings indicate that LRD3 is essential for correct early phloem development. There is a subsequent spontaneous recovery of normal phloem morphology, which is correlated tightly with increased phloem delivery and growth of the primary root. The LRD3 gene is one of very few genes described to affect phloem development, and the only one that is specific to early phloem development. Continuous growth on auxin also leads to recovery of phloem development and function in lrd3, which demonstrates that auxin plays a key role in early phloem development. The root system architecture and the pattern of phloem allocation in the lrd3 root system suggested that there may be regulated mechanisms for selectively supporting certain lateral roots when the primary root is compromised. Therefore, this study provides new insights into phloem-mediated resource allocation and its effects on plant root system architecture.     

Phosphate transport in plants

Transport of inorganic phosphate (P_i) through plant membranes is mediated by a number of families of transporter proteins. Studies on the topology, function, regulation and sites of expression of the genes that encode the members of these transporter families are enabling roles to be ascribed to each of them. The Pht1 family, of which there are nine members in the Arabidopsis genome, includes proteins involved in the uptake of P_i from the soil solution and the redistribution of P_i within the plant. Members of this family are H₂PO₄ ^–/H⁺ symporters. Most of the genes of the Pht1 family that are expressed in roots are up-regulated in P-stressed plants. Two members of the Pht1 family have been isolated from the cluster roots of white lupin. These same genes are expressed in non-cluster roots. The evidence available to date suggests that there are no major differences between the types of transport systems that cluster roots and non-cluster roots use to acquire P_i. Differences in uptake rates between cluster and non-cluster roots can be ascribed to more high-affinity P_i transporters in the plasma membranes of cluster roots, rather than any difference in the characteristics of the transporters. The efficient acquisition of P_i by cluster roots arises primarily from their capacity to increase the availability of soil P_i immediately adjacent to the rootlets by excretion of carboxylates, protons and phosphatases within the cluster. This paper reviews P_i transport processes, concentrating on those mediated by the Pht1 family of transporters, and attempts to relate those processes involved in P_i acquisition to likely P_i transport processes in cluster roots.     

植物根系向地性感应的分子机理与养分吸收

植物根系向地性是决定根系空间生长趋势的主要因素之一, 对于养分吸收具有重要影响。认识根系向地性感应和根系生长变化的分子机理及其与养分吸收的关系, 可为遗传改良根系性状、提高植物养分吸收效率提供理论依据。本文从重力感应、信号转导和生长素非对称分布等方面总结了植物根系向地性感应的分子机理, 探讨了根系在养分胁迫下(特别是磷胁迫下)向地性变化的生理基础及其与养分吸收(特别是磷吸收)的关系, 最后对根系向地性研究的若干问题进行了展望。     

植物根系向地性感应的分子机理与养分吸收

植物根系向地性是决定根系空间生长趋势的主要因素之一,对于养分吸收具有重要影响.认识根系向地性感应和根系生长变化的分子机理及其与养分吸收的关系,可为遗传改良根系性状、提高植物养分吸收效率提供理论依据.本文从重力感应、信号转导和生长素非对称分布等方面总结了植物根系向地性感应的分子机理,探讨了根系在养分胁迫下(特别是磷胁迫下)向地性变化的生理基础及其与养分吸收(特别是磷吸收)的关系,最后对根系向地性研究的若干问题进行了展望.     

The Effect of Pressurized Gas Transport on Nutrient Uptake During Hypoxia of Alder Roots*

The uptake of nitrate, sulphate, phosphate, and potassium from a nutrient solution by young alder trees (Alnus glutinosa) was reduced during hypoxia. Such a decrease of ion uptake was not observed when the internal oxygen supply of the tree roots was improved by pressurized gas transport. These results demonstrate the beneficial effect of this gas transport phenomenon on the nutrition of trees growing on wet sites characterized by anaerobic soil.