Root Development and Nutrient Uptake

Root system formation proceeds in close coordination with shoot growth. Accordingly, root growth and its functions are regulated tightly by the shoot through materials cycling between roots and shoots. A plant root system consists of different kinds of roots that differ in morphology and functions. The spatial configuration and distribution of these roots determine root system architecture in the soil, which in turn primarily regulates the acquisition of soil resources like nutrients and water. Morphological and physiological properties of each root and the concomitant tissues further affect nutrient uptake and transport, while the root traits that are related to such acquisition also depend on the kinds of nutrients and their mobility in the soil. In addition, mechanisms involved in the uptake and transport of mineral nutrients recently have been elucidated at the molecular level. A number of genes for acquisition and transport of various mineral nutrients have been identified in model plant systems such as Arabidopsis thaliana, and rice, and in other plant species. An integration of studies on nutrient behavior in soils and the morphological and physiological functions of root systems will further elucidate the mechanism of plant nutrient uptake and transport by roots, and offer a real possibility of genetically improving crop productivity in problem soils.

     

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。     

Growth Reductions of Rice at Low Root Temperature: Decreases in Nutrient Uptake and Development of Chlorosis

The physiological mechanisms for growth reductions of rice atlow root temperatures were investigated in detail via time coursesin nutrient status of several cultivars. During short-term exposureto low temperature, i.e. between 0–2.5 d with roots at10°C, leaf extension rates were reduced approximately 80%-95%in all cultivars. In contrast, relative growth rates of shootson a dry weight basis were often even greater for plants withroots at 10°C relative to 30°C. During long-term growthat low root temperatures, i.e. between 2.5–10 d, relativegrowth rates of shoots were reduced, chlorosis developed andcultivar differences were observed which were consistent withfield observations of cold-tolerant and cold-intolerant cultivars. The results indicate that decreases in nutrient concentrationsin plants could not account for growth reductions during short-termexposure to low root temperatures. However, it is possible thatthey are responsible for most of the growth reductions and chlorosislater than 2.5 d. The latter suggestion is not proven unequivocallybut is supported by: (i) similar results when plants were transferredto CaSO⁴ solutions at 30°C in terms of growth, nutrientdecreases with time and chlorosi (ii) N and sometimes P concentrationsfalling below critical levels for rice and (iii) lower nutrientuptakes and concentrations, particularly of N, in a cold-intolerantthan a cold-tolerant cultivar. Key words: Root temperature, growth, rice, nutrient uptake     

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.     

Root Morphology and Nitrogen Uptake of Maize Simultaneously Supplied with Ammonium and Nitrate in a Split-root System

We studied the response of maize (Zea mays L. cv. Anjou 256)to a simultaneous, but separated supply of ammonium and nitrate(localized supply, LS). A split-root system was used to supplyhalf of the roots with ammonium and the other half with nitrate.A homogeneously distributed supply of both nitrogen forms (HS)was the control treatment. Seedlings were grown for 12 d fromthe two-leaf to the three-leaf stage in hydroponics at threepH levels (4, 5·5 and 7). The total N concentration was3 mol m^-3. The split-root system was established by removingthe seminal root system and using only four nodal roots perplant. Total root length and root surface area were recordedautomatically with a modified Delta- T area meter. Other morphologicalroot traits (such as main axis length and diameter, number,density, and length of laterals) were recorded manually. Uptakeof ammonium and nitrate was measured by the depletion of thenutrient solution. As compared with LS, HS was superior in shootand root DM, total root length and root surface area, ammoniumand nitrate uptake and shoot nitrogen concentration, irrespectiveof pH level. This indicates that, also under field conditions,mixed ammonium and nitrate fertilization is only beneficialto plant growth if both N forms are evenly distributed in thesoil. At both HS and LS, ascending pH increased the ammonium:nitrateuptake ratio. At LS, declining pH induced a considerable shiftin the distribution of root DM, root length, and root surfacearea the nitrate-fed compartment.Copyright 1993, 1999 AcademicPress Maize, Zea may L., ammonium, nitrate, pH, root morphology, split-root     

Role of Root Hairs and Lateral Roots in Silicon Uptake by Rice

The rice plant (Oryza sativa L. cv Oochikara) is known to be a Si accumulator, but the mechanism responsible for the high uptake of Si by the roots is not well understood. We investigated the role of root hairs and lateral roots in the Si uptake using two mutants of rice, one defective in the formation of root hairs (RH2) and another in that of lateral roots (RM109). Uptake experiments with nutrient solution during both a short term (up to 12 h) and relatively long term (26 d) showed that there was no significant difference in Si uptake between RH2 and the wild type (WT), whereas the Si uptake of RM109 was much less than that of WT. The number of silica bodies formed on the third leaf in RH2 was similar to that in WT, but the number of silica bodies in RM109 was only 40% of that in WT, when grown in soil amended with Si under flooded conditions. There was also no difference in the shoot Si concentration between WT and RH2 when grown in soil under upland conditions. Using a multi-compartment transport box, the Si uptake at the root tip (0-1 cm, without lateral roots and root hairs) was found to be similar in WT, RH2, and RM109. However, the Si uptake in the mature zone (1-4 cm from root tip) was significantly lower in RM109 than in WT, whereas no difference was found in Si uptake between WT and RH2. All these results clearly indicate that lateral roots contribute to the Si uptake in rice plant, whereas root hairs do not. Analysis of F(2) populations between RM109 and WT showed that Si uptake was correlated with the presence of lateral roots and that the gene controlling formation of lateral roots and Si uptake is a dominant gene.     

Root Foraging Increases Performance of the Clonal Plant Potentilla reptans in Heterogeneous Nutrient Environments

Background

Plastic root-foraging responses have been widely recognized as an important strategy for plants to explore heterogeneously distributed resources. However, the benefits and costs of root foraging have received little attention.

Methodology/Principal Findings

In a greenhouse experiment, we grew pairs of connected ramets of 22 genotypes of the stoloniferous plant Potentilla reptans in paired pots, between which the contrast in nutrient availability was set as null, medium and high, but with the total nutrient amount kept the same. We calculated root-foraging intensity of each individual ramet pair as the difference in root mass between paired ramets divided by the total root mass. For each genotype, we then calculated root-foraging ability as the slope of the regression of root-foraging intensity against patch contrast. For all genotypes, root-foraging intensity increased with patch contrast and the total biomass and number of offspring ramets were lowest at high patch contrast. Among genotypes, root-foraging intensity was positively related to production of offspring ramets and biomass in the high patch-contrast treatment, which indicates an evolutionary benefit of root foraging in heterogeneous environments. However, we found no significant evidence that the ability of plastic foraging imposes costs under homogeneous conditions (i.e. when foraging is not needed).

Conclusions/Significance

Our results show that plants of P. reptans adjust their root-foraging intensity according to patch contrast. Moreover, the results show that the root foraging has an evolutionary advantage in heterogeneous environments, while costs of having the ability of plastic root foraging were absent or very small.     

Nitrogen Uptake by Apple Seedlings as Affected by Light, and Nutrient Stress in Part of the Root System

The adaptation of apple seedlings, Pyrus malus L., to localized nutrient stress was studied by measuring nitrogen uptake. Seedlings with split root systems were grown in nutrient solution. Various proportions of the roots were subjected to nutrient stress by placing some of the roots in water. The nitrogen uptake by stressed plants was measured under constant and varied lighting. Under optimum lighting it was found that if part of the root system was deprived of nitrogen, then the remainder partially compensated for this deficiency by increasing its uptake. This adaptation, however, was substantially reduced under low levels of lighting.     

水稻根系研究进展

水稻(Oryza sativa)是我国最重要的粮食作物之一, 在保障国家持续的粮食供给中扮演着重要角色。根系作为水稻生长发育必不可少的器官, 间接地决定着水稻地上部产量、品质、抗逆及广适性等诸多农艺性状的表现。近年来, 随着水稻根系法的不断改进和图位克隆技术的完善及广泛应用, 水稻根系研究也取得了较大进展, 并已成功定位、分离、克隆了一些控制水稻根系的相关基因。该文从水稻根系法、相关性、基因定位、克隆及功能解析等层面综述了国内外水稻根系的研究进展, 并阐述了水稻根系研究存在的问题和今后研究的重点。     

Root Morphology Was Improved in a Late-Stage Vigor Super Rice Cultivar

This study aimed to test the hypothesis that root morphology might be improved and consequently contributing to superior post-heading shoot growth and grain yield in late-stage vigor super rice. A pot experiment was carried out to compare yield attributes, shoot growth and physiological properties and root morphological traits between a late-stage vigor super rice cultivar (Y-liangyou 087) and an elite rice cultivar (Teyou 838). Grain yield and total shoot biomass were 7–9% higher in Y-liangyou 087 than in Teyou 838. Y-liangyou 087 had 60–64% higher post-heading shoot growth rate and biomass production than Teyou 838. Average relative chlorophyll concentration and net photosynthetic rate in flag leaves were 7–11% higher in Y-liangyou 087 than in Teyou 838 during heading to 25 days after heading. Y-liangyou 087 had 41% higher post-heading shoot N uptake but 17–25% lower root biomass and root-shoot ratio at heading and maturity than Teyou 838. Specific root length and length and surface area of fine roots were higher in Y-liangyou 087 than in Teyou 838 at heading and maturity by more than 15%. These results indicated that root-shoot relationships were well balanced during post-heading phase in the late-stage vigor super rice cultivar Y-liangyou 087 by improving root morphology including avoiding a too great root biomass and developing a large fine root system.     

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.     

Effect of Phosphorus Deficiency Stress on Rice Lateral Root Growth and Nutrient Absorption

Six rice (Oryza sativa L.) genotypes with different performances under phosphorus (P) deficiency stress were tested in mixed growth medium of vermiculite and sand under different conditions of P supply to evaluate the effects of P deficiency stress on lateral root growth and the relations between lateral root growth induced by P deficiency and P absorption. The results showed that elongation and development of lateral root were induced by P deficiency. There was significant genotypic variation in lateral root growth in response to P deficiency. A significant positive correlation was observed between the increase of lateral root length per cm of nodal root and the increase of root surface area per cm of nodal root (RSAP), while no significant correlation was observed between the increase of lateral root number per cm of nodal root and the increase of RSAP. The result suggested that the increase of root surface area under P deficiency condition could be mainly attributable to the increase of lateral root length induced. P uptake was significantly positively correlated with the total root surface area and positively correlated with the total lateral root length and the total lateral root number under P deficiency, which implied that elongation and development of lateral root were important to the ability of P uptake from growth medium where P supply was poor. Analysis of soluble sugar content indicated that P deficiency stress changed the distribution of carbohydrate between roots and shoots.     

重金属镉对水稻根毛细胞钾离子吸收过程的影响

重金属镉进入植物体后会引起一系列的毒害反应,然而迄今为止有关镉毒害的机制并不明了。本研究综合使用了膜电势测定、非损伤微测和膜片钳等电生理学实验技术,检测了镉对水稻根毛细胞钾离子吸收过程的影响。研究结果显示,外源施用50μmol·L-1 CdCl2能明显造成水稻根毛细胞膜的去极化,抑制根毛细胞质膜内向K＋通道活性,同时诱导外向K＋通道开放,导致根系内K＋外渗,进而降低了水稻根部K＋含量。通过上述影响,镉扰乱了水稻根系对钾离子的吸收过程,造成钾元素缺失,成为植物体镉毒害作用的机理之一。     

Variability of Relationships between Transpiration, Shoot and Root Metabolism, and Nutrient Uptake in Intact Plants

Reasons are given for rejecting recent criticisms of methodsused in earlier work on relationships between transpirationand the transfer of nutrients to the shoots of intact plants.     

OsCBL1 Modulates Lateral Root Elongation in Rice via Affecting Endogenous Indole-3-Acetic Acid Biosynthesis

<正>Root growth is important for plants to efficiently acquire water and mineral nutrients from soil.Root system architecture(RSA),which is determined mainly by root branching through lateral root formation and root angles,has a significant influence on root growth.Generally,the growth and development of roots are regulated by numerous plant hormones,which respond to external environmental stimulation through com-     

Alterations in Membrane Lipids and Nutrient Uptake during Root Development of Rape-Seed (Brassica napus L.)

Diepenbrock, W. 1988. Alterations in membrane lipids and nutrientuptake during root development of rape-seed (Brassica napusL.). J. exp. Bot. 39: 193–198. Oil-seed rape was grown hydroponically in two experiments. Inthe first one, the effects of root development on phosphorusbound in lipids (lipid-P) and on nutrient uptake were tested.The content of lipid-P in root tissue decreased markedly withtime. This decline was accompanied by reduced rates of nitrogenaccumulation in the shoot. In the second experiment, plantswere grown in a split-root system with two chambers per pot.A part of the root system was harvested at 28 d after seedlingtransfer (DAS) referring to ‘continuous growth’.The other part was cut at 14 DAS and roots from the same chamberwere gathered at 14 d after root cutting (DAR) referring to‘re-growth’ Not only at 14 DAS but also at 14 DARhigh concentrations of lipid-P were detected whereas at 28 DASthe lipid-P content decreased dramatically. Changes in lipid-Pwere reflected in the fluctuation of fatty acid compositionof phosphatidyl choline, a major phospholipid in root tissue.It was clearly demonstrated that during re-growth, nutrientuptake was intensified as compared to continuous growth. Generally,membrane lipids and nutrient uptake were closely related. Key words: Root, lipids, nutrient uptake     

低磷胁迫对水稻苗期侧根生长及养分吸收的影响

用蛭石与石英砂作为混合培养介质研究了低磷胁迫对水稻（Oryza sativa L.)苗期侧根发生发育的影响及其与磷吸收的相关关系。结果表明：低磷对水稻的侧根发生发育具有明显的诱导作用及基因型差异。相关性分析表明：单位侧根长度的增加与单位根表面积的增大极显相关,而单位侧根数量的增多与单位根表面积的增大无显的相关性。表明单位根表面积的增加主要来自于单位侧根的伸长。侧根参数与磷含量的相关性分析表明：低磷条件下,侧根总长度和侧根数量都与植株磷含量存在显的正相关,根系总表面积与磷含量存在极显的正相关。表明在低磷条件下,侧根的发生发育对水稻的磷吸收具有重要的作用。根系和地上部的可溶性糖含量分析表明;低磷胁迫改变了同化物在地上部和根系的分配。生物量测定表明：低磷胁迫显增大了植株的根冠比。