Phytochelatin synthesis plays a similar role in shoots of the cadmium hyperaccumulator Sedum alfredii as in non‐resistant plants

Phytochelatin (PC) synthesis is considered necessary for Cd tolerance in non‐resistant plants, but roles for PCs in hyper‐accumulating species are currently unknown. In the present study, the relationship between PC synthesis and Cd accumulation was investigated in the Cd hyperaccumulator Sedum alfredii Hance. PCs were most abundant in leaves followed by stems, but hardly detected by the reversed‐phase high‐performance liquid chromatography (HPLC) in roots. Both PC synthesis and Cd accumulation were time‐dependent and a linear correlation between the two was established with about 1:15 PCs : Cd stoichiometry in leaves. PCs were found in the elution fractions, which were responsible for Cd peaks in the anion exchange chromatograph assay. About 5% of the total Cd was detected in these elution fractions as PCs were found. Most Cd was observed in the cell wall and intercellular space of leaf vascular cells. These results suggest that PCs do not detoxify Cd in roots of S. alfredii. However, like in non‐resistant plants, PCs might act as the major intracellular Cd detoxification mechanism in shoots of S. alfredii.     

Arsenate-induced phytochelatins in white lupin: influence of phosphate status

White lupin ( Lupinus albus L.) is adapted to environments of low pH and low available phosphorus through the development of proteoid roots. The high-affinity phosphate/arsenate uptake system is much less sensitive to downregulation by phosphate in white lupin than in other plants. Arsenate is a phosphate analogue and its toxicity to plants is intimately linked to phosphate nutrition. The synthesis of phytochelatins (PCs) has been proposed as a detoxification mechanism for arsenic (As) in plants. The aim of this research was to study PC production by lupin plants in response to As, and the impact of the arsenate–phosphate interaction on PC production. PCs were the most abundant thiols in white lupin under high As exposure, reaching levels higher than in other plants tested. Together, glutathione (GSH) and PCs were able to complex the majority of As in shoots, while an additional PC-independent mechanism might function in roots. P deficiency increased As concentrations in plant tissues, causing an increase in PC accumulation and an increase in the average size of PCs. A direct relationship was observed between PC concentrations and the level of stress caused by As, i.e. the degree of growth inhibition in plants. This study suggests a key role for PCs and GSH in As detoxification by white lupin, especially in shoots. PC analysis may be useful as an early indicator of As exposure and as a tool to assess the degree of As stress of plants, even under P deficiency.     

Subcellular distribution and chemical forms of cadmium in Morus alba L.

Morus alba L. (mulberry) is a perennial woody tree and a species with great potential for Cd phyremediation owing to its large biomass and extensive root system. The mechanisms involved in Cd detoxification were investigated by analyzing the subcellular distribution and chemical forms of Cd in mulberry in the present study. These results indicated that 53.27–70.17% of Cd mulberry accumulated was stored in the root and only about 10% were in the leaves. Lots of the Cd was located in the cell wall of the mulberry root and in soluble fraction of the mulberry leaf. Moreover, in roots, the largest amount of Cd was in the form of undissolved Cd-phosphate. While in mulberry leaves and stems, most of the Cd was extracted by 2% Acetic acid and 0.6 M HCl, representing Cd-phosphate and Cd-oxalate. It could be concluded that the Cd combination with peptides and organo-ligands in vacuole of leaf or complexed with proteins or cellulose in the cell wall of root might be contributed to the tolerance of mulberry to Cd stress. The mulberry could be used to remediate the Cd polluted farmland soils.     

芦苇抗镉污染机理研究

研究了芦苇幼苗体内 Cd的积累、亚细胞微区分布、存在形态和其诱导蛋白以及植物络合素合成抑制剂 (BSO)对芦苇光合作用和生长的影响。在 Cd污染条件下 ,芦苇幼苗植株和根皮层细胞中可积累大量的Cd,但 Cd在芦苇各器官和根皮层细胞亚细胞结构中的分布显著不均 ;Cd在芦苇幼苗体内的分配为 :根 >叶片 >茎 >地下茎 ,在根皮层细胞中的分布为 :细胞间隙 >细胞壁 >液泡 >细胞质。受 Cd污染的芦苇幼苗体内的 Cd以不同化学形态存在 ,其中 Na Cl提取态的 Cd在根和叶片中占的比例均为最大 ,其次为根内的醋酸提取态 ;在叶片中以水提取态为主 ,其它形态的含量相对较低。层析结果表明 ,根和叶片中各存在一种Cd结合蛋白 ,其中根内的 Cd结合蛋白可能是一种植物络合素聚合体。受 Cd诱导 ,芦苇幼苗根中还新合成了一种小分子蛋白或多肽 ,但另有一种蛋白因 Cd影响而消失。此外 ,BSO实验证明了植物络合素对 Cd的解毒作用。可见 ,芦苇的抗 Cd机理与以下几个方面有关 :根部截留 ,细胞间隙积累 ,细胞壁沉淀 ,液泡区域化 ,形成活性较低的难溶化合物 ,形成 Cd结合蛋白     

Comparative analysis of the contribution of phytochelatins to cadmium and arsenic tolerance in soybean and white lupin

The biosynthesis of phytochelatins (PCs) plays a crucial role in the detoxification and homeostasis of heavy metals and metalloids in plants. However, in an increasing number of plant species metal(loid) tolerance is not well correlated with the accumulation of PCs: tolerant ecotypes frequently contain lower levels of PCs than non-tolerant ecotypes. In this study we have compared the responses of soybean (Glycine max L. cv. Resnik) and white lupin (Lupinus albus L. cv. Marta) to cadmium and arsenate in order to assess the role of homophytochelatins (hPCs) in the tolerance of soybean to these toxic elements. Soybean plants treated with Cd and As showed a high contribution of homo-glutathione (hGSH) to the pool of thiols in shoots in comparison to white lupin. Higher levels of hPCs in Cd-treated soybeans compared to PCs in lupins did not prevent growth inhibition. In contrast, the role of hPCs in the detoxification mechanism to arsenate in soybean seems to be clearer, showing higher thiol concentrations and lower growth reductions than those present in lupin plants.     

Subcellular Distribution and Chemical Forms of Cadmium in the Medicine Food Homology Plant <i>Platycodon grandiflorum</i> (Jacq.) A.DC.

Although Platycodon grandiflorum (Jacq.) A.DC. is a renowned medicine food homology plant, reports of excessive cadmium (Cd) levels are common, which affects its safety for clinical use and food consumption. To enable its Cd levels to be regulated or reduced, it is necessary to first elucidate the mechanism of Cd uptake and accumulation in the plant, in addition to its detoxification mechanisms. This present study used inductively couple plasma-mass-spectrometry to analyze the subcellular distribution and chemical forms of Cd in different tissues of P. grandiflorum. The experimental results showed that Cd was mainly accumulated in the roots [predominantly in the cell wall (50.96%–61.42%)], and it was found primarily in hypomobile and hypotoxic forms. The proportion of Cd in the soluble fraction increased after Cd exposure, and the proportion of insoluble phosphate Cd and oxalate Cd increased in roots and leaves, with a higher increase in oxalate Cd. Therefore, it is likely that root retention mechanisms, cell wall deposition, vacuole sequestration, and the formation of low mobility and low toxicity forms are tolerance strategies for Cd detoxification used by P. grandiflorum. The results of this study provide a theoretical grounding for the study of Cd accumulation and detoxification mechanisms in P. grandiflorum, and they can be used as a reference for developing Cd limits and standards for other medicine food homology plants.     

Heavy metals in white lupin: uptake, root-to-shoot transfer and redistribution within the plant

The translocation of manganese (Mn), nickel (Ni), cobalt (Co), zinc (Zn) and cadmium (Cd) in white lupin (Lupinus albus cv. Amiga) was compared considering root-to-shoot transport, and redistribution in the root system and in the shoot, as well as the content at different stages of cluster roots and in other roots. To investigate the redistribution of these heavy metals, lupin plants were labelled via the root for 24 h with radionuclides and subsequently grown hydroponically for several weeks. 54Mn, 63Ni and 65Zn were transported via the xylem to the shoot. 63Ni and 65Zn were redistributed afterwards via the phloem from older to younger leaves, while 54Mn remained in the oldest leaves. A strong retention in the root was observed for 57Co and 109Cd. Cluster roots contained higher concentrations of all heavy metals than noncluster roots. Concentrations were generally higher at the beginning of cluster root development (juvenile and immature stages). Mature cluster roots also contained high levels of 54Mn and 57Co, but only reduced concentrations of 63Ni, 65Zn and 109Cd.     

蒌蒿对镉的富集特征及亚细胞分布特点

以镉(Cd)富集植物蒌蒿(Artemisia selengensis)为试材, 采用超声波细胞破碎处理和超速离心的方法, 对蒌蒿根和叶中亚细胞水平的Cd分布状况进行研究, 同时测定Cd在蒌蒿不同器官中的富集效果。结果表明, 在30 mg·kg^–1Cd胁迫下, 蒌蒿叶片中Cd的富集浓度是根和茎中的2–3倍, 但因叶片所占植株的生物量比例较小, 其对Cd的积累量远小于茎和根; Cd在蒌蒿叶片细胞壁、胞液和细胞器中含量比为16:5:1。细胞壁固定是叶片对Cd的主要防御机制。随着Cd处理浓度的增加, 细胞壁和胞液中的Cd含量大幅上升, 但细胞器中Cd含量仍维持在较低水平。长时间和高浓度的Cd胁迫可使细胞壁解毒机制失活并诱导细胞器中的Cd含量增加, 导致植株死亡。根中液泡的Cd贮存量较大, 解毒效果显著。     

铜、镉胁迫下外源NO介导的番茄解毒途径

一氧化氮(NO)作为信号分子,在抵御重金属胁迫中起重要作用,但对不同离子胁迫下的解毒机制尚缺乏研究.本研究采用营养液培养法,研究了铜(Cu)、镉(Cd)单一或复合胁迫下,番茄幼苗对Cu、Cd的吸收转运特性及对外源NO的响应机制.结果表明: 50 μmol·L^-1的Cu²⁺、Cd²⁺均显著抑制番茄植株的生长,其中Cd胁迫对生长的抑制效应远高于Cu胁迫.Cu、Cd单一或复合胁迫均使番茄根系Cu、Cd含量显著升高,但根系对Cu、Cd吸收存在严格选择性.根细胞对必需元素Cu表现出“奢侈吸收”的现象,而对毒性较强的Cd则吸收相对较少,胞内Cd浓度仅为Cu的1/10左右.外源NO处理可不同程度地缓解Cu、Cd胁迫,其中缓解Cd胁迫的效能更强.番茄对被动进入细胞的Cu、Cd具有相似的解毒机制:一方面,Cu、Cd胁迫诱导细胞质中产生谷胱甘肽(GSH)、植物螯合肽(PCs)和金属硫蛋白(MTs),络合过多的Cu、Cd离子,降低其生物毒性;另一方面,过多的Cu、Cd离子或螯合物被转运至液泡区隔化.外源NO通过调控GSH-GSSG(氧化型谷胱甘肽)氧化还原状态及GSH-PCs代谢方向的改变,促进Cu、Cd离子转运至液泡区隔化来缓解胁迫抑制;NO还可诱导植株叶片或根系表达更多的金属硫蛋白、GSH和PCs,而且上述响应普遍存在叠加效应.这可能是NO介导番茄对Cu、Cd胁迫的另一主要解毒途径.     

Cadmium tolerance in Thlaspi caerulescens: II. Localization of cadmium in Thlaspi caerulescens

Tissue and cellular compartmentation of Cd in roots and leaves of the hyperaccumulator Thlaspi caerulescens was investigated, using energy-dispersive X-ray microanalysis. In roots, Cd was determined in cortex parenchyma cells, endodermis, parenchyma cells of the central cylinder and xylem vessels. In leaves, it was found in cells lying on the way of water migration from the vascular cylinder to epidermal cells, which is in line with passive Cd transport by the transpiration stream. The mechanisms of Cd-detoxification in roots seem to be localized both in apoplast (e.g. binding to cell wall compounds) and inside cells since Cd was accumulated in these two compartments. On the other hand, in leaves Cd was found only in electron-dense deposits inside vacuoles, which suggests that vacuoles are the main compartment of its storage and detoxification in these organs.     

Cadmium hyperaccumulation leads to an increase of glutathione rather than phytochelatins in the cadmium hyperaccumulator Sedum alfredii

Sedum alfredii has been reported to be a cadmium (Cd) hyperaccumulator. Phytochelatins (PCs) and other thiol (SH)-containing compounds have been proposed to play an important role in the detoxification and tolerance of some heavy metals, but it is not clear whether PCs are responsible for Cd hyperaccumulation and tolerance in S. alfredii. In this study, two geographically isolated populations of S. alfredii were studied: one population grew on an old Pb/Zn mine site, while the other on a non-mine site. The mine population of this species exhibited a stronger heavy metal tolerance than in the other population. Root-to-shoot transport of Cd was higher in population located at the mine site than at the non-mine site. Considerable amounts of Cd were accumulated in leaves and stems of mine plants, while most Cd was distributed in roots of non-mine plants. Non-protein SH in plant tissues of two populations were further investigated by a HPLC pre-column derivatization system. Upon exposure to Cd, no PCs were detected in all tissues of mine population, while an appreciable amount of glutathione (GSH) was observed in the descending order of stem>root>leaf. The concentrations of GSH consistently increased with the increase of exogenous Cd concentrations and time. On the contrary, Cd exposure strongly induced the production of PCs (mainly PC(2) and PC(3)) and GSH in plant tissues of non-mine population, and the concentrations of GSH showed an initial drop over the duration of 7-d exposure. The present results provided strong evidence that PCs are not involved in Cd transport, hyperaccumulation and tolerance in mine population of S. alfredii.     

Comparison of cadmium subcellular distribution in different organs of two water spinach (Ipomoea aquatica Forsk.) cultivars

Aims

Mechanisms of low cadmium (Cd) accumulations in cultivars of water spinach are poorly investigated. We aimed to improve understanding of the subcellular biochemical properties of the mechanisms involved.

Methods

A pot experiment was conducted to investigate the subcellular distributions of Cd in lateral and main roots, stems, and young and old leaves of a high-Cd (T308) and a low-Cd cultivar (QLQ).

Results

The ratio of main root:lateral roots Cd concentration in QLQ was lower (0.34–0.35) than that in T308 (0.39–0.55). The ratio of stem:main root Cd concentration in QLQ was much lower (0.60–0.73) than that in T308 (1.19–1.58). QLQ has higher capacity to sequester Cd in cell wall fractions of main and lateral roots than T308.

Conclusions

The difference in shoot Cd concentration between QLQ and T308 is attributable to the difference in Cd translocation from lateral to main roots and from roots to the stem. Fixation of large amounts of Cd in old leaves is beneficial to protect young leaves from Cd toxicity. Cadmium immobilization by the cell wall is important in Cd detoxification, especially in main and lateral roots of QLQ and the shoot of T308.     

Silicon deposition in roots minimizes the cadmium accumulation and oxidative stress in leaves of cowpea plants

Silicon (Si) frequently accumulates in plants tissues, mainly in roots of dicotyledons, such as cowpea. By contrast, Cadmium (Cd) is a metal that is extremely toxic to plant metabolism. This research aims to investigate if the deposition of Si in root can reduce Cd contents and minimize its negative effects on leaves, measuring gas exchange, chlorophyll fluorescence, antioxidant metabolism, photosynthetic pigments and growth, which may explain the possible role of Si in the attenuation of Cd toxicity in cowpea. This study had a factorial design, with all factors completely randomized and two Cd concentrations (0 and 500 µM Cd, termed as – Cd and + Cd, respectively) and three Si concentrations (0, 1.25 and 2.50 mM Si). Si reduced Cd contents in the roots and in other plant organs, such as stems and leaves. The Si contents were highest in roots, followed by stems and leaves, which was explained by the passive absorption of Si. The application of Si promoted increase in both the macro- and micronutrient contents in all tissues, suggesting that Si mitigates the effect of Cd on nutrient uptake. Si attenuated Cd-mediated effects on light absorption of photosystem II (PSII), increasing the effective quantum yield of PSII photochemistry and the electron transport rate. Additionally, toxic effects induced by Cd on gas exchange were mitigated by the action of Si. Plants treated with Cd + Si showed increase in the activities of antioxidant enzymes and reductions in oxidant compounds; these modifications were promoted by Si via detoxification mechanisms. Increases in the photosynthetic pigments and growth of plants treated with Si and exposed to Cd stress were detected and were due to the reduced deterioration of cell membranes and maintenance of chloroplasts, which had positive repercussions on growth and development. This study validated the hypothesis that the accumulation of Si in roots induces benefits on metabolism and alleviates the toxic effects caused by Cd in leaves of cowpea.     

Dynamics of Cadmium Distribution in the Intercellular Space and Inside Cells in Soybean Roots, Stems and Leaves

Soybean (Glycine max L.) plants grown in nutrient solution were exposed to 1 mM Cd(NO₃)₂ for 24 h. Dynamics of distribution of cadmium among its different forms (water soluble, Ca-exchangeable and complexed) in the intercellular space and the ratio of the intercellular and intracellular cadmium in roots, stems and leaves were studied. In roots, in the beginning of treatment the largest portion of Cd was found in the intercellular space and 1 h later Cd content started to decrease, so that between 13- and 24-h treatment an equilibrium was reached in which about 70 % of Cd was found inside cells. In stems, already after 1-h treatment, the Cd concentrations in the cells and intercellular space were similar, the equilibrium being disturbed after 13 h, so that after 24-h treatment 80 % of Cd was found inside cells. In leaves, up to the 13 h Cd distribution showed fluctuation, after that equilibrium was reached, with 70 % of intracellular Cd. The highest contents of all Cd forms in the intercellular space was observed in roots.     

Glutathione and phytochelatin contents in tomato plants exposed to cadmium

The effect of cadmium on growth and contents of glutathione (GSH) and phytochelatins (PCs) were investigated in roots and leaves of tomato plants (Lycopersicon esculentum Mill. cv. 63/5 F1). The accumulation of Cd increased with external Cd concentrations and was considerably higher in roots than in leaves. Dry mass production decreased under Cd treatment especially in leaves. In both roots and leaves, exposure to Cd caused an appreciable decline in GSH contents and increase in PCs synthesis proportional to Cd concentrations in the growth medium. At the same Cd concentration, PCs production was higher in roots than in leaves. The implication of glutathione in PC synthesis was strongly suggested by the use of buthionine sulfoximine (BSO). The major fraction of Cd accumulated by tomato roots was in the form of a Cd-PCs complex.     

CADMIUM AND MANGANESE ACCUMULATION IN PHYTOLACCA AMERICANA L. AND THE ROLES OF NON-PROTEIN THIOLS AND ORGANIC ACIDS

Phytolacca americana L. can accumulate large amounts of heavy metals in its aerial tissues, especially cadmium (Cd) and manganese (Mn). It has great potential for use in phytoextraction of metals from multi-metal-contaminated soils. This study was conducted to further investigate the Cd- and Mn-tolerance strategies of this plant. Concentrations of non-protein thiols (NPTs) and phytochelatins (PCs) in leaves and roots increased significantly as the concentration of Cd in solution increased. The molar ratios of PCs:soluble Cd ranged from 1.8 to 3.6 in roots and 8.1 to 31.6 in leaves, suggesting that the cellular response involving PC synthesis was sufficient to complex Cd ions in the cytosol, especially that of leaves. In contrast, excess Mn treatments did not result in a significant increase in NPT or PC concentrations in leaves or roots. Oxalic acid concentrations in leaves of plants exposed to 2 or 20 mM Mn reached 69.4 to 89.3 mg (0.771 to 0.992 mmol) g^–1 dry weight, respectively, which was approximately 3.7- to 8.6-fold higher than the Mn level in the 0.6 M HCl extract. Thus, oxalic acid may play an important role in the detoxification of Mn.     

Active chitinases in the apoplastic fluids of healthy white lupin (Lupinus albus L.) plants

Acidic exocellular class III chitinase (EC 3.2.1.14) was previously identified in healthy white lupin (Lupinus albus L.) plants and suspension-cultured cells by N-terminal microse-quencing. In this study, the detection of chitinase activity with Remazol Brilliant Violet 5R (RBV)-labelled chitin derivatives is described. Chitinase activity was observed in protein fractions of cytoplasmic or exocellular origin from roots, hypocotyls, cotyledons, and leaves of healthy white lupin plants. Using isoelectrofocusing followed by a new overlay technique with carboxymethyl chitin-RBV conjugate-containing gel, up to six different chitinase isoforms were visualised. Their activity was distributed fairly evenly within a plant with acidic isoforms predominating in cell walls and basic (or neutral) ones found intracellularly. Exocellular location of some chitinase isoforms were also confirmed by detection of their activities in intercellular washing fluids from white lupin tissues. Chitinase activity was demonstrated in culture filtrates and cell walls of suspension-cultured white lupin cells.     

Subcellular distribution and chemical forms of cadmium in Bechmeria nivea (L.) Gaud.

Bechmeria nivea (L.) Gaud. (Ramie) is a promising species for Cd phytoextraction with large biomass and fast growth rate. Nevertheless, little information is available on its tolerance mechanisms towards Cd. Determination of Cd distribution and chemical speciation in ramie is essential for understanding the mechanisms involved in Cd accumulation, transportation and detoxification. In the present study, ramie plants were grown in hydroponics with increasing Cd concentrations (0, 1, 3, 7 mg l^?1). The subcellular distribution and chemical forms of Cd in different tissues were determined after 20 days exposure to this metal. To assess the effect of Cd uptake on plant performance, nitrate reductase activity in leaves and root activity were analyzed during the entire experimental period. Increased Cd level in the medium caused a proportional increase in Cd uptake, and the highest Cd concentration occurred in roots, followed by stems and leaves. Subcellular fractionation of Cd-containing tissues indicated that about 48.2–61.9% of the element was localized in cell walls and 30.2–38.1% in soluble fraction, and the lowest in cellular organelles. Cd taken up by ramie rapidly equilibrated among different chemical forms. Results showed that the greatest amount of Cd was found in the extraction of 1 M NaCl and 2% HAC, and the least in residues in all test tissues. In roots, the subdominant amount of Cd was extracted by d-H₂O and 80% ethanol, followed by 0.6 M HCl. While in stems and leaves, the amount of 0.6 M HCl-extractable Cd was comparable with that extracted by 80% ethanol or d-H₂O. 1 mg l^?1 Cd stimulated nitrate reductase activity in leaves and root activity, while a concentration-dependent inhibitory effect was observed with increasing Cd concentration, particularly at 7 mg l^?1 Cd. It could be suggested that the protective mechanisms evolved by ramie play an important role in Cd detoxification at relatively low Cd concentrations (below 3 mg l^?1 Cd) but become restricted to maintain internal homeostasis with higher Cd stress.     

Effects of Cadmium and Mixed Heavy Metals on Rice Growth in Liaoning,China

Joint effects of Cd and other heavy metals (Pb, Cu, Zn and As) on the growth and development of rice plants and the uptake of these heavy metals by rice were studied using the pot-culture method combined with chemical and statistical analyses. The results showed that the growth and development of rice plants were strongly influenced by the double-element combined pollution. There was an average decrease in the height of rice plants of 4.0–5.0 cm, and grain yield was decreased by 20.0–30.0%, compared with the control. The uptake of Cd by rice plants was promoted due to the interactions between Cd and the other heavy metals added to the soil. The Cd concentration in roots, stems/leaves and seeds increased 31.6–47.7, 16.7–61.5 and 19.6–78.6%, respectively. Due to interactions, uptake of Pb, Cu and Zn by roots and stems/leaves was inhibited, accumulation of Pb, Cu and Zn in seeds was increased, uptake of As by roots was promoted and uptake of As by stems/leaves was inhibited. In particular, the upward transporting ability of the heavy metals absorbed by rice plants was significantly increased.     

Phosphorus acquisition from soil by white lupin (Lupinus albus L.) and soybean (Glycine max L.), species with contrasting root development

White lupin and soybean have contrasting root morphologies: white lupin develops proteoid or cluster roots, roots with discreet clusters of short, determinate branch roots (rootlets) while soybean develops a more fibrous root system with evenly distributed, longer branch roots. Growth and P acquisition by white lupin and soybean were compared in a soil high in bound, total P, with or without additional inorganic P applied in solution. Additional P increased biomass by 25% and doubled total P in soybean. In contrast, white lupin did not respond to additional P in biomass or total P. However added P decreased cluster development on proteoid roots indicating that white lupin sensed the added P. The reduction in cluster weight per plant was exactly countered by an increase in dry weight of other roots. Soybean root development responded to P application, proliferating branch roots with active meristems in the upper portion of the soil profile where P was applied, and reducing root weight to plant weight by 13%. White lupin did not proliferate roots in response to P application. When P was not added to soil, soybean and lupin acquired similar P per unit root dry weight. However, white lupin accumulated 4.8 times more P per unit root length, suggesting that P acquisition in these plants involved other mechanisms such as the exudation of P solubilizing compounds. Soybean accessed P by developing more root length thus colonising more soil volume than white lupin and, therefore, was better able to take advantage of the added P. Pericycle and root tip meristem activities were critical to the differences in root development between white lupin and soybean, and therefore their responses to plant and soil P.