Availability of cadmium and zinc accumulated in the leaves of Thlaspi caerulescens incorporated into soil

When grown on contaminated soil, hyperaccumulator plants contain high concentrations of metals which may return to the soil after senescence. This work was undertaken to assess the availability of Cd and Zn associated to the leaves of the hyperaccumulator Thlaspi caerulescens after incorporation into an uncontaminated soil. A Zn- and Cd- accumulator population of T. caerulescens was grown on a Cd- and Zn- contaminated soil previously labelled with ¹⁰⁹Cd. Leaves (TCL) were harvested, dried, ground and incorporated into the soil at a rate of 2.07 mg Cd kg⁻¹ and 51.9 mg Zn kg⁻¹. Then a pot experiment was conducted for 3 months with rye grass (Lolium perenne) and T. caerulescens. Rye grass was harvested monthly and T. caerulescens at the end of the experiment. Plant biomass was measured, along with the concentration of Cd, Zn and ¹⁰⁹Cd. Results showed that water-extractable metals in TCL were 69% for Zn and 33% for Cd. Addition of TCL to soil, depleted growth of rye grass, and improved that of T. caerulescens. At harvest, concentrations of both metals were increased in plants by TCL. Concentrations of Cd in rye grass increased with the cut number, while that of Zn decreased slightly. Rye grass extracted 1.6% of the total Cd and 0.9% of the total Zn, and T. caerulescens extracted up to 22.4% of the Cd and 7% of the Zn. About 94% of the Cd in rye grass and 86% in T. caerulescens was derived from TCL. In conclusion, metals associated with leaves of the hyperaccumulator T. caerulescens were very mobile after incorporation into the soil. This revised version was published online in June 2006 with corrections to the Cover Date.     

Subcellular localisation of Cd and Zn in the leaves of a Cd-hyperaccumulating ecotype of<Emphasis Type="Italic"> Thlaspi caerulescens</Emphasis>

Thlaspi caerulescens (Ganges ecotype) is able to accumulate large concentrations of cadmium (Cd) and zinc (Zn) in the leaves without showing any toxicity, suggesting a strong internal detoxification. The distribution of Cd and Zn in the leaves was investigated in the present study. Although the Cd and Zn concentrations in the epidermal tissues were 2-fold higher than those of mesophyll tissues, 65–70% of total leaf Cd and Zn were distributed in the mesophyll tissues, suggesting that mesophyll is a major storage site of the two metals in the leaves. To examine the subcellular localisation of Cd and Zn in mesophyll tissues, protoplasts and vacuoles were isolated from plants exposed to 50 M Cd and Zn hydroponically. Pure protoplasts and vacuoles were obtained based on light-microscopic observation and the activities of marker enzymes of cytosol and vacuoles. Of the total Cd and Zn in the mesophyll tissues, 91% and 77%, respectively, were present in the protoplast, and all Cd and 91% Zn in the protoplast were localised in the vacuoles. Furthermore, about 70% and 86% of total Cd and Zn, respectively, in the leaves were extracted in the cell sap, suggesting that most Cd and Zn in the leaves is present in soluble form. These results indicate that internal detoxification of Cd and Zn in Thlaspi caerulescens leaves is achieved by vacuolar compartmentalisation.     

Effects of land irrigation with partially-treated wastewater on Frankia survival and infectivity

Phytoextraction of Cd by some populations of Thlaspi caerulescens which have the ability to co-hyperaccumulate Cd and Zn requires information about the distribution of both metals within the plant at the organ-level. This work was conducted to determine whether the distribution and solubility of Cd and Zn in Thlaspi caerulescens are affected by the age of plant and organ, and whether Cd and Zn have a common distribution in the plant in soils contaminated by both metals. A series of pot experiments were conducted where a Cd- and Zn-hyperaccumulating population was grown on soils contaminated by Cd and Zn. Temporal changes in metal concentration of roots and of shoots was recorded, along with the water and CaCl₂ solubility of metals in the plant organs. Also, leaves were grouped according to their age and their respective content of Cd and Zn was measured. Both metals were present at higher concentrations in leaves than in roots. The whole-plant content of Zn decreased with time while that of Cd increased or remained unchanged. At harvest, young leaves exhibited higher Cd concentration than older, but the reverse was true for Zn. Both metals were more soluble in dry leaves and senescent leaves than in fresh material, and Zn was more water-soluble than Cd. In conclusion, the distribution of Cd and Zn in the hyperaccumulator T. caerulescensvaried according to the organ and plant age, and Cd and Zn were shown to have a different distribution within the plant.     

Physiological responses to Cd and Zn in two Cd/Zn hyperaccumulating Thlaspi species

In a model hyperaccumulation study a Cd/Zn hyperaccumulator Thlaspi caerulescens accession Ganges and a recently reported Cd/Zn hyperaccumulator Thlaspi praecox grown in increasing Cd and Zn concentrations in the substrate and in field collected polluted soil were compared. Plant biomass, concentrations of Cd and Zn, total chlorophylls and anthocyanins, antioxidative stress parameters and activities of selected antioxidative enzymes were compared. Increasing Cd, but not Zn in the substrate resulted in the increase of biomass of roots and shoots of T. praecox and T. caerulescens. The two species hyperaccumulated Cd in the shoots to a similar extent, whereas T. caerulescens accumulated more Zn in the shoots than T. praecox. Cadmium amendment decreased total chlorophyll concentration and glutathione reductase activity, and increased non-protein thiols concentration only in T. praecox, suggesting that it is less tolerant to Cd than T. caerulescens. In the field-contaminated soil, T. caerulescens accumulated higher Cd concentrations; but as T. praecox produced higher biomass, both species have similar ability to extract Cd.     

Assessing the potential for zinc and cadmium phytoremediation with the hyperaccumulator Thlaspi caerulescens

Thlaspi caerulescens is a Zn and Cd hyperaccumulator, and has been tested for its phytoremediation potential. In this paper we examine the relationships between the concentrations of Zn and Cd in soil and in T. caerulescens shoots, and calculate the rates of Zn and Cd extraction from soil. Using published data from field surveys, field and pot experiments, we show that the concentrations of Zn and Cd in the shoots correlate with the concentrations of Zn and Cd in soils in a log-linear fashion over three orders of magnitude. There is little systematic difference between different populations of T. caerulescens in the relationship between soil and plant Zn concentrations. In contrast, populations from southern France are far superior to those from other regions in Cd accumulation. Bioaccumulation factors (plant to soil concentration ratio) for Zn and Cd decrease log-linearly with soil metal concentration. Model calculations show that phytoremediation using T. caerulescens is feasible when soil is only moderately contaminated with Zn and Cd, and the phytoremediation potential is better for Cd than for Zn if the populations from southern France are used. Recent progress in the understanding of the mechanisms of Zn and Cd uptake by T. caerulescens is also reviewed.     

Organic Acids Accumulation and Antioxidant Enzyme Activities in Thlaspi caerulescens under Zn and Cd Stress

Growth, organic acid and phytochelatin accumulation, as well as the activity of several antioxidative enzymes, i.e. superoxide dismutase (SOD), ascorbate peroxidase (APX) guaiacol peroxidase (POX) and catalase (CAT) were investigated under Zn and Cd stress in hydroponically growing plants of Thlaspi caerulescens population from Plombières, Belgium. Tissue Zn and Cd concentration increased (the highest concentration of both was in roots) as the concentration of these metals increased in the nutrient solution. Increasing Zn concentration enhanced plant growth, while with Cd it declined compared to the control. Both metals stimulated malate accumulation in shoots, Zn also caused citrate to increase. Zn did not induce phytochelatin (PC) accumulation. In plants exposed to Cd, PC concentration increased with increasing Cd concentration, but decreased with time of exposure. Under Zn stress SOD activity increased, but APX activity was higher at 500 and 1000 μM Zn and CAT activity only at 500 μM Zn in comparison with the control. CAT activity decreased in Cd- and Zn-stressed plants. The results suggest that relative to other populations, a T. caerulescens population from Plombières, when grown in hydroponics, was characterized by low Zn and Cd uptake and their translocation to shoots and tolerance to both metals. The accumulation of malate and citrate, but not PC accumulation was responsible for Zn tolerance. Cd tolerance seems to be due to neither PC production nor accumulation of organic acids.     

Conformational isomerism of the binuclear N,N-pentamethylenedithiocarbamate cadmium(II) complex, [Cd2{S2CN(CH2)5}4] on multinuclear (N, Cd) CP/MAS NMR and single-crystal X-ray diffraction data

Crystalline N,N-cyclo-pentamethylenedithiocarbamate (PmDtc) cadmium(II) complex was prepared and studied by means of ¹⁵N, ¹¹³Cd CP/MAS NMR spectroscopy and single-crystal X-ray diffraction. The unit cell of the cadmium(II) compound comprises two centrosymmetric isomeric binuclear molecules [Cd₂{S₂CN(CH₂)₅}₄], which display structural inequivalence in both ¹⁵N and ¹¹³Cd NMR and XRD data. There are pairs of the dithiocarbamate ligands exhibiting different structural functions in both isomeric molecules. Each of the terminal ligands is bidentately coordinated to the cadmium atom and forms a planar four-membered chelate ring [CdS₂C]; whereas pairs of the tridentate bridging ligands combine two neighbouring cadmium atoms forming an extended eight-membered tricyclic moieties [Cd₂S₄C₂], whose geometry can be approximated by a ‘chair’ conformation. The structural states of cadmium atoms were characterised by almost axially symmetric ¹¹³Cd chemical shift tensors. All experimental ¹⁵N resonance lines were assigned to the nitrogen structural sites in both isomeric binuclear molecules.     

Soil pH Effects on Uptake of Cd and Zn by Thlaspi caerulescens

For phytoextraction to be successful and viable in environmental remediation, strategies that can optimize plant uptake must be identified. Thlaspi caerulescens is an important hyperaccumulator of Cd and Zn, whether adjusting soil pH is an efficient way to enhance metal uptake by T. caerulescens must by clarified. This study used two soils differing in levels of Cd and Zn, which were adjusted to six different pH levels. Thlaspi caerulescens tissue metal concentrations and 0.1 M Sr(NO₃)₂ extractable soil metal concentrations were measured. The soluble metal form of both Cd and Zn was greatly increased with decreasing pH. Lowering pH significantly influenced plant metal uptake. For the high metal soil, highest plant biomass was at the lowest soil pH (4.74). The highest shoot metal concentration was at the second lowest pH (5.27). For low metal soil, due to low pH induced Al and Mn toxicity, both plant growth and metal uptake was greatest at intermediate pH levels. The extraordinary Cd phytoextraction ability of T. caerulescens was further demonstrated in this experiment. In the optimum pH treatments, Thlaspi caerulescens extracted 40% and 36% of total Cd in the low and high metal soils, respectively, with just one planting. Overall, decreasing pH is an effective strategy to enhance phytoextraction. But different soils had various responses to acidification treatment and a different optimum pH may exist. This pH should be identified to avoid unnecessarily extreme acidification of soils.     

A pyridine adduct of bis(di-iso-butyldithiocarbamato-S,S′)cadmium(II): Multinuclear (C, N, Cd) CP/MAS NMR spectroscopy, crystal and molecular structure, and thermal behaviour

Crystalline bis(N,N-di-iso-butyldithiocarbamato-S,S′)(pyridine)cadmium(II) - adduct 1 was prepared and studied by means of multinuclear ¹³C, ¹⁵N, ¹¹³Cd CP/MAS NMR spectroscopy, single-crystal X-ray diffraction and simultaneous thermal analysis (STA). In molecular structure 1, the cadmium atom coordinates with four sulphur atoms and one nitrogen atom of pyridine, forming a coordination polyhedron [CdS₄N], whose geometry is an almost ideal tetragonal pyramidal (C_4v). The coordinated py molecule is in the apical position, while two structurally non-equivalent di-iso-butyldithiocarbamate ligands, playing the same terminal S,S′-chelating function, define the basal plane. To characterise additionally the structural state of the cadmium atom in this fivefold coordination, ¹¹³Cd chemical shift anisotropy (CSA) parameters, δ_aniso and η, were calculated from experimental MAS NMR spectra that revealed an almost axially symmetric ¹¹³Cd chemical shift tensor. From a combination of TG and DSC measurements taken under an argon atmosphere, we found that the mass of adduct 1 is lost in two steps involving initial desorption of coordinated py molecules with subsequent thermal destruction of liberated cadmium(II) di-iso-butyldithiocarbamate, with yellow-orange, fine-powdered solid CdS as the final product.     

Distribution of Zn in functionally different leaf epidermal cells of the hyperaccumulator Thlaspi caerulescens

The aim of this study was to show the potential of Thlaspi caerulescens in the cleaning‐up of a moderately Zn ‐contaminated soil and to elucidate tolerance mechanisms at the cellular and subcellular level for the detoxification of the accumulated metal within the leaf. Measured Zn concentrations in shoots were high and reached a maximum value of 83 mmol kg ^{? 1} dry mass, whereas total concentrations of Zn in the roots were lower (up to 13 mmol kg ^{? 1}). In order to visualize and quantify Zn at the subcellular level in roots and leaves, ultrathin cryosections were analysed using energy‐dispersive X‐ray micro‐analysis. Elemental maps of ultrathin cryosections showed that T. caerulescens mainly accumulated Zn in the vacuoles of epidermal leaf cells and Zn was almost absent from the vacuoles of the cells from the stomatal complex, thereby protecting the guard and subsidiary cells from high Zn concentrations. Observed patterns of Zn distribution between the functionally different epidermal cells were the same in both the upper and lower epidermis, and were independent of the total Zn content of the plant. Zinc stored in vacuoles was evenly distributed and no Zn‐containing crystals or deposits were observed. From the elemental maps there was no indication that P, S or Cl was associated with the high Zn concentrations in the vacuoles. In addition, Zn also accumulated in high concentrations in both the cell walls of epidermal cells and in the mesophyll cells, indicating that apoplastic compartmentation is another important mechanism involved in zinc tolerance in the leaves of T. caerulescens.     

Compartmentation of Zinc in Roots and Leaves of the Zinc Hyperaccumulator Thlaspi caerulescens J & C Presl

Thlaspi caerulescens is a metallophyte that is able to hyperaccumulate Zn. In the present study the subcellular compartmentation of Zn was investigated in roots and leaves of this species by means of X-ray microanalysis. Leaves accumulated higher average Zn concentrations than roots. In roots of plants exposed to 10 μM Zn, Zn concentrations in the apoplast were similar to those in vacuoles, while in plants treated with 100 μM Zn considerably higher Zn concentrations were detected in vacuoles than in the apoplast. In epidermal and sub-epidermal cells of leaves of plants from both treatments, Zn mainly accumulated in vacuoles and, to a lesser extent, in the apoplast. In vacuoles from plants exposed to 100 μM Zn, high Zn concentrations were associated with variable amounts of P, Ca and K. In leaves, the highest Zn concentrations (13,600 μg g^?1 d.m.) were found in globular crystals present in many vacuoles of epidermal and subepidermal cells. Smaller deposits with a variable Zn concentration between 1,000 and 18,300 μg g^?1 d.m. were observed in the epidermal and subepidermal cells of roots. Both the high Zn/P element ratios found in the crystals and the absence of Mg indicate that, in contrast to other plant species, myo-inositol hexaphosphate (phytate) is not the main storage form for Zn in Thlaspi caerulescens.     

Isolation of mitochondria from embryogenic cultures of Picea abies (L.) Karst. and Abies cephalonica Loud.: characterization of a K ATP + channel

A valuable method to isolate and purify mitochondria from embryonal masses of two coniferous species (Picea abies [L.] Karst. and Abies cephalonica Loud.) is described. Crude mitochondria from both species were shown to be intact, oxygen consuming (with malate plus glutammate, succinate and NADH as substrates) and well coupled (respiratory control ratio ca. 4). The oxidation of the substrates was only partially KCN-insensitive (alternative oxidase) in some cases. However, these fractions were contaminated by membranes (e.g. plasmalemma, tonoplast, Golgi and endoplasmic reticulum). After purification by a discontinuous Percoll gradient (18, 23, 40%, v/v), three mitochondrial populations were separated. The 0/18 interface fraction was composed mainly of broken and uncoupled mitochondria, while the other two (18/23 and 23/40 interface fractions) contained intact and coupled mitochondria, but only 23/40 interface fraction revealed to be better purified starting from both coniferous embryonal masses. In the latter purified fraction, the presence of a cyclosporin A-sensitive K_ATP⁺ channel was demonstrated. These findings were discussed in the light of the potential use of these mitochondrial fractions in bioenergetic studies, or in the involvement of these organelles to stress response in conifers.     

Involvement of calcium in the in vitro sensitivity change of the plasma membrane H+ ATPase to indole-3-acetic acid

The proton pumping activity of phase-partitioning purified plasma membrane fraction from spinach leaves was tested in vitro in the presence of exogenous indole-3-acetic acid. The sensitivity of the H+ pumping activity to the auxin was changed after flowering induction. We investigated the effect of whole spinach leaf treatments with substances affecting the phosphatidylinositol diphosphate transduction pathway on the in vitro sensitivity modification by photoperiodic induction. A role of calcium ions was supported by studies on leaves treated with a specific Ca²⁺ chelator (EGTA), a synthetic Ca²⁺ ionophore (A23187) or with calcium channel blokers (verapamil, lanthan chloride). An experiment using the transduction pathway inhibitor, lithium chloride, indicated that the intracellular concentration of Ca²⁺ was increased by inositol triphosphate.     

土壤不同镉水平对马缨丹生长及其抗氧化酶活性的影响

采用盆栽试验方法,分别设置0(对照,不添加镉)、30、60、90、120、150、180、210mg·kg-1共8个土壤镉处理水平,研究土壤不同镉水平对马缨丹(Lantana comara L.)生长及其抗氧化酶活性的影响,以探讨马缨丹对镉胁迫的生理响应机制。结果显示:(1)随着土壤镉处理浓度的升高,马缨丹干重呈先升高后降低的趋势,30mg·kg-1镉处理能促进植株的生长,而浓度高于60mg·kg-1时显著抑制马缨丹的生长。(2)马缨丹叶片和根系中O-·2产生速率、H2O2和MDA含量及电解质渗漏率均随土壤镉处理浓度的升高和胁迫时间的延长逐渐升高,胁迫90d时,叶片和根系中O-·2产生速率、H2O2和MDA含量及电解质渗漏率分别在镉浓度高于60和30mg·kg-1时显著低于对照。(3)叶片和根系抗氧化酶SOD、POD、APX和CAT活性随着土壤镉处理浓度的增加大体呈先升高后降低的趋势,并在镉浓度分别高于90和60mg·kg-1时,叶片和根系抗氧化酶活性显著低于对照。研究表明,低浓度镉处理土壤能促进马缨丹植株生长,而高浓度镉处理土壤显著降低了马缨丹体内抗氧化酶活性,导致活性氧大量积累,引起严重的膜脂过氧化伤害,从而显著抑制马缨丹植株的生长。     

Cadmium accumulation in relation to organic acids in leaves of Solanum nigrum L. as a newly found cadmium hyperaccumulator

The influence of various cadmium concentrations on organic acid levels in leaves of the Cd hyperaccumulator, Solanum nigrum L. and a closely related species, Solanum melongena L., were investigated. In particular, the relationship of organic acids with Cd accumulation in the two plants was investigated. The results showed that Cd accumulation in the shoots of S. nigrum was significantly higher than that of S. melongena. The accumulation of Cd in the leaves of S. nigrum ranged from 2.0 to 167.8 μg g⁻¹ dry weight (DW), but only from 1.2 to 64.0 μg g⁻¹ DW in S. melongena. Solanum melongena was considerably less tolerant to Cd than S. nigrum. Approximately 20% of the total Cd in S. nigrum leaves was water-soluble, suggesting that some accumulated Cd was associated with water-soluble compounds such as organic acids. Malic acid in the leaves of S. nigrum was the most abundant organic acid [up to 115.6–145.7 μmol g⁻¹ fresh weight (FW)], but this acid was not significantly affected by the Cd concentration in soil. However, the level of malic acid in S. melongena plants was much lower, only 16.3–75.4 μmol g⁻¹ FW. The significant positive correlations between total Cd and water-soluble Cd concentrations and both acetic and citric acid concentrations in the leaves of S. nigrum were observed. In contrast, there was no correlation between concentrations of the two acids and Cd concentrations in the leaves of S. melongena. These results indicated that acetic and citric acids in the leaves of S. nigrum might be related to its Cd hyperaccumulation.     

The unique alternation of conformationally different (‘chair’-‘saddle’) eight-membered metallocycles [Cd2S4P2] in the chains of cadmium dialkyldithiophosphates: C, P, Cd CP/MAS NMR and single-crystal X-ray diffraction studies

O,O′-Dipropyldithiophosphate and O,O′-dibutyldithiophosphate (Dtph) cadmium(II) complexes were prepared and studied by means of heteronuclear ³¹P, ¹¹³Cd, ³¹C CP/MAS NMR spectroscopy and single-crystal X-ray diffraction. Linear-chain polynuclear structures have been established for both cadmium(II) complexes, in which each pair of equivalent dithiophosphate groups, playing the same bridging structural function, asymmetrically links the neighbouring cadmium atoms. One remarkable structural feature of the synthesised cadmium(II) compounds is defined by the alternation of two types of conformationally different (‘chair’-‘saddle’) eight-membered rings [Cd₂S₄P₂] in the polymeric chains. Therefore, in both ³¹P NMR and XRD data, the bridging dithiophosphate ligands exhibit structural inequivalence in pairs. The structural states of both Dtph ligands and cadmium atoms have been characterised by the ³¹P and ¹¹³Cd chemical shift tensors, which display a profound axially symmetric and mainly rhombic characters, respectively. All experimental ³¹P resonances were assigned to the phosphorus structural sites in both resolved structures.     

EGTA对Cd胁迫下蓖麻Cd积累和营养元素吸收的影响

以‘淄蓖麻5号’蓖麻品种为材料,通过盆栽试验研究了重度Cd土壤污染（100 mg·kg^-1）条件下,不同浓度（0、0.5、1.0、2.0 mmol·kg^-1）外源螯合剂——乙二醇双(2-氨基乙基醚)四乙酸(EGTA)对蓖麻植株生长、Cd积累和营养元素吸收的影响,探讨外源螯合剂调控Cd污染土壤上植物生长和修复效应。结果显示：（1）在Cd胁迫下,土壤中外源添加0.5~2.0 mmol·kg^-1EGTA使蓖麻根系鲜、干重比不添加EGTA对照不同程度降低,但植株总干重没有受到显著影响。（2）外源EGTA能有效促进Cd从蓖麻根部向地上部的转移,2.0 mmol·kg^-1的EGTA处理使蓖麻叶片Cd 含量显著增加了41.34倍;与不添加EGTA对照相比,外源EGTA处理蓖麻叶片中Cd积累量随添加EGTA的浓度增加而显著大幅度增加14.0~45.6倍,占相应植株总积累量的36.89%~58.63%,而茎中Cd积累量增加幅度较小,根中Cd积累量则显著降低。（3）Cd胁迫条件下,外源EGTA对蓖麻各器官矿质元素含量的影响不一,EGTA促进K向蓖麻地上部的转运,同时抑制Mg向植株地上部转运;随土壤添加的EGTA浓度提高,蓖麻植株对Ca吸收表现为低促高抑,叶片Zn含量和植株Cu含量逐渐增加,叶片和根系Fe含量及植株各器官Mn含量显著增加。与无Cd胁迫对照相比,EGTA在提高植株Cd积累的同时,降低了根系对K的吸收。研究表明,Cd胁迫显著抑制了蓖麻植株的生长,适宜浓度的外源EGTA对Cd的这种抑制有显著的缓解作用;外源EGTA改变了Cd在蓖麻根、茎、叶中的积累分布情况,提高了Cd从根系向地上部,尤其是向叶片的转移能力,从而强化了蓖麻对Cd污染土壤的修复效率;在采用EGTA强化植物修复Cd污染土壤时,应适量增施K肥以保证植株的正常生理代谢。     

A 31P NMR study of the internal pH of yeast peroxisomes

The internal pH of peroxisomes in the yeasts Hansenula polymorpha, Candida utilis and Trichosporon cutaneum X4 was estimated by ³¹P nuclear magnetic resonance (NMR) spectroscopy. ³¹P NMR spectra of suspensions of intact cells of these yeasts, grown under conditions of extensive peroxisomal proliferation, displayed two prominent P_i-peaks at different chemical shift positions. In control cells grown on glucose, which contain very few peroxisomes, only a single peak was observed. This latter peak, which was detected under all growth conditions, was assigned to cytosolic P_i at pH 7.1. The additional peak present in spectra of peroxisome-containing cells, reflected P_i at a considerably lower pH of approximately 5.8–6.0. Experiments with the protonophore carbonyl cyanide m-chlorophenylhydrazon (CCCP) and the ionophores valinomycin and nigericin revealed that separation of the two P_i-peaks was caused by a pH-gradient across a membrane separating the two pools. Experiments with chloroquine confirmed the acidic nature of one of these pools. In a number of transfer experiments with the yeast H. polymorpha it was shown that the relative intensity of the P_i-signal at the low pH-position was correlated to the peroxisomal volume fraction. These results strongly suggest that this peak has to be assigned to P_i in peroxisomes, which therefore are acidic in nature. The presence of peroxisome-associated P_i was confirmed cytochemically.Abbreviations CCCP Carbonyl cyanide m-chlorophenylhydrazon - DCCD N,N-dicyclohexylcarbodiimide     

Root development and heavy metal phytoextraction efficiency: comparison of different plant species in the field

Heavy metal phytoextraction is a soil remediation technique which implies the optimal use of plants to remove contamination from soil. Plants must thus be tolerant to heavy metals, adapted to soil and climate characteristics and able to take up large amounts of heavy metals. Their roots must also fit the spatial distribution of pollution. Their different root systems allow plants to adapt to their environment and be more or less efficient in element uptake. To assess the impact of the root system on phytoextraction efficiency in the field, we have studied the uptake and root systems (root length and root size) of various high biomass plants (Brassica juncea, Nicotiana tabacum, Zea mays and Salix viminalis) and one hyperaccumulator (Thlaspi caerulescens) grown in a Zn, Cu and Cd contaminated soil and compared them with total heavy metal distribution in the soil. Changes from year to year have been studied for an annual (Zea mays) and a perennial plant (Salix viminalis) to assess the impact of the climate on root systems and the evolution of efficiency with time and growth. In spite of a small biomass, T. caerulescens was the most efficient plant for Cd and Zn removal because of very high concentrations in the shoots. The second most efficient were plants combining high metal concentrations and high biomass (willows for Cd and Zn and tobacco for Cu and Cd). A large cumulative root density/aboveground biomass ratio (L_A/B), together with a relative larger proportion of fine roots compared to other plants seemed to be additional favourable characteristics for increased heavy metal uptake by T. caerulescens. In general, for all plants correlations were found between L _A/B and heavy metal concentrations in shoots (r=0.758^***, r=0.594^***, r=0.798^*** (P<0.001) for Cd, Cu and Zn concentrations resp.). Differences between years were significant because of variations in climatic conditions for annual plants or because of growth for perennial plants. The plants exhibited also different root distributions along the soil profile: T. caerulescens had a shallow root system and was thus best suited for shallow contamination (0.2 m) whereas maize and willows were the most efficient in colonising the soil at depth and thus more applicable for deep contamination (0.7 m). In the field situation, no plant was able to fit the contamination properly due to heterogeneity in soil contamination. This points out to the importance and the difficulty of choosing plant species according to depth and heterogeneity of localisation of the pollution.     

A comparative study between a brain Na+,K(+)-ATPase inhibitor (endobain E) and ascorbic acid

In the search of Na⁺,K⁺-ATPase modulators, we have reported the isolation by gel filtration and HPLC of a brain fraction, termed endobain E, which highly inhibits Na⁺,K⁺-ATPase activity. In the present study we compared some properties of endobain E with those of ascorbic acid. Kinetic experiments assaying synaptosomal membrane K⁺-p-nitrophenylphosphatase (K⁺-p-NPPase) activity in the presence of endobain E or ascorbic acid showed that in neither case did enzyme inhibition prove competitive in nature versus K⁺ or p-NPP concentration. At pH 5.0, endobain E and ascorbic acid maximal UV absorbance was 266 and 258 nm, respectively; alkalinization to pH 14.0 led to absorption drop and shift for endobain E but to absorbance disappearance for ascorbic acid. After cysteine treatment, endobain E absorbance decreased, whereas that of ascorbic acid remained unaltered; iodine treatment led to absorbance drop and shift for endobain E but to absorbance disappearance for ascorbic acid. HPLC analysis of endobain E disclosed the presence of two components: one eluting with retention time and UV spectrum indistinguishable from those of ascorbic acid and a second, as yet unidentified, both exerting Na⁺,K⁺-ATPase inhibition.