Nitrogen as an important detoxification factor to cadmium stress in poplar plants

To verify the important role of nitrogen in detoxifying plants from heavy metals in Populus, the influence of nitrogen and cadmium on growth, chlorophyll (Chl) synthesis, and the expression of the Glutamine synthetase gene (GS₂) were studied in poplar plants. Experiments were carried out in potted plants treated with (NH₄)₂CO₃, Cd(NO₃)₂, CdCl₂ and CdCl₂ plus (NH₄)₂CO₃. After treatment, plant height, biomass, chlorophyll content, the precursors content and GS₂ were investigated. Results showed that the plants treated with cadmium showed toxicity symptoms, decrease in growth and Chl content. Cd inhibited Chl synthesis seriously by blocking the site located on the steps between UrogenIII and Coprogen III. However, the plants treated with cadmium and nitrogen grew well without any toxicity symptoms. Nitrogen supplement can alleviate Cd inhibition on chlorophyll synthesis by unblocking the pathway. The results indicated that nitrogen can effectively alleviate cadmium toxicity to poplar plants.     

Effects of nitrogen on the activity of antioxidant enzymes and gene expression in leaves of Populus plants subjected to cadmium stress

The research aimed to verify the important physiological effect of nitrogen (N) on plants exposed to cadmium (Cd). The poplar plants were grown in a Hoagland nutrient solution and treated with extra N, Cd, and N + Cd. After treatment, plant growth and chlorophyll content were recorded. The oxidative stress, the activity of antioxidant enzymes, and the expression of related genes were also examined. The results indicated the plants treated with sole Cd presented obvious toxicity symptoms, i.e. growth inhibition, reactive oxygen species accumulation, and chlorophyll content decrement. However, when N was added to the plants under Cd stress, plant growth was enhanced, chlorophyll synthesis was promoted, and the oxidative stress was alleviated. Further, the expression of antioxidant enzymes genes was upregulated by N. The results indicated that N partially reversed the toxic effect of Cd on poplar plants, which can provide new methodology to enhance the phytoremediation technology for heavy metal pollution soil.     

Supply of nitrogen can reverse senescence processes and affect expression of genes coding for plastidic glutamine synthetase and lysine-ketoglutarate reductase/saccharopine dehydrogenase

Nitrogen availability has a strong influence on developmental processes in plants. We show that the time of nitrogen supply regulates the course of leaf senescence in flag leaves of Hordeum vulgare . The senescence-specific decrease in chlorophyll content and photosystem II efficiency is clearly delayed when plants are fertilised with nitrate at the onset of leaf senescence. Concurrently, the additional supply of nitrate affects expression patterns of two marker genes of nitrogen metabolism. As shown by quantitative RT-PCR analyses, senescence-specific downregulation of plastidic glutamine synthetase ( GS2 ) and senescence-specific upregulation of lysine-ketoglutarate reductase/saccharopine dehydrogenase ( LKR/SDH ) are both clearly retarded. Depletion of nitrogen in experiments using hydroponic growth systems results in premature primary leaf senescence. The already started senescence processes can be even reversed by later nitrogen addition, as proved by a further increase in photosystem II efficiency and chlorophyll content, returning to the high values of controls which had not been deprived of nitrogen. Although both addition of nitrate or ammonium effectively reversed nitrogen depletion-induced primary leaf senescence, addition of urea did not. Additionally, effects of nitrogen supply on the course of leaf senescence were analysed in the model plant Arabidopsis thaliana. Leaves of A. thaliana show the same reversion of senescence processes after receiving additional nitrogen supply, indicating that the nitrogen response of leaf development is conserved in different plant species.     

Heavy Metal Tolerance and Accumulation in Indian Mustard (Brassica Juncea L.) Expressing Bacterial γ-Glutamylcysteine Synthetase or Glutathione Synthetase

The overexpression of either γ-glutamylcysteine synthetase (γ-ECS) or glutathione synthetase (GS) in Brassica juncea transgenics was shown previously to result in higher accumulation of glutathione (GSH) and phytochelatins (PCs), as well as enhanced Cd tolerance and accumulation. The present study was aimed at analyzing the effects of γ-ECS or GS overexpression on tolerance to and accumulation of other metal/loids supplied individually in agar medium (seedlings) or in hydroponics (mature plants). Also, as pollution in nature generally consists of mixtures of metals, glutamylcysteine synthetase (ECS) and GS seedlings were tested on combinations of metals. Compared to wild-type plants, ECS and GS transgenics exhibited a significantly higher capacity to tolerate and accumulate a variety of metal/loids (particularly As, Cd, and Cr) as well as mixed-metal combinations (As, Cd, Zn/As, Pb, and Zn). This enhanced metal tolerance and accumulation of the ECS and GS transgenics may be attributable to enhanced production of PCs, sustained by a greater availability of GSH as substrate, as suggested by their higher concentrations of GSH, PC2, PC3, and PC4 as compared to wild-type plants. Overexpression of GS and γ-ECS may represent a promising strategy for the development of plants with an enhanced phytoremediation capacity for mixtures of metals.     

Assembly of a cytosolic pine glutamine synthetase holoenzyme in leaves of transgenic poplar leads to enhanced vegetative growth in young plants

Over‐expression of glutamine synthetase (GS, EC 6.3.1.2), a key enzyme in nitrogen assimilation, may be a reasonable approach to enhance plant nitrogen use efficiency. In this work phenotypic and biochemical characterizations of young transgenic poplars showing ectopic expression of a pine cytosolic GS transgene in photosynthetic tissue (Gallardo et al., Planta 210, 19–26, 1999) are presented. Analysis of 22 independent transgenic lines in a 6 month greenhouse study indicated that expression of the pine GS transgene affects early vegetative growth and leaf morphology. In comparison with non‐transgenic controls, transgenic trees exhibited significantly greater numbers of nodes and leaves (12%), and higher average leaf length and width resulting in an increase in leaf area (25%). Leaf shape was not altered. Transgenic poplars also exhibited increased GS activity (66%), chlorophyll content (33%) and protein content (21%). Plant height was correlated with GS content in young leaves, suggesting that GS can be considered a marker for vegetative growth. Molecular and kinetic characterization of GS isoforms in leaves indicated that poplar GS isoforms are similar to their counterparts in herbaceous plants. A new GS isoenzyme that displayed molecular and kinetic characteristics corresponding to the octomeric pine cytosolic GS1 was identified in the photosynthetic tissues of transgenic poplar leaves. These results indicate that enhanced growth and alterations in biochemistry during early growth are the consequence of transgene expression and assembly of pine GS1 subunits into a new functional holoenzyme in the cytosol of photosynthetic cells.     

Stress magnitude matters: different intensities of pulsed water stress produce non‐monotonic resistance responses of host plants to insect herbivores

Abstract 1. Water stress may increase or reduce the suitability of plants for herbivores. The recently proposed ‘pulsed stress hypothesis’ suggests consideration of stress phenology (pulsed vs. continuous stress) to explain these conflicting effects of plant water stress on herbivore performance. 2. This hypothesis was tested for the effect of differing stress intensity on performance and preference of insect herbivores belonging to different feeding guilds, namely leaf‐chewing insects (Spodoptera littoralis caterpillars) and phloem‐feeding insects (Aphis pomi aphids), on apple plants (Malus domestica). The plants were non‐stressed or exposed to a low or high intensity of pulsed water stress. 3. Plant responses to the different stress levels were generally monotonic. Growth, stomatal conductance (g_s), leaf water, and old‐leaf nitrogen concentration decreased, whereas young‐leaf nitrogen concentration and leaf mass per area (LMA) increased with increasing stress intensity. The stable isotope composition of foliar carbon (δ¹³C) responded non‐monotonically to the drought treatments. The δ¹³C values were highest in low‐stress plants, intermediate in high‐stress plants, and lowest in non‐stressed plants. 4. The preference and performance responses of the caterpillars were also non‐monotonic. Non‐stressed plants were intermediately, low‐stress plants least, and high‐stress plants most attractive or suitable. Aphid population growth was highest on non‐stressed plants and lowest on low‐stress plants. 5. The results highlight the importance of water stress intensity for the outcome of interactions between herbivores and drought‐affected plants. They show that pulsed water stress may enhance or reduce insect herbivore performance and plant resistance, depending on stress intensity.     

Leaf-targeted phytochelatin synthase in Arabidopsis thaliana

One of the key steps in developing transgenic plants for the phytoremediation of metal containing soils is to develop plants that accumulate metals in the aerial tissues. With the goal of changing the distribution of phytochelatin (PC)-dependent cadmium accumulation from roots to the leaves, the phytochelatin synthase (PCS) deficient cad1-3 mutant and wild type (Col-0) Arabidopsis plants were transformed with an Arabidopsis phytochelatin synthase (AtPCS1) under the control of a leaf-specific promoter. Three independent transformant lines from each genetic background were chosen for further analysis and designated cad-PCS and WT-PCS. PCS activity in the cadPCS lines was restored in the leaves, but not in the roots. Additionally, when whole plants were treated with cadmium, PCs were found only in the leaves of cad-PCS plants. Although the inserted AtPCS1 gene was leaf-specific, cad-PCS lines showed an overall decrease in cadmium toxicity evidenced by a partial amelioration of the "brown-root" phenotype and root growth was restored to wild type levels when treated with cadmium and arsenate. WT-PCS lines showed an increase in leaf PCS activity but had only wild type PC levels. In addition, cadmium uptake studies indicated that there was no difference in cadmium accumulation among all types tested. So, while we were able to protect the plants against cadmium by expressing PC synthase only in the leaves, we were not able to limit cadmium accumulation to aerial tissues.     

Cadmium induced oxidative stress and changes in soluble and ionically bound cell wall peroxidase activities in roots of seedling and 3–4 leaf stage plants of <Emphasis Type="Italic">Brassica juncea</Emphasis> (L.) czern

Metabolic adaptations to heavy metal toxicity in plants are thought to be related with developmental growth stage and the type of metal by which plant is affected. In the present study, changes in ionically bound CWP, soluble peroxidase activity, H(2)O(2) level and Malonaldehyde content in roots of cadmium and copper stressed seedlings and cadmium stressed 3-4 leaf stage plants of Brassica juncea were investigated. Cadmium inhibits root growth and reduces fresh biomass. The reduction in root growth and fresh biomass is correlated with increased lipid peroxidation and reduced tolerance. Treatment with cadmium resulted in an increase in ionically bound CWP activity in roots of seedlings but no significant change in its activity was found in roots of 3-4 leaf stage plants. Increased level of H(2)O(2) in roots of cadmium and copper treated seedlings, show a direct correlation with increased activity of ionically bound CWP. H(2)O(2) level in 3-4 leaf stage plant roots was found to be very low. Soluble peroxidase activity decreased in cadmium (50 and 100 mu-icroM) treated seedlings but it was ineffective to cause any change in its activity in 3-4 leaf stage plants. Copper treated seedlings showed an increase in ionically bound CWP activity, H(2)O(2) level and MDA content. Ascorbic acid (50 mM) pretreated seedlings shows significant decrease in ionically bound CWP activity when exposed to 50 muM cadmium. Hence, it is concluded that inhibition of root growth in Brassica juncea seedlings by cadmium, is associated with CWP catalyzed H(2)O(2) dependent reactions which are involved in metabolic adaptations to heavy-metal stress.     

Enhanced toxic metal accumulation in engineered bacterial cells expressing Arabidopsis thaliana phytochelatin synthase

Phytochelatins (PCs) are metal-binding cysteine-rich peptides, enzymatically synthesized in plants and yeasts from glutathione in response to heavy metal stress by PC synthase (EC 2.3.2.15). In an attempt to increase the ability of bacterial cells to accumulate heavy metals, the Arabidopsis thaliana gene encoding PC synthase (AtPCS) was expressed in Escherichia coli. A marked accumulation of PCs was observed in vivo together with a decrease in the glutathione cellular content. When bacterial cells expressing AtPCS were placed in the presence of heavy metals such as cadmium or the metalloid arsenic, cellular metal contents were increased 20- and 50-fold, respectively. We discuss the possibility of using genes of the PC biosynthetic pathway to design bacterial strains or higher plants with increased abilities to accumulate toxic metals, and also arsenic, for use in bioremediation and/or phytoremediation processes.     

Cadmium phytoextraction potential of poplar clones (Populus spp.)

Biomass production, leaf number and area, photosynthetic and dark respiration rates, leaf concentration of photosynthetic pigments, nitrate reductase activity, as well as cadmium concentrations in leaves, stem, and roots were measured in poplar clones PE 4/68, B-229, 665, and 45/51. Plants were grown hydroponically under controlled conditions and treated with two different cadmium (Cd) concentrations (10(-5) and 10(-7) M) in the same background solution (Hoagland's solution). The presence of Cd did not cause serious disturbance of growth and physiological parameters in the studied poplar clones. Cd concentrations in plant tissues reflected external concentrations. In treated plants, root contents increased from 38.57 to 511.51 ppm, leaf contents from 0.91 to 7.50, while stem contents ranged from 1.37 to 9.50 ppm.     

Detection of phytochelatins in the hyperaccumulator Sedum alfredii exposed to cadmium and lead

Phytochelatins (PCs) are known to play an essential role in the heavy metal detoxification of some higher plants and fungi by chelating heavy metals. However, three recent papers reported that no PCs could be detected in the hyperaccumulator Sedum alfredii Hance upon cadmium, lead or zinc treatment, respectively. In this paper, PC synthesis was assayed again in the mine population of S. alfredii with the help of reversed phase high-performance liquid chromatography (HPLC), HPLC-mass spectrometry, and HPLC-tandem mass spectrometry. Our data showed that PC formation could be induced in the leaf, stem and root tissues of S. alfredii upon exposure to 400 microM cadmium, and only in the stem and root when exposed to 700 microM lead. However, no PCs were found in any part of S. alfredii when it was subjected to exposure to 1600 microM zinc.     

Response of transgenic poplar overexpressing cytosolic glutamine synthetase to phosphinothricin

Glutamine synthetase (GS) is the main enzyme involved in ammonia assimilation in plants and is the target of phosphinothricin (PPT), an herbicide commonly used for weed control in agriculture. As a result of the inhibition of GS, PPT also blocks photorespiration, resulting in the depletion of leaf amino acid pools leading to the plant death. Hybrid transgenic poplar (Populus tremula x P. alba INRA clone 7171-B4) overexpressing cytosolic GS is characterized by enhanced vegetative growth [Gallardo, F., Fu, J., Cantón, F.R., García-Gutiérrez, A., Cánovas, F.M., Kirby, E.G., 1999. Expression of a conifer glutamine synthetase gene in transgenic poplar. Planta 210, 19-26; Fu, J., Sampalo, R., Gallardo, F., Cánovas, F.M., Kirby, E.G., 2003. Assembly of a cytosolic pine glutamine synthetase holoenzyme in leaves of transgenic poplar leads to enhanced vegetative growth in young plants. Plant Cell Environ. 26, 411-418; Jing, Z.P., Gallardo, F., Pascual, M.B., Sampalo, R., Romero, J., Torres de Navarra, A., Cánovas, F.M., 2004. Improved growth in a field trial of transgenic hybrid poplar overexpressing glutamine synthetase. New Phytol. 164, 137-145], increased photosynthetic and photorespiratory capacities [El-Khatib, R.T., Hamerlynck, E.P., Gallardo, F., Kirby, E.G., 2004. Transgenic poplar characterized by ectopic expression of a pine cytosolic glutamine synthetase gene exhibits enhanced tolerance to water stress. Tree Physiol. 24, 729-736], enhanced tolerance to water stress (El-Khatib et al., 2004), and enhanced nitrogen use efficiency [Man, H.-M., Boriel, R., El-Khatib, R.T., Kirby, E.G., 2005. Characterization of transgenic poplar with ectopic expression of pine cytosolic glutamine synthetase under conditions of varying nitrogen availability. New Phytol. 167, 31-39]. In vitro plantlets of GS transgenic poplar exhibited enhanced resistance to PPT when compared with non-transgenic controls. After 30 days exposure to PPT at an equivalent dose of 275 g ha(-1), growth of GS transgenic poplar plantlets was 5-fold greater than controls. The response of young leaves to PPT treatment depends on physiological state as indicated by GS and Rubisco (LSU) levels. Young leaves from control plants, typically in a low differentiation state, respond to the herbicide showing up-regulation of GS and LSU. In contrast, young leaves from transgenic lines, with higher initial GS and LSU levels compared to control, display up-regulation of NADP(+)-isocitrate dehydrogenase. Differences between control and GS transgenics in their response to PPT are discussed in relation to their differences in photosynthetic and photorespiratory capacities (El-Khatib et al., 2004).     

Protective effect of jasmonic acid and potassium against cadmium stress in peas (Pisum sativum L.)

A combination of mineral nutrients and plant growth regulators should be assessed to improve crop performance under various abiotic stresses. There is a need to include plant growth regulators in fertilization regime of various crops along with essential mineral nutrients, especially when they are irrigated with polluted water with higher levels of heavy metals. The performance of pea was evaluated under cadmium (Cd) stress coupled with potassium (K) and jasmonic acid (JA) supplementation. The Cd stress (50 μM) was applied to soil (sandy loam) grown pea plants as basal dose after a month of sowing. The control and stressed plants were then supplemented with K (5 M), JA (0.5 mM) and their collective application along with control as distilled water. Cd stress showed a marked reduction in growth pattern, however, the collective supplementation sufficiently improved the growth pattern of stressed peas plants as evidenced by improvement in shoot length (cm), root length (cm), number of leaves per plant, leaf area (cm²), plant fresh and dry weight (gm). Potassium application under Cd stress significantly enhanced internodal distance (cm) while the number of seeds per pod and relative water contents remained nonsignificant. The applied treatment (JA + K) under Cd stress prominently improved enzymatic activities, which were measured as nitrate reductase activity (NRA), nitrite reductase activity (NiRA), superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT). Cd stress impacted the biochemical profile by enhancing antioxidant capacity (AC), antioxidant activity (AA), total phenols (TP), while reducing total soluble protein (TSP), chlorophyll ‘a’, chlorophyll ‘b’ and carotenoids. The combined application of JA and K under Cd stress enhanced AC, AA, TP, Chl a and b, TSP and carotenoids. The results indicate that foliar application of JA and K efficiently negated the harmful effects of Cd stress on peas.     

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.     

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.     

Arbuscular mycorrhizal fungi and biochar improves drought tolerance in chickpea

Arbuscular mycorrhizal fungi (AMF) inoculation and biochar amendment has been reported to improve growth of several crop plants however their role in stress amelioration individually as well as in combination has not been worked out. This experiment was conducted to evaluate the application of AMF and biochar on the performance of chickpea under drought stress. The treatments included the individual as well as combined treatment of AMF and biochar to drought stressed and normal chickpea plants. Plants inoculation improved growth in terms of shoot and root length, leaf area and number of branches which was observed to show a steep decline due to drought stress. Drought declined the AMF colonization potential though biochar amendment ameliorated the negative effects of drought significantly by improving the spore population, number of mycelium, vesicle and arbuscules and the percentage of colonization as well. Increased chlorophyll synthesis in biochar and AMF treated plants was obvious, which lead to significant enhancement in the net photosynthetic efficiency. Drought stress also declined the relative water content (RWC) and membrane stability index (MSI), while treatment of biochar and AMF either individually or in combination mitigated the deleterious effects to considerable extent and caused a significant enhancement in RWC and MSI under normal conditions. Amendments with biochar and AMF inoculation increased the nitrogen fixation attributes including the number and weight of nodules, leghemoglobin content and activity of nitrate reductase enzyme leading to greater uptake and assimilation of nitrogen in them when compared to drought stressed plants. Drought stressed chickpea plants exhibited considerable reduction in uptake of nitrogen and phosphorous which was ameliorated by biochar and AMF treatments. It could be suggested that increase in growth and physiological attributes in chickpea due to biochar amendments and AMF inoculation under drought stress were plausibly due to their involvement in nitrogen and phosphorous uptake, chlorophyll synthesis and photosynthesis.     

钙离子对盐胁迫小麦幼苗氮代谢的影响

为探讨增强小麦抗盐能力的调控途径,以普通小麦豫麦34为材料,研究了Ca2+对盐胁迫下小麦幼苗氮代谢及生长的影响.采用全营养液培养小麦幼苗至第一片叶完全展开,更换无钙营养液,并开始不同处理.处理分别为低盐胁迫(150 mmol · L-1 NaCl)、低盐胁迫+4 mmol · L-1 Ca2+、高盐胁迫(300 mmol · L-1 NaCl)、高盐胁迫+4mmol · L-1 Ca2+,以无NaCl胁迫的小麦为对照.5 d后取样,测定了氮同化酶活性、代谢物含量、积累量及幼苗生长状况.结果表明,Ca2+明显缓解了低盐胁迫对小麦幼苗的生长抑制,表现在鲜重、叶绿素及可溶性蛋白含量的增加,而对高盐胁迫下小麦幼苗的生长无明显改善效果;Ca2+改善了低盐胁迫下小麦幼苗的氮营养状况,表现在氮积累量的增加,这一效应主要是通过硝酸还原酶(NR)、谷氨酰胺合成酶(GS)以及异柠檬酸脱氢酶(NADP-ICDH)活性的增强而实现的.Ca2+未能改善高盐胁迫下小麦幼苗氮营养状况的主要限制因子在于NADP-ICDH活性未明显增加.     

Evaluation of Transgenic Poplars Over-Expressing Enzymes of Glutathione Synthesis for Phytoremediation of Cadmium

Abstract: Recently, phytoremediation of soils polluted with heavy metals has received a lot of attention. Since glutathione (GSH) and its derivatives (e.g., phytochelatins) play a major role in plant defence against environmental pollutants, we tested the effects of over-expression of bacterial genes for GSH synthesis in poplar on cadmium accumulation. A pilot experiment with CdCl₂ in hydroponics revealed that poplars over-expressing γ-glutamylcysteine synthetase (γ-ECS) accumulated significantly more Cd in root tissue than wild type or glutathione synthetase over-expressing poplars. To test the partitioning of Cd in different organs, poplar lines over-expressing γ-ECS in the cytosol and in chloroplasts were treated with 0.2 mM CdCl₂ in hydroponics. Significant amounts of Cd were translocated to leaves, but significant differences in Cd accumulation were not observed between transgenic and wild type plants. To evaluate these lines for large-scale phytoremediation of cadmium, plants were treated with 2 mM Cd in soil. Over a four-week period, the poplar plants were able to accumulate up to 5.3 mg Cd. Most remarkably, in young leaves of both transgenic lines, Cd was accumulated to concentrations 2.5 - 3 times higher than in the wild type. The increased allocation of cadmium to the young leaves represents a potentional advantage for the phytoremediation process using the same plants over several vegetation periods. The use of transgenic poplar lines with enhanced glutathione production capacity seems to be of particular advantage in highly polluted soils.