Morphophysiological responses and programmed cell death induced by cadmium in <Emphasis Type="Italic">Genipa americana</Emphasis> L. (Rubiaceae)

Cadmium (Cd) originating from atmospheric deposits, from industrial residues and from the application of phosphate fertilizers may accumulate in high concentrations in soil, water and food, thus becoming highly toxic to plants, animals and human beings. Once accumulated in an organism, Cd discharges and sets off a sequence of biochemical reactions and morphophysiological changes which may cause cell death in several tissues and organs. In order to test the hypothesis that Cd interferes in the metabolism of G. americana, a greenhouse experiment was conducted to measure eventual morphophysiological responses and cell death induced by Cd in this species. The plants were exposed to Cd concentrations ranging from 0 to 16 mg l⁻¹, in a nutritive solution. In TUNEL reaction, it was shown that Cd caused morphological changes in the cell nucleus of root tip and leaf tissues, which are typical for apoptosis. Cadmium induced anatomical changes in roots and leaves, such as the lignification of cell walls in root tissues and leaf main vein. In addition, the leaf mesophyll showed increase of the intercellular spaces. On the other hand, Cd caused reductions in the net photosynthetic rate, stomatal conductance and leaf transpiration, while the maximum potential quantum efficiency of PS2 (Fv/Fm) was unchanged. Cadmium accumulated in the root system in high concentrations, with low translocation for the shoot, and promoted an increase of Ca and Zn levels in the roots and a decrease of K level in the leaves. High concentrations of Cd promoted morphophysiological changes and caused cell death in roots and leaves tissues of G. americana.     

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     

Cadmium induces changes in sucrose partitioning, invertase activities, and membrane functionality in roots of Rangpur lime (Citrus limonia L. Osbeck)

Cadmium (Cd) uptake effects on sucrose content, invertase activities, and plasma membrane functionality were investigated in Rangpur lime roots ( CITRUS LIMONIA L. Osbeck). Cadmium accumulation was significant in roots but not in shoots and leaves. Cadmium produced significant reduction in roots DW and increment in WC. Leaves and shoots did not show significant differences on both parameters. Sucrose content was higher in control roots than in Cd-exposed ones. Apoplastic sucrose content was much higher in Cd-exposed roots than in control ones. Cd-exposed roots showed a significant decrease in both cell wall-bound and cytoplasmic (neutral) invertase activities; while the vacuolar isoform did not show any change. Alterations in lipid composition and membrane fluidity of Cd-exposed roots were also observed. In Cd-exposed roots phospholipid and glycolipid contents decreased about 50 %, while sterols content was reduced about 22 %. Proton extrusion was inhibited by Cd. Lipid peroxidation and proton extrusion inhibition were also detected by histochemical analysis. This work's findings demonstrate that Cd affects sucrose partitioning and invertase activities in apoplastic and symplastic regions in Rangpur lime roots as well as the plasma membrane functionality and H (+)-ATPase activity.     

Effects of cadmium on the co-ordination of nitrogen and carbon metabolism in bean seedlings

The effect of cadmium (Cd) was investigated on the in vitro activities of leaf and root enzymes involved in carbon (C) and nitrogen (N) metabolism of bean (Phaseolus vulgaris L. cv. Morgane). Cd induced a high increase in maximal extractable activity of glutamate dehydrogenase (NADH-GDH, EC 1.4.1.2). Cd promoted ammonium accumulation in leaves and roots, and a tight correlation was observed between ammonium amount and GDH activity. Changes in GDH activity appear to be mediated by the increase in ammonium levels by Cd treatment. Cd stress also enhanced the activities of phosphoenolypyruvate carboxylase (PEPC, EC 4.1.1.31) and NADP(+)-isocitrate dehydrogenase (NADP(+)-ICDH, EC 1.1.1.42) in leaves while they were inhibited in roots. Immuno-titration, the PEPC sensitivity to malate and PEPC response to pH indicated that the increase in PEPC activity by Cd was due to de novo synthesis of the enzyme polypeptide and also modification of the phosphorylation state of the enzyme. Cd may have modified, via a modulation of PEPC activity, the C flow towards the amino acid biosynthesis. In leaves, Cd treatments markedly modified specific amino acid contents. Glutamate and proline significantly accumulated compared to those of the control plants. This study suggests that Cd stress is a part of the syndrome of metal toxicity, and that a readjustment of the co-ordination between N and C metabolism via the modulation of GDH, PEPC and ICDH activities avoided the accumulation of toxic levels of ammonium.     

Hyperaccumulation of cadmium by hairy roots of Thlaspi caerulescens

Hairy roots were used to investigate cadmium uptake by Thlaspi caerulescens, a metal hyperaccumulator plant with potential applications in phytoremediation and phytomining. Experiments were carried out in nutrient media under conditions supporting root growth. Accumulation of Cd in short-term (9-h) experiments varied with initial medium pH and increased after treating the roots with H(+)-ATPase inhibitor. The highest equilibrium Cd content measured in T. caerulescens roots was 62,800 microg g(-1) dry weight, or 6.3% dry weight, at a liquid Cd concentration of 3710 ppm. Cd levels in live T. caerulescens roots were 1.5- to 1.7-fold those in hairy roots of nonhyperaccumulator species exposed to the same Cd concentration, but similar to the Cd content of autoclaved T. caerulescens roots. The ability to grow at Cd concentrations of up to 100 ppm clearly distinguished T. caerulescens hairy roots from the nonhyperaccumulators. The specific growth rate of T. caerulescens roots was essentially unaffected by 20 to 50 ppm Cd in the culture medium; in contrast, N. tabacum roots turned dark brown at 20 ppm and growth was negligible. Up to 10,600 microg g(-1) dry weight Cd was accumulated by growing T. caerulescens hairy roots. Measurement of Cd levels in whole roots and in the cell wall fraction revealed significant differences in the responses of T. caerulescens and N. tabacum roots to 20 ppm Cd. Most metal was transported directly into the symplasm of N. tabacum roots within 3 days of exposure; in contrast, T. caerulescens roots stored virtually all of their Cd in the wall fraction for the first 7 to 10 days. This delay in transmembrane uptake may represent an important defensive strategy against Cd poisoning in T. caerulescens, allowing time for activation of intracellular mechanisms for heavy metal detoxification.     

Cadmium-induced sulfate uptake in maize roots

The effect of cadmium (Cd) on high-affinity sulfate transport of maize (Zea mays) roots was studied and related to the changes in the levels of sulfate and nonprotein thiols during Cd-induced phytochelatin (PC) biosynthesis. Ten micromolar CdCl(2) in the nutrient solution induced a 100% increase in sulfate uptake by roots. This was not observed either for potassium or phosphate uptake, suggesting a specific effect of Cd(2+) on sulfate transport. The higher sulfate uptake was not dependent on a change in the proton motive force that energizes it. In fact, in Cd-treated plants, the transmembrane electric potential difference of root cortical cells was only slightly more negative than in the controls, the external pH did not change, and the activity of the plasma membrane H(+)-ATPase did not increase. Kinetics analysis showed that in the range of the high-affinity sulfate transport systems, 10 to 250 microM, Cd exposure did not influence the K(m) value (about 20 microM), whereas it doubled the V(max) value with respect to the control. Northern-blot analysis showed that Cd-induced sulfate uptake was related to a higher level of mRNA encoding for a putative high-affinity sulfate transporter in roots. Cd-induced sulfate uptake was associated to both a decrease in the contents of sulfate and glutathione and synthesis of a large amount of PCs. These results suggest that Cd-induced sulfate uptake depends on a pretranslational regulation of the high-affinity sulfate transporter gene and that this response is necessary for sustaining the higher sulfur demand during PC biosynthesis.     

Cadmium-induced changes in antioxidative systems, hydrogen peroxide content, and differentiation in Scots pine roots.

To investigate whether Cd induces common plant defense pathways or unspecific necrosis, the temporal sequence of physiological reactions, including hydrogen peroxide (H(2)O(2)) production, changes in ascorbate-glutathione-related antioxidant systems, secondary metabolism (peroxidases, phenolics, and lignification), and developmental changes, was characterized in roots of hydroponically grown Scots pine (Pinus sylvestris) seedlings. Cd (50 microM, 6 h) initially increased superoxide dismutase, inhibited the systems involved in H(2)O(2) removal (glutathione/glutathione reductase, catalase [CAT], and ascorbate peroxidase [APX]), and caused H(2)O(2) accumulation. Elongation of the roots was completely inhibited within 12 h. After 24 h, glutathione reductase activities recovered to control levels; APX and CAT were stimulated by factors of 5.5 and 1.5. Cell death was increased. After 48 h, nonspecific peroxidases and lignification were increased, and APX and CAT activities were decreased. Histochemical analysis showed that soluble phenolics accumulated in the cytosol of Cd-treated roots but lignification was confined to newly formed protoxylem elements, which were found in the region of the root tip that normally constitutes the elongation zone. Roots exposed to 5 microM Cd showed less pronounced responses and only a small decrease in the elongation rate. These results suggest that in cells challenged by Cd at concentrations exceeding the detoxification capacity, H(2)O(2) accumulated because of an imbalance of redox systems. This, in turn, may have triggered the developmental program leading to xylogenesis. In conclusion, Cd did not cause necrotic injury in root tips but appeared to expedite differentiation, thus leading to accelerated aging.     

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.     

Mechanisms of cadmium detoxification in cattail (Typha angustifolia L.)

Cadmium (Cd) is a widespread heavy metal pollutant and environmental and human health hazard, which may be partially resolved using green and cost-effective phytoremediation techniques. However, the efficiency of phytoremediation is often limited by the small biomass of Cd-hyperaccumulator plants. Although cattail (Typha angustifolia L.) is tolerant of heavy metals and has a high biomass, there is little information available on its detoxification mechanisms for heavy metals, especially Cd. In the present study we investigated the tolerance of cattail to Cd and mechanisms involved in its Cd detoxification. Our results show that: (a) cattail is tolerant of Cd; (b) the root Casparian band, cell wall, vacuole, glutathione (GSH), and glutathione peroxidase (GPX) play important roles in Cd detoxification; and (c) mechanisms of Cd detoxification differ in leaf cell cytoplasm (mainly a GSH-related antioxidant defense system) and root cell cytoplasm (mainly a GSH-related chelation system). In summary, cattail possesses multiple detoxification mechanisms for Cd and is a promising species for phytoremediation of Cd-polluted environments.     

Cadmium toxicity in tomato (Lycopersicon esculentum) plants grown in hydroponics

The effects of Cd have been investigated in tomato (Lycopersicon esculentum) plants grown in a controlled environment in hydroponics, using Cd concentrations of 10 and 100 μM. Cadmium treatment led to major effects in shoots and roots of tomato. Plant growth was reduced in both Cd treatments, leaves showed chlorosis symptoms when grown at 10 μM Cd and necrotic spots when grown at 100 μM Cd, and root browning was observed in both treatments. An increase in the activity of phosphoenolpyruvate carboxylase, involved in anaplerotic fixation of CO₂ into organic acids, was measured in root extracts of Cd-exposed plants. Also, significant increases in the activities of several enzymes from the Krebs cycle were measured in root extracts of tomato plants grown with Cd. In leaf extracts, significant increases in citrate synthase, isocitrate dehydrogenase and malate dehydrogenase activities were also found at 100 μM Cd, whereas fumarase activity decreased. These data suggest that at low Cd supply (10 μM) tomato plants accumulate Cd in roots and this mechanism may be associated to an increased activity in the PEPC–MDH–CS metabolic pathway involved in citric acid synthesis in roots. Also, at low Cd supply some symptoms associated with a moderate Fe deficiency could be observed, whereas at high Cd supply (100 μM) effects on growth overrule any nutrient interaction caused by excess Cd. Cadmium excess also caused alterations on photosynthetic rates, photosynthetic pigment concentrations and chlorophyll fluorescence, as well as in nutrient homeostasis.     

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.     

Dynamic flux cartography of hairy roots primary metabolism

A dynamic model for plant cell and hairy root primary metabolism is presented. The model includes nutrient uptake (Pi, sugars, nitrogen sources), the glycolysis and pentose phosphate pathways, the TCA cycle, amino acid biosynthesis, respiratory chain, biosynthesis of cell building blocks (structural hexoses, organic acids, lipids, and organic phosphated molecules). The energy shuttles (ATP, ADP) and cofactors (NAD/H, NADP/H) are also included. The model describes the kinetics of 44 biochemical reactions (fluxes) of the primary metabolism of plant cells and includes 41 biochemical species (metabolites, nutrients, biomass components). Multiple Michaelis-Menten type kinetics are used to describe biochemical reaction rates. Known regulatory phenomena on metabolic pathways are included using sigmoid switch functions. A visualization framework showing fluxes and metabolite concentrations over time is presented. The visualization of fluxes and metabolites is used to analyze simulation results from Catharanthus roseus hairy root 50 d batch cultures. The visualization of the metabolic system allows analyzing split ratios between pathways and flux time-variations. For carbon metabolism, the cells were observed to have relatively high and stable fluxes for the central carbon metabolism and low and variable fluxes for anabolic pathways. For phosphate metabolism, a very high free intracellular Pi turnover rate was observed with higher flux variations than for the carbon metabolism. Nitrogen metabolism also exhibited large flux variations. The potential uses of the model are also discussed.     

Origin of cadmium-induced reactive oxygen species production: mitochondrial electron transfer versus plasma membrane NADPH oxidase

* Cadmium (Cd(2+)) is an environmental pollutant that causes increased reactive oxygen species (ROS) production. To determine the site of ROS production, the effect of Cd(2+) on ROS production was studied in isolated soybean (Glycine max) plasma membranes, potato (Solanum tuberosum) tuber mitochondria and roots of intact seedlings of soybean or cucumber (Cucumis sativus). * The effects of Cd(2+) on the kinetics of superoxide (O2*-), hydrogen peroxide (H(2)O(2)) and hydroxyl radical ((*OH) generation were followed using absorption, fluorescence and spin-trapping electron paramagnetic resonance spectroscopy. * In isolated plasma membranes, Cd(2+) inhibited O2*- production. This inhibition was reversed by calcium (Ca(2+)) and magnesium (Mg(2+)). In isolated mitochondria, Cd(2+) increased and H(2)O(2) production. In intact roots, Cd(2+) stimulated H(2)O(2) production whereas it inhibited O2*- and (*)OH production in a Ca(2+)-reversible manner. * Cd(2+) can be used to distinguish between ROS originating from mitochondria and from the plasma membrane. This is achieved by measuring different ROS individually. The immediate (相似文献   

Assessing the relative contributions of phytochelatins and the cell wall to cadmium resistance in white lupin

In response to Cd stress, higher plants utilise a number of defence systems, such as retention in cell walls, binding by organic molecules in the cytosol and sequestration in the vacuole. White lupin is a Cd-resistant legume that is of interest for phytoremediation of acidified and Cd-contaminated soils. The aim of this research was to evaluate the contributions of various mechanisms of Cd detoxification used by this species, focusing on cell-wall retention and binding by thiol-rich compounds. Retention of Cd by the cell wall of white lupin was well described by a Langmuir isotherm model. The percentage of total Cd adsorbed by the cell wall ranged from 29 to 47% in leaves, from 38 to 51% in stems and from 26 to 42% in roots depending on the Cd supply. Cadmium induced the synthesis of high levels of phytochelatins (PCs) in lupin plants, mainly in roots, with PC₃ being the major PC. The amount of Cd complexed by thiols accounted for approximately 20% of the total Cd in leaves, 40% in stems and 20% in roots. Therefore, cell-wall retention could account for more than twice the amount of Cd complexed by PCs in leaves and roots. In stems, both mechanisms contributed equally to Cd detoxification. These studies indicate that white lupin plants use cell-wall binding and, secondarily, the production of PCs, as effective mechanisms of Cd detoxification.     

Physiological basis of different allelopathic reactions of cucumber and figleaf gourd plants to cinnamic acid

To provide an insight into the mechanism of interspecific interactions mediated by allelochemicals, cucumber and figleaf gourd seedlings were compared on their response to cinnamic acid, an autotoxin from root exudates of cucumber. Reactive oxygen species metabolism and plasma membrane H(+)-ATPase activity were examined in roots upon exposure to cinnamic acid. This exposure resulted in significant increases in activities of NADPH oxidase, superoxide dismutase, guaiacol peroxidase, and catalase, as well as in O(2)(.-) production and H(2)O(2) content, in cucumber roots but not in figleaf gourd roots. Notably, the cucumber roots produced significant amount of reactive oxygen species (ROS) immediately after cinnamic acid treatment, consequently increasing membrane peroxidation, decreasing membrane H(+)-ATPase activity, and losing root viability. By contrast, no such changes were observed in figleaf gourd roots. All these results indicated that there was an interspecies difference in the recognition of allelochemicals, which induced oxidative stress accompanied by root cell death in cucumber, an autotoxic plant, but not in figleaf gourd, a cucumber relative.     

Arbuscular mycorrhizal symbiosis elicits proteome responses opposite of P-starvation in SO4 grapevine rootstock upon root colonisation with two Glomus species

Although plant biotisation with arbuscular mycorrhizal fungi (AMF) is a promising strategy for improving plant health, a better knowledge regarding the molecular mechanisms involved is required. In this context, we sought to analyse the root proteome of grapevine rootstock Selection Oppenheim 4 (SO4) upon colonisation with two AMF. As expected, AMF colonisation stimulates plant biomass. At the proteome level, changes in protein amounts due to AMF colonisation resulted in 39 differentially accumulated two-dimensional electrophoresis spots in AMF roots relative to control. Out of them, 25 were co-identified in SO4 roots upon colonisation by Glomus irregulare and Glomus mosseae supporting the existence of conserved plant responses to AM symbiosis in a woody perennial species. Among the 18 proteins whose amount was reduced in AMF-colonised roots were proteins involved in glycolysis, protein synthesis and fate, defence and cell rescue, ethylene biosynthesis and purine and pyrimidine salvage degradation. The six co-identified proteins whose amount was increased had functions in energy production, signalling, protein synthesis and fate including proteases. Altogether these data confirmed that a part of the accommodation program of AMF previously characterized in annual plants is maintained within roots of the SO4 rootstock cuttings. Nonetheless, particular responses also occurred involving proteins of carbon metabolism, development and root architecture, defence and cell rescue, anthocyanin biosynthesis and P remobilization, previously reported as induced upon P-starvation. This suggests the occurrence of P reprioritization upon AMF colonization in a woody perennial plant species with agronomical interest.     

Growth responses of <Emphasis Type="Italic">Sagittaria sagittifolia</Emphasis> L. plants to water contamination with cadmium

Cadmium accumulation, the relative content of different chemical forms of Cd, as well as the toxic effect of Cd on nutrient element uptake, physiological parameters, and ultrastructure of Sagittaria sagittifolia L. seedlings were determined after the seedlings were exposed to different Cd concentrations for 4 days. The results showed that S. sagittifolia had the ability to accumulate large amounts of Cd. In the root, stem, and bulb, the predominant chemical Cd forms were NaCl extractable. With an increase in the Cd²⁺ concentration, the chlorophyll content, the relative membrane penetrability (RMP) of root cells, peroxidase (POD) activity, superoxide dismutase (SOD) activity in leaves, malondiadehyde (MDA) content and the superoxide anion (O₂⁻) generation rate in roots all decreased following an initial increase. On the other hand, catalase (CAT) activity, SOD activity in roots, MDA content, and the generation rate of O₂⁻ in leaves all increased gradually. The toxic effect of Cd²⁺ was more severe on roots than on leaves at the same concentration. Cadmium affected the mineral nutrition balance; mainly, it promoted the uptake of Ca, Cu, Mn, and Fe, while inhibited Mg, Na, and K uptake. The physiological toxic effect of Cd²⁺ was close to the ultrastructural damage induced by Cd contamination. A significant correspondence was observed between the Cd dose and its toxic effect. Cadmium could destroy the normal ultrastructure, disturb the ion balance, and interfere with cell metabolism.     

Root adaptations to cadmium-induced oxidative stress contribute to Cd tolerance in the hyperaccumulator Sedum alfredii

Short-term responses of Sedum alfredii roots to Cd exposure was compared in Cd hyperaccumulator (HE) and nonhyperaccumulating ecotype (NHE). Cadmium exposure significantly inhibited root elongation and induced loss of plasma membrane integrity and lipid peroxidation of roots tips in the NHE, whereas these effects were much less pronounced in the HE plants. A strong accumulation of reactive oxygen species with increasing Cd concentration was noted in the NHE root tips, but not in HE. After Cd exposure, a dose-dependent decrease in oxidized glutathione and marked increase in reduced glutathione and non-protein thiols were observed in root tips of HE, but were not seen in the NHE plants. These results suggest that the HE tolerates high Cd in the environment through the differential adaptations against Cd-induced oxidative stress.