Glutamine synthetase and glutamate dehydrogenase in cadmium-stressed triticale seedlings

The studies were performed on young triticale seedlings grown on a mineral medium containing 5 mM NO ₃ ⁻ as the nitrogen source, with the addition of 0.5 mM CdCl₂. It was determined that cadmium ions accumulated mainly in the plant roots. Decreases in nitrate concentrations both in the roots and shoots of seedlings, as well as decreases in soluble protein contents with simultaneous increases in endopeptidase activity were also observed. Both in roots and shoots significant decreases in glutamic acid were noted. Toxic cadmium ion accumulation in seedlings significantly modified activity of primary nitrogen assimilating enzymes, i.e. glutamine synthetase (GS, EC 6.3.1.2) and glutamate dehydrogenase (GDH, EC 1.4.1.2). There was a significant decrease in GS activity both in roots and in shoots of the stressed plants, in comparison to plants grown without cadmium. In shoots of the control plants and plants subjected to stress two GS isoforms were discovered: cytoplasmatic (GS₁) and chloroplastic (GS₂). Substantial decreases in total glutamine synthetase activity in green parts of seedlings, occurring under stress conditions, result from dramatic decrease in GS₂ activity (by 60 % in relation to the control plants); despite simultaneous increases in the cytoplasmatic isoform (GS₁) activity by approx. 96 %. Cadmium ions accumulating in roots and shoots of seedlings not only increased GDH activity, but also modified its coenzymatic specificity.     

Cadmium-Induced Changes in Leaf Epidermes, Photosynthetic Rate and Pigment Concentrations in Cajanus Cajan

Application of different concentrations of cadmium [5, 10, 15, 25 and 50 g(CdCl₂) g^–1(soil d.m.)] markedly affected leaves of Cajanus cajan (Linn.) Huth. Due to increased Cd content in leaves, stomatal density and size on abaxial epidermis, and the size of stomatal aperture and length and density of trichomes on both leaf epidermes decreased significantly in the treated plants. Net photosynthetic rate and stomatal conductance were reduced significantly at each concentration of cadmium, whereas reduction in intercellular carbon dioxide concentration was significant at 10 g Cd onwards. The contents of chlorophyll a, chlorophyll b and carotenoids were relatively low during early stages of plant development under the effect of Cd. Nitrate content, nitrate reductase activity and protein content were also lower in treated plants, compared with control.     

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.     

Cadmium toxicity is reduced by nitric oxide in rice leaves

We evaluate the protective effect of nitric oxide (NO) against Cadmium (Cd) toxicity in rice leaves. Cd toxicity of rice leaves was determined by the decrease of chlorophyll and protein contents. CdCl₂ treatment resulted in (1) increase in Cd content, (2) induction of Cd toxicity, (3) increase in H₂O₂ and malondialdehyde (MDA) contents, (4) decrease in reduced form glutathione (GSH) and ascorbic acid (ASC) contents, and (5) increase in the specific activities of antioxidant enzymes (superoxide dismutase, glutathione reductase, ascorbate peroxidase, catalase, and peroxidase). NO donors [N-tert-butyl-α-phenylnitrone, 3-morpholinosydonimine, sodium nitroprusside (SNP), and ASC + NaNO₂] were effective in reducing CdCl₂-induced toxicity and CdCl₂-increased MDA content. SNP prevented CdCl₂-induced increase in the contents of H₂O₂ and MDA, decrease in the contents of GSH and ASC, and increase in the specific activities of antioxidant enzymes. SNP also prevented CdCl₂-induced accumulation of NH₄ ⁺, decrease in the activity of glutamine synthetase (GS), and increase in the specific activity of phenylalanine ammonia-lyase (PAL). The protective effect of SNP on CdCl₂-induced toxicity, CdCl₂-increased H₂O₂, NH₄ ⁺, and MDA contents, CdCl₂-decreased GSH and ASC, CdCl₂-increased specific activities of antioxidant enzymes and PAL, and CdCl₂-decreased activity of GS were reversed by 2-(4-carboxy-2-phenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide, a NO scavenger, suggesting that protective effect by SNP is attributable to NO released. Reduction of CdCl₂-induced toxicity by NO in rice leaves is most likely mediated through its ability to scavenge active oxygen species including H₂O₂.     

Effects of cadmium and salicylic acid on growth, spectral reflectance and photosynthesis of castor bean seedlings

Salicylic acid (SA) is a potent signaling molecule in plants and is involved in eliciting specific responses to biotic and abiotic stresses. The aim of this study is to investigate whether the exogenous application of SA can improve cadmium (Cd) induced inhibition of photosynthesis in castor bean (Ricinus communis L.) plants. The effects of SA and Cd on plant growth, spectral reflectance, pigment contents, chlorophyll fluorescence and gas exchange were examined in a hydroponic cultivation system. Results indicate that Cd exposure significantly decreased the dry biomass, photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), pigment contents, quantum yield of PS II photochemistry (F_v/F_m), and effective quantum yield of PS II (??PS II) in the plants. Pretreatment with SA alone reduced the biomass and P_n in castor bean plants, whereas pigment contents, F_v/F_m and ??PS II remained unaffected. Reduced G_s, C_i and E, as well as increased stomatal limitation (L_s) and water use efficiency (WUE), were observed in plants pretreated with 500???M SA alone, whereas plants treated with 250???M SA were unaffected. Under Cd stress, SA pretreatment led to a significant decrease in P_n, G_s, E, C_i, and chlorophyll contents (Chl a, Chl b, Chl a+b, Car, Chl a/b), and an increase in L_s and WUE. Cd exposure enhanced spectral reflectance in the range 550?C680?nm and 750?C1,050?nm. It also decreased the normalized difference vegetation index (_chlNDI), the modified red edge simple ratio index (mSR₇₀₅), the red edge position (REP), water band index, and red/green ratio, whereas the structure independent pigment index (SIPI) was increased. Significant correlations (P?<?0.01) between spectral indices (mSR₇₀₅, _chlNDI, REP, red/green ratio) and pigment contents. SA significantly worsened plant growth and photosynthesis in Cd-stressed castor bean plants, in which a stomatal limitation was involved. The leaf spectral reflectance is a sensitive indicator in determining Cd toxicity in plants.     

The beneficial role of potassium in Cd-induced stress alleviation and growth improvement in Gladiolus grandiflora L.

Heavy metal contaminated agricultural soils are one of the most important constraints for successful cultivation of crops. The current research was conducted to evaluate the role of potassium (K) on plant growth and amelioration of cadmium (Cd) stress in Gladiolus grandiflora under greenhouse conditions. G. grandiflora corms were sown in media contaminated with 0 (C), 50 (Cd50) and 100 (Cd100) mg Cd kg^?1 soil. The plants growing in Cd-contaminated media exhibited reduced gas exchange attributes, chlorophyll (Chl) contents, vegetative and reproductive growth as compared to control. The plants raised in Cd contaminated media showed reduced nutrition yet higher Cd contents. However, supplementation of 60 mg Kg^?1 K in treated plants (C+K, Cd50+K and Cd100+K) improved quantity of total soluble protein and proline (Pro) along with activity of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and ascorbate peroxidase (APX) under Cd stress. Similarly, K supplementation reduced the level of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) in treated plants. Potassium supplemented plants exhibited better vegetative and reproductive growth. The improved stress tolerance in K supplemented plants was attributed to the reduced quantity of MDA and H₂O₂, enhanced synthesis of protein, proline, phenols, flavonides and improved activity of antioxidant enzymes. The present research supports the application of K for alleviation of Cd stress in G. grandiflora.     

Cadmium-Induced Hydrogen Accumulation Is Involved in Cadmium Tolerance in Brassica campestris by Reestablishment of Reduced Glutathione Homeostasis

Hydrogen gas (H₂) was recently proposed as a therapeutic antioxidant and signaling molecule in clinical trials. However, the underlying physiological roles of H₂ in plants remain unclear. In the present study, hydrogen-rich water (HRW) was used to characterize the physiological roles of H₂ in enhancing the tolerance of Brassica campestris against cadmium (Cd). The results showed that both 50 μM CdCl₂ and 50%-saturated HRW induced an increase of endogenous H₂ in Brassica campestris seedlings, and HRW alleviated Cd toxicity related to growth inhibition and oxidative damage. Seedlings supplied with HRW exhibited increased root length and reduced lipid peroxidation, similar to plants receiving GSH post-treatment. Additionally, seedlings post-treated with HRW accumulated higher levels of reduced glutathione (GSH) and ascorbic acid (AsA) and showed increased GST and GPX activities in roots. Molecular evidence illustrated that the expression of genes such as GS, GR1 and GR2, which were down-regulated following the addition of Cd, GSH or BSO, could be reversed to varying degrees by the addition of HRW. Based on these results, it could be proposed that H₂ might be an important regulator for enhancing the tolerance of Brassica campestris seedlings against Cd, mainly by governing reduced glutathione homeostasis.     

Cd2+ influences metabolism and elemental distribution in roots of Acanthus ilicifolius L.

Abstract

Effect of cadmium (Cd) on the primary metabolic activities and elemental distribution in roots was explored in Acanthus ilicifolius L., a halophyte with phytostabilization potential. The rate of photosynthesis decreased in the CdCl₂ treated plants and this reduction was mainly attributed to the reduction of leaf area, photosynthetic pigments, impaired gaseous exchange caused by the stomatal closure and tissue water status. However, respiration rate was significantly higher in the CdCl₂ treated plants which aid the plant with additional energy required for the metabolic activities. Distribution of essential elements in the roots exhibited significant differences from that of control, which indicate the nutritional adaptation developed by A. ilicifolius under the influence of toxic metal ions. Thus, Cd toxicity is neutralized through the resource allocation from the growth process to processes that increase the fitness of the plant to encounter adverse environmental condition. In addition, the absorbed Cd is retained in the cortical cells of root thereby preventing the upward movement to shoot thereby making the plant a potential candidate for phytostabilization of Cd.     

Root nutrient uptake enhances photosynthetic assimilation in prey-deprived carnivorous pitcher plant <Emphasis Type="Italic">Nepenthes talangensis</Emphasis>

Carnivorous plants grow in nutrient-poor habitats and obtain substantial amount of nitrogen from prey. Specialization toward carnivory may decrease the ability to utilize soil-derived sources of nutrients in some species. However, no such information exists for pitcher plants of the genus Nepenthes, nor the effect of nutrient uptake via the roots on photosynthesis in carnivorous plants is known. The principal aim of present study was to investigate, whether improved soil nutrient status increases photosynthetic efficiency in prey-deprived pitcher plant Nepenthes talangensis. Gas exchange and chlorophyll (Chl) fluorescence were measured simultaneously and were correlated with Chl and nitrogen concentration as well as with stable carbon isotope abundance (δ¹³C) in control and fertilized N. talangensis plants. Net photosynthetic rate (P _N) and maximum- (F_v/F_m) and effective quantum yield of photosystem II (Φ_PSII) were greater in the plants supplied with nutrients. Biomass, leaf nitrogen, and Chl (a+b) also increased in fertilized plants. In contrast, δ¹³C did not differ significantly between treatments indicating that intercellular concentration of CO₂ did not change. We can conclude that increased root nutrient uptake enhanced photosynthetic efficiency in prey-deprived N. talangensis plants. Thus, the roots of Nepenthes plants are functional and can obtain a substantial amount of nitrogen from the soil.     

Nitrate photo-assimilation in tomato leaves under short-term exposure to elevated carbon dioxide and low oxygen

The role of photorespiration in the foliar assimilation of nitrate (NO₃^–) and carbon dioxide (CO₂) was investigated by measuring net CO₂ assimilation, net oxygen (O₂) evolution, and chlorophyll fluorescence in tomato leaves (Lycopersicon esculentum). The plants were grown under ambient CO₂ with ammonium nitrate (NH₄NO₃) as the nitrogen source, and then exposed to a CO₂ concentration of either 360 or 700 µmol mol^?1, an O₂ concentration of 21 or 2%, and either NO₃^– or NH₄⁺ as the sole nitrogen source. The elevated CO₂ concentration stimulated net CO₂ assimilation under 21% O₂ for both nitrogen treatments, but not under 2% O₂. Under ambient CO₂ and O₂ conditions (i.e. 360 µmol mol^?1 CO₂, 21% O₂), plants that received NO₃^– had 11–13% higher rates of net O₂ evolution and electron transport rate (estimated from chlorophyll fluorescence) than plants that received NH₄⁺. Differences in net O₂ evolution and electron transport rate due to the nitrogen source were not observed at the elevated CO₂ concentration for the 21% O₂ treatment or at either CO₂ level for the 2% O₂ treatment. The assimilatory quotient (AQ) from gas exchange, the ratio of net CO₂ assimilation to net O₂ evolution, indicated more NO₃^– assimilation under ambient CO₂ and O₂ conditions than under the other treatments. When the AQ was derived from gross O₂ evolution rates estimated from chlorophyll fluorescence, no differences could be detected between the nitrogen treatments. The results suggest that short‐term exposure to elevated atmospheric CO₂ decreases NO₃^– assimilation in tomato, and that photorespiration may help to support NO₃^– assimilation.     

Heat shock proteins are induced by cadmium in Drosophila cells

Drosophila cells were treated with increasing concentrations of CdCl₂ (10 μM-1 mM). The toxicity of cadmium, as observed by cellular death and the ability of the cells to survive after removal of CdCl₂, depended on concentration and duration of treatment. The overall synthesis of protein, measured by incorporation of [³⁵S]methionine, decreased. It fell to 66% of the controls after 24 h of exposition to 50 μM CdCl₂ and to 29% after 48 h. We showed that cadmium induced the synthesis of ‘heat shock proteins’ (hsps), which started after 6 h and was maximal after 24 h of 50–100 μM CdCl₂ treatment.     

Antioxidant capacity and cadmium accumulation in parsley seedlings exposed to cadmium stress

Parsley (Petroselinum hortense L.) plants cultivated under controlled conditions were exposed to different doses of cadmium to investigate the antioxidant capacity and cadmium accumulation in the samples. Two-months-old parsley seedlings were treated with four different concentrations of CdCl₂ (0, 75, 150, and 300 μM) for fifteen days. Cadmium level in leaves increased significantly by increasing the Cd contamination in the soil. Total chlorophyll and carotenoid content declined considerably with Cd concentration. Cd treatment caused a significant increase lipid peroxidation in tissue of leaf. Superoxide dismutase activity (SOD, EC 1.15.1.1) increased partially at 75 and 150 μM CdCl₂ concentrations whereas the activity decreased at 300 μM CdCl₂. Catalase (CAT, EC 1.11.1.6) and ascorbate peroxidase (APX, EC 1.11.1.11) activities were reduced by Cd application. Total phenolic compound amount increased significantly with increasing Cd concentration, as ferric reduction power, superoxide anion radical, and DPPH˙ free radical scavenging activities elevated slightly by the concentration. These results suggest that antioxidant enzymes activities were repressed depending on accumulation of cadmium in leaves of parsley while the non-enzymatic antioxidant activities slightly increased.     

Cadmium toxicity of rice leaves is mediated through lipid peroxidation

Oxidative stress, in relation to toxicity of detached rice leaves,caused by excess cadmium was investigated. Cd content inCdCl₂-treated detached rice leaves increased with increasingdurationof incubation in the light. Cd toxicity was followed by measuring the decreasein chlorophyll and protein. CdCl₂ was effective in inducing toxicityand increasing lipid peroxidation of detached rice leaves under both light anddark conditions. These effects were also observed in rice leaves treated withCdSO₄, indicating that the toxicity was indeed attributed to cadmiumions. Superoxide dismutase (SOD), ascorbate peroxidase (APOD), and glutathionereductase (GR) activities were reduced by excess CdCl₂ in the light.The changes in catalase and peroxidase activities were observed inCdCl₂-treated rice leaves after the occurrence of toxicity in thelight. Free radical scavengers reduced CdCl₂-induced toxicity and atthe same time reduced CdCl₂-induced lipid peroxidation and restoredCdCl₂-decreased activities of SOD, APOD, and GR in the light. Metalchelators (2,2-bipyridine and 1,10-phenanthroline) reducedCdCl₂ toxicity in rice leaves in the light. The reduction ofCdCl₂ toxicity by 2,2-bipyridine (BP) is closely associatedwith a decrease in lipid peroxidation and an increase in activities ofantioxidative enzymes. Furthermore, BP-reduced toxicity of detached riceleaves,induced by CdCl₂, was reversed by adding Fe²⁺ orCu²⁺, but not by Mn²⁺ or Mg²⁺.Reduction of CdCl₂ toxicity by BP is most likely mediated throughchelation of iron. It seems that toxicity induced by CdCl₂ mayrequire the participation of iron.     

Multi-Wall Carbon Nanotubes Effects on Plant Seedlings Growth and Cadmium/Lead Uptake In Vitro

The effects of multi-wall carbon nanotubes (MWCNTs) on plant growth and Cd/Pb accumulation was investigated on seedlings of three plant species including Brassica napus L., Helianthus annus L. and Cannabis sativa L. The experiment consisted of MWCNTs on three concentration levels (0, 10, 50 mg/L) and 200 μM CdCl₂ or 500 μM Pb(NO₃)₂. MWCNTs application effectively improved root and shoot growth inhibited by Cd and Pb salts. In B. napus, total chlorophyll (Chl) content increased by both MWCNTs 10 and 50 mg/L exposure under cadmium or lead stress. MWCNT 10 mg/L mitigated the deleterious effects of Cd ions on total chlorophyll content of H. annus and C. sativa. Wherease higher concentration of MWCNTs decreased Chl content under either Cd or Pb treatments on sunflower seedlings. MWCNT10 effectivly raised cadmium accumulation in seedlings of all three species. MWCNT10 and 50 mg/L also caused higher Pb accumulation in canola and cannabis seedlings, respectively. Based on the results, it seems that the effects of MWCNTs on growth parameters and heavy metal accumulation in plant seedlings is strongly depends on heavy metal type, MWCNTs concentration and plant species.     

Inhibition of chlorophyll biosynthesis by lead in greeningPisum sativum leaf segments

Supply of 0.01 to 1.0 mM lead acetate to greening pea(Pisum sativum L.) leaf segments either in the absence or in the presence of inorganic nitrogen lowered total chlorophyll (Chl) content. During a time course study, there was not any appreciable effect of Pb²⁺ upto 4 h but thereafter Pb inhibited Chl synthesis. While supply of succinate, cysteine dithiothreitol, 5,5-dithio-bis-2-nitrobenzoic acid and NH₄C1 had no protective action against Pb²⁺ toxicity, and glycine, glutamate 2-oxoglutarate, MgCl₂, KH₂PO₄, CaCl₂, KC1 protected only partially, reduced glutathione (GSH) could completely overcome the inhibition of Chl biosynthesis by the metal. It is suggested that Pb²⁺ interferes with Chl biosynthesis through GSH availability     

Exogenous nitric oxide enhances cadmium tolerance of rice by increasing pectin and hemicellulose contents in root cell wall

To study the mechanisms of exogenous NO contribution to alleviate the cadmium (Cd) toxicity in rice (Oryza sativa), rice plantlets subjected to 0.2-mM CdCl₂ exposure were treated with different concentrations of sodium nitroprusside (SNP, a NO donor), and Cd toxicity was evaluated by the decreases in plant length, biomass production and chlorophyll content. The results indicated that 0.1 mM SNP alleviated Cd toxicity most obviously. Atomic absorption spectrometry and fluorescence localization showed that treatment with 0.1 mM SNP decreased Cd accumulation in both cell walls and soluble fraction of leaves, although treatment with 0.1 mM SNP increased Cd accumulation in the cell wall of rice roots obviously. Treatment with 0.1 mM SNP in nutrient solution had little effect on the transpiration rate of rice leaves, but this treatment increased pectin and hemicellulose content and decreased cellulose content significantly in the cell walls of rice roots. Based on these results, we conclude that decreased distribution of Cd in the soluble fraction of leaves and roots and increased distribution of Cd in the cell walls of roots are responsible for the NO-induced increase of Cd tolerance in rice. It seems that exogenous NO enhances Cd tolerance of rice by increasing pectin and hemicellulose content in the cell wall of roots, increasing Cd accumulation in root cell wall and decreasing Cd accumulation in soluble fraction of leaves.     

Cadmium modulates NADPH oxidase activity and expression in sunflower leaves

The production of reactive oxygen species (ROS) and the ways by which ROS are generated are very important facts related to heavy metal toxicity in plants. In this work, superoxide anion (O₂ ^·−) generation diminished in cadmium treated sunflower (Helianthus annuus L.) leaf discs, and this reduction was time and Cd-concentration dependent. In line with these findings, we observed that NADPH-dependent oxidase activity was significantly inhibited by 0.1 and 0.5 mM Cd²⁺ treatments and the expression of the NADPH oxidase putative gene related to O₂ ^·− synthesis in sunflower leaves was 83 % inhibited by 0.1 mM CdCl₂ and almost completely depleted by 0.5 mM CdCl₂.     

Rhizoremediation of Cadmium Soil Using a Cadmium-Resistant Plant Growth-Promoting Rhizopseudomonad

Three pseudomonad strains (MKRh1, MKRh3, and MKRh4) isolated from rhizospheres showed a high growth potential in the presence of cadmium, with a minimal inhibitory concentration of 7 mM for cadmium chloride (CdCl₂). Among them, isolate MKRh3 was specifically chosen as the most favorable cadmium-resistant plant growth-promoting rhizobacterium based on its higher 1-aminocyclopropane carboxylic acid deaminase activity, siderophore production, phosphate solubilization, and auxin synthesis and the in vivo growth increment of black gram plants. 16S ribosomal RNA gene sequencing identified MKRh3 as Pseudomonas aeruginosa. The effect of cadmium on black gram plants was studied in soil amended with a gradient of CdCl₂ concentration and the toxicity was evident from stunted growth, poor rooting, and cadmium accumulation. Application of isolate MKRh3 by seed coating overcomes the cadmium toxicity; plants showed lessened cadmium accumulation, extensive rooting, and enhanced plant growth. Further research and development of this promising innate strategy for scale-up to higher-efficiency and large-scale application will be a potent tool to prevent accumulation of cadmium in plants, thereby ensuring food security for humans.     

Effects of pH and nitrogen on cadmium uptake in potato

This study investigated the effects of pH and nitrogen form and concentration on cadmium (Cd) uptake by potato (Solanum tuberosum L.) grown in hydroponic culture. Potato plants grown in a pH-buffered nutrient solution for 10 d were exposed for 24 h to 25 nM CdCl₂ labelled with ¹⁰⁹Cd. Plants showed a significantly higher Cd uptake and accumulation at pH 6.5 than at pH 4.5 and 5.5. Nitrogen supplied as nitrate (NO₃ ^?) generally resulted in a higher Cd uptake and accumulation than N supplied as ammonium (NH₄ ⁺). This effect was most pronounced at pH 6.5. The N concentration increasing from 6.5 to 26 mM resulted in a decreased Cd influx when either NO₃ ^? or NH₄ ⁺ was used. Cd translocation to the shoot was increased when NO₃ ^? was used as the sole N source. In conclusion, pH had a strong influence on Cd uptake by roots and N form is especially important for Cd translocation within the potato plant.     

Acquired tolerance of tomato (Lycopersicon esculentum cv. Micro‐Tom) plants to cadmium‐induced stress

The effects of varying concentrations of cadmium (Cd) on the development of Lycopersicon esculentum cv. Micro‐Tom (MT) plants were investigated after 40 days (vegetative growth) and 95 days (fruit production), corresponding to 20 days and 75 days of exposure to CdCl₂, respectively. Inhibition of growth was clearly observed in the leaves after 20 days and was greater after 75 days of growth in 1 mM CdCl₂, whereas the fruits exhibited reduced growth following the exposure to a concentration as low as 0.1 mM CdCl₂. Cd was shown to accumulate in the roots after 75 days of growth but was mainly translocated to the upper parts of the plants accumulating to high concentrations in the fruits. Lipid peroxidation was more pronounced in the roots even at 0.05 mM CdCl₂ after 75 days, whereas in leaves, there was a major increase after 20 days of exposure to 1 mM CdCl₂, but the fruit only exhibited a slight significant increase in lipid peroxidation in plants subjected to 1 mM CdCl₂ when compared with the control. Oxidative stress was also investigated by the analysis of four key antioxidant enzymes, which exhibited changes in response to the increasing concentrations of Cd tested. Catalase (EC 1.11.1.6) activity was shown to increase after 75 days of Cd treatment, but the major increases were observed at 0.1 and 0.2 mM CdCl₂, whereas guaiacol peroxidase (EC 1.11.1.7) did not vary significantly from the control in leaves and roots apart from specific changes at 0.5 and 1 mM CdCl₂. The other two enzymes tested, glutathione reductase (EC 1.6.4.2) and superoxide dismutase (SOD, EC 1.15.1.1), did not exhibit any significant changes in activity, apart from a slight decrease in SOD activity at concentrations above 0.2 mM CdCl₂. However, the most striking results were obtained when an extra treatment was used in which a set of plants was subjected to a stepwise increase in CdCl₂ from 0.05 to 1 mM, leading to tolerance of the Cd applied even at the final highest concentration of 1 mM. This apparent adaptation to the toxic effect of Cd was confirmed by biomass values being similar to the control, indicating a tolerance to Cd acquired by the MT plants.