Influence of cadmium on antioxidant capacity and four microelement concentrations in tomato seedlings (Lycopersicon esculentum)

Tomato (Lycopersicon esculentum) seedlings were grown in four cadmium (Cd) levels of 0-10 microM in a hydroponic system to analyze the antioxidative enzymes, Cd concentration in the plants, and the interaction between Cd and four microelements. The results showed that there was a significant increase in malondialdehyde (MDA) concentration, and superoxide dismutase (SOD) and peroxidase (POD) activities in the plants subjected to 1-10 microM Cd. This indicates that Cd stress induces an oxidative stress response in tomato plants, characterized by an accumulation of MDA and increase in activities of SOD and POD. Root, stem and leaf Cd concentrations increased with its exposure Cd level, and the highest Cd concentration occurred in roots, followed by leaves and stems. A concentration- and tissue-dependent response was found in the four microelement concentrations to Cd stress in the tomato leaves, stems and roots. Regression analysis showed that there was a significantly negative correlation between Cd and Mn, implying the antagonistic effect of Cd on Mn absorption and translocation. The correlation between Cd and Zn, Cu and Fe were inconsistent among leaves, stems and roots.     

Chromium induced lipid peroxidation in the plants of Pistia stratiotes L.: role of antioxidants and antioxidant enzymes

In the plant, Pistia stratiotes L., the effect of different concentrations of chromium (0, 10, 40, 80 and 160 microM) applied for 48, 96 and 144 h was assessed by measuring changes in the chlorophyll, protein, malondialdehyde (MDA), cysteine, non-protein thiol, ascorbic acid contents and superoxide dismutase (SOD), ascorbate peroxidase (APX) and guiacol peroxidase (GPX) activity of the plants. Both in roots and leaves, an increase in MDA content was observed with increase in metal concentration and exposure periods. In roots, the activity of antioxidant enzymes viz. SOD and APX increased at all the concentrations of Cr at 144 h than their controls. The GPX activity of the treated roots increased with increase in Cr concentration at 48 and 96 h of exposures, however, at 144 h its activity was found declined beyond 10 microM Cr. The level of antioxidants in the roots of the treated plant viz. cysteine and ascorbic acid was also found increased at all the concentrations of Cr at 144 h than their respective controls, however, an increase in the non-protein thiol content was recorded up to 40 microM Cr followed by decrease. The chlorophyll content decreased with increase in Cr concentrations and exposure periods. However, the protein content of both roots and leaves were found decreased with increase in Cr concentrations at all the exposure periods except an increase was recorded at 10 microM Cr at 48 h. In Cr treated plants, the no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for leaves chlorophyll and protein contents were 40 and 80 microM Cr, respectively after 48 h exposure while NOEC and LOEC for root protein content were 10 and 40 microM, respectively after 48 h. The analysis of correlation coefficient data revealed that the metal accumulation in the roots of the plant was found positively correlated with antioxidant parameters except SOD after 48 h of exposure, however, negatively correlated with most of all the parameters studied at 144 h in both part of the plant. It may be suggested from the present study that toxic concentrations of Cr cause oxidative damage as evidenced by increased lipid peroxidation and decreased chlorophyll and protein contents. However, the higher levels of enzymatic and non-enzymatic antioxidants suggest the reason for tolerating higher levels of metals.     

Antioxidant responses to simulated acid rain and heavy metal deposition in birch seedlings

This study measured the responses of different anti-oxidants in 2-year-old birch (Betula pendula Roth) seedlings subjected to simulated acid rain (pH 4.0) and heavy metals (Cu/Ni), applied alone or in combination for 2 months. The applied concentrations of pollutants did not significantly affect seedling biomass or total glutathione levels. Acid rain alone increased superoxide dismutase (SOD) activity both in leaves and roots, while heavy metals alone inhibited SOD activity in roots. Both acid rain and heavy metals applied singly increased ascorbate peroxidase (APX) and guaiacol peroxidase (GPX) activities in leaves but decreased activities in roots. In contrast, acid rain and heavy metal treatments increased glutathione reductase (GR) activity in roots but not in leaves. Spraying birch seedlings with a mixture of acid rain and heavy metals increased SOD, APX and GPX activities in leaves and GR activity in roots. However, the effects of mixed pollutants on enzyme activities usually were less than the summed effects of individual pollutants. Enzyme responses also depended on where pollutants were applied: spraying pollutants onto the shoots initiated higher responses in SOD, APX and GPX than did application to the soil surface, while the opposite was true for GR.     

Involvement of abscisic acid in regulating antioxidative defense systems and IAA-oxidase activity and improving adventitious rooting in mung bean [Vigna radiata (L.) Wilczek] seedlings under cadmium stress

In vitro experiments were conducted to investigate the effects of abscisic acid (ABA) and Cd on antioxidative defense systems and indole-3-acetic acid (IAA) oxidase during adventitious rooting in mung bean [Vigna radiata (L.) Wilczek] seedlings. The exogenous ABA significantly enhanced the number and fresh weight of the adventitious roots. CdCl₂ strongly inhibited adventitious rooting. Pretreatment with 10 μM ABA clearly alleviated the inhibitory effect of Cd on rooting. ABA significantly reduced superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT) activities, as well as the levels of glutathione (GSH) and ascorbic acid (ASA) during adventitious rooting. ABA strongly increased IAA-oxidase activity during the induction (0–12 h) and expression (after 48 h) phases and increased the phenols levels. Cd treatment significantly reduced the activities of SOD, APX, POD, and IAA oxidase, as well as GSH level. Cd strongly increased ASA levels. ABA pretreatment counteracted Cd-induced alterations of certain antioxidants and antioxidative enzymes, e.g., remarkably rescued APX and POD activities, reduced the elevated SOD and CAT activities and ASA levels, and recovered the reduced GSH levels, caused by Cd stress. Thus, the physiological effects of the combination of ABA and Cd treatments were opposite of those obtained with Cd treatment alone, suggesting that ABA involved in the regulation of antioxidative defense systems and the alleviation of wounding- and Cd-induced oxidative stress.     

Effect of iron on lipid peroxidation, and enzymatic and non-enzymatic antioxidants and bacoside-A content in medicinal plant Bacopa monnieri L

The effect of Fe was investigated in medicinally important plant, Bacopa monnieri L. and the response on malondialdehyde (MDA) content, superoxide dismutase (SOD), peroxidase (POD) and ascorbate peroxidase (APX) was found different in roots and leaves of the metal treated plants. Iron induced stress was observed as indicated by high level of lipid peroxidation, being more steep increase in leaves than roots. In roots, SOD activity was found to increase in metal treated plants except 80 and 160 microM at 72 h, whereas, it decreased in leaves except 10 and 40 microM after 48 h as compared to their respective controls. Among H2O2 eliminating enzymes, POD activity increased in roots, however, it decreased in leaves except at 10 and 40 microM Fe after 48 h as compared to control. At 24 and 48 h, APX activity and ascorbic acid content followed the similar trend and were found to increase in both parts of the metal treated plants as compared to their respective controls. The level of cysteine content in the roots increased at initial period of exposure; however, no marked change in its content was noticed in leaves. In both roots and leaves, non-protein thiol content was found to increase except at higher metal concentrations at 72 h. The data of proline content have shown significant (p<0.01) increase at 40 microM onwards in both part of the plants after 48 and 72 h. Correlation coefficient was evaluated between metal accumulations with various parameters and also between different antioxidant parameters with MDA. Since the level of bacoside-A (active constituent) content in metal treated plants increases, therefore, it is advisable to assess the biological activity of the plants before using for medicinal purposes, particularly in developing countries.     

Role of salicylic acid in alleviating oxidative damage in rice roots (Oryza sativa) subjected to cadmium stress

Time-dependent changes in enzymatic and non-enzymatic antioxidants, and lipid peroxidation were investigated in roots of rice (Oryza sativa) grown hydroponically with Cd, with or without pretreatment of salicylic acid (SA). Exposure to 50 microM Cd significantly decreased root growth, and activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), but increased the concentrations of H(2)O(2), malondialdehyde (MDA), ascorbic acid (AsA), glutathione (GSH) and non-protein thiols (NPT). However, pretreatment with 10 microM SA enhanced the activities of antioxidant enzymes and the concentrations of non-enzymatic antioxidants, but lowered the concentrations of H(2)O(2) and MDA in the Cd-stressed rice compared with the Cd treatment alone. Pretreatment with SA alleviated the Cd-induced inhibition of root growth. The results showed that pretreatment with SA enhanced the antioxidant defense activities in Cd-stressed rice, thus alleviating Cd-induced oxidative damage and enhancing Cd tolerance. The possible mechanism of SA-induced H(2)O(2) signaling in mediating Cd tolerance was discussed.     

Cadmium accumulation and its influence on lipid peroxidation and antioxidative system in an aquatic plant, Bacopa monnieri L

Bacopa monnieri L. plants exposed to 10, 50, 100 and 200 microM cadmium (Cd) for 48, 96 and 144 h were analysed with reference to the accumulation of metal and its influence on various enzymatic and non-enzymatic antioxidants, thiobarbituric acid reactive substances (TBARS), photosynthetic pigments and protein content. The accumulation of Cd was found to be increased in a concentration and duration dependent manner with more Cd being accumulated in the root. TBARS content of the treated roots and leaves increased with increase in Cd concentration and exposure periods, indicating the occurrence of oxidative stress. Induction in the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and guiacol peroxidase (GPX) was recorded in metal treated roots and leaves of B. monnieri. In contrast, a significant reduction in catalase activity in Cd treated B. monnieri was observed. An increase was also noted in the levels of cysteine and non-protein thiol contents of the roots of B. monnieri followed by a decline. However, in leaves, cysteine and non-protein thiol contents were found to be enhanced at all the Cd concentrations and exposure periods. A significant reduction in the level of ascorbic acid was observed in a concentration and duration dependent manner. The total chlorophyll and protein content of B. monnieri decreased with increase in Cd concentration at all the exposure periods. Results suggest that toxic concentrations of Cd caused oxidative damage as evidenced by increased lipid peroxidation and decreased chlorophyll and protein contents. However, B. monnieri is able to combat metal induced oxidative injury involving a mechanism of activation of various enzymatic and non-enzymatic antioxidants.     

Biological detection and analysis of mercury toxicity to alfalfa (Medicago sativa) plants

Mercury has become one of the major causes of toxic metal pollution in agricultural lands. Accumulation of mercury by plants may disrupt many cellular functions and block growth and development. To assess mercury toxicity, we performed an experiment focusing on the responses of alfalfa (Medicago sativa) to Hg(2+)-induced oxidative stress. Alfalfa plants were treated with 0-40microM HgCl(2) for 7d. The concentrations of Hg(2+) were positively correlated with the generation of O2- and H(2)O(2) in leaves. Treatment with Hg(2+) increased the activities of NADH oxidase and lipoxygenase (LOX) and damaged the biomembrane lipids. To understand biochemical responses under Hg stress, activities of several antioxidant enzymes, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) were assayed. Analysis of SOD activity by non-denaturing polyacrylamide gel electrophoresis revealed five isoforms in leaves, but they showed different patterns. Also, eight isoenzymes of APX and seven of POD in leaves were detected. However, only one isoform of CAT was visualized. The total activities of APX, POD and CAT were generally enhanced. We also measured several antioxidative metabolites such as ascorbate and glutathione (GSH), and found that both differentially accumulated in leaves. These results indicate that the increased levels of O2- and H(2)O(2) under Hg stress were closely linked to the improved capacity of antioxidant enzymes. The data not only provide the important information for better understanding of the toxic and tolerance mechanisms, but as well can be used as a bio-indicator for soil contamination by Hg.     

Bioaccumulation and physiological effects of mercury in Sesbania drummondii

The accumulation of mercury and its effect on growth, photosynthesis and antioxidative responses were studied in Sesbania drummondii seedlings. Mercury concentration in shoots as well as in the roots increased with increasing Hg concentrations in the growth solution. The accumulation of Hg was more in roots than shoots. At 100 mg l-1 Hg concentration, shoots accumulated 998 mg Hg kg -1 dry weight (dw) while roots accumulated 41,403 mg Hg kg-1 dw. Seedlings growth was not significantly affected at lower concentrations of Hg. A concentration of 100 mg l-1 Hg inhibited growth by 36.8%, with respect to control. Photosynthetic activity was assessed by measuring chlorophyll a fluorescence by determination of Fv/Fm and Fv/Fo values. Photosynthetic integrity was not affected up to 50 mg l-1 Hg concentration, however, concentrations higher than 50 mg l-1 affected photosynthetic integrity. Sesbania responded to Hg induced oxidative stress by modulating non-enzymatic antioxidants [glutathione (GSH) and non-protein thiols (NPSH)] and enzymatic antioxidants: superoxide dismutase (SOD), ascorbate peroxidase (APX) and glutathione reductase (GR). Glutathione content and GSH/GSSG ratio increased up to a concentration of 50 mg l-1 while slight down at 100 mg l-1 Hg. The content of NPSH significantly increased with increasing Hg concentrations in the growth medium. The activities of antioxidative enzymes, SOD, APX and GR followed the same trends as antioxidants first increased up to a concentration of 50 mg l-1 Hg and then slight decreased. The results of present study suggest that Sesbania plants were able to accumulate and tolerate Hg induced stress using an effective antioxidative defense mechanisms.     

Joint stress of chlorimuron-ethyl and cadmium on wheat Triticum aestivum at biochemical levels

Biochemical responses to joint stress of chlorimuron-ethyl and cadmium (Cd) in wheat Triticum aestivum were examined. The joint action of chlorimuron-ethyl and Cd weakened the inhibition of Cd or chlorimuron-ethyl on the formation of chlorophyll. It was deduced that wheat plants had the capability to protect themselves by increasing the activity of the antioxidant enzyme peroxidase (POD) with the exposure time. The joint effect of chlorimuron-ethyl and Cd on the superoxide dismutase (SOD) activity in leaves was additive, while the joint effect on the SOD activity in roots was determined by the interaction of chlorimuron-ethyl and Cd in wheat. It was also concluded that the change of malondialdehyde (MDA) content in wheat might not be a good biomarker in the oxidative damage by chlorimuron-ethyl, while a decrease in the soluble protein content and POD activity in roots could be considered as a biomarker in the damage of wheat by chlorimuron-ethyl and Cd.     

Biphasic effects of lanthanum on Vicia faba L. seedlings under cadmium stress, implicating finite antioxidation and potential ecological risk

In the present study, lanthanum (La) as a representative REE was used to explore the mechanisms for alleviation of Cd-induced oxidative damage by extraneous La at appropriate concentrations, and to assess ecological risk of combination of Cd and La at higher concentrations in roots of Vicia faba L. seedlings. The seedlings were hydroponically cultured for 15 d under nutrient solution, 6 μmol L⁻¹ CdCl₂, and combination of 6 μmol L⁻¹ CdCl₂ and increasing concentrations of La, respectively. The results showed that the supplementation with low concentrations of exogenous La (<120 μmol L⁻¹) led to reduced contents of Cd, Ca, Cu, Zn, Mn or Fe element and increased activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) isozymes as well as heat shock protein 70 (HSP 70) production in the roots. However, the supplementation with higher La (>120 μmol L⁻¹) showed the adverse effects. The contents of Cd elevated above the single Cd treatment in the roots, accompanying with the decline of antioxidant isozyme’s activities and HSP 70, and increment of carbonylated proteins and endoprotease isozyme’s activities. The results also showed that the root growth was not only related to carbonylated proteins, but also to indole acetic acid oxidase activities. Therefore, the supplemented extraneous La contributed to biphasic effects: stimulated antioxidation at lower concentrations and pro-oxidation at higher concentrations against Cd-induced oxidative stress in the roots.     

Lead detoxification by coontail (Ceratophyllum demersum L.) involves induction of phytochelatins and antioxidant system in response to its accumulation

Coontail (Ceratophyllum demersum L.) plants when exposed to various concentrations of Pb (1-100microM) for 1-7days, exhibited both phytotoxic and tolerance responses. The specific responses were function of concentration and duration. Plants accumulated 1748mugPbg(-1) dw after 7d which reflected its metal accumulation ability, however most of the metal (1222microgg(-1) dw, 70%) was accumulated after 1d exposure only. The toxic effect and oxidative stress caused by Pb were evident by the reduction in biomass and photosynthetic pigments and increase in malondialddehyde (MDA) content and electrical conductivity with increase in metal concentration and exposure duration. Morphological symptoms of senescence phenomena such as chlorosis and fragmentation of leaves were observed after 7d. The metal tolerance and detoxification strategy adopted by the plant was investigated with reference to antioxidant system and synthesis of phytochelatins. Protein and antioxidant enzymes viz., superoxide dismutase (SOD, EC 1.15.1.1), guaiacol peroxidase (GPX, EC 1.11.1.7) ascorbate peroxidase (APX, EC 1.11.1.11), catalase (CAT, EC 1.11.1.6) and glutathione reductase (GR, EC 1.6.4.2) showed induction at lower concentration and duration followed by decline. All enzymes except GPX showed maximum activity after 1d. An increase in cysteine, non-protein thiols (NP-SH) and glutathione (GSH) content was observed at moderate exposure conditions followed by decline. Phytochelatins (PC(2) and PC(3)) were synthesized to significant levels at 10 and 50microM Pb with concomitant decrease in GSH levels. Thus production of PCs seems important for the detoxification of metal, however it may lead to depletion of GSH and consequently oxidative stress. Results suggest that plants responded positively to moderate Pb concentrations and accumulated high amount of metal. Due to metal accumulation coupled with detoxification potential, the plant appears to have potential for its use as phytoremediator species in aquatic environments having moderate pollution of Pb.     

Biological responses of wheat (Triticum aestivum) plants to the herbicide chlorotoluron in soils

Chlorotoluron is a phenylurea herbicide that is widely used for controlling grass weeds in the land of cereal, cotton and fruit production. However, extensive use of this herbicide may lead to its accumulation in ecosystems, thus inducing the toxicity to crops and vegetables. To assess chlorotoluron-induced toxicity in plants, we performed the experiment focusing on the metabolic adaptation of wheat plants (Triticum aestivum) to the chlorotoluron-induced oxidative stress. The wheat plants were cultured in the soils with chlorotoluron at concentrations of 0-25mg/kg. Chlorotoluron accumulation in plants was positively correlated with the external chlorotoluron concentrations, but negatively with the plant growth. Treatment with chlorotoluron induced the accumulation of O(2)(-) and H(2)O(2) in leaves and resulted in the peroxidation of plasma membrane lipids in the plant. We measured the endogenous proline level and found that it accumulated significantly in chlorotoluron-exposed roots and leaves. To understand the biochemical responses to the herbicide, activities of the antioxidant enzymes, such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) were assayed. Analysis of SOD activity by non-denaturing polyacrylamide gel electrophoresis (PAGE) revealed that there were three isoforms in the roots and leaves, but the isoforms in the tissues showed different patterns. Also, using the native PAGE, 6 isoforms of root POD and 10 in leaves were detected. The total activity of POD in roots was significantly enhanced. Activities of APX in roots and leaves showed a similar pattern. The CAT activities were generally suppressed under the chlorotoluron exposure.     

Antioxidative responses in relation to growth of mustard (Brassica juncea cv. Pusa Jaikisan) plants exposed to hexavalent chromium

Effect of hexavalent chromium (Cr6+) was seen on Brassica juncea cv. Pusa Jaikisan grown for 15 days in hydroponic culture supplemented with 0.2, 2 and 20 microM Cr. The inhibitory response of Cr6+ on growth of B. juncea was concentration and time dependent. The stimulation of plant growth, observed in response to exposure to 0.2 microM Cr6+, during initial 5 days was reversed on prolonged treatment and at higher Cr6+ concentrations (2 and 20 microM Cr6+). Despite reduction in growth, chlorophyll content increased substantially on 15 days exposure to 20 microM Cr6+. Significant increases in lipid peroxidation and tissue concentration of H2O2 occurred in plants exposed to 2 and 20 microM Cr6+. Effect of Cr6+ on antioxidative enzymes in roots and leaves was differential. SOD and CAT activities at lower levels of Cr6+ supply remained higher all through the treatment. While APX was very susceptible to excess Cr6+, GR and GST increased at elevated levels of Cr6+. The results suggested Cr6+ induced depression in plant growth of B. juncea to be a function of increased cellular accumulation of Cr despite increase in the activities of some of the antioxidative enzymes.     

Antioxidant metabolism of coffee cell suspension cultures in response to cadmium

The antioxidant responses of coffee (Coffea arabica L.) cell suspension cultures to cadmium (Cd) were investigated. Cd accumulated very rapidly in the cells and this accumulation was directly correlated with an increase in applied CdCl(2) concentration in the external medium. At 0.05mM CdCl(2), growth was stimulated, but at 0.5mM CdCl(2), the growth rate was reduced. An alteration in activated oxygen metabolism was detected by visual analysis as well as by an increase in lipid peroxidation at the higher CdCl(2) concentration. Catalase (CAT; EC 1.11.1.6), glutathione reductase (GR; EC 1.6.4.2) and superoxide dismutase (SOD; EC 1.15.1.1) activity increased, particularly at the higher concentration of CdCl(2). Ascorbate peroxidase (APX; EC 1.11.1.11) activity was increased at the lower CdCl(2) concentration used, but could not be detected in cells growing in the higher CdCl(2) concentration after 24h of growth, whilst guaiacol peroxidase (GOPX; EC 1.11.1.7) did not show a clear response to Cd treatment. An analysis by non-denaturing PAGE followed by staining for enzyme activity, revealed one CAT isoenzyme, nine SOD isoenzymes and four GR isoenzymes. The SOD isoenzymes were differently affected by CdCl(2) treatment and one GR isoenzyme was shown to specifically respond to CdCl(2). The results suggest that the higher concentrations of CdCl(2) may lead to oxidative stress. The main response appears to be via the induction of SOD and CAT activities for the removal of reactive oxygen species (ROS), and by the induction of GR to ensure the availability of reduced glutathione for the synthesis of Cd-binding peptides, which may also be related to the inhibition of APX activity probably due to glutathione and ascorbate depletion.     

Response of antioxidant enzymes in Nicotiana tabacum clones during phytoextraction of heavy metals

Background, aim, and scope  Tobacco, Nicotiana tabacum, is a widely used model plant for growth on heavy-metal-contaminated sites. Its high biomass and deep rooting system make it interesting for phytoextraction. In the present study, we investigated the antioxidative activities and glutathione-dependent enzymes of different tobacco clones optimized for better Cd and Zn accumulation in order to characterize their performance in the field. Main features  The improved heavy metal resistance also makes the investigated tobacco clones interesting for understanding the plant defense enzyme system in general. Freshly harvested plant material (N. tabacum leaves) was used to investigate the antioxidative cascade in plants grown on heavy metal contaminated sites with and without amendments of different ammonium nitrate and ammonium sulfate fertilizers. Materials and methods  Plants were grown on heavily polluted soils in north-east Switzerland. Leaves were harvested at the field site and directly deep frozen in liquid N₂. Studies were concentrated on the antioxidative enzymes of the Halliwell–Asada cycle, and spectrophotometric measurements of catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), superoxide dismutase (SOD, EC 1.15.1.1), glutathione peroxidase (GPX, EC 1.11.1.9), glutathione reductase (GR, EC 1.6.4.2), glutathione S-transferase (GST, EC 2.5.1.18) were performed. Results and discussion  We tried to explain the relationship between fertilizer amendments and the activity of the enzymatic defense systems. When tobacco (N. tabacum) plants originating from different mutants were grown under field conditions with varying fertilizer application, the uptake of cadmium and zinc from soil increased with increasing biomass. Depending on Cd and Zn uptake, several antioxidant enzymes showed significantly different activities. Whereas SOD and CAT were usually elevated, several other enzymes, and isoforms of GST were strongly inhibited. Conclusions  Heavy metal uptake represents severe stress to plants, and specific antioxidative enzymes are induced at the cost of more general reactions of the Halliwell–Asada cycle. In well-supplied plants, the glutathione level remains more or less unchanged. The lack of certain glutathione S-transferases upon exposure to heavy metals might be problematic in cases when organic pollutants coincide with heavy metal pollution. When planning phytoremediation of sites, mixed pollution scenarios have to be foreseen and plants should be selected according to both, their stress resistance and hyperaccumulative capacity.     

Lead induced changes in antioxidant metabolism of horsegram (Macrotyloma uniflorum (Lam.) Verdc.) and bengalgram (Cicer arietinum L.)

One-month old horsegram (Macrotyloma uniflorum (Lam.) Verdc. cv VZM1) and bengalgram (Cicer arietinum L. cv Annogiri) were exposed to different regimes of lead stress as Pb(NO3)2 at 0, 200, 500 and 800 ppm concentrations. The extent of oxidative damage as the rate of lipid peroxidation, antioxidative response and the accumulation of lead in roots and shoots of both plants were evaluated after 12 days of lead stress. Lead (Pb) treated plants showed increased levels of lipid peroxidation as evidenced from the increased malondialdehyde content coupled with the increase in the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), glutathione reductase (GR), glutathione S-transferase (GST) compared to control (untreated) plants. Lead stress caused significant changes in the activity of antioxidative enzymes. The effect of lead was found to be concentration dependent. Higher concentration of lead (800 ppm) resulted 2- to 3-fold increase in SOD, catalase and peroxidase activities, 3- to 5-fold increase in GR activity and 3- to 4-fold increase in GST activity in roots and leaves of both horsegram and bengalgram plants. Lead stress caused a significant increase in the rate of peroxidation as showed in the levels of malondialdehyde content in roots and leaves of both plant species. Horsegram registered lower Pb accumulation than bengalgram, however localization of Pb was greater in roots than leaves in both plants. In general, lipid peroxide levels and antioxidative enzyme activities were higher in horsegram than bengalgram and also more in roots than leaves which best concordance with the lead contents of both the plants and organs. These results suggest that Pb toxicity causes oxidative stress in plants and the antioxidative enzymes SOD, CAT, POD, GR, GST could play a pivotal role against oxidative injury.     

Antioxidant enzyme activities as affected by trivalent and hexavalent chromium species in Fontinalis antipyretica Hedw

The detoxification mechanisms of the aquatic moss, Fontinalis antipyretica Hedw., exposed to Cr was analyzed. In addition, the influence of Cr salts (as Cr nitrate, chloride and potassium bichromate) on these mechanisms has also been studied. The activity of antioxidant enzymes superoxide dismutase (SOD, EC 1.15.1.1.), catalase (EC 1.11.1.6.), ascorbate peroxidase (APX, EC 1.11.1.11.), guaiacol peroxidase (GPX, EC 1.11.1.7.) and glutathione reductase (GR, EC 1.6.4.2.) increased in plants treated with Cr concentrations ranging from 6.25x10(-5) to 6.25mM when given as Cr(NO(3))(3). Antioxidant enzymes responded to the other two salts CrCl(3) and K(2)Cr(2)O(7) only with Cr concentrations higher than 6.25x10(-2)mM. Glutathione level and GSSG/GSH ratio also responded to Cr exposure but no dose-effect relationship could be observed. Moreover, two unknown thiol compounds were observed in mosses exposed to the highest Cr concentrations. Effects on chlorophyll contents and chlorophyll a/b ratios were also shown even at low Cr concentrations. Our results indicated that environmentally realistic concentrations of Cr could lead to impairment of the cellular activity towards F. antipyretica and that Cr(III), when present as a nitrate salt, was as harmful as Cr(VI).     

Effect of heavy metal stress on antioxidative enzymes and lipid peroxidation in leaves and roots of two mangrove plant seedlings (Kandelia candel and Bruguiera gymnorrhiza)

The effects of multiple heavy metal stress on the activity of antioxidative enzymes and lipid peroxidation were studied in leaves and roots of two mangrove plants, Kandelia candel and Bruguiera gymnorrhiza, grown under control (10 per thousand NaCl nutrient solution) or five levels of multiple heavy metal stress (10 per thousand NaCl nutrient solution containing different concentration of Pb2+, Cd2+, and Hg2+). Leaves and roots of control and heavy metal-stressed plants were harvested after two months. In leaves of heavy metal-stressed plants superoxide dismutase (SOD) and peroxidase (POD) activities fluctuated in different stress levels compared to the control, while catalase (CAT) activity increased with stress levels in K. candel, but remained unchanged in leaves of B. gymnorrhiza. In comparison with the control, the dynamic tendency of SOD, CAT, and POD activities in roots of heavy metal-stressed plants all ascended, and then declined. The increase in enzyme activities demonstrated that K. candel is more tolerant to heavy metals than B. gymnorrhiza. Lipid peroxidation was enhanced only in leaves of heavy metal-stressed B. gymnorrhiza. These results indicate that in heavy-metal stress antioxidative activities may play an important role in K. candel and B. gymnorrhiza and that cell membrane in leaves and roots of K. candel have greater stability than those of B. gymnorrhiza. For pollution monitoring purposes, POD activity in roots and leaves maybe serve as a biomarker of heavy metal stress in K. candel, while lipid peroxidation maybe serve as biomarker in B. gymnorrhiza.     

Effects of cadmium exposure on digestive enzymes, antioxidant enzymes, and lipid peroxidation in the freshwater crab Sinopotamon henanense

In this study, the effects of cadmium (Cd) stress on the activities of disaccharidases (sucrase, lactase, and maltase), amylase, trypsin, pepsase, superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and malondialdehyde (MDA) content in the alimentary system of freshwater crabs Sinopotamon henanense were studied. Results showed that the enzyme activities in the stomach, intestine, and hepatopancreas changed with Cd concentration. In terms of digestive enzymes, Cd exposure had an inhibitory effect on the activities of the disaccharidases, amylase, and pepsase (only in the stomach). Significant induction of trypsin activity by Cd at a lower concentration was observed, but as Cd concentration increased, trypsin activity decreased. Maltase activity showed a slight recovery after inhibition by Cd. The activities of SOD and CAT increased initially and decreased subsequently. Cd significantly inhibited the activity of GPx. MDA content increased with increasing concentration of Cd. These results showed that acute Cd exposure led to harmful effects on the alimentary system of crabs, which are likely linked to Cd induced oxidative stress.