Cadmium-Zinc interactions in a hydroponic system using Ceratophyllum demersum L.: adaptive ecophysiology, biochemistry and molecular toxicology

Antioxidant system of garden cress sprouts for using in bio-monitor of cadmium and lead contamination

Based on garden cress significantly used for phytoremediation, the antioxidant system included antioxidant-phenolic compounds and antioxidant-enzymes of 6-day-garden cress sprouts (GCS) were assessed as potential bio-indicators for cadmium (Cd) and lead (Pb) contamination. Total phenolic and flavonoid contents of GCS germinated under Cd and Pb treatments (25-150 mg kg^-1) gradually increased with increasing concentration of metals and peaked by 2.0, 2.6, and 2.5, 2.3 folds at 150 mg kg^-1, respectively. By using DPPH, ABTS, and PMC antioxidant assays, the total antioxidant activity of phenolic compounds of GCS increased 6.1, 13.0, and 5.8-fold for Cd and 5.9, 14.6, and 8.2-fold for Pb at 150 mg kg^-1, respectively. The antioxidant enzymes of GCS (POD, CAT, GR, and GST) were significantly activated in response to Cd and Pb stress, and two new electrophoretic POD bands were detected. GCS was absorbed 19.0% and 21.3% of Cd and Pb at 150 mg metal kg^-1, respectively. In conclusion, the approaches of the antioxidant defense system of GSC could potentially be used as bio-indicator for monitoring Cd and Pb contamination in a short time of germination process.

Zinc Biofortification through Basal Zinc Supply Reduces Grain Cadmium in Mung Beans: Metal Partitioning and Health Risks Assessment

Grain zinc (Zn) biofortification with less cadmium (Cd) accumulation is of paramount importance from human health and environmental point of view. A pot experiment was carried out to determine the influence of Zn and Cd on their accumulations in Mung bean tissues (Vigna radiata) in two contrast soil types (Dermosol and Tenosol). The soil types with added Zn and Cd exerted a significant effect on translocation and accumulation of metals in different tissues. The accumulation of Zn and Cd was higher for Tenosol than that for Dermosol. At control, the concentration of Cd followed a pattern, e.g., root > stem > petiole > pod > leaflet > grain for both soils. A basal Zn supply (5 mg kg−1) increased the grain Zn concentration to a significant amount (up to 67%). It also reduced Cd accumulation in tissues, including grains (up to 34%). No non-carcinogenic effect was observed for either the children or the adults as the EDI and PTDI values were below the safety limit; however, the ILCR values exceeded the safety limit, indicating the possibility of some carcinogenic effects. Added Zn helped to reduce the carcinogenic and non-carcinogenic health risks on humans.

Application of palm oil mill waste to enhance biogas upgrading and hornwort cultivation

The potential of oil palm ash (OPA) to enhance H₂S and CO₂ removal from biogas by scrubbing with maturation pond effluent (MPE), and further the treatment of biogas scrubber effluent (BSE) by Ceratophyllum demersum L. (hornwort) cultivation were investigated in this study. The results show that OPA + MPE solution with pH 9.3 and alkalinity 7525 mg CaCO₃/L was obtained with 0.7 kg/L OPA loading. A pilot scale scrubber was used to study the effects of absorbent flow rates of 60-210 L/h on upgrading to 300 L/h field biogas stream. At 210 L/h, the CO₂ removal efficiencies were 33% and 53% for MPE and OPA + MPE, respectively. To approach 100% H₂S removal efficiency, the minimum flow rates were 120 L/h for MPE and 90 L/h for OPA + MPE. 50-150 g wet weight of hornwort in 30 L diluted POME were loaded to investigate appropriate initial hornwort loading level for hornwort cultivation. The highest specific growth rate of 0.045 day^-1 with biomass production of 3.8 g/day were obtained with a 50 g initial loading. Among the wastewaters (MPE, OPA + MPE, and BSE) treatment using hornwort cultivation, the highest 0.035 day^-1 specific growth rate and 2.6 g/day biomass production of hornwort were obtained in diluted BSE cultivation, and in 3 weeks of cultivation. COD, nitrate, phosphate, and alkalinity decreased by 76%, 76%, 55%, and 5%, respectively. The Eco-Efficiency concept for palm oil mill waste utilization proposed in this study has a high potential for enhanced biogas upgrading by using OPA + MPE, and hornwort is a good candidate for BSE post-treatment integrated with biomass production.

Effects of Boron and NaCl on Antioxidant Defence Mechanisms in Duckweeds (Spirodela polyrhiza L.)

<b>Background and Objective:</b> Boron is one of the principal elements required for plant's growth but extreme amounts of boron are toxic to humans, animals and plants. This study aimed to utilized growth rates, dry biomass and antioxidant enzyme activities to evaluate the potential of <i>Spirodela polyrhiza</i> L., in which <i>S. polyrhiza</i> produced for 120 hrs in water containing control, 10, 20, 40 and 80 mg L<sup>1</sup> of Boron and sodium chloride (NaCl) concentrations changing from 0-50 mM. <b>Materials and Methods:</b> In this study, we have done with <i>S. polyrhiza</i>, Boron and NaCl applications were continued for 120 hrs. After 120 hrs, the plants were harvested, cleaned with pure water, frozen at fluid nitrogen and stored at -80°C until further usage for enzymes activity. To determine the amount of Boron in <i>S. polyrhiza</i>, the samples were dried at 70 and then measured with Thermo ICP-MS. <b>Results:</b> The results indicated that the Boron accumulation capacity of <i>S. polyrhiza</i> diminished with accelerating salinity. <i>Spirodela polyrhiza</i> may have utilized various mechanisms to collecting Boron in high and low salt concentrations. As a conclusion of the study, it was stated that the growth rate of <i>S. polyrhiza</i> and total chlorophyll synthesis were considerably obstructed when NaCl amounts reached 50 mM. <b>Conclusion:</b> Our results indicate that CAT, APX and SOD can serve as substantial biomarkers in Boron-rich habitats. This <i>S. polyrhiza</i> is a very beneficial exemplary plant for phytoremediation advancement of contaminated wastewater with low Boron content.

Characterization of cadmium accumulation and phytoextraction in three species of the genus Atriplex (canescens, halimus and nummularia) in the presence or absence of salt

This study aims to establish for the first time a comparison between the resistance to cadmium (Cd) stress of three halophyte species, Atriplex canescens, Atriplex halimus and Atriplex nummularia in addition to their already known tolerance for salt and drought. Plants were exposed to CdCl₂ (20 and 50 μM) in the presence or in the absence of salt (50 mM NaCl) for one and two months. The amount of accumulated Cd was determined in the roots and leaves as well as the amount excreted on the surface of the leaves. Physiological parameters such as chlorophyll content and stress biomarkers, including malondialdehyde and enzymatic activities, were then analyzed. The results show that these plants are able to neutralize the excess of reactive oxygen species resulting from treatments by activating the antioxidant defense mechanisms in order to restore the homeostasis of cells. All three species are also able to accumulate high amounts of Cd in the leaves (several hundred mg of Cd/kg of dry leaves) and this phenomenon is amplified in the presence of salt. All together our results allow to consider the three Atriplex species as hyperaccumulators in the presence/absence of salt and as good candidates in a strategy of Cd phytoextraction in the presence of low concentrations of the pollutant. Nevertheless, both A. canescens and A. nummularia species seem to have a higher capacity to hyper-accumulate Cd when the concentration of Cd reaches higher level of contamination.

Potential of ornamental monocot plants for rhizofiltration of cadmium and zinc in hydroponic systems

Cadmium (Cd) and zinc (Zn) accumulation and uptake ability have been investigated in three ornamental monocot plants (Heliconia psittacorum x H. spathocircinata, Echinodorus cordifolius, and Pontederia cordata) grown in hydroponic systems. All study plants in the highest heavy metal treatments were found to be excluders for Cd and Zn with translocation factor values < 1 and bioconcentration factor (BCF) values > 100. The highest Cd and Zn accumulations were found in roots of E. cordifolius (4766.6 mg Zn kg^-1 and 6141.6 mg Cd kg^-1), followed by H. psittacorum x H. spathocircinata (4313.5 mg Zn kg^-1) and P. cordata (3673.3 mg Cd kg^-1), respectively, whereas shoots had lower performances. However, P. cordata had the lowest dry biomass production compared to the other two plant species in this study. As a result of dilution effects, heavy metal accumulation for all study plants was lower in the combined heavy metal treatments than in solely Cd and Zn only treatments. At the end of experiments, the highest uptakes of Cd and Zn were found in H. psittacorum x H. spathocircinata (62.1% Zn²⁺ from 10 mg Zn L^-1 solution) and E. cordifolius (27.3% Cd²⁺ from 2 mg Cd L^-1 solution). Low percentage metal uptakes were found in P. cordata; therefore, E. cordifolius and H. psittacorum x H. spathocircinata are clearly better suited for removing Cd and/or Zn from contaminated waters and hydroponic systems.

Optimization of eco-friendly novel amendments for sustainable utilization of Fly ash based on growth performance, hormones, antioxidant, and heavy metal translocation in chickpea (Cicer arietinum L.) plant

The present study has focused on the evaluation of the maximum amount of flyash (FA) utilization augmentation in the acidic soil (pH 6.1) with the manure during the growth performance and impact of toxic heavy metals under the pot experiment. The 15 days pre-incubated 40% FA treated combination (T16) significantly (P < 0.05) influenced growth performance of chickpea plant after 60 days. The dry weight as well as the contents of N, P, and K increased from 38.8 to 78.53%, 118 to 86%, 148 to 115%, and 95.8 to 95%, respectively, over control in T15 combination after 30 and 60 days. T15 and T16 both treatments induced a significant rise in IAA and GB from 76 to 75.5% and 50%-45%, respectively, after 60 days. The significant increase in the activities of SOD, APX, CAT, and GR with 47%, 56%, 42%, and 28%, respectively, over control was observed in T16 treated combination after 60 days. The significant (P < 0.05) influence in the antioxidant activities, levels of GB, Proline, TSS, and RS were observed across the treatments and durations. The levels of BCF and TF both were <1 in T16 treated plants for toxic heavy metals (Pb, Mo, Cd, and Al), which indicated a negligible extent of translocation from root to shoot and shoot to edible parts in the plants. The results demonstrated that 40% FA supplementation with manure could induce the growth of chickpea in slightly acidic soil and reduce the translocation of toxic metals in the edible parts of the plant.

Oxidative stress, growth inhibition, and DNA damage in earthworms induced by the combined pollution of typical neonicotinoid insecticides and heavy metals

Heavy metals pollution of soil and widespread application of neonicotinoid insecticides have caused environmental problems worldwide. To evaluate ecological toxicity resulting from the combined pollution of neonicotinoids and heavy metals, typical representatives of neonicotinoid insecticides (imidacloprid, thiamethoxam, dinotefuran) and heavy metals (cadmium, copper, zinc) were selected as soil pollutants; earthworms were used as test organisms. Analysis of the main and interaction effects of a combined pollution process were performed using a uniform design method. Results showed that the reactive oxygen species (ROS) content of earthworms in most treatment groups was higher during exposure than that of the control group. The malondialdehyde (MDA) and ROS content of earthworms demonstrated relatively low values on the 21st day and increased by the 28th day. The interaction between dinotefuran and Cd had significant antagonistic effects on ROS and MDA. The combined pollution adversely affected both the growth and genes of earthworms and also caused damage to the epidermis, midgut, and DNA. The interaction between imidacloprid and Cd was synergistic to ROS, weight inhibition rate, and Olive tail moment (OTM), but was antagonistic to MDA. Of all the single and combined exposures, Zn as a single chemical affected ROS and DNA damage the most, and MDA was significantly enhanced by imidacloprid. Composite pollutants may create different primary effects and interactions causing potential harm to soil organisms.

Growth responses and physiological and biochemical changes in five ornamental plants grown in urban lead-contaminated soils

An increasing concentration of lead (Pb) in urban contaminated soil due to anthropogenic activities has been a global issue threatening human health. The use of urban ornamental plants as phytoremediation of Pb-contaminated soil is a new choice. In the present experiment, the physiological and biochemical response of five ornamental plants to increase in concentrations of C4H6O4Pb·H2O in the soil were measured to investigate these plans' Pb tolerance strategies and abilities. Our results showed that Pb stress significantly inhibited the growth and the biomass of all the plants. The root activity (RA), net photosynthetic rate (P n), and chlorophyll (Chl) content in Pb-stressed leaves were significantly decreased, whereas the leaf proline (Pro), soluble sugar (SS), and membrane stability index (MSI) were remarkable increased compared with those in the control group. By application of all-subsets regression and linear regression, the reduction in photosynthetic capacity in the five plants is mainly due to the decrease in the leaf Chl content caused by Pb stress. The bioconcentration factor (BCF) in Canna generalis was greater than 1, while in the other plants were lower than 1, suggesting that Canna generalis had the highest Pb accumulation ability. The translocation factor (TF) in all the plants were lower than 1, suggesting that Pb preferentially accumulated in the external part of roots. By calculating the comprehensive evaluation value (CEV), Iris germanica L. was found to be the most sensitive species, and Canna generalis was the most tolerant species, to Pb stress among the five ornamental plants.

The presence of zinc reduced cadmium uptake and translocation in Cosmos bipinnatus seedlings under cadmium/zinc combined stress

Cadmium (Cd) and zinc (Zn) coexist in the environment but interact differently in plants. Cosmos bipinnatus has been potentially considered as a Cd-accumulator. Thus, this study investigated the detoxification mechanism in C. bipinnatus seedlings under Cd, Zn and Cd + Zn stresses. In the present study, the presence of Zn inhibited Cd uptake and translocation, whereas Cd merely hindered Zn uptake. The concentration of Cd in soluble fraction significantly decreased and Cd was bounded to the cell wall in root under Cd + Zn stress. Meanwhile, Zn and Cd mutually decreased their concentrations in the ethanol extractable form (F_E) and water extractable form (F_W) in roots and shoots. Furthermore, Cd + Zn stress enhanced the activities of superoxide dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7) and catalase (CAT, EC 1.11.1.6) compared to Cd stress alone. These results suggested that Zn effectively decreased Cd uptake and translocation, changed their subcellular distributions, regulated their chemical forms composition and increased antioxidative enzyme activities, thereby enhancing the tolerance to Cd in C. bipinnatus. This study physiologically revealed the interactive effect of Cd and Zn on the detoxification mechanism of Cd in C. bipinnatus and provided new information on phytoremediation of the heavy metal contaminated soils.

Polyamines (spermidine and putrescine) mitigate the adverse effects of manganese induced toxicity through improved antioxidant system and photosynthetic attributes in Brassica juncea

Polyamines (PAs) are recognized as plant growth regulators that are involved in the stress management in various crops. In the current study, mitigative roles of spermidine (Spd) and putrescine (Put) were assessed in manganese (Mn) stressed Brassica juncea plants. Spd or Put (1.0 mM) were applied to the foliage of Brassica juncea at 35 days after sowing (DAS) grown in the presence of Mn (30 or 150 mg kg^-1 soil). The higher level of Mn (150 mg kg^-1) diminished photosynthetic attributes and growth, enhanced the production of reactive oxygen species (ROS) like hydrogen peroxide (H₂O₂) and superoxide anion ( [Formula: see text] ) content, affected stomatal movement and increased the Mn concentration in roots and shoots of the plant at 45 DAS, whereas it enhanced the activities of various antioxidant enzymes and proline content in the foliage of Brassica juncea plants. On the other hand, treatment of PAs (Spd or Put) to Mn stressed as well as non-stressed plants resulted in a remarkable improvement in the stomatal behaviour, photosynthetic attributes, growth and biochemical traits, decreased the production of ROS (H₂O₂ and [Formula: see text] ) and concentration of Mn in different parts of plant. It is concluded that out of the two polyamines (Spd or Put), Spd proved more efficient and enhanced growth, photosynthesis, and metabolic state of the plants which bestowed tolerance and helped the plants to cope efficiently under Mn stress.

24-epibrassinolide and spermidine alleviate Mn stress via the modulation of root morphology, stomatal behavior, photosynthetic attributes and antioxidant defense in Brassica juncea

Brassinosteroids and polyamines are generally used to surpass different abiotic stresses like heavy metal toxicity in plants. The current study was conducted with an aim that 24-epibrassinolide (EBL) and/or spermidine (Spd) could modify root morphology, movement of stomata, cell viability, photosynthetic effectiveness, carbonic anhydrase and antioxidant enzyme activities in Brassica juncea under manganese (Mn) stress (30 or 150 mg kg^-1 soil). EBL (10^-8 M) and/or Spd, (1.0 mM) were applied to the foliage of B. juncea plants at 35 days after sowing (DAS), grown in the presence of Mn (30 or 150 mg kg^-1 soil). High Mn concentration (150 mg kg^-1 soil) altered root morphology, affected stomatal movement, reduced the viability of cells and photosynthetic effectiveness and increased the production of reactive oxygen species (O₂ ^·- and H₂O₂) in the leaves and antioxidant defense system of B. juncea at 45 DAS. Furthermore, exogenous treatment of EBL and Spd under stress and stress- free conditions improved the aforesaid traits while decreased the O₂ ^·- and H₂O₂ production. Therefore, EBL and Spd could be applied to the foliage of B. juncea plants for the better growth under metal stress.

Background concentrations and quality reference values for some potentially toxic elements in soils of São Paulo State, Brazil

Quality reference values (QRV) for potentially toxic elements (PTE) in soils are established as a tool for prevention and monitoring of soil pollution. These values should be periodically revised in order to ensure soil safety for agricultural purposes. Brazil is market leader for several commodities; therefore, the safety of Brazilian soils is of worldwide strategic importance. The objective of this study was to determine the natural background concentrations and the QRV for As, Ba, Cd, Cr, Ni, Pb, Se, and Zn by investigating 30 representative pedotypes in the São Paulo State, one of the most important agro-industry economy at worldwide level. Multivariate statistical analysis was applied to determine the sources of PTE and their variability. The mean natural background concentrations of PTE in the soils were generally lower to those reported in literature. QRV, calculated for each element as the 75th and 90th percentiles, were lower (75th for As, Cd, Pb, and Zn), similar (75th for Ba, Cr, and Se) or above (90th for Ba, Cr, and Se and 75-90th for Ni) those previously proposed by the Brazilian environmental protection agencies. The results indicate that 75th percentile may be too restrictive. The PTE in the investigated soils appear to have comes mainly from two primary natural sources: a prevalent one of geogenic and a secondary of pedogenic origin. These results confirm the predominant natural source of selected PTE in the investigated soils, thus sustaining the possibility of using the data set to develop QRV for the State of São Paulo.

Effects on Eichhornia crassipes under Zn stress

Eichhornia crassipes is a macrophyte widely used in phytoremediation, demonstrating a high ability to remove metals from water. The aim of this work was to evaluate its enzymatic detoxification strategies and metal accumulation when it is exposed to different Zn concentrations (0, 2, 4, 6, and 9 ppm) for periods of 24, 48, and 72 h. Zn concentration in roots was significantly higher than in aerial parts. Independently of the treatment, in the first 48 h, concentrations of photosynthetic pigments were not affected. However, a significant increase (between 19 and 34%) in Chl-b concentrations for all treatments was observed at 72 h. Carotenoid concentration was not affected during the first 48 h, while at 72 h, there was a significant increase regarding the control (between 11 and 24%) for all treatments. Malondialdehyde concentration in aerial parts and roots was not affected during the experiment. Nonetheless, a significant increase in the enzymatic activity of the antioxidant system was observed. Results suggest that Zn could have potential antioxidant properties, which may result in the activation of different antioxidant enzymes involved in the protection against metal stress.

The humic acid-induced changes in the water status, chlorophyll fluorescence and antioxidant defense systems of wheat leaves with cadmium stress

The using of bio-stimulant in plants grown under stress conditions for enhancing nutrition efficiency and crop quality traits is an effective approach. One of the bio-stimulants, humus material, is defined as humic acid (HA). HA application as a promotion of plant growth to plants grown in the heavy metals-contaminated soils has promised hope in terms of effects on plants but the its limiting effect is the application dose. Therefore, the wheat seedlings were grown in hydroponic culture for 21 d and the various concentrations of humic acid (HA; 750 or 1500 mg L^-1) were treated alone or in combination with cadmium (Cd) stress (100 or 200 μM) for 7 d. The results showed that after Cd stress treatment, water content (RWC), osmotic potential (Ψ_Π) and chlorophyll fluorescence parameters decreased and proline content (Pro) increased for 7 d. In spite of activated peroxidase (POX) and ascorbate peroxidase (APX), stress induced the toxic levels of hydrogen peroxide (H₂O₂) accumulation. Cd stress triggered lipid peroxidation (TBARS content). HA application successfully eliminated the negative effects of stress on RWC, Ψ_Π and photosynthetic parameters. In the presence of HA under stress, the increased activation of superoxide dismutase (SOD), catalase (CAT) and NADPH-oxidase (NOX) enzymes and ascorbate, glutathione and GSH/GSSG ratio observed. Only 750 mg L^-1 HA under stress conditions induced the activities of monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR), and dehydroascorbate (DHA) content. After the combined application of HA and Cd stress, the low contents of H₂O₂ and TBARS maintained in wheat leaves. Hence, HA successfully eliminated the toxicity of Cd stress by modulating the water status, photosynthetic apparatus and antioxidant activity in wheat leaves.

Comparative study of Cd uptake and tolerance of two Italian ryegrass (Lolium multiflorum) cultivars

Cadmium (Cd) is one of the most toxic heavy metals and is difficult to be removed from contaminated soil and water. Italian ryegrass (Lolium multiflorum), as an energy crop, exhibits a valuable potential to develop Cd polluted sites due to its use as a biofuel rather than as food and forage. Previously, via a screening for Cd-tolerant ryegrass, the two most extreme cultivars (IdyII and Harukaze) with high and low Cd tolerance during seed germination, respectively, were selected. However, the underlying mechanism for Cd tolerance was not well investigated. In this study, we comparatively investigated the growth, physiological responses, and Cd uptake and translocation of IdyII and Harukaze when the seedlings were exposed to a Cd (0–100 μM) solution for 12 days. As expected, excess Cd inhibited seedling growth and was accompanied by an accumulation of malondialdehyde (MDA) and reduced photosynthetic pigments in both cultivars. The effects of Cd on the uptake and translocation of other nutrient elements (Zn, Fe, Mn and Mg) were dependent on Cd concentrations, cultivars, plant tissues and elements. Compared with Harukaze, IdyII exhibited better performance with less MDA and higher pigment content. Furthermore, IdyII was less efficient in Cd uptake and translocation compared to Harukaze, which might be explained by the higher non-protein thiols content in its roots. Taken together, our data indicate that IdyII is more tolerant than Harukaze, which partially resulted from the differences in Cd uptake and translocation.

Mixture toxicity of copper, cadmium, and zinc to barley seedlings is not explained by antioxidant and oxidative stress biomarkers

The analysis of metal mixture toxicity to plants is complicated by mutual interactions. In the present study, mixture effects of zinc (Zn), cadmium (Cd), and copper (Cu) on barley (Hordeum vulgare L.) root elongation were analyzed using oxidative stress parameters. The hypothesis was that toxic mixture effects on plant growth are better explained by biochemical parameters than by exposure information, because the former excludes interactions among metals for root uptake. Barley seedlings were exposed for 5 d or 14 d to these metals in nutrient solutions, added in isolation and as mixtures. Root elongation in Cu+Cd mixtures was well predicted from free metal ion concentrations in solution, using concentration addition (CA) or independent action (IA) reference models. In contrast, Zn acted antagonistically when combined with Cu and/or Cd, relative to both CA and IA. This protective effect of Zn correlated with the biomarkers measured in the long-term experiment; oxidative stress (indicated by malondialdehyde level, for example) decreased after addition of Zn. In addition, it was found that some biomarkers were sensitive to both Cu and Cd dosed in isolation, but not to Cu+Cd mixtures. Overall, the exposure explained mixture effects better than most of the 16 measured biomarkers (i.e., the biochemical effects). It is concluded that these biomarkers are not robust indicators for metal mixture toxicity, potentially because different metals have different parallel modes of action on growth that are insufficiently indexed by the biomarkers. Environ Toxicol Chem 2017;36:220-230. © 2016 SETAC.

Modulatory role of mineral nutrients on cadmium accumulation and stress tolerance in Oryza sativa L. seedlings

Cadmium (Cd)-contaminated rice is a serious health concern. In the present study, Cd accumulation and stress responses in Oryza sativa L. cv MTU 7029 seedlings were characterized under varying concentrations of plant nutrients in Hoagland media. It has been found that nutrient supplement modulates Cd accumulation and related stress tolerance while efficacy of each nutrient varies. Supplementation of Fe, Mn, N, Ca, and S were found to reduce Cd accumulation in leaf whereas Mn and Fe supply effect was also observed in roots. Analysis of maximum quantum efficiency of photosynthesis indicated that Fe and S supplements confer highest Cd stress tolerance. The present study highlighted the potential of plant nutrients for minimizing Cd accumulation and its toxicity in rice seedlings.

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.

Molecular, Biochemical and Ultrastructural Changes Induced by Pb Toxicity in Seedlings of Theobroma cacao L

Pb is a metal which is highly toxic to plants and animals, including humans. High concentrations of Pb have been observed in beans of T. cacao, as well as in its products. In this work, we evaluated the molecular, biochemical, and ultrastructural alterations in mature leaves and primary roots of seedlings of two progenies of T. cacao, obtained from seed germination in different concentrations of Pb (0, 0.05, 0.1, 0.2, 0.4, 0.8 g L^-1), in the form of Pb(NO₃)₂. The progenies resulted from self-fertilization of Catongo and a cross of CCN-10 x SCA-6. The Pb, supplied via seminal, caused alterations in the ultrastructures of the mesophyll cells and in the amount of starch grains in the chloroplasts. The dosage of substances reactive to thiobarbituric acid showed that Pb induced lipid peroxidation. The activity of guaiacol peroxidases and the expression of genes associated to synthetase of phytochelatin, SODcyt and PER increased in response to Pb. In addition, there was alteration in the expression of stress-related proteins. The progeny of CCN-10 x SCA-6 was more tolerant to Pb stress when compared to Catongo, since: (i) it accumulated more Pb in the roots, preventing its translocation to the shoot; (ii) it presented higher activity of peroxidases in the roots, which are enzymes involved in the elimination of excess of reactive oxygen species; and (iii) increased expression of the gene in the phytochelatin biosynthesis route. The results of the proteomic analysis were of paramount importance to differentiate the defense mechanisms used by both progenies of T. cacao.

Zinc stress induces physiological, ultra-structural and biochemical changes in mandarin orange (Citrus reticulata Blanco) seedlings

Zinc (Zn) is an essential micronutrient for higher plants; yet, at higher concentrations it is toxic. In order to explore the effect of Zn stress on growth, biochemical, physiological and ultra-structural changes, 1 year old mandarin plants were grown under various Zn concentrations (1, 2, 3, 4, 5, 10 15 and 20 mM) for 14 weeks. The biomass of the plants increased with increasing Zn concentrations and finally declined under excess Zn concentration but the prime increase was observed at 4 and 5 mM Zn. Zn stress reduced the photosynthetic rate, stomatal conductance, and transpiration along with reduction of chlorophyll a, chlorophyll b, and carotenoids content in leaf. Superoxide anion, malondialdehyde, hydrogen peroxide and electrolyte leakage were elevated in Zn stressed plants. The activities of ascorbate peroxidase (EC 1.11.1.11), catalase (EC 1.11.1.6), superoxide dismutase (EC 1.15.1.1) and peroxidase (EC 1.11.1.7) enzymes were increased in both Zn-deficient and Zn-excess plants. Therefore it is suggested that antioxidant defense system did not sufficiently protect the plants under rigorous Zn stress which was also corroborated by the alteration in cell ultrastructure as revealed by transmission electron microscopy.

Cadmium background concentrations to establish reference quality values for soils of São Paulo State, Brazil

Proper assessment of soil cadmium (Cd) concentrations is essential to establish legislative limits. The present study aimed to assess background Cd concentrations in soils from the state of São Paulo, Brazil, and to correlate such concentrations with several soil attributes. The topsoil samples (n = 191) were assessed for total Cd contents and for other metals using the USEPA 3051A method. The background concentration was determined according to the third quartile (75th). Principal component analysis, Spearman correlation, and multiple regressions between Cd contents and other soil attributes (pH, cation exchange capacity (CEC), clay content, sum of bases, organic matter, and total Fe, Al, Zn, and Pb levels) were performed. The mean Cd concentration of all 191 samples was 0.4 mg kg(-1), and the background concentration was 0.5 mg kg(-1). After the samples were grouped by parent material (rock origin) and soil type, the background Cd content varied, i.e., soils from igneous, metamorphic, and sedimentary rocks harbored 1.5, 0.4, and 0.2 mg kg(-1) of Cd, respectively. The background Cd content in Oxisols (0.8 mg kg(-1)) was higher than in Ultisols (0.3 mg kg(-1)). Multiple regression demonstrated that Fe was primarily attributed to the natural Cd contents in the soils (R (2) = 0.79). Instead of a single Cd background concentration value representing all São Paulo soils, we propose that the concentrations should be specific for at least Oxisols and Ultisols, which are the primary soil types.

The effects of cadmium-zinc interactions on biochemical responses in tobacco seedlings and adult plants

The objective of the present study was to investigate the effects of cadmium-zinc (Cd-Zn) interactions on their uptake, oxidative damage of cell macromolecules (lipids, proteins, DNA) and activities of antioxidative enzymes in tobacco seedlings as well as roots and leaves of adult plants. Seedlings and plants were exposed to Cd (10 µM and 15 µM) and Zn (25 µM and 50 µM) as well as their combinations (10 µM or 15 µM Cd with either 25 µM or 50 µM Zn). Measurement of metal accumulation exhibited that Zn had mostly positive effect on Cd uptake in roots and seedlings, while Cd had antagonistic effect on Zn uptake in leaves and roots. According to examined oxidative stress parameters, in seedlings and roots individual Cd treatments induced oxidative damage, which was less prominent in combined treatments, indicating that the presence of Zn alleviates oxidative stress. However, DNA damage found in seedlings, and lower glutathione reductase (GR) and superoxide dismutase (SOD) activity recorded in both seedlings and roots, after individual Zn treatments, indicate that Zn accumulation could impose toxic effects. In leaves, oxidative stress was found after exposure to Cd either alone or in combination with Zn, thus implying that in this tissue Zn did not have alleviating effects. In conclusion, results obtained in different tobacco tissues suggest tissue-dependent Cd-Zn interactions, which resulted in activation of different mechanisms involved in the protection against metal stress.

Bioaccumulation potential and physiological responses of aquatic macrophytes to Pb pollution

In view of their potential bioaccumulation of heavy metals, Ceratophyllum demersum and Myriophyllum spicatum was studied under hydroponic cultures enriched by different Pb concentrations (25, 50, 75 mg/l) for 1-7 days. Both species exerted remarkable capabilities to concentrate Pb in their tissues as compared to control. The highest accumulation value of Pb (164.26 mg/g x dw) was recorded in C. demersum and the most of metal (91.72 mg/g dw) accumulated after 1 d. Significant reduction in photosynthetic pigments and appearance of morphological symptoms such as chlorosis and fragmentation of leaves were evident after 7d at 75 mg/l. The activity of POX and APX, carotenoids and proline showed induction at lower concentration and duration followed by decline. Major re-shuffle in protein patterns appeared as a tolerant mechanism, which both species developed under Pb toxicity. Results suggest that both species responded positively to Pb concentration and accumulated high amount of metal. Due to metal accumulation coupled with detoxification potential, both species appear to have potential for use as phytoremediators and the developed responses can be used as reliable biomarkers for Pb water pollution.

Cadmium-induced upregulation of lipid peroxidation and reactive oxygen species caused physiological, biochemical, and ultrastructural changes in upland cotton seedlings

Cadmium (Cd) toxicity was investigated in cotton cultivar (ZMS-49) using physiological, ultrastructural, and biochemical parameters. Biomass-based tolerance index decreased, and water contents increased at 500 μM Cd. Photosynthetic efficiency determined by chlorophyll fluorescence and photosynthetic pigments declined under Cd stress. Cd contents were more in roots than shoots. A significant decrease in nutrient levels was found in roots and stem. A significant decrease in nutrient levels was found in roots and stems. In response to Cd stress, more MDA and ROS contents were produced in leaves than in other parts of the seedlings. Total soluble proteins were reduced in all parts except in roots at 500 μM Cd. Oxidative metabolism was higher in leaves than aerial parts of the plant. There were insignificant alterations in roots and leaves ultrastructures such as a little increase in nucleoli, vacuoles, starch granules, and plastoglobuli in Cd-imposed stressful conditions. Scanning micrographs at 500 μM Cd showed a reduced number of stomata as well as near absence of closed stomata. Cd depositions were located in cell wall, vacuoles, and intracellular spaces using TEM-EDX technology. Upregulation of oxidative metabolism, less ultrastructural modification, and Cd deposition in dead parts of cells show that ZMS-49 has genetic potential to resist Cd stress, which need to be explored.

Differential physiological, ultramorphological and metabolic responses of cotton cultivars under cadmium stress

Cadmium (Cd) stress may cause serious physiological, ultramorphological and biochemical anomalies in plants. Cd-induced physiological, subcellular and metabolic alterations in two transgenic cotton cultivars (BR001, GK30) and their parent line (Coker 312) were evaluated using 10, 100 and 1000 µM Cd. Germination, fresh biomass of roots, stems and leaves were significantly inhibited at 1000 µM Cd. Root volume tolerance index significantly increased (124.16%) in Coker 312 at 1000 µM Cd. In non-Cd stressed conditions, electron micrographs showed well-configured root meristem and leaf mesophyll cells. At 1000 µM Cd, greater ultramorphological alterations were observed in BR001 followed by GK30 and Coker 312. These changes were observed in nucleus, vacuoles, mitochondria and chloroplast. Dense precipitates, probably Cd, were seen in vacuoles, which were also attached to the cell walls. A considerable increase in number of nuclei, vacuoles, starch granules and plastoglobuli was observed in the electron micrographs of both roots and leaves at 1000 µM Cd. MDA contents were higher in roots of BR001 at 1000 µM Cd. Mean values of SOD activity in leaves of both BR001 and GK30 at 1000 µM Cd significantly increased as compared to the controls. POD activity in roots of BR001 and Coker 312 was greater at all Cd (10, 100, 1000 µM) levels over the control. Regarding APX, highest percent increase (71.64%) in roots of GK30 at 1000 µM Cd was found. Non-significant differences in CAT activity were observed at all levels of Cd stress in leaves of BR001 and GK30. Both transgenic cotton cultivars and their parental line invariably responded towards Cd stress. However, Coker 312 showed Cd-resistant behavior as compared to its progeny lines (BR001 and GK30).

Molecular Mechanism of Heavy Metal Toxicity and Tolerance in Plants: Central Role of Glutathione in Detoxification of Reactive Oxygen Species and Methylglyoxal and in Heavy Metal Chelation

Heavy metal (HM) toxicity is one of the major abiotic stresses leading to hazardous effects in plants. A common consequence of HM toxicity is the excessive accumulation of reactive oxygen species (ROS) and methylglyoxal (MG), both of which can cause peroxidation of lipids, oxidation of protein, inactivation of enzymes, DNA damage and/or interact with other vital constituents of plant cells. Higher plants have evolved a sophisticated antioxidant defense system and a glyoxalase system to scavenge ROS and MG. In addition, HMs that enter the cell may be sequestered by amino acids, organic acids, glutathione (GSH), or by specific metal-binding ligands. Being a central molecule of both the antioxidant defense system and the glyoxalase system, GSH is involved in both direct and indirect control of ROS and MG and their reaction products in plant cells, thus protecting the plant from HM-induced oxidative damage. Recent plant molecular studies have shown that GSH by itself and its metabolizing enzymes—notably glutathione S-transferase, glutathione peroxidase, dehydroascorbate reductase, glutathione reductase, glyoxalase I and glyoxalase II—act additively and coordinately for efficient protection against ROS- and MG-induced damage in addition to detoxification, complexation, chelation and compartmentation of HMs. The aim of this review is to integrate a recent understanding of physiological and biochemical mechanisms of HM-induced plant stress response and tolerance based on the findings of current plant molecular biology research.

The impacts of heavy metals on oxidative stress and growth of spring barley

Oxidative stress is accepted to play a significant role in stress symptoms, caused by different stressors in a variety of organisms. In this study seedlings of spring barley (Hordeum vulgare L.) were exposed to a wide range of copper, zinc, chromium, nickel, lead and cadmium concentrations in order to determine the relationships between heavy metals-induced oxidative stress and plant growth inhibition. All investigated heavy metals induced an essential increase in lipid peroxidation and a reduction of dry biomass along with an increase in metal concentration in the nutrient solution. A very close and statistically significant exponential relationship between lipid peroxidation and growth inhibition was detected in this study. According to the results of analysis of variance (ANOVA), the intensity of nonspecific oxidative stress is identified as the main factor of barley growth inhibition, explaining 75% of total variance. Almost 10% of growth inhibition is attributed to the specific impact of heavy metals. The most pronounced increase of malondialdehyde content and growth inhibition was observed in Cu and Cd treatments, whereas the lowest changes in observed indicators were detected after exposure to Zn and Pb.

Linking protein oxidation to environmental pollutants: redox proteomic approaches

Environmental pollutants, such as compounds used in agriculture or deriving from vehicles, industries and human activities, can represent major concern for human health since they are considered to contribute significantly to many diseased states with major public health significance. Besides considerable epidemiological evidence linking environmental pollutants with adverse health effects, little information is provided on the effects of these compounds at the cellular and molecular level. Though oxidative stress is generally acknowledged as one of the most important mechanisms of action for pollutant-induced toxicity, redox proteomics, the elective tool to identify post-translationally oxidized proteins, is still in its very infancy in this field of investigation. This review will provide the readers with an outline of the use of redox proteomics in evaluating pollutant-induced oxidative damage to proteins in various biological systems. Future potential applications of redox proteomic approaches from an environmental point of view will be discussed as well.

Biochemical responses of Lemna minor experimentally exposed to cadmium and zinc

The effects of 5 μM cadmium (Cd), a non-essential toxic element and 25 and 50 μM zinc (Zn), an essential micronutrient, were investigated in aquatic plant Lemna minor L. after 4 and 7 days of exposure to each metal alone or to their combinations. Both metals showed tendency to accumulate with time, but when present in combination, they reduced uptake of each other. Cd treatment increased the lipid peroxidation and protein oxidation indicating appearance of oxidative stress. However, Zn supplementation in either concentration reduced values of both parameters, while exposure to Zn alone resulted in elevated level of lipid peroxidation and protein oxidation but only on the 7th day. Enhanced DNA damage, which was found on the 4th day in plants treated with Cd alone or in combination with Zn, was reduced on the 7th day in combined treatments. Higher catalase activity obtained in all treated plants on the 4th day of experiment was reduced in Zn-treated plants, but remained high in plants exposed to Cd alone or in combination with Zn after 7 days. Cd exposure resulted in higher peroxidase activity, while Zn addition prominently reduced peroxidase activity in the plants subjected to Cd stress. In conclusion, Cd induced more pronounced oxidative stress and DNA damage than Zn in applied concentrations. Combined treatments showed lower values of oxidative stress parameters--lipid peroxidation, protein oxidation and peroxidase activity as well as lower DNA damage, which indicates alleviating effect of Zn on oxidative stress in Cd-treated plants.

Physiological and antioxidant responses of Salvinia natans exposed to chromium-rich wastewater

Salvinia natans possess capacity to accumulate high concentrations of chromium (Cr). Studies were carried out to evaluate physiological efficiency and defensive potential of plant exposed to Cr-rich wastewater. Among photochemical reactions, photosystem I (PS I) and photosystem II (PS II) activity noted an increase in plants exposed to Cr-rich wastewater. Fluorescence ratio F(v)/F(m) depicted no alteration in plants exposed to Cr. The activity of ribulose-1,5-biphosphate carboxylase-oxygenase (Rubisco) noted a decline, while transthylakoidal pH gradient (DeltapH) (correlative of photophosphorylation) showed increase in plants exposed to Cr-rich wastewater. Plants lacked the ability to produce malondialdehyde, but possessed efficient enzymic and non-enzymic antioxidant defense mechanisms that played important role in curtailing oxidative stress. The activities of antioxidant enzymes showed alleviation in plants exposed to Cr-rich wastewater. The levels of cellular antioxidants noted decline suggesting a defensive role in protection against oxidative stress caused by Cr. The present findings suggest that Salvinia possess efficient antioxidant machinery that curtails oxidative stress caused by Cr-rich wastewater and protects photosynthetic machinery from damage.

Application of fly ash on the growth performance and translocation of toxic heavy metals within Cajanus cajan L.: implication for safe utilization of fly ash for agricultural production

The present study was undertaken to examine the influence of the application of fly ash (FA) into garden soil for Cajanus cajan L. cultivation and on accumulation and translocation of hazardous metals from FA to edible part. Numerous studies have been reported on the growth and yield of agricultural crops under FA stress; however, there is a dearth of studies recommending the safe utilization of fly ash for crop production. Pot experiments were conducted on C. cajan L., a widely cultivating legume in India for its highly nutritious seeds. C. cajan L. were grown in garden soil and amended with varying concentrations of FA in a weight/weight ratio (0%, 25%, 50% and 100%; w/w). Incorporation of fly ash from 25% to 100% in garden soil increases the levels of pH, particle density, porosity and water holding capacity from 3.47% to 26.39%, 3.98% to 26.14%, 37.50% to 147.92% and 163.16% to 318.42%, respectively, than the control while bulk density decrease respectively from 8.94% to 48.89%. Pot experiment found that accumulation and translocation of heavy metals in tested plant depends on the concentration of FA. Addition of FA at lower concentration (25%) had shown positive results in most of the studied parameters of growth and yield (14.23% than control). The experimental results confirmed that lower concentration of FA (25%) is safe for C. cajan cultivation, which not only enhanced the yield of C. cajan L. significantly but also ensured the translocation of heavy metals to edible parts within the critical limits.

Cadmium-induced functional and ultrastructural alterations in roots of two transgenic cotton cultivars

The toxic effect of cadmium (Cd) at increasing concentrations was studied with special attention being given to the root morphological and ultrastructural changes in two transgenic cotton cultivars viz. BR001 and GK30 and their wild relative viz. Coker 312. In comparison to their respective controls, low concentration (10 and 100microM) of Cd greatly stimulated seed germination, while it was inhibited by highest concentration of Cd (1000microM) in case of two transgenic cultivars. However, in Coker 312 the seed germination percentage progressively decreased over the control at all Cd levels. Various physiological and morphological parameters of the root and whole plant in both transgenic cotton cultivars and their relative wild cotton genotype respond differently towards the Cd toxicity. Bioavailability of Cd was concentration-dependent where seedling root captured more Cd as compared to shoot. BR001 accumulated more Cd followed by GK30, while Coker 312 was less Cd accumulator. The ultrastructural modifications in the root tip cells of both the transgenic cotton cultivars and their wild relative were also dose-dependent. With the increase in Cd levels, the fine structures of their root cells also invariably changed. Increase in plasmolysis of the plasma membrane, greater number of nucleoli and vacuoles and enlarged vacuoles could be observed in both transgenic cotton cultivars. In comparison to them, Coker 312 showed relatively well developed ultrastructures of the root tips except enlarged vacuoles and greater number of mitochondria. Moreover, the accumulation of Cd in the form of electron dense granules and crystals both in vacuoles and attached to cell walls were visible in both transgenic cotton cultivars and their wild relative. These results suggest that both transgenic cotton cultivars and their wild relative cotton genotype responded positively towards Cd stress at seedling stage, the internal Cd-detoxification might be through apoplastic and symplastic binding. Moreover, as a whole BR001 proved to be sensitive whereas; GK30 and Coker 312 were found as tolerant.

Zinc protects Ceratophyllum demersum L. (free-floating hydrophyte) against reactive oxygen species induced by cadmium

Evidence for Zn protection against Cd-induced reactive oxygen species in the free-floating hydrophyte Ceratophyllum demersum L. is presented in this paper. Metal treatments of 10 micromol/L Cd, 10 Cd micromol/L supplemented with Zn (10, 50, 100 and 200 micromol/L) and Zn-alone treatments of the same concentrations were used. Using 5,5 dimethyl pyrroline-N-oxide as the spin-probe, electron spin resonance spectra indicated a drastic increase in hydroxyl radicals (OH()) in Cd-10 micromol/L treatments, which was closely correlating with the enhanced formation of hydrogen peroxide (H(2)O(2)) and generation of superoxide radical (O(2)(-)) triggered by the oxidation of NADPH. The supplementation of adding Zn (10-200 micromol/L) to the Cd-10 micromol/L treatments significantly decreased the production of free radicals especially by eliminating the precursors of OH() through inhibition of NADPH oxidation. Cd-enhanced ROS production which substantially increased the oxidative products of proteins measured as carbonyls was effectively inhibited by Zn supplementation.

Cadmium toxicity causes oxidative stress and induces response of the antioxidant system in cucumber seedlings

In this study, the effects of cadmium (Cd) on lipid peroxidation, electrolyte leakage, protein oxidation, ascorbate peroxidase (APX; E.C. 1.11.1.11), catalase (CAT; E.C. 1.11.1.6) and superoxide dismutase (SOD; E.C. 1.15.1.1) activities, and ascorbic acid, non-protein thiol groups and total soluble protein contents in cucumber seedlings (Cucumis sativus L.) were investigated. Seedlings were grown in vitro in an agar-solidified substrate containing four Cd levels as CdCl2 (0, 100, 400, and 1000 µmol L-1) for 10 d. The lowest Cd level decreased the malondialdehyde concentration. Electrolyte leakage increased only at 1000 µmol Cd L-1, whereas protein oxidation and total soluble protein content were enhanced at 400 and 1000 µmol Cd L-1. Activity of APX was inhibited while the activities of CAT and SOD were increased at all Cd concentrations. Ascorbic acid was enhanced at 400 and 1000 µmol Cd L-1 whereas non-protein thiol groups were increased at all Cd supplies. The results evidence the importance of the enzymatic and non-enzymatic antioxidant system in response to cadmium toxicity in cucumber seedlings.

Effects of Zn and Cd accumulation on structural and physiological characteristics of barley plants

The objectives of this study were to identify the structural changes caused by Zn and Cd accumulation in shoots and roots of barley (Hordeum vulgare) plants; and to correlate metal accumulation with anatomical, physiological and morphological changes. Potted plants were exposed to metal treatments of Zn and Cd for 19 and 16 d respectively. Leaves, stems and roots were harvested to identify structural changes and analyze metal accumulation. Barley effectively accumulated Zn (up to 11283 mg kg-1) and Cd (up to 584 mg kg-1) in the shoots. Microscopic structural changes, such as a decrease in intercellular spaces, breakdown of vascular bundles, and shrinkage of palisade and epidermal cells, occurred in leaves, stems and roots of plants treated with high concentrations of Zn. Zinc accumulation also resulted in a significant decrease in water content, fresh weight, dry weight and plant height. Cadmium only caused structural changes in roots at the higher concentrations. Barley plants were able to accumulate significant amounts of Zn and Cd without exhibiting symptoms of phytotoxicity when the metal concentrations were relatively low.

Growth performance and biochemical responses of three rice (Oryza sativa L.) cultivars grown in fly-ash amended soil

The disposal of fly-ash (FA) from coal-fired power stations causes significant economic and environmental problems. Use of such contaminated sites for crop production and use of contaminated water for irrigation not only decreases crop productivity but also poses health hazards to humans due to accumulation of toxic metals in edible grains. In the present investigation, three rice cultivars viz., Saryu-52, Sabha-5204, and Pant-4 were grown in garden soil (GS, control) and various amendments (10%, 25%, 50%, 75% and 100%) of FA for a period of 90 days and effect on growth and productivity of plant was evaluated vis-a-vis metal accumulation in the plants. The toxicity of FA at higher concentration (50%) was reflected by the reduction in photosynthetic pigments, protein and growth parameters viz., plant height, root biomass, number of tillers, grain and straw weight. However, at lower concentrations (10-25%), FA enhanced growth of the plants as evident by the increase of studied growth parameters. The cysteine and non-protein thiol (NP-SH) content showed increase in their levels up to 100% FA as compared to control, however, maximum content was found at 25% FA in Saryu-52 and Pant-4 and at 50% FA in Sabha-5204. Accumulation of Fe, Si, Cu, Zn, Mn, Ni, Cd and As was investigated in roots, leaves and seeds of the plants. Fe accumulation was maximum in all the parts of plant followed by Si and both showed more translocation to leaves while Mn, Zn, Cu, Ni and Cd showed lower accumulation and most of the metal was confined to roots in all the three cultivars. As was accumulated only in leaves and was not found to be in detectable levels in roots and seeds. The metal accumulation order in three rice cultivars was Fe > Si > Mn > Zn > Ni > Cu > Cd > As in all the plant parts. The results showed that rice varieties Saryu-52 and Sabha-5204 were more tolerant and could show improved growth and yield in lower FA application doses as compared to Pant-4. Thus, Sabha-5204 and Saryu-52 are found suitable for cultivation in FA amended agricultural soils for better crop yields.

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.