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.     

Elucidation of lead-induced oxidative stress in Talinum triangulare roots by analysis of antioxidant responses and DNA damage at cellular level

Hydroponic experiments were performed with Talinum triangulare (Jacq.) Willd. focusing the root cellular biochemistry with special emphasis on DNA damage, structural, and elemental analyses in Pb(NO₃)₂ exposed with 0, 0.25, 0.5, 0.75, 1.0, and 1.25 mM for 7 days. Lead (Pb) increased reactive oxygen species production, lipid peroxidation, protein oxidation, cell death, and DNA damage and decreased the protein content in a dose-dependent manner. Likewise, a dose-dependent induction of antioxidative enzymes superoxide dismutase and catalase by Pb was evident. Ascorbate peroxidase on the other hand responded biphasically to Pb treatments by showing induction at low (0.25 and 0.50) and repression at high (0.75–1.25 mM) concentrations. The estimation of proline content also indicated a similar biphasic trend. Scanning electron microscope and energy-dispersive X-ray spectroscopy analysis showed that 1.25 mM Pb treatment resulted in ultrastructural modifications in roots and stem tissue that was marked by the change in the elemental profile. The findings pointed to the role of oxidative stress in the underlying Pb phytotoxicity and genotoxicity in T. triangulare.     

Sulphate toxicity to the aquatic moss, Fontinalis antipyretica

The aquatic moss, Fontinalis antipyretica was exposed to elevated sulphate concentrations for 21-days. Gametophores were sectioned to 2 cm lengths and exposed to sulphate concentrations up to 1500 mg/l, in waters of different water hardness. Significant reductions in shoot length, dry weight, and chlorophyll a and b concentrations (per gram dry weight) were observed in soft water (19 mg/l as CaCO3); however, effects were significantly reduced in waters of increasing hardness (up to 105 mg/l as CaCO3). The substantial reduction of sulphate toxicity in waters of increasing hardness suggests water chemistry plays a significant role in affecting sulphate toxicity and should be considered when setting sulphate discharge limits.     

Toxicity of copper excess on the lichen Dermatocarpon luridum: antioxidant enzyme activities

The aim of this study was to investigate the toxicity of copper on the aquatic lichen Dermatocarpon luridum focusing on the activities of some antioxidant enzymes. Investigations were conducted using increasing copper concentrations (0.00, 0.25, 0.50, 0.75 and 1.00 mM CuSO(4) x 5H(2)O) in synthetic freshwater that emulated the major ion compositions of its natural water biota; time course measurement was 0, 3, 6, 12, 24 and 48 h. The copper concentration in thalli increased with its increase in the medium and the duration of treatment. Copper induced lipid peroxidation, measured using the hydroperoxi-conjugated dienes (HPCD) concentration. The decrease in the protein concentrations was similar in thalli exposed to copper concentrations above 0.50 mM and the decrease was twice lower in thalli exposed to 0.25 mM copper. The activities of antioxidant enzymes measured were differently affected by copper excess. For 0.25 mM copper, the activities of SOD (superoxide dismutase) and APX (ascorbate peroxidase) were unchanged when compared with unstressed thalli whereas the CAT (catalase) activity increased and the GR (glutathione reductase) activity decreased. The activities of SOD and APX increased in thalli exposed to concentrations above 0.50mM copper. The CAT activity increased after the first 3h of experiments at these concentrations and then decreased with the duration of treatment at an activity lower than in the unstressed plant. Whereas the APX activity increased, the GR activity similarly decreased for the copper concentration tested whatever the duration of the experiment.     

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 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.     

Mercury toxicity induces oxidative stress in growing cucumber seedlings

In this study, the effects of exogenous mercury (HgCl(2)) on time-dependent changes in the activities of antioxidant enzymes (catalase and ascorbate peroxidase), lipid peroxidation, chlorophyll content and protein oxidation in cucumber seedlings (Cucumis sativus L.) were investigated. Cucumber seedlings were exposed to from 0 to 500microM of HgCl(2) during 10 and 15 days. Hg was readily absorbed by growing seedlings, and its content was greater in the roots than the in shoot. Time and concentration-dependent reduction in root and shoot length was observed at all concentrations tested, equally in the roots and shoot, at both 10 and 15 days. At 50microM HgCl(2), root fresh weight of 15-day-old seedlings increased, and at other concentrations, it reduced. For 10-day-old seedlings, reduction in root and shoot fresh biomass was observed. At 15 days, only at 50microM HgCl(2) was there no observed reduction in shoot fresh biomass. Dry weight of roots increased at 500microM both at 10 and 15 days, though at 250microM HgCl(2) there was only an increase at 15 days. There was a significant effect on shoot dry weight at all concentrations tested. Hg-treated seedlings showed elevated levels of lipid peroxides with a concomitant increase in protein oxidation levels, and decreased chlorophyll content when exposed to between 250 and 500microM of HgCl(2). At 10 days, catalase activity increased in seedlings at a moderately toxic level of Hg, whereas at the higher concentration (500microM), there was a marked inhibition. Taken together, our results suggest that Hg induces oxidative stress in cucumber, resulting in plant injury.     

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.     

Excess lead alters growth, metabolism and translocation of certain nutrients in radish

To elucidate the deleterious effects of excess lead on radish (Raphanus sativus) cv. Jaunpuri plants were grown in refined sand in complete nutrient solution for 30 days. On the 31st day lead nitrate was superimposed at 0.1 and 0.5mM to radish for 65 days. A set of plants in complete nutrient solution was maintained as control for the same period without lead. Excess Pb at 0.5mM showed growth depression with interveinal chlorosis on young leaves at apex. Excess Pb reduced the fresh and dry weight pronouncedly at d 65. Lead accumulation reduced the concentration of chlorophyll, iron, sulphur (in tops), Hill reaction activity and catalase activity whereas increased the concentration of phosphorus, sulphur (in roots) and activity of peroxidase, acid phosphatase and ribonuclease in leaves of radish.     

Physiological and biochemical responses to high Mn concentrations in two contrasting Populus cathayana populations

We exposed the cuttings of Populus cathayana to Hoagland's solution containing four different manganese (Mn) concentrations (0, 0.1, 0.5 and 1mM) in a greenhouse to characterize the physiological and biochemical basis of Mn resistance in woody plants. Two contrasting populations of P. cathayana were used in our study, which were from the wet and dry climate regions in western China, respectively. The results showed that Mn treatments significantly decreased chlorophyll content and growth characteristics, including shoot height, basal diameter, biomass accumulation and total leaf area in the two populations. Mn treatments also significantly increased the levels of abscisic acid (ABA), polyamines and free amino acids especially proline (Pro), histidine (His) and phenylalanine (Phe) available for cellular signaling and heavy metal chelation. In addition, high Mn concentrations also caused oxidative stress indicated as the accumulation of hydrogen peroxide (H(2)O(2)) and malondialdehyde (MDA) contents. On the other hand, there were different responses to Mn stress between the two contrasting populations. Compared with the dry climate population, the wet climate population accumulated more Mn in plant tissues especially in leaves; it showed lower tolerance index and more pronounced decrease in growth and chlorophyll contents. The wet climate population not only accumulated less ABA, putrescine and free amino acids, but also exhibited lower activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX), thus suffering from more serious oxidative damage. Therefore, our results showed that the wet climate population was more susceptible to Mn stress than the dry climate population.     

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.     

Effects of heavy metals on the nitrogen metabolism of the aquatic moss Fontinalis antipyretica L. ex Hedw. A 15N tracer study

The assessment of pollution in aquatic systems necessitates an accurate indication of toxicity of heavy metals for organisms and ecosystems. We used the stable nitrogen isotope 15N to estimate the influence of the heavy metals Cd, Pb and Zn on the synthesis of nitrogen-containing fractions in the aquatic moss Fontinalis antipyretica. This method permits conclusions concerning inhibitory effects of these heavy metals on the assimilation of nitrogen and the biosynthesis of amino acids and proteins. The moss was exposed to metal concentrations of 25-500 microM over a period of 5-10 days. 15N abundance of exposed plants was compared with that of control plants. Similar to a loss of vitality determined using a fluorometric assay, a decrease of the 15N abundance in the N fractions of Fontinalis antipyretica was measured in dependence on the metal concentration. Nevertheless, the individual inhibition by the distinct metals was different, so that the following order of toxicity was derived: Cd > Pb > Zn.     

Chromium(VI) resistance and removal by actinomycete strains isolated from sediments

Forty-one isolated actinomycetes were used to study qualitative and semi-quantitative screening of chromium(VI) resistance. Chromate-removing activity was estimated using the Cr(VI) specific colorimetric reagent 1,5-diphenylcarbazide. Twenty percent of the isolates from El Cadillal (EC) and 14% of isolates from a copper filter plant (CFP) were able to grow at 13 mM of Cr(VI). All isolates from sugar cane (SCP) could grow up to Cr(VI) concentration of 17 mM. EC, CFP and SCP strains were able to remove 24%, 30% and more than 40% of Cr(VI), respectively. The highest and lowest Cr(VI) specific removal values were 75.5 mg g(-1) cell by M3 (CFP), and 1.5 mg g(-1) cell by C35 (EC) strains. Eleven Cr(VI) resistant strains were characterized and identified as species of the genera Streptomyces (10) and Amycolatopsis (1). Differences on actinomycete community composition between contaminated and non-contaminated soil were found. This study showed the potential capacity of actinomycetes as tools for Cr(VI) bioremediation.     

Sperm count in earthworms (Lumbricus terrestris) as a biomarker for environmental toxicology: effects of cadmium and chlordane

Earthworms, Lumbricus terrestris, exposed in artificial soil to sublethal concentrations of technical chlordane (6.25, 12.5, and 25 ppm) and cadmium nitrate (100, 200, and 300 ppm) exhibited significant reduction in spermatozoa from testes and seminal vesicles. The onset time of reduction varied with exposure concentration, but absolute depression in sperm count was independent of exposure concentration or exposure duration after reduction was first manifested, demonstrating a threshold effect. Earthworm sperm counts show potential as a rapid-measurement endpoint biomarker for measuring sublethal effects of chemical pollutants on reproduction.     

28-homobrassinolide protects chickpea (Cicer arietinum) from cadmium toxicity by stimulating antioxidants

In the present experiment the seeds of Cicer arietinum (L.) cv. Uday were inoculated with specific Rhizobium grown in sandy loam soil and were allowed to grow for 15 days. At this stage, the seedlings were supplied with 0, 50, 100 or 150 microM of cadmium in the form of cadmium chloride and sprayed with 0.01 microM of 28-homobrassinolide (HBL) at 30-day stage. The data indicated that plant fresh and dry mass, number of nodules, their fresh and dry mass, leghemoglobin content, nitrogen and carbohydrate content in the nodules, leaf chlorophyll content, nitrate reductase and carbonic anhydrase activities decreased proportionately with the increasing concentrations of cadmium but the content of proline and the activities of catalase, peroxidase and superoxide dismutase increased. The ill effect, generated by cadmium, was overcome if the stressed plants were sprayed with HBL.     

Effects of ozone on chlorophyll and quantum yield of tobacco (Nicotiana tabacum L.) varieties

Plants of Bel-W3 and of seven commercial tobacco varieties (Nicotiana tabacum L.) were exposed to two relatively low ozone concentrations (90 or 135 ppb) for 20 consecutive days, for 8 h per day. Ozone caused necrotic and chlorotic spots, acceleration of leaf senescence, depression of photosynthetic mechanism, chlorophyll diminution and greater destruction of chl a than of chl b. The higher sensitivity of chl a was also confirmed by exposure of segments of leaves in test tubes to high ozone concentration (>1000 ppb) as well as by bubbling of ozone in extracts of chlorophyll in vitro. The quantum yield (QY) of photosynthesis was positively correlated with the chlorophyll content and negatively correlated with the visible injury and the chl b/a ratio.     

Bioaccumulation of 4-nonylphenol in marine animals--a re-evaluation

The bioaccumulation of 4-nonylphenol (NP) has been studied in shrimps (Crangon grangon L.), mussels (Mytilus edulis L.) and sticklebacks (Gasterosteus aculeatus L.) exposed to (14)C-NP in running seawater. NP was extracted with high recovery from tissues which were pretreated with pancreatic enzymes. The bioconcentration factor determined of NP in fish was 1300 and in mussels, 3400. These values are 5 and 340 times higher, respectively, than values reported earlier.     

Environmental cadium exposure and metabolic responses of the Nile tilapia, Oreochromis niloticus

The contamination of water by metal compounds is a worldwide environmental problem. This study was undertaken to evaluate the impact of short-term cadmium exposure on metabolic patterns of the freshwater fish Oreochromis niloticus. The fish were exposed to 320, 640, 1,280 and 2,560 microg/l sublethal concentrations of Cd++ (CdCl2) in water for 7 days. The specific activities of the enzymes phosphofructo kinase (PFK-E.C.2.7.1.11.), lactate dehydrogenase (LDH-E.C.1.1.1.27.) and creatine kinase (CKE.C.2.7.3.2.) were decreased in white muscle after cadmium treatments, indicating decreases in the capacity of glycolysis in this tissue. Cadmium exposure induced increased glucose concentration in white muscle of fish. On the other hand, cadmium exposure at sublethal concentrations increased phosphofructo kinase and LDH in red muscle of fish. Cadmium significantly decreased total protein concentrations in liver and white muscle regardless of tissue glycogen levels. The data suggest that cadmium acts as a stressor, leading to metabolic alterations similar to those observed in starvation.     

Effects of past sewage sludge additions on heavy metal availability in light textured soils: implications for crop yields and metal uptakes

The effect of heavy metal additions in past sewage sludge applications on soil metal availability and the growth and yield of crops was evaluated at two sites in the UK. At Gleadthorpe, sewage sludges enriched with salts of zinc (Zn), copper (Cu) and nickel (Ni) had been applied to a loamy sand in 1982 and additionally naturally contaminated Zn and Cu sludge cakes in 1986. At Rosemaund, sewage sludges naturally contaminated with Zn, Cu, Ni and chromium (Cr) had been applied in 1968-1971 to a sandy loam. From 1994 to 1997, the yields of both cereals and legumes at Gleadthorpe were up to 3 t/ha lower than the no-sludge control where total topsoil Zn and Cu concentrations exceeded 200 and 120 mg/kg, respectively, but only when topsoil ammonium nitrate extractable metal levels also exceeded 40 mg/kg Zn and 0.9 mg/kg Cu. At Rosemaund, yields were only decreased where total topsoil Cu concentrations exceeded 220 mg/kg or 0.7 mg/kg ammonium nitrate extractable Cu. These results demonstrate the importance of measuring extractable as well as total heavy metal concentrations in topsoils when assessing likely effects on plant yields and metal uptakes, and setting soil quality criteria.     

Self-organizing feature map (neural networks) as a tool in classification of the relations between chemical composition of aquatic bryophytes and types of streambeds in the Tatra national park in Poland

Concentrations of the elements Al, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb and Zn were measured in the aquatic bryophytes Fontinalis antipyretica, Platyhypnidium riparioides and Scapania undulata. These bryophytes were sampled from streams flowing through granites/gneisses, limestones/dolomites and sandstones in the Tatra national park in Poland. The Self-organizing feature map (SOFM) or Kohonen network was used to classify the bryophytes according to the concentrations of the elements. This method was verified using principal component analysis (PCA) to check whether this well-known technique would give similar results. Both the self-organizing map and ordination by PCA yielded distinct groups of aquatic bryophytes growing in streams flowing through different types of rock, groups which differed significantly in the concentrations of certain elements. Bryophytes from granites/gneisses were distinguished by higher concentrations of Cd and Pb, while those from sandstones had a higher concentration of Cr and those from limestones/dolomites had higher concentrations of Ca and Mg. The SOFM and PCA ordinations thus yield identical classifications of bryophytes from the Tatra mountains streams.