Different compensatory mechanisms in two metal-accumulating aquatic macrophytes exposed to acute cadmium stress in outdoor artificial lakes

Comprehensive transcriptome, physiological and biochemical analyses reveal that key role of transcription factor WRKY and plant hormone in responding cadmium stress

Cadmium (Cd) is readily absorbed by tobacco and accumulates in the human body through smoke inhalation, posing threat to human health. While there have been many studies on the negative impact of cadmium in tobacco on human health, the specific adaptive mechanism of tobacco roots to cadmium stress is not well understood. In order to comprehensively investigate the effects of Cd stress on the root system of tobacco, the combination of transcriptomic, biochemical, and physiological methods was utilized. In this study, tobacco growth was significantly inhibited by 50 μM of Cd, which was mainly attributed to the destruction of root cellular structure. By comparing the transcriptome between CK and Cd treatment, there were 3232 up-regulated deferentially expressed genes (DEGs) and 3278 down-regulated DEGs. The obvious differential expression of genes related to the nitrogen metabolism, metal transporters and the transcription factors families. In order to mitigate the harmful effects of Cd, the root system enhances Cd accumulation in the cell wall, thereby reducing the Cd content in the cytoplasm. This result may be mediated by plant hormones and transcription factor (TF). Correlational statistical analysis revealed significant negative correlations between IAA and GA with cadmium accumulation, indicated by correlation coefficients of -0.91 and -0.93, respectively. Conversely, ABA exhibited a positive correlation with a coefficient of 0.96. In addition, it was anticipated that 3 WRKY TFs would lead to a reduction in Cd accumulation. Our research provides a theoretical basis for the systematic study of the specific physiological processes of plant roots under Cd stress.

Seasonality Affects Low-Molecular-Weight Organic Acids and Phenolic Compounds' Composition in Scots Pine Litterfall

BACKGROUND AND AIMS

Secondary plant metabolites, including organic acids and phenolic compounds, have a significant impact on the properties of organic matter in soil, influencing its structure and function. How the production of these compounds in foliage that falls to the forest floor as litterfall varies across tree age and seasonality are of considerable interest for advancing our understanding of organic matter dynamics.

METHODS

Monthly, we collected fallen needles of Scots pine (Pinus sylvestris L.) across stands of five different age classes (20, 40, 60, 80, and 100 years) for one year and measured the organic acids and phenolic compounds.

RESULTS

Seven low-molecular-weight organic acids and thirteen phenolic compounds were detected in the litterfall. No differences were observed across stand age. Significant seasonal differences were detected. Most compounds peaked during litterfall in the growing season. Succinic acid was the most prevalent organic acid in the litterfall, comprising 78% of total organic acids (351.27 ± 34.27 µg g- 1), and was 1.5 to 11.0 times greater in the summer than all other seasons. Sinapic acid was the most prevalent phenolic compound in the litterfall (42.15 µg g- 1), representing 11% of the total phenolic compounds, and was 39.8 times greater in spring and summer compared to autumn and winter. Growing season peaks in needle concentrations were observed for all thirteen phenolic compounds and two organic acids (lactic, succinic). Citric acid exhibited a definitive peak in late winter into early spring.

CONCLUSIONS

Our results highlight the seasonal dynamics of the composition of secondary plant metabolites in litterfall, which is most different at the onset of the growing season. Fresh inputs of litterfall at this time of emerging biological activity likely have seasonal impacts on soil's organic matter composition as well.

Red light alleviates Cd toxicity in Egeria densa by modifying carbon-nitrogen metabolism and boosting energy metabolism

Among the various pollutants detected in aquatic ecosystems, cadmium (Cd) is considered as one of the most hazardous. Freshwater macrophytes have been recognized as possible candidates for eliminating Cd from environment. Nevertheless, the impact of light quality on their ability to tolerate Cd toxicity remains unclear, and the underlying mechanisms have yet to be fully elucidated. In this study, we utilized physiological testing and metabolomics to explore the potential mechanisms by which light quality influences the ability of Egeria densa, a significant Cd hyperaccumulator, to withstand Cd toxicity. The study demonstrated that following Cd treatment, E. densa grown under red light exhibited superior photosynthetic efficiency compared to those grown under blue light, as evidenced by significantly increased photosynthetic rate, higher starch content, and greater activity of photosynthetic enzymes. Moreover, metabolomic analyses revealed that under Cd stress, E. densa grown under red light exhibited an enhanced glycolysis for increased energy production. Sucrose metabolism was also improved to generate sufficient sugar including glucose, fructose and mannose for osmotic adjustment. Moreover, under red light, the heightened production of α-ketoglutarate via tricarboxylic acid (TCA) cycle redirected nitrogen flow towards the synthesis of resilient substances such as γ-Aminobutyric Acid (GABA) and methionine. The production of these substances was ∼2.0 and 1.3 times greater than that of treatment with Cd under blue light, thereby improving E. densa's capacity to withstand Cd stress. This study represents the initial investigation into the possible mechanisms by which light quality influences the ability of E. densa to withstand Cd toxicity through regulating CN metabolism. Furthermore, these findings have the potential to improve phytoremediation strategies aimed at reducing Cd pollution.

Blue Light Enhances Cadmium Tolerance of the Aquatic Macrophyte Potamogeton crispus

Cadmium (Cd) is highly toxic and widely distributed in aquatic systems due to its high solubility and mobility in water, which can severely inhibit the survival of aquatic macrophytes. The phytotoxicity of Cd depends on environmental factors; however, it remains unclear whether and how light quality affects its toxicity on aquatic macrophytes. In this study, we investigated the effects of Cd on aquatic macrophytes Potamogeton crispus under different light qualities (white, blue, and red light). We evaluated morphological and photo-physiological traits, as well as the cellular antioxidant defense system. Our findings indicate that P. crispus under Cd stress showed notable damage in leaf morphology, decreased photosynthetic efficiency, inhibited HCO₃^- uptake, and reduced antioxidant enzyme activities, as well as oxidative damage indicated by MDA accumulation and superoxide (O₂^-) overproduction. However, compared with white or red light under Cd stress, blue light reduced structural damage and oxidative stress caused by Cd while increasing pigment synthesis and photosynthetic efficiency, as well as increasing ascorbate peroxidase (APX) activity. In conclusion, the changes induced by blue light in P. crispus's photosynthesis and antioxidant system strengthen its tolerance to Cd. Further research on signal transmission in relation to light quality in Cd-exposed aquatic plants is still needed.

Profile and concentration of the low molecular weight organic acids and phenolic compounds created by two-year-old Acer platanoides seedlings growing under different As forms

Two-year-old seedlings of Acer platanoides were cultivated during a three-month hydroponic experiment in modified Knop solution enriched with inorganic (As(III), As(V)) and organic (dimethylarsinic acid - DMA) arsenic forms at 0.06 mM, 0.6 mM and their combinations. The profile and content of low molecular weight organic acids (LMWOAs) and phenolic compounds were also determined in the rhizosphere, roots and leaves. Arsenic (As) treatment caused an elevated creation of the above mentioned metabolites, which was higher in leaves than in the rhizosphere or roots, and their overall content was correlated with the concentration of As in A. platanoides organs. The addition of all As forms strongly induced the exudation of citric and oxalic acids into the rhizosphere, while malonic, acetic, citric and malic acids were formed in the roots. The most differential profile of roots was confirmed for As(V) 0.06 mM (4-hydroxybenzoic (4-HBA), syringic, 2,5 dihydroxybenzoic (2,5-DHBA), caffeic, chlorogenic, ferulic, p-coumaric and sinapic acids and catechin). The obtained results indicate that the presence of particular As forms has a significant impact on the content and profile of exuded and created LMWOAs and phenolic compounds, and can also have a decisive influence on the activation of appropriate detoxification mechanisms.

Involvement of glutathione metabolism in Eichhornia crassipes tolerance to arsenic

Aquatic macrophytes are potentially useful for phytoremediation programmes in environments contaminated by arsenic (As). Biochemical and physiological modification analyses in different plant parts are important to understand As tolerance mechanisms. The objective was to evaluate glutathione metabolism in leaves and roots of Eichhornia crassipes (Mart.) Solms treated to As. Specimens of E. crassipes were cultured for 3 days in Clark's nutrient solution containing 7 μm As. The enzymes ATP sulphurylase (ATPS), glutathione reductase (GR), glutathione peroxidase (GSH-Px), glutathione sulphotransferase (GST) and γ-glutamylcysteine synthetase (γ-ECS) activity, glutathione content, total protein and non-protein thiols were evaluated. The ATPS activity increased in roots. GR activity in leaves and GSH-Px in roots were lower. GST activity was higher in roots and lower in leaves, and γ-ECS activity was higher in leaves. Glutathione levels were lower, total thiol levels were higher and non-protein levels did not change in E. crassipes leaves and roots. Exposure to As increased enzyme activity involved with sulphur metabolism, such as ATPS. Higher GR activity and lower GSH-Px indicate increased glutathione conjugation to As due to increased GSH availability. The higher GST activity indicates its participation in As detoxification and accumulation through As GSH conjugation. Changes in glutathione and thiol levels suggest high phytochelatin synthesis. In conclusion, the increments in ATPS, GR, GST and γ-ECS activity indicate that these enzymes are involved in GSH metabolism and are part of the E. crassipes As detoxification mechanism.

Myriophyllum alterniflorum biochemical changes during in vitro Cu/Cd metal stress: Focusing on cell detoxifying enzymes

Given the toxicity of trace metals, their concentration, speciation and bioavailability serve to induce various plant detoxification processes, which themselves are specific to several parameters like plant species, tissue type and developmental stage. In this study, Myriophyllum alterniflorum (or alternate watermilfoil) enzyme activities (ascorbate peroxidase, catalase, glutathione peroxidase and superoxide dismutase) from in vitro cultures was measured over 27 days in response to copper (Cu) or cadmium (Cd) stress. These enzymes are unique to reactive oxygen species (ROS) scavenging (mainly hydrogen peroxide H₂O₂ and superoxide anion O₂^-) and moreover showed specific or unspecific activity profiles, depending on the metal concentrations used. Our results suggest a higher-priority protection of chloroplasts during the initial days of exposure to both metals. At the same time, the increased catalase activity could indicate an H₂O₂ diffusion in peroxisome in order to protect other organelles from ROS accumulation. However, as opposed to the Cd effects, high Cu concentrations appear to induce a "limited oxidative threshold" for some antioxidant enzymes, which could suggest an ion absorption competition between Cu²⁺ and Fe²⁺. In spite of an overall analysis conducted of the scavenging processes occurring in plant cells, biochemical analyses still yielded relevant indications regarding the watermilfoil strategies used for ROS management.

Assessing interactions between environmental factors and aquatic toxicity: Influences of dissolved CO2 and light on Cd toxicity in the aquatic macrophyte Potamogeton crispus

The objective of this study was to investigate the combined effects of varying dissolved CO₂ concentration (ambient CO₂, 3˜17 μmol L^-1, elevated CO₂, 48˜81 μmol L^-1) and light intensity (high light, c. 150 μmol photon m^-2 s^-1, low light, c. 25 μmol photon m^-2 s^-1) on the bioaccumulation and phytotoxicity of cadmium (Cd) in a macrophyte Potamogeton crispus, under constant Cd exposure. The data confirmed that 100 μM Cd led to adverse changes in morphology, ultrastructure and biochemistry in P. crispus. The toxic effects depended strongly on CO₂ concentration and light intensity: elevated CO₂ and high light both increased Cd concentrations in P. crispus, and there was a significant interaction between the two factors. Compared to high light grown plants, the photochemical efficiency and chlorophyll content of low light grown P. crispus were much less affected and the MDA content was lower, when exposed to 100 μM Cd. In addition, an antioxidative response was observed with a significant increase in SOD, POD and GST activities, indicating that low light grown P. crispus are more protected against Cd toxicity. When compared with ambient CO₂ concentrations, chlorophyll content, chlorophyll fluorescence, photosynthetic rate and starch content, as well as the activity of SOD and GST, were significantly enhanced in Cd treated P. crispus under elevated CO₂. This suggests that elevated CO₂ reduced Cd toxicity in P. crispus by increasing photosynthesis and enhancing the antioxidant system. Moreover, the statistical results showed that dissolved CO₂ and light had additive effects on Cd toxicity in P. crispus, reflected by the physiological parameters of total chlorophyll content, SOD activity and MDA content, indicating that the combination of high CO₂ and low light produced more protection against Cd toxicity than did the factors alone. Based on the results of this study, it appears clear that referring to a specific site in aquatic ecosystem, dissolved CO₂ concentration and light availability should be considered when assessing and managing Cd impacts on aquatic plants.

Salix viminalis L. - A highly effective plant in phytoextraction of elements

The aim of the study was to compare specimens of Salix viminalis L. able to grow in polluted mining sludge (A1) with specimens of the same willow clone growing in two unpolluted areas (A2 and A3). Plants from the polluted area were characterized by the highest accumulation of the majority of elements in their organs with a clear limitation of their uptake to roots and effective translocation to aboveground organs. Willows from the unpolluted areas were characterized by significantly higher biomass than the treated plants, as shown in the content of cellulose/holocellulose. The different chemical characteristics of the substrates influenced tree physiology, including the organic acids and phenolic compounds profile and/or content. The total content of organic acids in lateral roots was higher for S. viminalis L. grown in unpolluted areas, while for leaves the opposite situation was observed. However, their creation was significantly correlated with the content of the majority of elements in the organs of S. viminalis L. Enhanced synthesis of phenolic compounds in roots (besides quercetin) and in leaves (besides myricetin and quercetin) was confirmed in the polluted area, and correlated with metal content in plant organs. Resilient plants characterized not only by their survivability but also by their effective phytoextraction of toxic metals, have great potential for widespread practical application on highly polluted mining sludge and for reducing the associated threat to human health. The obtained results suggest that further investigation of these plants is necessary to determine the mechanism(s) responsible for their high survivability.

The effect of hazardous pollutants from coal combustion activity: Phytotoxicity assessment of aqueous soil extracts

Airborne fly ash and related hazardous particles derived from coal combustion contaminate soil and groundwater, negatively affecting ecosystems. The aim of this study was chemical and toxicological evaluation of aqueous extracts of soil collected from the vicinity of a coal-fired Plomin power plant (PPP), using Lemna (Lemna minor L.) bioassay and additional biochemical indicators - photosynthetic pigments, lipid peroxidation, antioxidative enzymes and glutathione. Topsoil samples were collected from distances of 200, 300, 400 and 800 m from the PPP in accordance with the prevailing SW wind direction. Elevated levels of polycyclic aromatic hydrocarbons (up to 15,765 ng L^-1) and potentially toxic trace elements were detected in the Plomin soil extracts (PEs) in comparison to control soil extract (CE). Trace elements accumulated in L. minor were mostly in accordance with their concentrations in PEs. The results demonstrate that PEs induced significant growth inhibition and other phytotoxic effects. Those effects can be related to damage caused by increased production of reactive oxygen species and impaired antioxidant levels. The connection among the phytotoxicity, a distribution of analyzed contaminants, and distances from the PPP is clearly established.

Modulation of cadmium-induced phytotoxicity in Cabomba caroliniana by urea involves photosynthetic metabolism and antioxidant status

Urea is a widespread organic pollutant, which can be a nitrogen source, playing different roles in the growth of submerged macrophytes depending on concentrations, while high cadmium (Cd) concentrations are often toxic to macrophytes. In order to evaluate the combined effect of urea and Cd on a submerged macrophyte, Cabomba caroliniana, the morphological and physiological responses of C. caroliniana in the presence of urea and Cd were studied. The results showed that high concentrations of urea (400mgL^-1) and Cd (500µmolL^-1) had negative effects on C. caroliniana. There were strong visible symptoms of toxicity after 4 days of exposure under Cd-alone, 400mgL^-1 urea, and Cd+400mgL^-1 urea treatments. In addition, 400mgL^-1 urea and Cd had adverse effects on C. caroliniana's pigment system. Significant losses in chlorophyll fluorescence and photosynthetic rates, as well as Rubisco activity were also observed under Cd-alone, 400mgL^-1 urea, and Cd+400mgL^-1 urea treatments. 400mgL^-1 urea markedly enhanced Cd toxicity in C. caroliniana, reflected by a sharp decrease in photosynthetic activity and more visible toxicity symptoms. The results of thiobarbituric acid reactive substances (TBARS) pointed to extreme oxidative stress in C. caroliniana induced under Cd or 400mgL^-1 urea exposure. Exogenous ascorbate (AsA) protected C. caroliniana from adverse damage in 400mgL^-1 urea, which further corroborated the oxidative stress claim under 400mgL^-1 urea. However, results also demonstrated that lower urea concentration (10mgL^-1) alleviated Cd-induced phytotoxicity by stimulating chlorophyll synthesis and photosynthetic activity, as well as activating the activity of catalase (CAT) and glutathione-S-transferase (GST), which may explain the alleviating effect of urea on C. caroliniana under Cd stress.

Thiols as biomarkers of heavy metal tolerance in the aquatic macrophytes of Middle Urals, Russia

Aquatic macrophytes, viz. Sagittaria sagittifolia L., Lemna gibba L., Elodea canadensis Michx., Batrachium trichophyllum (Chaix.) Bosch., Ceratophyllum demersum L. and Potamogeton sp. (P. perfoliatus L., P. alpinus Balb., P. crispus L., P. berchtoldii Fieber, P. friesii Rupr., P. pectinatus L.) were collected from 11 sites for determining their metal accumulation and thiols content. Cu(2+), Ni(2+), Mn(2+), Zn(2+), and Fe(3+) exceeded maximum permissible concentrations in chosen sites. Significant transfer of metals from water to leaves is observed in the order of Ni(2+) < Cu(2+) < Zn(2+) < Fe(3+) < Mn(2+). The maximum variation of bioconcentration factor was noticed for manganese. The accumulation of heavy metals in leaves was correlated with non-protein and protein thiols, confirming their important role in metal tolerance. The largest contribution was provided by Cu(2+) (on the average r = 0.88, p < 0.05), which obviously can be explained as an important role of these ions in thiols synthesis. Increased synthesis of thiols in the leaves allows the usage of SH-containing compounds as biomarkers of metal tolerance. Considering accumulation of metals and tolerance, B. trichophyllum, C. demersum and L. gibba are the most suitable species for phytoremediation of highly multimetal contamination, while E. canadensis and some species of Potamageton are suitable for moderately metal-polluted sites.

Phytofiltration of arsenic and cadmium by using an aquatic plant, Micranthemum umbrosum: phytotoxicity, uptake kinetics, and mechanism

Arsenic (As) and cadmium (Cd) are noxious and carcinogenic pollutants that can be removed from water by using emerging, ecofriendly, phytofiltration technology that employs Micranthemum umbrosum. After culturing M. umbrosum for 7 days in a hydroponic experiment, accumulation of 1219±44.11 µg As g(-1) and 799.40±30.95 µg Cd g(-1) were observed in the leaves, from 1000 µg As L(-1) and 1000 µg Cd L(-1) of water, respectively. Plant and water samples were analyzed for assessing the As and Cd accumulations, translocations, phytotoxic effects, uptake mechanisms and kinetics, and for evaluating the potential of M. umbrosum in As and Cd phytofiltration. The uptake pattern was leaf>stem>root for both pollutants. The plant showed higher resistance to As than to that to Cd. Uptake of inorganic As species was much greater than that of organic As and was found at above the substrate concentration. However, Cd showed similar uptake pattern to that of inorganic As species, and the data was better fit to a non-linear than a linear model. Low molecular weight substances that have thiol group(s) may be responsible for the binding of As in plants whereas Cd showed a different mechanism to that of As. M. umbrosum showed good As phytofiltration capabilities without any phytotoxic effects, but it was found to be a moderate accumulator of Cd with some phytotoxic effect compare to some other previously studied plant.

Exogenous application of methyl jasmonate lowers the effect of cadmium-induced oxidative injury in rice seedlings

Rice seedlings grown under 50 μM cadmium alone or in combination with 5 μM methyl jasmonate were investigated for Cd-induced oxidative injury at 3, 7 and 10 days of treatment. MeJA treatments alone did not have any significant change in antioxidant enzyme activities or levels of H2O2 and O2(·-) in roots/shoots, as compared to controls during 3-10 days. The Cd-stressed plants When supplemented with exogenous MeJA revealed significant and consistent changes in activities of antioxidant enzymes CAT, SOD, POD and GR paralleled with an increased GSH-pools than that in plants subjected to Cd-stress alone. Synthesis of GSH driven by increasing demand for GSH in response to Cd-induced oxidative stress in rice was evident. Increased activity of LOX under Cd-stress was noted. Results suggest enhanced Cd-tolerance, lowered Cd(2+) uptake, an improved membrane integrity and 'switching on' of the JA-biosynthesis by LOX in the Cd-stressed rice roots/shoots exposed to MeJA. Exposure to MeJA improved antioxidant response and accumulation of antioxidants which perhaps lowered the Cd-induced oxidative stress in rice. It is this switching on/off of the JA-biosynthesis and ROS mediated signal transduction pathway involving glutathione homeostasis via GR which helps MeJA to mitigate Cd-induced oxidative injury in rice.

Evaluation of the potential of Pistia stratiotes L. (water lettuce) for bioindication and phytoremediation of aquatic environments contaminated with arsenic

Specimens of Pistia stratiotes were subjected to five concentrations of arsenic (As) for seven days. Growth, As absorption, malondialdehyde (MDA) content, photosynthetic pigments, enzymatic activities, amino acids content and anatomical changes were assessed. Plant arsenic accumulation increased with increasing metalloid in the solution, while growth rate and photosynthetic pigment content decreased. The MDA content increased, indicating oxidative stress. Enzymatic activity and amino acids content increased at the lower doses of As, subsequently declining in the higher concentrations. Chlorosis and necrosis were observed in the leaves. Leaves showed starch accumulation and increased thickness of the mesophyll. In the root system, there was a loss and darkening of roots. Cell layers formed at the insertion points on the root stems may have been responsible for the loss of roots. These results indicate that water lettuce shows potential for bioindication and phytoremediation of As-contaminated aquatic environments.

Strategies for Cd accumulation in Dittrichia viscosa (L.) Greuter: role of the cell wall, non-protein thiols and organic acids

Dittrichia viscosa (L.) Greuter is plant species commonly found in degraded zones of Asturias (Spain), where it accumulates high levels of Cd, but the mechanisms involved in this response in non-model plants have not been elucidated. In this way, we analysed the fraction of the total Cd bound to the cell walls, the ultrastructural localization of this metal, and non-protein thiol and organic acid concentrations of two clones of D. viscosa: DV-A (from a metal-polluted soil) and DV-W (from a non-polluted area). After 10 days of hydroponic culture with Cd, fractionation and ultrastructural localisation studies showed that most of the Cd accumulated by D. viscosa was kept in the cell wall. The non-protein thiol content rose in D. viscosa with Cd exposure, especially in the non-metallicolous DV-W clone, and in both clones we found with Cd exposure a synthesis de novo of phytochelatins PC2 and PC3 in shoots and roots and also of other phytochelatin-related compounds, particularly in roots. Regarding organic acids, their concentration in both clones decreased in shoots after Cd treatment, but increased in roots, mainly due to changes in the citric acid concentration. Thus, retention of Cd in the cell wall seems to be the first strategy in response to metal entry in D. viscosa and once inside cells non-protein thiols and organic acids might also participate in Cd tolerance.

Cadmium accumulation, activities of antioxidant enzymes, and malondialdehyde (MDA) content in Pistia stratiotes L

The aquatic plant Pistia stratiotes L. (water lettuce) was studied due to its capability of absorption of contaminants in water and its subsequent use in wetlands constructed for wastewater treatment. The effects of Cd on root growth, accumulation of Cd, antioxidant enzymes, and malondialdehyde (MDA) content in P. stratiotes were investigated. The results indicated that P. stratiotes has considerable ability to accumulate Cd. Cadmium induced higher superoxide dismutase (SOD) and peroxidase (POD) activities than catalase activity, suggesting that SOD and POD provided a better defense mechanism against Cd-induced oxidative damage. The accumulation of Cd promoted MDA production.

Pistia stratiotes (Jalkumbhi)

Pistia stratiotes (Family: Araceae) is commonly used in Ayurvedic medicine. This review article is a compilation of all the updated information on its phytochemical and pharmacological activities, which were performed by different methods. Studies indicate that P. stratiotes possesses diuretic, antidiabetic, antidermatophytic, antifungal, and antimicrobial properties. These results are very encouraging and indicate that this plant should be studied more extensively to confirm the reproducibility of these results and also to reveal other potential therapeutic effects, along with some “leads” with possible isolation of active biomoieties and their mechanism of action.

Bioacumulation and ultrastructural effects of Cd, Cu, Pb and Zn in the moss Scorpiurum circinatum (Brid.) Fleisch. & Loeske

This paper tested if culturing the moss Scorpiurum circinatum (Brid.) Fleisch. & Loeske with metal solutions (Cd, Cu, Pb and Zn) for 30 days causes metal bioaccumulation and ultrastructural changes. The results showed that despite the high heavy metal concentrations in treatment solutions, treated samples did not show severe ultrastructural changes and cells were still alive and generally well preserved. Bioaccumulation highlighted that moss cells survived to heavy metal toxicity by immobilizing most toxic ions extracellularly, likely in binding sites of the cell wall, which is the main site of metal detoxification.

Cadmium-induced oxidative stress and the response of the antioxidative defense system in Spartina densiflora

Spartina densiflora is an invasive cordgrass that is colonizing new habitats and ousting indigenous species in pro-oxidative environments like cadmium-polluted salt marshes in the Odiel estuary (Spain). The aim of our study was to characterize its antioxidative system in order to find out if the system underlies the tolerance of S. densiflora to cadmium toxicity. S. densiflora plants were firstly evaluated to ascertain its antioxidative status in the natural habitat and then they were cultured in the laboratory in unpolluted sand for 28 days. Throughout this period, plants acclimatized and oxidative stress markers reached stable low levels. Then, S. densiflora plants were exposed to cadmium concentrations (10, 100 and 1000 microM Cd) for another 28 days. Higher Cd content in leaves was related to higher level of reactive oxygen species (ROS) causing important oxidative cell damage (lipid peroxidation and lower chlorophyll content). However, S. densiflora possesses a well-organized and appropriately modulated antioxidative defense system which comprises enzymatic activities of guaiacol peroxidase (EC 1.11.1.7), catalase (EC 1.11.1.6), ascorbate peroxidase (EC 1.11.1.11) and superoxide dismutase (EC 1.15.1.1) coupled with the activation of the ascorbate cycle, including enzymatic activities of glutathione reductase (EC 1.6.4.2), dehydroascorbate reductase (EC 1.8.5.1) and monodehydroascorbate reductase (EC 1.6.5.4). This activation was sufficient to reduce Cd-induced ROS accumulation and oxidative damage caused by the lowest Cd-concentrations, but not by the highest Cd-concentration (1000 microM). Nevertheless, the antioxidant system seems to be efficient to achieve a tolerance to cadmium toxicity, allowing normal plant development, even at the presence of highest Cd concentration.

Responses of Lemna trisulca L. (Duckweed) exposed to low doses of cadmium: thiols, metal binding complexes, and photosynthetic pigments as sensitive biomarkers of ecotoxicity

Lemna species are reported to accumulate a variety of metals from contaminated/polluted sites. Cadmium is a nonessential element for plant metabolism. In this work, we aimed to investigate physiological responses to low doses of cadmium (up to 100 microM). From exposure to the lowest Cd concentration (1 microM) to the highest (100 microM), photosynthetic pigments (Chl a, b, carotenoids) and the ratios of Chl a/b, Chl (a + b)/carotenoids decreased as a function of the Cd dose. The content of soluble proteins decreased in a dose-dependent manner, while total soluble thiols drastically increased. In Cd-treated fronds, the dose-dependent accumulation of a polypeptide with an apparent molecular weight of 24 kDa, as well as the appearance of two smaller polypeptides with molecular weights <6.5 kDa, was observed in sodium dodecyl sulfate polyacrylamide gel electrophoresis. Our results show that in Lemna trisulca, different adaptative mechanisms may be involved in counterbalancing low and high doses of a particular toxicant (cadmium). This feature makes this plant potentially useful material in biomonitoring and phytotoxicity testing.

Response of phytochelatins and their relationship with cadmium toxicity in a floating macrophyte Pistia stratiotes L. at environmentally relevant concentrations

An indoor experiment was undertaken to investigate the response of phytochelatins and their relationship to cadmium toxicity in Pistia stratiotes L., a free-floating macrophyte, exposed to low concentrations of cadmium typically found in realistic environments. Cadmium concentrations of 0.01 to 0.08 microM had no toxic effects on the growth of this plant, as indicated by no significant changes in the fresh weights of leaves and roots and the slight induction of phytochelatins in plant tissues, whereas cadmium concentrations of 0.16 to 1 microM were toxic, and cadmium toxicity increased with the increase of cadmium concentrations in solutions, accompanied by the dramatic production of phytochelatins in plant tissues, especially in roots. There was a positive correction between root phytochelatin levels and cadmium toxicity, as measured by the growth inhibition rate of the root fresh weight. The results suggested that phytochelatins in aquatic macrophytes can serve as sensitive biomarkers for heavy metal toxicity in a moderately polluted water environment.

Effect of different soil conditions on selected heavy metal accumulation by Salix viminalis tissues

This investigation was undertaken to determine efficiency of selected heavy metal ions by different Salix viminalis tissues in relation to local physicochemical parameters. Seven heavy metals (Cd, Co, Cr, Cu, Ni, Pb and Zn) were analyzed in 5 types of tissues (bark, root, shoots, leaves and petioles). The results presented here show different accumulation rates of tested metals in individual tissues depending on location and soil characteristics. A similar trend in the accumulation of elements in leaves and petioles was observed except for zinc and chromium. The quantities of heavy metals in shoots indicate their limited migration in plant (especially lead and cadmium). In contrast high levels of zinc in leaves were observed, which suggests strong migration of this metal to upper parts of plants. Analyzed willows were characterized by selective accumulation of ions of investigated heavy metals, with different metal migration abilities depending on location (soil properties e.g. limited migration of lead and intensive migration of cadmium and zinc to aboveground organs). A correlation between metal accumulation in the tissue and soil factors (pH, redox potential, total organic carbon) was observed. The total accumulation and translocation of heavy metal ions (especially chromium) depend on soil parameters and to some extent wood structure (cellulose, lignin).

Identification and characterization of Cd-induced peptides in Egeria densa (water weed): Putative role in Cd detoxification

Egeria densa has ability to grow in heavy metal contaminated and polluted bodies of water. Shoots exposed to Cd at concentrations up to 300microM for 7 days showed a pronounced decrease in chlorophyll a and in total protein concentration. Thiol-containing compounds and low-molecular-weight polypeptides were detected in Cd-treated plant extracts by gel filtration chromatography. Two Cd-binding fractions, a thiol-enriched fraction and a non-thiol fraction with a lower molecular weight were identified in extracts by gel filtration. The main fraction of thiol-containing polypeptide, purified by gel filtration and anion-exchange chromatography had a molecular weight of approximately 10kDa. This peptide was characterized by a broad absorption band specific to mercaptide bonds and Cd-sensitive fluorescence emission of aromatic amino acid residues. Our results indicate that cadmium exposure of plants resulted in both a formation of thiol-enriched cadmium complexing peptides and a synthesis of low-molecular-weight metal chelators. The putative role of these compounds in Cd detoxification is discussed.

Cadmium toxicity and phytochelatin production in a rooted-submerged macrophyte Vallisneria spiralis exposed to low concentrations of cadmium

Phytochelatins (PCs) have been involved in metal detoxification, and used as potential biomarkers for an evaluation of metal toxicity. However, most studies have generally been limited to high concentrations of metals. In this study, low concentrations of cadmium (Cd) (0.01-0.64 microM) usually present in moderately polluted environments were adopted to investigate Cd toxicity, PC production, and their relationship in a rooted-submerged macrophyte Vallisneria spiralis. It was observed that 0.01-0.04 microM Cd had no significant effects on the growth of this plant when compared with the control plant without Cd, whereas 0.08-0.64 microM Cd showed toxicity, as indicated by the gradual decreases of leaf and root fresh weights. Cadmium accumulation was significantly higher in leaves than in the roots. Correspondingly, PCs were induced in leaves and roots at every Cd concentrations studied, in particular 0.16-0.64 microM, which were higher in leaves than in roots. There existed a positively linear relationship between PC concentrations and Cd toxicity in leaf and root. Furthermore, the levels of glutathione (GSH) in leaves and roots increased with increasing Cd concentrations in solutions and exposure time, but the extent of such increase was lower than that of PCs. Cadmium uptake antagonized Zn uptake. Combined effects of Cd and Fe or Cd and Mn were antagonistic in leaves and synergistic in roots. On the basis of the present results, it was further suggested that PCs can be used as potential biomarkers for monitoring the metal toxicity in moderately polluted environments.

Copper toxicity in leaves of Elodea canadensis Michx

Elodea canadensis (Canadian waterweed) has an ability to accumulate and bioconcentrate heavy metals. In this work, selected cellular responses for Cu treatment were studied in leaves of E. canadensis. Short term experiments, i.e. 1 week exposure to 0.5, 1, 5, and 10 microM of Cu indicated that concentrations up to 10 microM Cu causes a pronounced accumulation of photosynthetic pigments, a drastic degradation of soluble proteins with molecular weight above 18 kDa and a rapid accumulation of polypeptides with molecular weight below 14 kDa. The connection of these observations with copper detoxification mechanisms in aquatic macrophytes are discussed.