Iron plaque formation in the roots of Pistia stratiotes L.: importance in phytoremediation of cadmium.

Aquatic macrophytes play an important role in the removal of toxic metals from wastewater. Therefore, the induction of Fe plaque on the roots, and its consequences on Cd tolerance investigated in an aquatic macrophyte Pistia stratiotes L. The presence of Fe2+ ion but not Fe3+ resulted in Fe plaque formation. Induction of Fe plaque decreased Ca and increased K and Fe accumulations in the root. Plaque formed plants had accumulated less Cd until 50.0 µM CdCl2 treatments because plaque acted as a barrier to Cd exposure. However, at higher concentrations (500.0 µM CdCl2), plaque formed plants contained more Cd in the roots. Cadmium inducible ion leakage in the root and lowering of the photosynthetic pigment content were less in plants with a plaque. Stretching of aromatic carbonyl groups and alkyl groups among plaque formed plants upon Cd treatments indicated the putative role of phenolics in Cd detoxification.

Plant-lead interactions: Transport, toxicity, tolerance, and detoxification mechanisms.

Natural and human activities introduced an excess level of toxic lead (Pb) to the environment. Pb has no known biological significance and its interactions with plants lead to the production of reactive oxygen species (ROS). Pb and/or ROS have the potential to cause phytotoxicity by damaging the tissue ultrastructure, cellular components, and biomolecules. These damaging effects may possibly result in the inhibition of normal cellular functioning, physiological reactions, and overall plant performances. ROS play a dual role and act as a signaling molecule in plant defense system. This system encircles enzymatic and non-enzymatic antioxidative mechanisms. Catalase, superoxide dismutase, peroxidase, and enzymes from the ascorbate-glutathione cycle are the major enzymatic antioxidants, while non-enzymatic antioxidants include phenols, flavonoids, ascorbic acid, and glutathione. Pb removal from contaminated sites using plants depend on the plant's Pb accumulation capacity, Pb-induced phytotoxicity, and tolerance and detoxification mechanisms plants adopted to combat against this phytotoxicity. However, the consolidated information discussing Pb-plant interaction including Pb uptake and its translocation within tissues, Pb-mediated phytotoxic symptoms, antioxidative mechanisms, cellular, and protein metabolisms are rather limited. Thus, we aimed to present a consolidated information and critical discussions focusing on the recent studies related to the Pb-induced toxicity and oxidative stress situations in different plants. The important functions of different antioxidants in plants during Pb stress have been reviewed. Additionally, tolerance responses and detoxification mechanisms in the plant through the regulation of gene expression, and glutathione and protein metabolisms to compete against Pb-induced phytotoxicity are also briefly discussed herein.

Potentially toxic elements to maize in agricultural soils-microbial approach of rhizospheric and bulk soils and phytoaccumulation.

Maize fields near Mae Tao Creek in Pha Te Village, Tak Province, Thailand are contaminated with Zn, Cd, and Pb. This research studied the interaction between levels of the metals contaminating the soil and maize development, heavy metal accumulation in the seeds, and the soil bacterial community structure. Our field experiment was carried out in five plots with metal contents that gradually decreased from a high level near the creek to a lower level further into the land: Zn 380-4883 mg kg-1, Cd 6-85 mg kg-1, and Pb 34-154 mg kg-1. Cultivation and isolation on nutrient agar (NA) was utilized to study the culturable bacterial community, and polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) was utilized for the unculturable bacterial communities. All statistical analyses clearly indicated that rainfall and irrigation were the main factors affecting total Zn concentration and bioavailable Zn, Cd, and Pb in the field. The variation in the contents of the heavy metals was weakly correlated with the culturable bacterial community indices (Shannon-Wiener, evenness and richness), but the contents resulted in a difference in the overall diversity of the bacteria in the soil. The richness, numbers of culturable rhizobacteria, and maize growth stage significantly affected the amount of Zn and Cd that accumulated in the roots. In addition, maize accumulated a high level of Zn in the seeds, while the low contents of Cd and Pb in the seeds were below our limit of detection. The results obtained could be informative for the management of maize cultivation in the area.

Bioaccumulation of nutrients and metals in sediment, water, and phoomdi from Loktak Lake (Ramsar site), northeast India: phytoremediation options and risk assessment.

In order to determine the potential of phoomdi to accumulate nutrients and metals, 11 dominant species belonging to 10 different families, sediment, and water were analyzed for a period of 2 years from the largest freshwater wetland of north-east India, Loktak (Ramsar site). Results revealed nutrient (TN and TP) and metal (Fe, Mn, Zn, and Cu) compartmentalization in the order phoomdi > sediment > water. Iron concentrations in water (0.37 ± 0.697 to 0.57 ± 1.010 mg L(-1)) and sediments (81.8 ± 0.45 to 253.1 ± 0.51 mg kg(-1)) show high metal discharge into the wetland. Metal accumulation in phoomdi ranged up to 212.3 ± 0.46-9461.4 ± 1.09 mg kg(-1) for Fe; 85.9 ± 0.31-3565.1 ± 0.87 mg kg(-1) for Mn; 9.6 ± 0.41-85.39 ± 0.58 mg kg(-1) for Zn; and 0.31 ± 0.04-9.2 ± 0.04 mg kg(-1) for Cu, respectively. High bioaccumulation factors (BAF) for metals (S. cucullata, 5.8 × 10(4) Fe, 3.9 × 10(4) Mn, and 1.7 × 10(4) Cu, and O. javanica, 4.9 × 10(3) Zn) and nutrients (S. polyrhiza, 9.7 × 10(2) TN, and Z. latifolia, 7.9 × 10(4) TP) revealed good accumulation in phoomdi compared to the wetland water column and indicate their potential to maintain a safe environment of Loktak. Further, the paper analyzed the health hazard of metals via phoomdi wild edible consumption, with the results confirming potential risk. Thus, the paper showed the need of in-depth monitoring and ample management strategies to ensure nutritional safety conditions of locals from the metals.

Kinetics of nickel bioaccumulation and its relevance to selected cellular processes in leaves of Elodea canadensis during short-term exposure.

Elodea canadensis is an aquatic macrophyte used widely as a bioindicator for the monitoring of water quality and in the phytoremediation of metal-contaminated waters. This study considers the kinetics of nickel bioaccumulation and changes in accompanying metabolic and stress-related physiological parameters. These include photosynthetic activity, pigment content, the accumulation of thiol-containing compounds, thiobarbituric acid-reactive substance (TBARS) products, and the activity of selected antioxidant enzymes (catalase, glutathione reductase, superoxide dismutase). Elodea leaves accumulated nickel according to pseudo-second-order kinetics, and the protective responses followed a time sequence which was related to the apparent rates of nickel accumulation. The applicability of second-order kinetics to the Ni uptake by Elodea leaves during the first 8 h of exposure to the metal suggested that the passive binding of metal ions (chemisorption) was a rate-limiting step at the initial phase of Ni accumulation. This phase was accompanied by an increase in photosynthetic activity together with elevated photosynthetic pigments and protein synthesis, the enhanced activity of antioxidant enzymes, and increased thiol concentration. In contrast, there was a decrease in metabolic activity upon the accumulation of TBARS, and the decline in enzyme activity was observed in the saturation phase of Ni accumulation (8-24 h). These results show that a correlation exists between the protective response and the apparent kinetic rate of Ni uptake. Thus, the time of exposure to the toxicant is a crucial factor in the activation of specific mechanisms of Ni detoxification and stress alleviation.

Toxicological evaluation of the aqueous stem bark extract of Bridelia ferruginea (Euphorbiaceae) in rodents.

Bridelia ferruginea is a woody shrub that grows in the Savannah or rain forests of Africa and has traditionally been used to treat diabetes, arthritis and boils. Despite all these uses, extensive toxicological evaluation has not been carried out. The aim of the present investigation was to evaluate the sub-chronic toxicological effects of the stem bark aqueous extract of Bridelia ferruginea in rats. The lethal dose (LD50) was determined using probit analysis and graded doses of the extract (250-4000 mg/kg) were administered to the animals via oral and intraperitoneal routes and observed for mortality, behavioral changes and signs of toxicity. Sub-chronic toxicity study was carried out at doses of 1 000, 2 000 and 4 000 mg/kg administered daily for 60 days. The animals were sacrificed after 60 days. Blood was collected for biochemical (renal and hepatic), hematological, oxidative stress, sperm and histopathological examinations, using standard methods. LD50 of the extract was estimated as >4 000 mg/kg orally; neither significant visible signs of toxicity nor mortality were observed. There were no significant differences in the animals and organ weights, hematological and biochemical parameters in the treated groups compared to the control group. However, a significant increase (p<0.05) in the level of lipid peroxidation and a significant (p<0.05) decrease in sperm count were observed in the treated animals compared with the control group. The stem-bark aqueous extract of Bridelia ferruginea was found to be relatively safe, though it has the potential to cause lipid peroxidation and damage sperm quality and should thus be used with caution.

Potential use of halophytes to remediate saline soils.

Salinity is one of the rising problems causing tremendous yield losses in many regions of the world especially in arid and semiarid regions. To maximize crop productivity, these areas should be brought under utilization where there are options for removing salinity or using the salt-tolerant crops. Use of salt-tolerant crops does not remove the salt and hence halophytes that have capacity to accumulate and exclude the salt can be an effective way. Methods for salt removal include agronomic practices or phytoremediation. The first is cost- and labor-intensive and needs some developmental strategies for implication; on the contrary, the phytoremediation by halophyte is more suitable as it can be executed very easily without those problems. Several halophyte species including grasses, shrubs, and trees can remove the salt from different kinds of salt-affected problematic soils through salt excluding, excreting, or accumulating by their morphological, anatomical, physiological adaptation in their organelle level and cellular level. Exploiting halophytes for reducing salinity can be good sources for meeting the basic needs of people in salt-affected areas as well. This review focuses on the special adaptive features of halophytic plants under saline condition and the possible ways to utilize these plants to remediate salinity.

Trace metals accumulation in Bacopa monnieri and their bioaccessibility.

Bacopa monnieri is commonly known as "Brahmi" or "Water hyssop" and is a source of nootropic drugs. Aboveground parts of plant samples collected from peri-urban Indian areas were analysed for total trace metal concentrations. Subsequently, three samples with high concentrations of Cd and Pb were subjected to in vitro gastrointestinal digestion to assess the bioaccessibility of the trace metals in these plants. The total concentrations of trace metals on a dry weight basis were 1.3 to 6.7 mg·kg⁻¹ Cd, 1.5 to 22 mg·kg⁻¹ Pb, 36 to 237 mg·kg⁻¹ Cu, and 78 to 186 mg·kg⁻¹ Zn. The majority of Bacopa monnieri samples exceeded threshold limits of Cd, Pb, Cu, and Zn for use as raw medicinal plant material or direct consumption. Therefore, it is necessary to evaluate Bacopa monnieri collected in nature for their trace metal content prior to human consumption and preparation of herbal formulations.

Climate change driven plant-metal-microbe interactions.

Various biotic and abiotic stress factors affect the growth and productivity of crop plants. Particularly, the climatic and/or heavy metal stress influence various processes including growth, physiology, biochemistry, and yield of crops. Climatic changes particularly the elevated atmospheric CO2 enhance the biomass production and metal accumulation in plants and help plants to support greater microbial populations and/or protect the microorganisms against the impacts of heavy metals. Besides, the indirect effects of climatic change (e.g., changes in the function and structure of plant roots and diversity and activity of rhizosphere microbes) would lead to altered metal bioavailability in soils and concomitantly affect plant growth. However, the effects of warming, drought or combined climatic stress on plant growth and metal accumulation vary substantially across physico-chemico-biological properties of the environment (e.g., soil pH, heavy metal type and its bio-available concentrations, microbial diversity, and interactive effects of climatic factors) and plant used. Overall, direct and/or indirect effects of climate change on heavy metal mobility in soils may further hinder the ability of plants to adapt and make them more susceptible to stress. Here, we review and discuss how the climatic parameters including atmospheric CO2, temperature and drought influence the plant-metal interaction in polluted soils. Other aspects including the effects of climate change and heavy metals on plant-microbe interaction, heavy metal phytoremediation and safety of food and feed are also discussed. This review shows that predicting how plant-metal interaction responds to altering climatic change is critical to select suitable crop plants that would be able to produce more yields and tolerate multi-stress conditions without accumulating toxic heavy metals for future food security.

Nature's cure for cleanup of contaminated environment- a review of bioremediation strategies.

Population explosion, to the tune of -7.2 billion, along with excessive use of natural resources and a variety of anthropogenic activities, has resulted in large-scale contamination of the environment, especially the soil and groundwater.Contamination in the environment is an ever-increasing phenomenon, and often, regulatory systems and cleaning operations are not commensurate with waste generation. It is therefore necessary to search for effective and low-cost methods, especially following and stimulating the mechanisms of nature's cure. Bioremediation technologies resting upon the vast potential of biodiversity for the monitoring and abatement of environmental pollution have been briefly reviewed.

Potential of siderophore-producing bacteria for improving heavy metal phytoextraction.

Phytoremediation holds promise for in situ treatment of heavy metal contaminated soils. Recently, the benefits of combining siderophore-producing bacteria (SPB) with plants for metal removal from contaminated soils have been demonstrated. Metal-resistant SPB play an important role in the successful survival and growth of plants in contaminated soils by alleviating the metal toxicity and supplying the plant with nutrients, particularly iron. Furthermore, bacterial siderophores are able to bind metals other than iron and thus enhance their bioavailability in the rhizosphere of plants. Overall, an increase in plant growth and metal uptake will further enhance the effectiveness of phytoremediation processes. Here, we highlight the diversity and ecology of metal resistant SPB and discuss their potential role in phytoremediation of heavy metals.

Anti-proliferative and cytotoxic effects of Strychnos nux-vomica root extract on human multiple myeloma cell line - RPMI 8226.

Multiple myeloma (MM) is an incurable hematological malignancy with high incidence in the elderly. The currently used chemotherapeutic drugs show severe side effects, dose-limiting toxicity and development of resistance. In search of novel plant derived anti-cancer agents, Strychnos nux-vomica L. (SN) root extract was screened using the human MM-cell line, RPMI 8226. SN-extract exhibited anti-proliferative activity in a dose and time dependent manner. The morphological assessment of SN-extract treated cells showed significant features associated with apoptosis. Cell cycle analysis using flow cytometry of cells stained with propidium iodide revealed accumulation of cells at sub-G(0)/G(1) phase. In addition, disruption of mitochondrial membrane potential and subsequent leakage of mitochondrial cytochrome c was observed in SN-extract treated myeloma cells. The anti-proliferative and cytotoxic activity could be due to the alkaloids strychnine and brucine, which have been identified by LC-mass spectral analysis of the SN-extract in comparison to the reference standards analyzed under identical conditions.

Modulation of cadmium-induced oxidative stress in Ceratophyllum demersum by zinc involves ascorbate-glutathione cycle and glutathione metabolism.

To understand the interaction between Zn, an essential micronutrient and Cd, a non-essential element, Cd-10 microM and Zn supplemented (10, 50, 100, and 200 microM) Cd 10 microM treated Ceratophyllum demersum L. (Coontail), a free floating freshwater macrophyte was chosen for the study. Cadmium at 10 microM concentration decreased thiol content, enhanced oxidation of ascorbate (AsA) and glutathione (GSH) to dehydroascorbate (DHA) and glutathione disulfide (GSSG), respectively, a clear indication of oxidative stress. Zinc supplementation to Cd (10 microM) treated plants effectively restored thiols, inhibited oxidation of AsA and GSH maintaining the redox molecules in reduced form. Cd-10 microM slightly induced ascorbate peroxidase (APX, E.C. 1.11.1.11) but inhibited monodehydroascorbate reductase (MDHAR, E.C. 1.6.5.4), dehydroascorbate reductase (DHAR, E.C. 1.8.5.1) and glutathione reductase (GR, E.C. 1.6.4.2), enzymes of ascorbate-glutathione cycle (AGC). Zn supplementation restored and enhanced the functional activity of all the AGC enzymes (APX, MDHAR, DHAR and GR). Gamma-glutamylcysteine synthetase (gamma-GCS, E.C. 6.3.2.2) was not affected by Cd as well as Zn, but Zn supplements increased glutathione-S-transferase (GST, E.C. 2.5.1.18) activity to a greater extent than Cd and simultaneously restored glutathione peroxidase (GSH-PX, E.C. 1.11.1.9) activity impaired by Cd toxicity. Zn-alone treatments did not change above investigated parameters. These results clearly indicate the protective role of Zn in modulating the redox status of the plant system through the antioxidant pathway AGC and GSH metabolic enzymes for combating Cd induced oxidative stress.