Ana Maria Mota

Cadmium Impact on Root Exudates of Sorghum and Maize Plants: A Speciation Study

ABSTRACT The effect of cadmium (Cd) on root exudates of sorghum and maize was investigated in order to get further insight into the mechanisms of plant tolerance to Cd. Plants were grown hydroponically and supplemented with: 0, 0.5, and 5.0 mg Cd L− 1. Hydroponic solutions containing exudates were analyzed by high performance liquid chromatography (HPLC). The results showed different exudation patterns by sorghum and maize with cadmium supply. While sorghum enhanced malate exudation over the entire range of applied Cd in the uptake solutions, maize increased mainly citrate. Moreover, malate concentration exuded in sorghum rhizosphere presented higher values than citrate (from maize). With the aid of the HYPERQUAD speciation program, a significant decrease in the bioavailable Cd (free Cd plus Cd chloro-complexes) was found due to the increase of Cd organic complexation in the hydroponic solution. Furthermore, similar metal organic complex concentrations were obtained for both plants, which turned the maize and sorghum overall detoxification process equivalent. Exudation of malate and citrate should contribute to tolerance mechanisms of these plants, reducing deleterious effects of free Cd on root growth. These findings support the idea that the metal-binding capabilities of root exudates may be an important mechanism for stabilizing metals in soil.

Oxidative stress induced by cadmium in Nicotiana tabacum L.: effects on growth parameters, oxidative damage and antioxidant responses in different plant parts

Tobacco (Nicotiana tabacum L.) is a tolerant species that accumulates cadmium. We studied the effect of Cd (0, 10, 25, 50, 100xa0μM) on growth parameters, chlorophyll and proline contents, enzymatic antioxidative response and lipid peroxidation of tobacco plants grown in hydroponic culture for 11xa0days to clarify the strategy of plant response against oxidative stress caused by this heavy metal. Cadmium accumulated more in roots than in shoots. Plant growth was not significantly affected by the cadmium concentrations used. Young leaves were more affected, showing visible chlorosis and a significant decrease in chlorophyll content at high Cd concentrations. Dry weight of both leaves and roots increased indicating a lower capacity for roots to absorb water. An increase in malondialdehyde levels was observed, indicating that lipid peroxidation occurred as a result of ROS formation. The activity of guaiacol peroxidase in leaves increased, indicating that it was very important in the scavenging of H2O2, while superoxide dismutase activity only increased in old leaves. Ascorbate peroxidase showed constant activity levels in tobacco leaves, suggesting that the ascorbate–glutathione pathway was less important as a defense mechanism.

Pathways and speciation of mercury in the environmental compartments of Deception Island, Antarctica.

This work reports the first integrated mercury study in an Antarctic ecosystem. Sample collection took place in Deception Island, an active volcano in the South Shetland Islands, in several environmental compartments (water, snow, sediments and vegetation) and different locations, during December 2011. The results suggest that volcanic activity is the most important Hg source. Mercury levels in water and sediments sampled at two fumaroles were up to 10,000 times higher than in the other sampling sites. Dissolved methylmercury (MeHg) is below the detection limit in those samples, probably due to the very high temperature found in fumaroles (above 80 °C). On the other hand MeHg accounted for, on average, 23% of total dissolved Hg in the saline waters of Foster bay, which suggests exceptional conditions for Hg methylation. Combined with the high residence time of the water in Foster bay, the results point to the existence of a MeHg pool available for aquatic living organisms.

Cadmium accumulation and antioxidative defences in Brassica juncea L. Czern, Nicotiana tabacum L. and Solanum nigrum L.

Remediation of sites contaminated with heavy metals using hyperaccumulators seems a promising alternative to engineering approaches. In this work, we compared cadmium (Cd) accumulation and tolerance (based on responses to oxidative stress) in three different species, Brassica juncea (L.) Czern, Nicotiana tabacum L. and Solanum nigrum L., described in the literature as very tolerant or even as hyperaccumulators. The plants were grown in soil spiked with different Cd concentrations (0 – 35 mg kg−1) over a period of 90 days. The translocation factor (TF), used to measure the effectiveness to translocate Cd from roots to shoots, depended greatly on the species. N. tabacum was the plant which exhibited the highest TF values. It was the only plant under study that fulfilled the conditions of a hyperaccumulator for all levels of soil contamination. On the other hand, S. nigrum presented the highest Cd concentration in plant tissues, with TF >1 in the presence of 5 mg Cd kg−1 of soil. Although B. juncea had presented the lowest TF and Cd concentrations, it was the only plant with TF values increasing with the level of cadmium. Oxidative stress in plants was evaluated by lipid peroxidation and activities of catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and superoxide dismutase (SOD), both in roots and shoots. A significant enhancement (versus control) on lipid peroxidation and enzymatic activity of CAT and APX in shoots of B. juncea, N. tabacum and S. nigrum was observed for the highest levels of Cd in soil, 15 and/or 35 mg Cd kg−1. B. juncea presented the most sensitive response of GPX, for all levels of Cd in soil. Lipid peroxidation and CAT activity were greater in shoots than in roots for all plants and soil Cd concentrations. SOD activity did not present consistent trends for any plant.

Assessing trace element contamination in Fildes Peninsula (King George Island) and Ardley Island, Antarctic

King George Island, situated in the South Shetland Islands archipelago, is one of the most visited sites in Antarctica. This has contributed to a high density of scientific stations and shelters in the region, especially in Fildes Peninsula. In order to evaluate the natural and anthropogenic sources of trace elements (As, Cd, Cu, Zn, Pb and Hg) soil and moss samples were collected from different sites in January 2013. In general, the results revealed homogeneous concentrations (μgg(-)(1)) for each element in the majority of collected samples (As: 3.8±1.4; Cd: 0.4±0.9; Cu: 34±4; Zn: 115±13; Pb: 20±5; Hg; 0.011±0.009). However, some samples in specific areas of Fildes Bay showed the existence of local anthropogenic activities that have contributed to the enrichment of contaminants in soils and moss samples that correlated to one another (e.g. Pb: 1101μgg(-)(1)). Human presence is linked to examples of contamination and environmental perturbation, making essential the implementation of this type of study in order to understand and protect unique places in Antarctica.

Sources and transport of As, Cu, Cd and Pb in the environmental compartments of Deception Island, Antarctica

Sources and transport processes of As, Cu, Cd and Pb were studied in different environmental compartments of Deception Island, an active volcano in the South Shetland Islands, Antarctica. Element concentrations in fresh water samples are consistent with the lowest values reported elsewhere in Antarctica. Interestingly, higher concentration values of As were found in samples collected in or near spring water courses and its transport may be related with processes of lixiviation in underground waters. While in saline waters Cu and Pb had important punctual sources, concentration values for Cd were consistently high pointing to the existence of a natural and diffuse source possibly related with the hydrothermal activity. The high Si/Al ratio, low carbon content, and a non-significant anthropogenic heavy metal input may explain the surprisingly homogeneous heavy metal content found in sediment samples.

Depuration kinetics of paralytic shellfish toxins in Mytilus galloprovincialis exposed to Gymnodinium catenatum: laboratory and field experiments.

The kinetics of paralytic shellfish toxins in Mytilus galloprovincialis, previously exposed to Gymnodinium catenatum, was studied under depuration laboratory conditions and over a declining bloom of the dinoflagellate in the field. The variation of the levels observed throughout the laboratory experiment was characterized by a fast depuration of B1, C1 + 2, dcSTX and dcGTX2 + 3, possibly due to the gut evacuation of unassimilated toxins or microalgae cells, or loss during digestive mechanisms. Subsequent enhancements were observed for all compounds with emphasis to dcSTX and dcGTX2 + 3, pointing to biotransformation of the assimilated toxins. Then levels decreased gradually. A first-order depuration kinetic model fitted well to the decrease of B1, C1 + 2 and dcGTX2 + 3 concentrations, but not for dcSTX. Mussels exposed to a declining bloom of Gymnodinium catenatum exhibited a loss of toxins following the same pattern. Despite the low abundance of this dinoflagellate, a similar kinetic model was applied to the field data. The depuration rate of dcGTX2 + 3 in the field experiment (0.153 ± 0.03 day(-1)) significantly exceeded the value calculated in the laboratory (0.053 ± 0.01 day(-1)), while smaller differences were obtained for B1 (0.071 ± 0.02 and 0.048 ± 0.01 day(-1)) and similar values for C1 + 2 (0.082 ± 0.03 and 0.080 ± 0.03 day(-1)). The slower depuration rate of dcGTX2 + 3 in the heavily contaminated mussels at the laboratory may be related to a more effective contribution of C1 + 2 biotransformation.

Comparison of cadmium-induced oxidative stress in Brassica juncea in soil and hydroponic cultures

AimsThe objective of this study was to investigate the response of Brassica juncea in the presence of Cd, in hydroponic and soil experiments, and to conclude about common and divergent trends in both cultures.MethodsWe studied the effect of Cd on growth, oxidative damage and antioxidant responses in roots and shoots of B. juncea grown in soil and hydroponic cultures, using typical time-scales for each one. Major ROS-scavenging enzymes such as catalase, ascorbate peroxidase and guaiacol peroxidase were evaluated, as well as lipid peroxidation.ResultsSmall Cd concentrations in the plant led to enhanced plant growth, while large Cd concentrations impaired growth. The increase in lipid peroxidation observed in the presence of Cd was always greater in shoots than in roots. The physiological response to enhanced levels of reactive oxygen species in the presence of Cd included an increase in guaiacol peroxidase, ascorbate peroxidase and catalase activities, but those enzymes were not always enhanced in a similar manner in both cultures.ConclusionsThe main factors responsible for the differences between the experiments in soil and nutrient solution, were the different Cd content in the plant tissues and the different time-scale of the experiments.

Sorghum detoxification mechanisms

ABSTRACT The influence of cadmium (Cd) on internal and external defense mechanisms of Sorghum bicolor (L.) Moench. x Sorghum sudanense was studied by electrochemical methods to infer the type of detoxification processes developed by the plant under environmental stress conditions. Hydroponic experiments with sorghum were conducted in nutrient solutions in the absence and presence of 0.1 mg Cd L−1. Plant exposure to Cd stimulated the release of root exudates with metal-binding affinity. However, their presence should not affect significantly the bioavailability of Cd, since the complex was dissociated within a very short period (≤ 50 milliseconds) in response to the consumption of the free metal ion at the root interface. The presence of Cd in the solution also stimulated a very significant increase of thiolic groups inside the plant, even at the very low concentration of 0.1 mg Cd L−1. These results suggest that the main defense mechanism developed by sorghum against metal toxicity is an internal process, i.e., the synthesis of phytochelatins.

REMEDIATION OF SANDY SOIL ARTIFICIALLY CONTAMINATED WITH CADMIUM USING A POLYACRYLATE POLYMER

Soil pollution with toxic metals has become an important social and environmental challenge. When the polluted area is large and the site poses little immediate risk to health or environment, in situ remediation technologies can be envisaged. Here we used a polyacrylate polymer to immobilize cadmium (Cd) in a sandy soil artificially contaminated with the metal. Growth of perennial ryegrass in pots with 9.5 kg of soil was stimulated in polymer-amended soil. Even in pots with the highest levels of Cd, growth was much less impaired than in pots without polymer. Shoot Cd concentrations were smaller in the plants cultivated in the amended soil. Because water soluble Cd was considerably reduced in the contaminated polymer-amended soil, the effect of the polymer on plant growth was attributed to the decrease of Cd concentration in soil solution.