The enzymatic and antioxidative stress response of Lemna minor to copper and a chloroacetamide herbicide

Abstract

Lemna minor L., a widely used model plant for toxicity tests has raised interest for its application to phytoremediation due to its rapid growth and ubiquitous occurrence. In rural areas, the pollution of water bodies with heavy metals and agrochemicals poses a problem to surface water quality. Among problematic compounds, heavy metals (copper) and pesticides are frequently found in water bodies. To establish duckweed as a potential plant for phytoremediation, enzymatic and antioxidative stress responses of Lemna minor during exposure to copper and a chloroacetamide herbicide were investigated in laboratory studies. The present study aimed at evaluating growth and the antioxidative and glutathione-dependent enzyme activity of Lemna plants and its performance in a scenario for phytoremediation of copper and a chloroacetamide herbicide. Lemna minor was grown in Steinberg medium under controlled conditions. Plants were treated with CuSO4 (ion conc. 50 and 100 μg/L) and pethoxamide (1.25 and 2.5 μg/L). Measurements following published methods focused on plant growth, oxidative stress, and basic detoxification enzymes. Duckweed proved to survive treatment with the respective concentrations of both pollutants very well. Its growth was inhibited scarcely, and no visible symptoms occurred. On the cellular basis, accumulation of O2(-) and H2O2 were detected, as well as stress reactions of antioxidative enzymes. Duckweed detoxification potential for organic pollutants was high and increased significantly with incubation. Pethoxamide was found to be conjugated with glutathione. Copper was accumulated in the fronds at high levels, and transient oxidative defense reactions were triggered. This work confirms the significance of L. minor for the removal of copper from water and the conjugation of the selective herbicide pethoxamide. Both organic and inorganic xenobiotics induced different trends of enzymatic and antioxidative stress response. The strong increase of stress responses following copper exposure is well known as oxidative burst, which is probably different from the much more long-lasting responses found in plants exposed to pethoxamide. Lemna sp. might be used as a tool for phytoremediation of low-level contamination with metals and organic xenobiotics, however the authors recommend a more detailed analysis of the development of the oxidative burst following copper exposure and of the enzymatic metabolism of pethoxamide in order to elucidate the extent of its removal from water.

Protective Responses Induced by Chiral 3-Dichloroacetyl Oxazolidine Safeners in Maize (Zea mays L.) and the Detoxification Mechanism

“…POD and CAT were shown to protect crops from the stress caused by herbicides because their activities are related to the reduction of oxidative stress induced by high-dose herbicides [30]. In order to evaluate the protective effectiveness of safeners, the influences of safeners and chlorsulfuron on the activity levels of POD and CAT were determined (Table 4).…”

“…To investigate the effect of the target safener, POD activity was determined based on a modified method from Obermeier et al [30]. The mixture, which consisted of 1 mL of 50 mM sodium phosphate buffer (pH 7.0), 2 mL of 0.3% hydrogen peroxide, and 0.95 mL of 0.2% guaiacol was used for determination.…”

Phytoremediation of Effluents Contaminated with Heavy Metals by Floating Aquatic Macrophytes Species

“…In an experiment done by [47] the efficiency of Hg removal is tested by comparing the species E. crassipes and Lemna minor, proving a higher uptake by the first, both with indications of morphological changes due to toxicity, and although the rapid reproduction of Lemna minor, the one with the most resistance is E. crassipes. According to [48], when compared to other plant species Lemna minor is not the first desirable one to be chosen, since its performance does not support peaks of contaminant concentration and grows well in places with low concentration pollution although these are also of risk because its bioaccumulation is great, it would be ideal to use it for attributions such as polishing the water after pretreatment or even using its sensitivity characteristics for biomonitoring. Another comparison is made between P. stratiotes, L. minor and Spirodela intermedia, where they obtained excellent absorption values, especially P. stratiotes, although the L. minor species did not survive at the end of the experiment, the theory proposed by the author due to vegetal cover in the water layer that prevents the increase of oxygen dissolved in the recipient, leading to the death of individuals [49].…”

“…According to the studied macrophytes, one of the most outstanding in the literature was the Eichhornia crassipes species, which has resistance attributes, including to pesticides [31], their replication rate and accumulation are favorable for the metals analyzed [38,40], however it is necessary to emphasize that the other species may still be appropriate for the environmental remediation functions, since it is noted that the values of bioaccumulation, absorption and tolerance to metals have divergences in each experiment. Such plants are effective in the capture of heavy metals in the aquatic environment, and may even serve as biosensors, such as the species S. auriculata [41] and L. minor [46,48] that are more suitable for this task or for the polishing of the water, according to the morphological characteristics presented when in contact with potential contaminants. The four species (Eichhornia crassipes, Pistia stratiotes, Salvinia auriculata and Lemna minor) are of great value in the aspect of contaminant removal [38,41,44,45] because they facilitate the post-capture process of metals, where floating macrophytes take advantage over the rooted ones and contribute to the process of plant removal, consequently the extraction of the metals from the medium is facilitated.…”

The guanidine thiocyanate‐high EDTA method for total microbial RNA extraction from severely heavy metal‐contaminated soils

“…Heavy metals always coexist with organic pollutants, giving a low microbial biomass in soil under the severely contaminated conditions (Yang et al ., 2006; Huang et al ., 2016). In the metabolic processes, heavy metals and organic pollutants may cause harm to microbes by reactive oxygen species (ROS)‐induced RNA damage, such as 7,8‐dihydro‐8‐oxoguanine, heavy metal‐RNA adducts, apurinic/apyrimidinic (AP) sites, and strand breaks (Salnikow and Zhitkovich, 2008; Santos‐Escobar et al ., 2014; Obermeier et al ., 2015). Besides, heavy metal residues in RNA also interfere with the enzymes involved in the molecular operations, including PCR, microarrays, and metatranscriptomic sequencing.…”