Comparative transcriptome and proteome analysis to reveal the biosynthesis of gold nanoparticles in Arabidopsis

© 2016, Nature Publishing Group. All rights reserved. A large number of plants have been tested and exploited in search of a green chemistry approach for the fabrication of gold or other precious metal nanomaterials. Despite the potential of plant based methods, very little is known about the underlying biochemical reactions and genes involved in the biotransformation mechanism of AuCl4 into gold nanoparticles (AuNPs). In this research, we thus focused on studying the effect of Au on growth and nanoparticles formation by analyses of transcriptome, proteome and ionome shift in Arabidopsis. Au exposure favored the growth of Arabidopsis seedling and induced formation of nanoparticles in root and shoot, as indicated by optical and hyperspectral imaging. Root transcriptome analysis demonstrated the differential expression of the members of WRKY, MYB and BHLH gene families, which are involved in the Fe and other essential metals homeostasis. The proteome analysis revealed that Glutathione S-transferases were induced in the shoot and suggested its potential role in the biosynthesis AuNPs. This study also demonstrated the role of plant hormone auxin in determining the Au induced root system architecture. This is the first study using an integrated approach to understand the in planta biotransformation of KAuCl4 into AuNPs

Evidence for Exocellular Arsenic in Fronds of Pteris vittata

The arsenic (As) hyperaccumulating fern species Pteris vittata (PV) is capable of accumulating large quantities of As in its aboveground tissues. Transformation to AsIII and vacuolar sequestration is believed to be the As detoxification mechanism in PV. Here we present evidence for a preponderance of exocellular As in fronds of Pteris vittata despite numerous reports of a tolerance mechanism involving intracellular compartmentalization. Results of an extraction experiment show that 43–71% of the As extruded out of the fronds of PV grown in 0.67, 3.3 and 6.7mM AsV. SEM-EDX analysis showed that As was localized largely on the lower pinna surface, with smaller amounts on the upper surface, as crystalline deposits. X-ray fluorescence imaging of pinna cross-sections revealed preferential localization of As on the pinna surface in the proximity of veins, with the majority localized near the midrib. Majority of the As in the pinnae is contained in the apoplast rather than vacuoles. Our results provide evidence that exocellular sequestration is potentially a mechanism of As detoxification in PV, particularly at higher As concentrations, raising concern about its use for phytoremediation

Differential protein abundance of vetiver grass in response to acid mine drainage

Acid mine drainage (AMD) is an acidic and metalliferous discharge that imposes oxidative stress on living things through bioaccumulation and physical exposure. The abandoned Tab-Simco mining site of Southern Illinois generates highly acidic AMD with elevated sulfate (SO42−) and various metals. Vetiver grass (Chrysopogon zizanioides) is effective for the remediation of Tab-Simco AMD at both mesocosm and microcosm levels over extended periods. In this study, we conducted a proteomic investigation of vetiver shoots under short and long-term exposure to AMD. Our objective was to decipher the physiological responses of vetiver to the combined abiotic stresses of AMD (metal and low pH). Differential regulation was observed for longer-term (56 days) exposure to AMD, which resulted in 17 upregulated and nine downregulated proteins, whereas shorter-term (7 days) exposure led to 14 upregulated and 14 downregulated proteins. There were significant changes to photosynthesis, including upregulation of electron transport chain proteins for light-dependent reactions after 56 days, whereas differential regulation of enzymes relating to C4 carbon fixation was observed after 7 days. Significant changes in amino acid and nitrogen metabolism, including upregulation of ethylene and flavonoid biosynthesis, along with plant response to nitrogen starvation, were observed. Short-term changes also included upregulation of glutathione reductase and methionine sulfoxide reductase, whereas longer-term changes included changes in protein misfolding and ER-associated protein degradation for stress management and acclimation

Metabolic response of vetiver grass (Chrysopogon zizanioides) to acid mine drainage

Acid mine drainage (AMD) is a sulfuric discharge containing metals and particulates that can spread to nearby water sources, imposing toxicity and physical stress to living things. We have shown that vetiver grass (Chrysopogon zizanioides) is capable of tolerating and treating AMD-impacted water from the abandoned Tab-Simco mining site from southern Illinois, though little is known about its tolerance mechanisms. We conducted metabolomic analyses of vetiver shoots and roots after relatively short- and long-term periods of exposure to Tab-Simco AMD. The metabolic shift of vetiver shoots was dramatic with longer-term AMD exposure, including upregulation of amino acid and glutathione metabolism, cellular respiration and photosynthesis pathways, with downregulation of phosphorylated metabolites. Meanwhile, the roots demonstrated drastic downregulation of phospholipids and phosphorylated metabolites, cellular respiration, glyoxylate metabolism, and amino acid metabolism. Vetiver accumulated ornithine and oxaloacetate in the shoots, which could function for nitrogen storage and various intracellular functions, respectively. Organic acids and glutathione were secreted from the roots for rhizospheric metal-chelation, whereas phosphorylated metabolites were recycled for phosphorus. These findings reveal AMD-induced metabolic shifts in vetiver grass, which are seemingly unique in comparison to independent abiotic stresses reported previously

Phytoremediation of Explosive-Contaminated Soils

In order to select appropriate plant species for phytoremediation of explosive compounds, phytotoxicity, uptake proficiency, capability of the plant to degrade/transform the compounds, and several environmental factors need to be considered. The environmental factors comprise climatic attributes, soil type, the water environment, root penetration depth, contaminant kinetics, and bioavailability. Out of the plant species that have shown efficient TNT uptake, there are only a few that can do so in a variety of environments, which is imperative in case of contaminants that are widespread, such as TNT and RDX. The two most effective species for TNT uptake reported to date are Eurasian water milfoil, Myriophyllum spicatum and vetiver grass, Chrysopogon zizanioides. For RDX phytoremediation, reed canary grass, fox sedge, and rice have shown promise, although degradation of RDX in the plant tissue is limited. Over the past few decades, a considerable amount of information on phytotoxicity and metabolism of TNT and RDX in plants and microorganisms have been collected, which has led to the identification of potential plant species for use in TNT and RDX phytoremediation, as well as candidate genes for developing effective transgenic plants. Recent research has also revealed promising non-transgenic approaches, such as use of chaotropic agents for enhanced solubilization and uptake of TNT, which could prove to be practical and effective for military sites. Field trials of some of these promising new technologies are necessary for the development of effective, low-cost, and environmentally friendly phytoremediation of explosive-contaminated sites

A preliminary study to design a floating treatment wetland for remediating acid mine drainage-impacted water using vetiver grass (Chrysopogon zizanioides)

© 2017, Springer-Verlag GmbH Germany. Acid mine drainage (AMD) is extremely acidic, sulfate-rich effluent from abandoned or active mine sites that also contain elevated levels of heavy metals. Untreated AMD can contaminate surface and groundwater and pose severe ecological risk. Both active and passive methods have been developed for AMD treatment consisting of abiotic and biological techniques. Abiotic techniques are expensive and can create large amounts of secondary wastes. Passive biological treatment mainly consists of aerobic or anaerobic constructed wetlands. While aerobic wetlands are economical, they are not effective if the pH of the AMD is \u3c 5. Anaerobic wetlands use organic-rich substrates to provide carbon source to iron- and sulfate-reducing bacteria. The efficiency of these systems declines overtime and requires continuous maintenance. Our objective is to develop an alternative, low-cost, and sustainable floating wetland treatment (FWT) system for AMD for the abandoned Tab-Simco coal mining site in Illinois using vetiver grass (Chrysopogon zizanioides). Tab-Simco AMD is highly acidic, with mean pH value of 2.64, and contains high levels of sulfate and metals. A greenhouse study was performed for a 30-day period in order to screen and optimize the necessary parameters to design a FWT system. Water quality and plant growth parameters were continuously monitored. Results show significant SO42− removal, resulting in increased pH, particularly at higher planting densities. Vetiver also helped in metal removal; high amounts of Fe, Zn, and Cu were removed, with relatively lower amounts of Pb, Al, and Ni. Iron plaque formation on the root was observed, which increased metal stabilization in root and lowered root to shoot metal translocation. Vetiver was tolerant of AMD, showing minimal change in biomass and plant growth. Results obtained are encouraging, and a large scale mesocosm study is now in progress, as the next step to develop the vetiver-based system for AMD treatment

Remediation of acid mine drainage-impacted water by vetiver grass (Chrysopogon zizanioides): A multiscale long-term study

Acid mine drainage (AMD) is an acidic discharge from mining sites that contains elevated levels of metals and sulfate (SO42−). AMD can inflict health and environmental dangers through metal toxicity and physical stress. Current methods for AMD treatment, including chemical or passive biological treatments, are often non-sustainable owing to expense, require continuous maintenance, or are unsuitable for prolonged treatment. Our ultimate goal is to develop a cost efficient and sustainable floating treatment wetland system using vetiver grass (Chrysopogon zizanioides). Year-long large- and small-scale hydroponic experiments were used to determine the effectiveness of vetiver for treating AMD-impacted waters from the Tab-Simco mine site in southern Illinois. For the large-scale mesocosmic study, vetiver rafts were suspended in 100-gallon containers. Water quality was monitored by chemical analysis of samples every 28 days and at the end of the experiment (364 days); plant health was monitored by measuring changes in biomass and recording visual changes in root and shoot coloration and morphology. There was higher net removal of Fe (81%) and Pb (81%) with lower removal of Ni (38%), Zn (35%), SO42− (28%), Mn (27%), Cr (21%), Al (11%) and Cu (8.0%). Metals were mainly localized on the root surface as Fe plaques, whereas Mn and Zn showed greater translocation from root to shoot. Furthermore, toxicity characteristic leaching procedure showed that vetiver biomass was not hazardous waste as a result of metal accumulation. From the small-scale experiment, there was near complete removal of SO42− (91%) and metals (90–100%) with the exception of Pb (15%) and Cu (0.0%). These experiments demonstrate that vetiver can effectively remediate AMD-impacted waters over an extended period of time