Metabolomics reveals defensive mechanisms adapted by maize on exposure to high molecular weight polycyclic aromatic hydrocarbons

doi:10.1016/j.chemosphere.2018.09.170

Chemosphere

Volume 214, January 2019, Pages 771-780

https://doi.org/10.1016/j.chemosphere.2018.09.170 Get rights and content

Highlights

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Assessed the impact of PAHs on regulation of maize metabolism.
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Metabolite response was significant between control, individual & PAHs mixtures.
•
Galactose & aminoacyl tRNA biosynthesis pathways were greatly affected by PAHs.
•
Provide better insights on overall stress response of maize towards PAHs.
•
Adaptive defensive mechanisms actuated by PAHs exposure.

Abstract

Polycyclic aromatic hydrocarbons are an important group of persistent organic pollutants. Using plants to remediate PAHs has been recognized as a cost-effective and environmentally friendly technique. However, the overall impact of PAHs on the regulation of plant metabolism has not yet been explored. In this study, we analyzed the alteration in the maize (Zea mays L.) metabolome on exposure to high molecular weight PAHs such as benzo[a]pyrene (BaP) and pyrene (PYR) in a hydroponic medium, individually and as a mixture (BaP + PYR) using GC-MS. The differences in the metabolites were analyzed using XCMS (an acronym for various forms (X) of chromatography-mass spectrometry), an online-based data analysis tool. A significant variation in metabolites was observed between treatment groups and the unspiked control group. The univariate, multivariate and pathway impact analysis showed there were more significant alterations in metabolic profiles between individual PAHs and the mixture of BaP and PYR. The marked changes in the metabolites of galactose metabolism and aminoacyl tRNA biosynthesis in PAHs treated maize leaves exhibit the adaptive defensive mechanisms for individual and PAHs mixture. Therefore, the metabolomics approach is essential for an understanding of the complex biochemical responses of plants to PAHs contaminants. This knowledge will shed new light in the field of phytoremediation, bio-monitoring, and environmental risk assessment.

Graphical abstract

Introduction

Plants produce a more extensive range of metabolites than any other group of organisms, and thus metabolomics has a correspondingly higher importance in plant science (Kawamoto et al., 2010). Hence non-targeted metabolomics and unbiased analysis were employed for high throughput study of the metabolites in plants (Hill and Roessner, 2014). Currently, there are numerous techniques available to investigate the metabolomic profile in diverse biological systems, each with different degree of advantages and their choice depends on the purpose of the analysis (Fiehn, 2002). Among the various methods, gas chromatography (GC-MS) is widely used for determining the plant metabolites with high reproducibility and sharp separation (Lisec et al., 2006).

Recently, the use of untargeted metabolomics in environmental science has received much attention and has remained as a field of interest among the scientific community for the development of pollutant exposure/specific biomarkers, and the assessment of the risk of the organic and inorganic contaminants to living organisms (Jones et al., 2014; Carrizo et al., 2017). Among organic pollutants, the PAHs are ubiquitous due to their hydrophobic and recalcitrant nature. PAHs are formed naturally and by human activities such as fossil fuel burning and vehicle exhausts (Abdel-Shafy and Mansour, 2016). Despite their hydrophobicity, there are many reports on the occurrence of these compounds on the surface and groundwater bodies (Fähnrich et al., 2002; Zhang et al., 2012).

Among the PAHs, Benzo(a)pyrene, a high molecular weight PAH, is most extensively studied because of its ability to cause mutagenic, carcinogenic and teratogenic effects in living organisms (Samanta et al., 2002). PAHs in general are a class of aromatic hydrocarbon pollutants capable of causing cancer and mutations in animals including human beings. There are many strategies developed to mitigate PAHs pollution around the world (Kuppusamy et al., 2017). Among them, phytoremediation - use of plant species to remediate contamination, is considered as one of the best remediation strategies for the remediation of environments contaminated with PAHs. The plants with C4 photosystems especially maize was reported with high efficiency to degrade PAHs in contaminated soil (Zamani et al., 2016; Sivaram et al., 2018b). However, the application of untargeted metabolomics to study the response of maize and changes in their metabolites to PAHs exposure has not yet been investigated.

To address the knowledge gap, a differential untargeted metabolic profiling study was conducted with maize exposed to high molecular weight PAHs; BaP, and PYR alone and as a mixture (BaP+PYR). Derivatization and analysis of total metabolites from the maize leaf samples was carried out through GC-MS, with the aim to unravel the role of PAHs in inducing the metabolic alterations in maize seedlings grown in Hoagland's solution. To the best of our knowledge, this is the first report of maize metabolomic profiling exposed to PAHs in Hoagland's medium.

Section snippets

Chemicals

Analytical grade BaP and PYR were purchased from Sigma-Aldrich (Sydney, Australia). The stock solutions were prepared in dimethylformamide (DMF) as this solvent was considered as a solvent of choice for toxicity studies (Subashchandrabose et al., 2015).

PAHs spiking

The Hoagland's solution was prepared according to Hoagland and Arnon (1950). The stock solution of BaP and PYR were spiked into 50 mL sterile Hoagland's solution (10 mg L⁻¹) in Erlenmeyer's flask (250 mL). The selected concentration was in the

Growth parameters and metabolomic analysis of maize exposed to PAHs

Maize (Zea mays L.) is one of the major cereal crops cultivated throughout the world. It is a fast-growing plant with an adventitious root system (Wuana et al., 2010). Maize has been previously reported to have the potential for phytoremediation of a variety of contaminants including PAHs (Sivaram et al., 2018b). In this study, the growth parameters such as the root and shoot length of maize seedlings were decreased in all treatments compared to their control. The maize seedlings that are

Conclusion

In summary, this study provides a framework for the metabolomic responses that are taking place in maize plant systems on exposure to BaP and PYR individually and as a mixture. Non-targeted metabolic profiling will further enhance the understanding of plant systems. It can be concluded that the non-targeted metabolomics approach has valuable functional futures in determining the biochemical changes and metabolic adaptation of plants when exposed to priority, and or persistent contaminants. The

Conflicts of interest

The authors declare that they have no conflict of interest.

Acknowledgments

We thank Prof. Ute Roessner and Dr. Daniel Anthony Dias, The University of Melbourne for their help with GC MS analysis. This research was supported by the Australian Government and the University of South Australia through an International Postgraduate Research Scholarship (IPRS) in collaboration with Cooperative Research Centre for Contamination Assessment and Remediation of the Environment (CRC CARE).

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Metabolomics reveals defensive mechanisms adapted by maize on exposure to high molecular weight polycyclic aromatic hydrocarbons

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Chemicals

PAHs spiking

Growth parameters and metabolomic analysis of maize exposed to PAHs

Conclusion

Conflicts of interest

Acknowledgments

Egypt. J. Pet.

Chemosphere

Environ. Res.

Aquat. Toxicol.

Chemosphere

Mol. Plant

Mar. Pollut. Bull.

Chemosphere

Environ. Pollut.

Environ. Pollut.

J. Hazard Mater.

Environ. Pollut.

Arch. Biochem. Biophys.

Trends Biotechnol.

Chemosphere

Trends Plant Sci.

Food Chem.

J. Hazard Mater.

Environ. Pollut.

The aspartic acid metabolic pathway, an exciting and essential pathway in plants

Amino Acids

Purine and pyrimidine biosynthesis in higher plants

Physiol. Plant.

Environmental metabolomics: a critical review and future perspectives

Metabolomics

Accumulation and food chain transfer of fluoranthene and benzo [a] pyrene in Chironomus riparius and Lepomis macrochirus

Arch. Environ. Contam. Toxicol.

Plant uptake of non-ionic organic chemicals

Environ. Sci. Technol.

Chemical hydrophobicity and uptake by plant roots

Environ. Sci. Technol.

Immunochemical detection of polycyclic aromatic hydrocarbons (PAHs)

Anal. Lett.

Metabolomics–the link between genotypes and phenotypes

Plant Mol. Biol.

Interactive XCMS Online: simplifying advanced metabolomic data processing and subsequent statistical analyses

Anal. Chem.

Advances in high-throughput untargeted LC-MS analysis for plant metabolomics