Varied environmental compartments including soils are being contaminated by a myriad toxic metal(loid)s (hereafter termed as "metal/s") mainly through anthropogenic activities. These metals may contaminate food chain and bring irreparable consequences in human. Plant-based approach (phytoremediation) stands second to none among bioremediation technologies meant for sustainable cleanup of soils/sites with metal-contamination. In turn, the capacity of plants to tolerate potential consequences caused by the extracted/accumulated metals decides the effectiveness and success of phytoremediation system. Chelation is among the potential mechanisms that largely govern metal-tolerance in plant cells by maintaining low concentrations of free metals in cytoplasm. Metal-chelation can be performed by compounds of both thiol origin (such as GSH, glutathione; PCs, phytochelatins; MTs, metallothioneins) and non-thiol origin (such as histidine, nicotianamine, organic acids). This paper presents an appraisal of recent reports on both thiol and non-thiol compounds in an effort to shed light on the significance of these compounds in plant-metal tolerance, as well as to provide scientific clues for the advancement of metal-phytoextraction strategies.

Central European Institute of Technology Brno University of Technology Brno Czech Republic ; Department of Chemistry and Biochemistry Mendel University in Brno Brno Czech Republic

Centre for Environmental and Marine Studies and Department of Chemistry University of Aveiro Aveiro Portugal

Centre for Environmental and Marine Studies and Department of Chemistry University of Aveiro Aveiro Portugal ; Centre for Environmental and Marine Studies and Department of Biology University of Aveiro Aveiro Portugal

Department of Agronomy Faculty of Agriculture Sher e Bangla Agricultural University Dhaka Bangladesh

Department of Environmental Science School of Life Sciences Periyar University Salem India

Department of Genetics and Plant Breeding Bangladesh Agricultural University Mymensingh Bangladesh

Laboratory of Plant Stress Responses Faculty of Agriculture Kagawa University Miki cho Japan

Post Graduate Department of Biotechnology St Xavier's College Kolkata India

Stress Physiology and Molecular Biology Lab Centre for Biotechnology Maharshi Dayanand University Rohtak India

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