Cadmium toxicity in crop plants and its alleviation by arbuscular mycorrhizal (AM) fungi: An overview

Cadmium (Cd), a toxic metal released into agricultural settings induces numerous changes in plant growth and physiology. The main known mechanisms of Cd toxicity include its affinity for sulfhydryl groups in proteins and its ability to replace some essential metals in active sites of enzymes, thus causing inhibition of enzyme activities and protein denaturation. This article reviews detrimental effects of Cd toxicity on the functional biology of plants and summarizes the mechanisms that are activated by plants to prevent the absorption or to detoxify Cd ions such as synthesis of antioxidants, osmolytes, phytochelatins, metallothioneins, etc. Arbuscular mycorrhizal (AM) fungi are reported to be present on the roots of plants growing in metal-contaminated soils and play an important role in metal tolerance. Through mycorrhizal symbiosis, heavy metals are immobilized in the rhizosphere through precipitation in the soil matrix, adsorption onto the root surface or accumulation within roots, and compartmentalized in aboveground parts of the plant. This article unfolds the potential role of AM fungi in enhancing Cd tolerance of plants.