Thinking for the future: Phytoextraction of cadmium using primed plants for sustainable soil clean-up

Cadmium (Cd) soil contamination is a global problem for food security due to its ubiquity, toxicity at low levels, persistence, and bioaccumulation in living organisms. Humans' intake of heavy metals is usually due to direct contact with contaminated soil, through the food chain (Cd accumulation in crops and edible plants) or through drinking water in cases of coupled groundwater-surface water systems. Phytoextraction is one of the eco-friendly, sustainable solutions that can be used as a method for soil clean-up with the possibility of re-use of extracted metals through phytomining. Phytoextraction is often limited by the tolerance level of hyperaccumulating plants and the restriction of their growth. Mechanisms of hyperaccumulation of heavy metals in tolerant species have been studied, but there are almost no data on mechanisms of further improvement of the accumulation capacity of such plants. Priming can influence plant stress tolerance by the initiation of mild stress cues resulting in acclimation of the plant. The potential of plant priming in abiotic stress tolerance has been extensively investigated using different types of molecules that are supplemented exogenously to plant organs (roots, leaves, etc.), resulting in enhanced tolerance of abiotic stress. This review focuses on mechanisms of enhancement of plant stress tolerance in hyperaccumulating plants for their exploitation in phytoextraction processes.