Hyperaccumulator

Hyperaccumulator is a plant species that naturally accumulates unusually high concentrations of metals in its above-ground tissues when growing on metal-rich soils. For a plant to be classified as a hyperaccumulator, shoot concentrations of certain metals must exceed species-specific thresholds and be ecologically consistent in the plant's native habitat. Commonly cited thresholds (in mg of metal per kg dry weight) are roughly: nickel ≥1000, zinc ≥1000, cobalt ≥100, cadmium ≥100, and manganese ≥10000, though exact cutoffs vary by metal and species.

Hyperaccumulation is associated with enhanced uptake, translocation, and tolerance mechanisms, including root transporters that take up metals, chelation by phytochelatins or metallothioneins, and sequestration in leaf vacuoles or cell walls. Genomic and physiological studies have highlighted transporters such as ZIP family members and HMA transporters in model and crop plants, with Arabidopsis halleri and Noccaea caerulescens providing key insights. Notable nickel hyperaccumulators include Alyssum murale and Alyssum corsicum; zinc and cadmium hyperaccumulators include Arabidopsis halleri and Noccaea caerulescens.

Hyperaccumulators have potential use in phytoremediation of polluted soils and, in the case of certain species, phytomining, where metal-rich biomass is harvested for metal recovery. Limitations include slow growth, limited biomass, site-specific metal availability, and ecological and economic considerations. Ongoing research focuses on understanding regulatory networks and breeding or engineering plants to improve accumulation and tolerance.