Plants that Hyperaccumulate Heavy Metals Original paper

What was reviewed?

This chapter, “Plants that Hyperaccumulate Heavy Metals” by Elisa Fasani, provides a detailed review of the physiological, genetic, and ecological mechanisms underlying metal hyperaccumulation in plants, with a particular emphasis on angiosperm species. It defines hyperaccumulators as plants that uptake, translocate, and sequester heavy metals in their aerial tissues at concentrations vastly exceeding those of typical plants, and systematically reviews the elements for which hyperaccumulation occurs (e.g., nickel, zinc, cadmium, arsenic). It also discusses the evolutionary distribution of this trait, highlighting its prevalence in specific plant families, notably the Brassicaceae and Euphorbiaceae, and examines the molecular determinants of hyperaccumulation such as transporters, chelators, and stress-response proteins.

Who was reviewed?

The review encompasses approximately 500 hyperaccumulator taxa, primarily angiosperms, focusing on model species like Arabidopsis halleri and Noccaea caerulescens. These species are genetically similar to A. thaliana and have been extensively studied for their abilities to hyperaccumulate Zn, Cd, and Ni. The genus Alyssum, particularly Alyssum bertolonii and Alyssum lesbiacum, also features prominently, especially in relation to Ni accumulation. Although most hyperaccumulator species are herbaceous perennials adapted to metalliferous soils, the review also includes ferns (e.g., Pteris vittata) for arsenic hyperaccumulation and other non-Brassicaceae families that contribute to the small number of Cd and Se hyperaccumulators.

What were the most important findings?

A central finding of the review is the disproportionate representation of Brassicaceae among metal hyperaccumulator plants, with about 25% of known hyperaccumulator species belonging to this family. This family dominates zinc hyperaccumulation, and includes the only two known angiosperm arsenic hyperaccumulators. The genus Alyssum within Brassicaceae is especially rich in nickel hyperaccumulators, highlighting this family’s strong metallomic signature. Importantly, hyperaccumulation of one metal often correlates with the uptake of others—particularly Zn with Cd and Pb—due to shared ionic characteristics. The physiological mechanisms facilitating hyperaccumulation include enhanced uptake, symplastic mobility, xylem loading, and vacuolar sequestration, while detoxification involves metal ligands like histidine and nicotianamine. A significant portion of the review is dedicated to the molecular biology of hyperaccumulation, emphasizing gene families such as ZIP, CDF, NRAMP, HMA, and YSL, and the roles they play in metal homeostasis. Notably, the review supports the “elemental defense” hypothesis, wherein metal accumulation deters herbivores and pathogens. This is especially relevant for microbiome research: hyperaccumulator plants harbor metal-tolerant microbial communities, a parallel to dysbiotic profiles seen in metal-rich environments or metal-exposed tissues in humans. These plant-microbiome-metal interactions may mirror microbial shifts seen in chronic inflammatory diseases with elevated heavy metal burden, such as endometriosis.

What are the greatest implications of this review?

The implications for clinical microbiome research are substantial. The review reinforces the concept that chronic exposure to dietary heavy metals—even from otherwise health-associated vegetables like those in the Brassicaceae family—could influence host microbiome composition by selecting for metal-resistant, pro-inflammatory taxa. In the context of endometriosis, this is particularly compelling given the elevated presence of these metals in the metallomic signature of the condition. The well-documented accumulation of arsenic, cadmium, lead, nickel, and zinc in Brassicaceae suggests that excessive consumption of these vegetables—especially when sourced from contaminated soils—could contribute to microbial dysbiosis and worsen disease pathology. Furthermore, the elemental defense mechanism in plants that favors metal accumulation over chemical defenses may have unintended consequences when translated to human exposure, especially when these plants become regular components of the diet. The review thus supports reevaluating blanket dietary recommendations for high Brassicaceae intake in individuals with microbiome-mediated conditions or impaired metal detoxification.