The nickel hyperaccumulators of Borneo

Are patterns of tissue-level nickel distribution different in phylogenetically distant hyperaccumulator species on the island of Borneo?

Plants require some trace elements in minor quantities for healthy growth, with an excess of these leading to potential toxicity. Nickel is essential to the synthesis of some plant enzymes, notably urease. However, too much nickel can lead to necrosis, reduced plant growth and in extreme cases, plant death.

Hyperaccumulators are rare plants that accumulate trace elements, such as nickel, to extreme concentrations in their living shoots without typical symptoms of toxicity. There are currently over 500 nickel hyperaccumulator plant species known globally, with the greatest number of species recorded in Cuba, New Caledonia and the Mediterranean Region.

Nickel hyperaccumulator plants have the potential to be used in phytomining, an environmentally sustainable ‘green’ technology to produce nickel that can then be used in manufacturing. The Malaysian state of Sabah on the island of Borneo has recently emerged as a global hotspot of nickel hyperaccumulator plants, with 28 hyperaccumulator species native to the area.

The nickel hyperaccumulator plant Actephila alanbakeri in its native habitat in Sabah, Malaysia with two insert panels showing elemental maps depicting the distribution of calcium and nickel in a young stem of this species. Image credit: Abubakari et al.

In their new study published in AoBP, Abubakari et al. focus on the tissue-level distribution of nickel and other physiologically relevant elements in four different nickel hyperaccumulator species (Flacourtia kinabaluensis, Actephila alanbakeri, Psychotria sarmentosa and Glochidion brunneum) from the Sabah, Malaysia. The roots, old stems, young stems and leaves of the four species studied using nuclear microprobe (micro-PIXE and micro-BS) analysis. The tissue-level distribution of nickel found in these species has the same overall pattern as in most other hyperaccumulator plants studied before, with substantial enrichment in the epidermal cells and the phloem.

Even though nickel hyperaccumulation has seemingly evolved numerous times independently in distant phylogenetic lineages in different areas around the world, the physiological mechanisms are convergent in the tropical woody species that were studied from Borneo.

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