Chemical analysis in Berkheya zeyheri: a South African nickel hyperaccumulator

Berkheya zeyheri, a South African Ni-hyperaccumulator, was chemically characterized using plants from two serpentine outcrops in Barberton, South Africa. Analysis of the serpentine soil for total and bioavailable metals (Cr, Mn, Fe and Ni) revealed that majority of the HMs present are bound to silicate material and therefore unavailable for uptake. In particular, only 17 - 33% of Ni is bioavailable. In the plant, Ni concentrations were in the range 9,240 - 12,860 mg kg^-1 in leaves dry weight (d.w), the primary site for Ni-hyperaccumulation. A range of relevant organic and amino acids were quantified with chelidonic acid (8,430 - 12,598 mg kg^-1) and malic acid (4,343 - 6,323 mg kg^-1) identified as the organic acids with the highest concentration in the leaves, potentially associating them with Ni uptake. Additionally, malic acid and citric acid (4,343 - 14,332 mg kg^-1) are likely involved in the uptake, transport and storage process of Ni as they are conventionally associated with uptake in other hyperaccumulators. The plants contain elevated concentrations of aspartic acid and proline likely due to antioxidant activities and abiotic stresses. The study identified the potential role players in Ni uptake mechanisms and highlights the complexity of Ni-hyperaccumulation in plants. B. zeyheri, has been understudied as a potential phytoremediator and no significant research has been reported to date.