Contrasting nickel and zinc hyperaccumulation in subspecies of Dichapetalum gelonioides from Southeast Asia

Hyperaccumulator plants have the unique ability to concentrate specific elements in their shoot in concentrations that can be thousands of times greater than in normal plants. Whereas all known zinc hyperaccumulator plants are facultative hyperaccumulators with only populations on metalliferous soils hyperaccumulating zinc (except for Arabidopsis halleri and Noccaea species that hyperaccumulate zinc irrespective of the substrate), the present study discovered that Dichapetalum gelonioides is the only (zinc) hyperaccumulator known to occur exclusively on 'normal' soils, while hyperaccumulating zinc. We recorded remarkable foliar zinc concentrations (10 730 mu g g(-1), dry weight) in Dichapetalum gelonioides subsp. sumatranum growing on 'normal' soils with total soil zinc concentrations of only 20 mu g g(-1). The discovery of zinc hyperaccumulation in this tropical woody plant, especially the extreme zinc concentrations in phloem and phloem-fed tissues (reaching up to 8465 mu g g(-1)), has possible implications for advancing zinc biofortification in Southeast Asia. Furthermore, we report exceptionally high foliar nickel concentrations in D. subsp. tuberculatum (30 260 mu g g(-1)) and >10 wt% nickel in the ash, which can be exploited for agromining. The unusual nickel and zinc accumulation behaviour suggest that Dichapetalum-species may be an attractive model to study hyperaccumulation and hypertolerance of these elements in tropical hyperaccumulator plants