Abstract
Hyperaccumulation is generally highly specific for a single element, for example nickel (Ni). The recently-discovered hyperaccumulator Glochidion cf. sericeum (Phyllanthaceae) from Malaysia is unusual in that it simultaneously accumulates nickel and cobalt (Co) with up to 1500 μg g−1 foliar of both elements. We set out to determine whether distribution and associated ligands for Ni and Co complexation differ in this species. We postulated that Co hyperaccumulation coincides with Ni hyperaccumulation operating on similar physiological pathways. However, the ostensibly lower tolerance for Co at the cellular level results in the exudation of Co on the leaf surface in the form of lesions. The formation of such lesions is akin to phytotoxicity responses described for manganese (Mn). Hence, in contrast to Ni, which is stored principally inside the foliar epidermal cells, the accumulation response to Co consists of an extracellular mechanism. The chemical speciation of Ni and Co, in terms of the coordinating ligands involved and principal oxidation state, is similar and associated with carboxylic acids (citrate for Ni and tartrate or malate for Co) and the hydrated metal ion. Some oxidation to Co3+, presumably on the surface of leaves after exudation, was observed.
Highlights
Hyperaccumulators are rare plants that accumulate metal and metalloid elements to extraordinarily high concentrations in their living biomass that may be hundreds or thousands of times greater than is normal for most plants[1,2,3]
The current study used synchrotron X-ray fluorescence microscopy (XFM) and X-ray absorption spectroscopy (XAS) to investigate whether the distribution and associated ligands for Ni and Co complexation differ in Glochidion cf. sericeum
Subsequent bulk analysis with ICP-AES of fragments obtained from these herbarium specimens gave mean values of 1159 ± 217 μg g−1 for Co and 2037 ± 205 μg g−1 for Ni
Summary
Hyperaccumulators are rare plants that accumulate metal and metalloid elements to extraordinarily high concentrations in their living biomass that may be hundreds or thousands of times greater than is normal for most plants[1,2,3]. Most chemical speciation studies on hyperaccumulator plants have reported results from bulk measurements, and could not distinguish between the different compartments across the biopathways, including root, xylem, phloem, and leaves[30]. Recent investigations on the distribution and chemical speciation of Ni in three different hyperaccumulator species from Sabah revealed that Ni is present in the form of Ni:citrate and preferentially accumulated in the epidermis and in the spongy mesophyll in the leaves and in the phloem in the roots and branches[33]. We aimed to determine the chemical speciation in frozen hydrated samples of different plant organs, tissues and transport liquid (xylem and phloem) from the root to leaves to gain an understanding of the mechanisms of transport and storage in this species
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
