|Marcus, M. a.|
|Sparks, D. l.|
Submitted to: New Phytologist
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/23/2007
Publication Date: 5/25/2007
Citation: Tappero, R., Peltier, E., Heidel, K., Marcus, M., Chaney, R.L., Sparks, D. 2007. Hyperaccumulator Alyssum Murale Relies on a Different Metal Storage Mechanism for Cobalt than for Nickel. New Phytologist. On line. 175(4):641-654. Interpretive Summary: The Ni hyperaccumulator species Alyssum murale has been domesticated for phytominiing of soil Ni and Co. As part of the characterization of which metals are accumulated by this species, and how the plant tolerate such high concentrations of metals in shoots, it has been found that Ni is accumulated within vacuoles of leaf cells at very high concentrations. Cobalt is also accumulated, and Zn may co-occur in the contaminated or mineralized soils where Ni phytomining would be conducted. Thus uptake and distribution in tissues of Ni, Co and Zn were studied in nutrient solutions. In leaves, Ni was distributed to all leaf cells, especially epidermal cells, and were mostly within vacuoles. Interestingly, Co which is also accumulated to quite high concentrations in A. murale shoots without reducing yield was found to be within the xylem translocation system and not accumulated within leaf cells. Zn on the other hand was not hyperaccumulated, nor were shoots higher in Zn than roots. Zn was not accumulated in epidermal leaf vacuoles. These studies illustrate that the evolved trait that benefits Alyssum for grown on serpentine soils rich in Ni is Ni hyperaccumulation. In these soils, Ni is present at about 10-fold higher concentration than Co, and Ni inhibits uptake of Co. The remarkable difference in how the plant translocated different elements, and the vacuolar storage of Ni but not Co shows that it should not be assumed that hyperaccumulator plant species will accumulate more than one or a few metals, and that the mechanism of tolerance and storage of these three metals in shoots differ for Alyssum murale.
Technical Abstract: Nickel hyperaccumulator Alyssum murale has been developed as a commercial crop for phytoremediation/phytomining Ni-enriched soils (anthropogenic/geogenic) containing elevated concentrations of other metals. Metal co-tolerance, accumulation, and localization were investigated for Alyssum exposed to co-contaminant metals (Co and Zn). Alyssum in perlite culture were irrigated with Ni-enriched nutrient solutions containing elevated concentrations of Co or Zn. Metal localization and elemental associations were investigated with synchrotron X-ray fluorescence (SXRF) and computed-microtomography (CMT). Alyssum hyperaccumulated Ni and Co (>1000 g g-1 DW) from mixed-metal systems. Zinc was not hyperaccumulated. Biomass was not affected by treatments. Elevated Co or Zn concentrations did not alter Ni accumulation or localization. CMT leaf tomograms (virtual cross-section) showed Co was limited to the vasculature. SXRF images revealed a uniform Ni distribution in leaves. Cobalt was preferentially localized at leaf tips/margins (older leaves) and excreted as 'sap-like' guttation fluid. Nickel phytomining could be achieved despite elevated Co or Zn in (soil) solution. Alyssum relies on a different metal sequestration mechanism for Co than for Ni to maintain metal homeostasis."