Submitted to: Environmental Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/18/2004
Publication Date: 11/1/2004
Citation: Broadhurst, C.L., Chaney, R.L., Angle, J.S., Maugel, T.K., Erbe, E.F., Murphy, C.A. 2004. Simultaneous hyperaccumulation of nickel, manganese and calcium in alyssum leaf trichomes. Environmental Science and Technology. 38(21):5797-5802. Interpretive Summary: We have demonstrated a new technology for removing metals from contaminated or mineralized soils which uses metal hyperaccumulator plants grown as a new crop. For Ni, the value of Ni in the plant biomass is sufficient to make phytomining soil Ni a new commercial farming business opportunity. As part of the basic research done in association with technology development for phytomining, we have examined the distribution of Ni within plants and within leaves. The epidermal cells are enriched compared to other leaf cells. Although one paper had reported that Ni was accumulated in the trichomes (leaf hairs) of Alyssum murale, our earlier work showed that the trichome body was loaded with Ca but not Ni. With further examination of more plants, another pattern became apparent: Both Mn and Ni were more highly localized in the basal portion of trichome cell vacuoles than in other cells; additionally, the Ni and Mn localization within this basal portion of the trichome cells was separate rather than overlapping. Although the mechanism of multiple ion hyperaccumulation and tolerance is not yet clear, this observation gives evidence that particular cells play a more important role than previously recognized. These localized volumes of Ni and Mn accumulation appear to represent the highest concentration of Ni in any plant tissue reported to date.
Technical Abstract: We have developed commercially viable phytoremediation/phytomining technologies employing Alyssum Ni-hyperaccumulator species to quantitatively extract Ni from soils. Nickel is mainly stored in Alyssum leaf epidermal cells. The leaf epidermis is covered with an overlapping network of stellate trichomes. The trichome basal compartment, trichome pedicle, and the epidermal cells adjacent to the trichome basal compartment strongly concentrate Ni, but there is no appreciable Ni in trichome rays. Here we report simultaneous and region-specific localization of high levels of Ni, Mn and Ca within Alyssum trichomes as determined by scanning electron microscopy/energy dispersive x-ray analysis (SEM/EDX). Plants were grown in high Ni soil, achieving up to 48,400 ppm Ni in total leaf concentration, however Ca and Mn were not enriched in the experimental soils. Simultaneous and region-specific localization of hyperaccumulated Ca, Mn, and Ni occurred in 3 soil types, 5 Alyssum species/ecotypes, and over a wide range of soil Ni content. The metal content in the trichome basal compartment is ~15-20 dry wt%, the highest ever reported for healthy higher plant tissue.