Submitted to: Plant and Soil
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/24/2008
Publication Date: 8/2/2008
Publication URL: hdl.handle.net/10113/27662
Citation: Broadhurst, C.L., Tappero, R.V., Maugel, T.K., Erbe, E.F., Sparks, D.L., Chaney, R.L. 2008. Nickel and Manganese Accumulation, Interaction and Localization in Leaves of the Ni Hyperaccumulators Alyssum murale and Alyssum corsicum. Plant and Soil Journal. 314:35-48. Interpretive Summary: Our research team developed a Ni phytoextraction and Ni phytomining technology using the natural Ni hyperaccumulator species Alyssum murale. This species can accumulate over 2% Ni in shoot biomass when grown on mineralized or contaminated soils. Both improved cultivars were developed, and production practices needed for high annual biomass yield and high shoot Ni levels were identified by prior research. During the prior research, we showed that Ni was highly accumulated in the vacuoles of leaf epidermal cells, and that no Ni but most of the leaf Ca was accumulated in the leaf trichomes. Using X-ray absorption specrometry, we found that the very highest Ni concentrations were in the vacuole of the base of the cells which elaborated trichomes, and that manganese (MN) was also highly accumulated in this cell compartment even when the leaves contained only basal levels of total Mn. Thus, we conducted a test of the interaction of Mn supply with Ni hyperaccumulation and localization in Alyssum species. Plants were grown in potting soil with factorial addition of three levels of Ni and three levels of Mn. Plants were grown for 3 months and leaves analyzed. The leaf analyses showed that increasing Ni did not decrease leaf Mn, but increasing leaf Mn decreased leaf Ni. But the pattern of localization of Ni, Mn and Ca was not affected by the factorial levels of Ni and Mn – that is, the Ni was highest in vacuoles of trichomes and adjacent epidermal cells as well as in all other epidermal cells, and Mn was high only in the trichome cell bases and occassionally in the adjacent cells. In addition, using the capability of X-ray absorption spectroscopy, we found that the high localized Mn remained in the Mn2+ valence in contrast with sunflower and some other species which accumulate insoluble oxidized Mn4+ at points across the leaf when the plants are supplied high Mn levels. In contrast with a recent paper which suggested that Ni was also located in the trichomes, this study clearly showed very low levels of Ni in the trichomes. The use of X-ray absorption spectroscopy allows study of fresh leaves with no preparation of samples which could cause redistribution of elements as in the traditional preparation of samples for transmission electron microscopy. Taken together, these findings suggest that Ni hyperaccumulation may have developed from a pre-existing plant process which caused accumulation of Mn in vacuoles at the base of trichomes.
Technical Abstract: The genus Alyssum contains >50 Ni hyperaccumulator species; many can achieve 3% Ni in dry leaf. In soils with normal Mn levels, Alyssum trichome bases were observed previously to accumulate Ni and Mn to high levels. Here we report concentration and localization patterns in A. murale and A. corsicum grown in soils with nonphytotoxic factorial additions of Ni and Mn salts. Four leaf type subsets based on size and age accumulated Ni and Mn similarly. The greatest Mn accumulation (A. corsicum Ni40/Mn40) was 10 times control. Whole leaf Ni concentrations decreased as Mn increased. Synchotron X-ray fluorescence mapping of whole fresh leaves showed Mn localized in distinct high-concentration spots associated with trichomes. Nickel and Mn distributions were strongly spatially correlated, but the metals were not interspersed. Standard x-ray fluorescence point analysis/mapping of freeze-dried cryofractured samples found that Ni and Mn were co-located and strongly concentrated only in trichome bases/pedicles and in cells adjacent to trichomes. Nickel was also strongly spatially and concentrationally correlated with sulfur. Results indicate that maximum Ni phytoextraction by Alyssum may be reduced in soils with higher phytoavailable Mn, and that Ni hyperaccumulation in Alyssum species may have developed from a Mn handling system.