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In Situ Distribution And Speciation Of Toxic Copper, Nickel, And Zinc In Hydrated Roots Of Cowpea
Citation:
Kopittke, P. M., N. W. Menzies, M. D. de Jonge, B. A. McKenna, E. Donner, R. I. Webb, D. J. Paterson, D. L. Howard, C. G. Ryan, C. J. Glover, K. G. SCHECKEL, AND E. Lombi. In Situ Distribution And Speciation Of Toxic Copper, Nickel, And Zinc In Hydrated Roots Of Cowpea. PLANT PHYSIOLOGY. American Society of Plant Biologists, Rockville, MD, 156:663-673, (2011).
Impact/Purpose:
To investigate the in situ distribution and speciation of Cu, Ni, and Zn in roots of a non-hyperaccumulator (cowpea, Vigna unguiculata (L.) Walp.) following short periods of exposure (1 to 24 h) to toxic, but environmentally relavant, levels of trace metals.
Description:
The phytotoxicity of trace metals is of global concern due to contamination of the landscape by human activities. Using synchrotron-based X-ray fluorescence microscopy and X-ray absorption spectroscopy, the distribution and speciation of Cu, Ni, and Zn was examined in situ using hydrated roots of cowpea (Vigna unguiculata (L.) Walp.) exposed to 1.5 µM Cu, 5 µM Ni, or 40 µM Zn for 1 to 24 h. After 24 h exposure, most Cu was bound to polygalacturonic acid of the rhizodermis and outer cortex, suggesting that binding of Cu to walls of cells in the rhizodermis possibly contributes to the toxic effects of Cu. When exposed to Zn, cortical concentrations remained comparatively low with much of the zn accumulating in the meristematic region and moving into the stele; ca. 60 to 85% of the total Zn stored as Zn-phytate within 3 h of exposure. Whilst Ni concentrations were high in both the cortex and meristem, concentrations in the stele were comparatively low. To our knowledge, this is the first report of the in situ distribution and speciation of Cu, Ni, and Zn in hydrated (and fresh) plant tissues, providing valuable information on the potential mechanisms by which they are toxic.
