Abstract
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 copper (Cu), nickel (Ni), and zinc (Zn) was examined in situ using hydrated roots of cowpea (Vigna unguiculata) exposed to 1.5 μm Cu, 5 μm Ni, or 40 μm Zn for 1 to 24 h. After 24 h of 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; approximately 60% to 85% of the total Zn stored as Zn phytate within 3 h of exposure. While 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.
Highlights
The phytotoxicity of trace metals is of global concern due to contamination of the landscape by human activities
The mechanisms by which trace metals are toxic to plants remain unclear, despite their toxic effects having been researched for .100 years in the case of
On the basis of the above discussion, this study aims to investigate the in situ distribution and speciation of Cu, Ni, and Zn in roots of a nonhyperaccumulator following short periods of exposure (1–24 h) to toxic, but environmentally relevant, levels of trace metals
Summary
The phytotoxicity of trace metals is of global concern due to contamination of the landscape by human activities. While 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. It is interesting to note that many studies have examined the distribution and speciation of trace metals in plants, most have used hyperaccumulators (for example, see the review of Callahan et al, 2006) Somewhat surprisingly, despite their agronomic and environmental importance, data examining the in situ distribution and speciation of metals in nonhyperaccumulating plants are comparatively scarce. One likely reason is that analyses in nonhyperaccumulating plants are more challenging due to their lower concentrations (Lombi and Susini, 2009)
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