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United States Department of Agriculture

Agricultural Research Service

Research Project: USING ELECTRON MICROSCOPY TECHNOLOGY TO SOLVE AGRICULTURAL PROBLEMS Title: Accumulation of zinc and cadmium and localization of zinc in Picris divaricata

Authors
item Broadhurst, C -
item Bauchan, Gary
item Murphy, Charles
item Tang, Ye-Tao -
item Pooley, Christopher
item Davis, Allen -
item Chaney, Rufus

Submitted to: Environmental and Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 28, 2012
Publication Date: January 1, 2013
Citation: Broadhurst, C.L., Bauchan, G.R., Murphy, C.A., Tang, Y., Pooley, C.D., Davis, A.P., Chaney, R.L. 2013. Accumulation of zinc and cadmium and localization of zinc in Picris divaricata. Environmental and Experimental Botany. 87:1-9.

Interpretive Summary: Large areas of cultivated land in China, Japan and Thailand have been contaminated with lead (Pb), zinc (Zn) and cadmium (Cd) to the extent that demonstrable effects on human health have been reported. The extent of contamination virtually prohibits either removal of soils or agricultural utilization. Phytoremediation, the use of plants to extract toxic metals from soils is one of the only viable options to relatively quickly remove excess metals from soils and return them to safe, productive use. Consequently there is a need for plants native to tropical and subtropical Asia that are suitable candidates for phytoremediation. Picris divaricata, a member of the Aster family and native to subtropical China, was recently identified as a plant that was excellent at accumulating Cd and Zn in plants tissue. We discovered through the use of scanning electron microscopy x-ray analysis that these plants do accumulate low levels of both Cd and Zn, mostly in association with silicon. The specific location for the accumulation of these toxic metals is within the trichomes (leaf hairs). Thus, these plants have the potential for use in the phytoremediation of soils which contain toxic metals.

Technical Abstract: Picris divaricata Vant., native to subtropical China, was recently identified as the first Cd/Zn hyper-accumulator from Asteraceae. Wild collected seed of P. divaricata was grown in a series of pH buffered test soils with Zn levels 00-7000 gkg-1 and Cd levels 00-150 gkg-1 for four months. Plants did not hyper-accumulate Zn and weakly hyper-accumulated Cd with little or no dose-response. P. divaricata has multicellular simple trichomes concentrated on the leaf edge and midrib. Scanning electron microscope X-ray analysis showed that Zn is localized in larger trichomes and epidermal cells adjacent to the trichome but virtually absent in other leaf tissues. Within the trichomes, Zn is localized in ovate spots around the tips of individual cells. These tips and other locations in the trichome cell contained black electron dense material when examined with transmission electron microscopy. Silicon and Mn were concentrated in the same areas as Zn. Si has been previously associated with alleviating Zn, Mn and Cd toxicity; our results support this and further investigation is warranted. Calcium and P were concentrated in the distal tips of trichomes, similar to patterns previously observed for calcicole plants grown in elevated Ca soils. Overall, nonesecretory trichomes from many plant families may have a common origin as tissues adapted to handle a variety of environmental metals.

Last Modified: 10/23/2014
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