Permeability of Plant Young Root Endodermis to Cu Ions and Cu-Citrate Complexes in Corn and Soybean
2015
Fu, Yanzhao | Lei, Wenrui | Shen, Zhenguo | Luo, Chunling
The non-selective apoplastic passage of Cu and Cu-citrate complexes into the root stele of monocotyledonous corn and dicotyledonous soybean was investigated using an inorganic-salt-precipitation technique. Either Cu ions or Cu-citrate complexes were drawn into root through the apoplast from the root growth medium, and K ₄[Fe(CN) ₆] was subsequently perfused through xylem vessels or the entire root cross section. Based on microscopic identification of the reddish-brown precipitates of copper ferrocyanide in the cell walls of the xylem of corn and soybean roots, Cu ²⁺ passed through the endodermal barrier into the xylem of both species. When the solution containing 200 μM CuSO ₄ and 400 μM sodium citrate (containing 199.98 μM Cu-citrate, 0.02 μM Cu ²⁺) was drawn via differential pressure gradients into the root xylem while being perfused with K ₄[Fe(CN) ₆] through the entire root cross-section, reddish-brown precipitates were observed in the walls of the stele of soybean, but not corn root. However, when a CuSO ₄ solution containing 0.02 or 0.2 μM free Cu ²⁺ was used, no reddish-brown precipitates were detected in the stele of either of the two plants. Results indicated that endodermis was permeable to Cu-citrate complexes in primary roots of soybean, but not corn. The permeability of the endodermal barrier to the Cu-citrate complex may vary between dicotyledonous and monocotyledonous plants, which has considerable implications for chelant-enhanced phytoextraction.
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