Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 15, 2002
Publication Date: N/A
Interpretive Summary: Excessive lifetime Cd ingestion can induce kidney proximal tubule dysfunction, and food Cd limits are used to prevent human health effects from dietary Cd. Our research has shown the unique role of flooded soil rice in moving soil Cd into the human food chain, and the role of plant Zn in reducing plant Cd bioavailability to animals. The present study tested the interactions between Zn and Cd in uptake and translocation of Cd in bread wheat. Chelator-buffered nutrient solutions were was used to control the activity of Zn and Cd ions in the nutrient solution; This method allows one to control the activity of free metal ions in the range which occurs in soil solutions. Ferrous was buffered with a Ferrozine, a ferrous-chelating agent for which we had previously measured the chelate formation constant, and used to test the ferrous requirement of plants. The Cd and Zn activities were buffered with a different chelator which has much stronger chelation of Cd than Zn, and which allows one to buffer Cd activity at low levels while attaining phytotoxic Zn levels. Using this new system, we tested whether increasing Zn affected Cd uptake or translocation. Increasing Zn reduced shoot-Cd to rood-Cd ratio, indicating that Cd translocation was inhibited by Zn. At the highest Zn activities tested, Zn did not reach phytotoxic levels in hard red spring wheat but inhibited Cd uptake and translocation (rice was more susceptible to soluble Zn activity than wheat). The test of the inverse relationship, Cd inhibition of Zn uptake or translocation, showed no effects. Interactions of Cd and Zn in hard red spring wheat were different from rice reported in our first experiment of this type reported earlier.
Technical Abstract: Wheat grown on Cd-uncontaminated soils can still potentially translocate unacceptable levels of Cd to grain. The effect of Zn and Cd levels on Cd uptake and translocation in hard red spring wheat (HRSW) cultivar Grandin (Triticum aestivum L.) was investigated using a multi-chelator buffered nutrient solution (EGTA used to buffer Cd, Zn, Cu, Mn, and Ni; and Ferrozine used to buffer Fe2+). In the Zn level series of treatments, Cd2+ activity was held constant at 10E-10.7 M, and the Zn2+ activity was varied from 10E-7.6 to 10E-5.2 M. As pZn2+ increased, the translocation of Cd to the shoots decreased. The shoot:root Cd concentration ratio decreased from 0.20 to 0.03 as pZn2+ went from 7.6 to 5.2, indicating that adequate to high levels of Zn are effective in reducing Cd translocation to the shoots of Grandin HRSW. In the Cd series, the Zn activity was at 10E-6.6 M, while Cd activity was increased from 10E-10.7 to 10E-9.2 M. High levels of Cd did not significantly effect the uptake and translocation of Zn in the roots and shoots. While at pCd2+ of 9.2, the root and shoot Cd concentrations significantly increased, there was not a significant increase in the shoot:root Cd ratio. This would indicate that even at high Cd2+ activities, Zn is effective in regulating Cd uptake and translocation in Grandin HRSW.