Effects of nutrient solution zinc activity on net uptake, translocation, and root export of cadmium and zinc by separated sections of intact durum wheat (Triticum turgidum L-var durum) seedling roots

Cd accumulation in durum wheat presents a potential health risk to consumer s. In an effort to understand the physiological mechanisms involved with Cd accumulation, this study examined the effects of Zn on Cd root uptake and phloem translocation in a split- root system. Durum wheat seedlings were gr own in chelate-buffered nutrient solution with intact root systems divided into two sections. Each root section grew in a separate 1 l pot, one of whi ch contained 0.2 mu M CdSO4. In addition, each two-pot system contained ZnS O4 in the following combinations (in mu m) (for -cd root system: +cd root s ystem): 1:1, 1:10, 10:1,10:10, 1:19, and 19:1. Harvested plant material was analyzed for Cd and Zn. In addition, rates of Cd and Zn net uptake, transl ocation to the shoot, and root export (translocation from one root segment to the other) between days 8 and 22 were calculated. Results show that Zn w as not translocated from one root section to its connected root section. Up take rates of Cd increased as solution Zn concentrations increased. Cd tran slocation from one root section to the other decreased significantly when t he Zn concentration in either pot was greater than 1 mu M. These results sh ow the potential of Zn to inhibit movement of Cd via the phloem, and sugges ts that providing adequate Zn levels may limit phloem loading of Cd into wh eat grain. Increasing the rhizosphere activity of Zn2+ in Cd-containing soi ls may therefore result in reduced Cd accumulation in grain even while net Cd uptake is slightly enhanced.