Submitted to: New Phytologist
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/7/2005
Publication Date: 8/1/2005
Citation: Hart, J.J., Welch, R.M., Norvell, W.A., Clarke, J.M., Kochian, L.V. 2005. Zinc effects on cadmium accumulation and partitioning in near-isogenic lines of durum wheat that differ in grain cadmium concentration. New Phytologist. 167:391-401. Interpretive Summary: A large percentage of the durum wheat produced in the U.S. is grown in North Dakota, where soils may contain naturally-occurring trace amounts of the heavy metal cadmium (Cd). Durum wheat tends to accumulate Cd in grain to levels that can exceed limits proposed by international regulatory agencies. An understanding of the factors that regulate Cd accumulation in durum grain is therefore desirable. This study examined the effectiveness of two approaches for reducing the amount of Cd that accumulates in durum grain: 1) application of supplemental zinc (Zn), which has been shown in some cases to reduce Cd accumulation in crops; and 2) the use of cultivars that have been bred to exhibit reduced grain Cd concentrations. Two lines of durum wheat that differ in grain Cd accumulation and that are nearly genetically identical were used. Plants were grown to maturity in a hydroponic system that allowed careful control of the amounts of Cd and other elements that were available to roots. The results showed that the low Cd-accumulating line had Cd concentrations in grains and shoots 60 to 70 percent lower than the high Cd-accumulating line. Increasing Zn levels in nutrient solution decreased the amount of Cd in grains and shoots of both lines, probably through interference with Cd uptake by roots. Patterns of Cd partitioning between roots and shoots suggest that low Cd accumulation is related to Cd retention in roots in the low Cd-accumulating line. The results suggest that agronomic practices such as Zn fertilization may contribute to reducing Cd accumulation in durum wheat grain. The use of durum wheat lines bred for low Cd accumulation may also be an effective solution to the problem.
Technical Abstract: Excessive levels of cadmium (Cd) in durum wheat represent a potential threat to international markets and consumers. This study examined the effectiveness of two approaches for reducing the amount of Cd that accumulates in durum grain: 1) application of supplemental zinc (Zn), which has been shown in some cases to reduce Cd accumulation; and 2) the use of cultivars that have been bred to exhibit reduced grain Cd concentrations. Two near isogenic durum wheat lines that differ in grain Cd accumulation were grown to maturity in nutrient solution culture using a chelating agent to buffer the free activities of Zn and Cd at levels approximating those of field conditions. The results showed that the low Cd accumulating isoline had Cd concentrations in grains and shoot parts 60 to 70 percent lower than the high Cd accumulating isoline, even though total plant Cd uptake was similar in seedlings of the two isolines. Increasing Zn levels in nutrient solution from deficient to sufficient concentrations also reduced the amount of Cd accumulation in grains and vegetative shoot parts of both isolines. The results suggest that the effect of supplemental Zn in reducing Cd tissue concentrations is related to its ability to inhibit Cd uptake into roots. Patterns of Cd partitioning between roots and shoots and between components of spikes suggest that the physiological basis for the low Cd trait may be related to compartmentation or symplasmic translocation of Cd.