Characterization of zinc uptake, binding, and translocation in intact seedlings of bread and durum wheat cultivars

Durum wheat (Triticum turgidum L. var durum) cultivars exhibit lower Zn efficiency than comparable bread wheat (Triticum aestivum L.) cultivars. To understand the physiological mechanism(s) that confers Zn efficiency, this study used 65Zn to investigate ionic Zn2+ root uptake, binding, and translocation to shoots in seedlings of bread and durum wheat cultivars. Time-dependent Zn2+ accumulation during 90 min was greater in roots of the bread wheat cultivar. Zn2+ cell wall binding was not different in the two cultivars. In each cultivar, concentration-dependent Zn2+ influx was characterized by a smooth, saturating curve, suggesting a carrier-mediated uptake system. At very low solution Zn2+ activities, Zn2+ uptake rates were higher in the bread wheat cultivar. As a result, the Michaelis constant for Zn2+ uptake was lower in the bread wheat cultivar (2.3 &mgr;M) than in the durum wheat cultivar (3.9 &mgr;M). Low temperature decreased the rate of Zn2+ influx, suggesting that metabolism plays a role in Zn2+ uptake. Ca inhibited Zn2+ uptake equally in both cultivars. Translocation of Zn to shoots was greater in the bread wheat cultivar, reflecting the higher root uptake rates. The study suggests that lower root Zn2+ uptake rates may contribute to reduced Zn efficiency in durum wheat varieties under Zn-limiting conditions.