Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/11/1998
Publication Date: N/A
Citation: Interpretive Summary: There are many soils in the northern Great Plains region of the U.S., where much of the nation's wheat is grown, that are low in available zinc (Zn). Considerable evidence has been accumulating in the literature indicating that marginal Zn deficiency reduces crop yield and quality in many different regions throughout the U.S. and the world. There is considerable genetic variability in the ability of different crops to grow on low Zn soils. For example, bread wheats are considerably more zinc efficient than Durum wheats, exhibiting significantly greater productivity on low Zn soils. This study attempted to identify possible mechanisms of zinc efficiency in bread wheat, and focused on characterizing and comparing rates of Zn uptake in bread versus Durum wheats as a potential mechanism of Zn efficiency. The results of the study showed that rates of Zn uptake into roots were similar in bread and Durum wheat. Additionally, there were no significant differences in Zn binding to root cell walls, and in rates of Zn translocation to the shoot in bread and durum wheat. The results indicate that root Zn absorption and translocation from the root to the shoot are not mechanisms of the observed Zn efficiency in bread wheat, and suggest that Zn efficiency involves either differences in partitioning within the shoot, or improved utilization of Zn within the plant.
Technical Abstract: Durum wheat cultivars have been shown to exhibit lower Zn efficiency than comparable bread wheat cultivars. The physiological mechanism(s) conferring Zn efficiency have not been identified, but could include such processes as root uptake rates, translocation rates & chelation or compartmentation within a cellular component. This study examined 65Zn uptake, binding & translocation in seedlings of bread & durum wheat cultivars. Time-dependen Zn2+ accumulation in roots was linear in both cultivars. Desorption with 0.2 mM CaSO4 & 100 mM ZnSO4 was very effective in removing Zn2+ from the cell wall free space, particularly at low Zn2+ activities. Concentration dependent Zn2+ uptake in both cultivars was characterized by a smooth, saturating curve, suggesting a single protein-mediated uptake system. The bread wheat variety showed a slightly higher affinity for Zn2+ transport, while maximal uptake rates were similar in both varieties. Low temperature was very effective in decreasing the rate of Zn2+ uptake in intact seed- lings, suggesting that metabolism is important in Zn2+ uptake. A small amount of Zn2+ taken up by roots treated with 2:1 (v:v) methanol:chloroform to remove cellular contents was interpreted as undesorbed Zn2+ bound to cell wall components. Differences between durum & bread wheat cultivars in Zn2+ binding were not detected. Rates of Zn2+ uptake & translocation were higher in the bread wheat cultivar than in the durum wheat cultivar only when roots were exposed to Zn2+ activities near the Km for uptake. At low Zn2+ activity, uptake & translocation rates were similar in both varieties. The results suggest that reduced Zn efficiency in durum wheat varieties under Zn-limiting conditions is not due to lower short-term root Zn2+ uptake rates.