Effects of nickel on zinc uptake and translocation in two wheat cultivars differing in zinc efficiency

Low availability of zinc (Zn) in soil can limit plant growth and yields. In soils with elevated nickel (Ni) concentrations, which can be due to anthropogenic and geogenic sources, Zn uptake by plants may be inhibited due to competition between the two elements. Here we used a hydroponic system to investigate short-term effects of a wide range of Ni concentrations on Zn uptake and translocation in two spring wheat cultivars at two different levels of Zn supply. Seedlings of the Zn efficient cultivar Back Cross Rushan and the Zn inefficient cultivar Kavir were grown for three weeks in Zn and Ni free nutrient solution and then exposed for two days to either 0, 1, 2, 10, 20, or 40 μM Ni and either 400 nM or 2 μM Zn, before they were harvested. Increasing Ni had no influence on Zn uptake by Kavir at the low Zn level and even slightly enhanced it in Back Cross Rushan, which means that competition by Ni for uptake sites was irrelevant and suggests that Zn uptake was governed by a highly selective uptake system under these conditions. At the high Zn level, Ni had contrasting effects on the uptake of Zn in the two cultivars: Increasing Ni led to a strong increase in Zn uptake in Kavir as opposed to a slight decrease in Back Cross Rushan. The difference indicates that the two cultivars strongly differ in their low-affinity Zn uptake systems. Also the fraction of Zn translocated to the shoots differed between the two cultivars at high Zn supply, while they were very similar at the low Zn level. A strong decrease with increasing Ni solution concentration was observed in Kavir at the high Zn level, whereas there was little Ni dependence of root-to-shoot translocation in Back Cross Rushan. The findings suggest that differences in root Zn compartmentalization may be involved in the different Zn efficiencies of the cultivars.