Using zinc (Zn) foliar fertilizers to enhance the grain quality of wheat (Triticum aestivum) can be an effective alternative or supplement to Zn soil fertilizers. However, knowledge about the mechanisms of Zn absorption and translocation following foliar application is scarce. Here, autoradiography and γ-spectrometry were used to investigate the behavior of 65Zn applied to wheat leaves as soluble 65Zn chloride (65ZnCl2), chelated 65Zn (65ZnEDTA), 65Zn oxide nanoparticle (65ZnO-NP) suspensions, and 65ZnO microparticle (65ZnO-MP) suspensions. The largest amount of 65Zn absorption occurred in 65ZnCl2 treated leaves. However, this treatment (65ZnCl2) also had the lowest proportion of absorbed 65Zn translocated away from the treated leaf after 15 d due to leaf scorching (p = 0.0007). Foliar-applied 65ZnO-NPs and 65ZnO-MPs had the lowest absorption, but 65ZnO-NPs had the highest relative translocation. 65Zinc EDTA was intermediate, with higher 65Zn absorption than 65ZnO treatments but similar translocation. Regardless, the majority of the foliar-applied 65Zn remained in the treated leaf for all treatments. Furthermore, 65ZnO-NPs and 65ZnO-MPs accumulated in plant nodes, suggesting that Zn was absorbed as dissolved 65Zn and particulate 65ZnO. Overall, the form and amount of absorbed 65Zn affected translocation.
Keywords: ZnO; foliar fertilizer; nanoparticles; radiotracers; wheat; zinc.