Is grain zinc concentration in wheat limited by source?

Increasing zinc (Zn) concentration in wheat grain is important to human health. In order to clarify the source limitations of grain Zn concentration, ears of winter wheat were grown in detached ear culture under different Zn supply levels (0, 30, 60, 90 and 120 mumol l-1) and sucrose supply levels (2%, 4% and 6%). To investigate sink limitations, some ears were subjected to partial spikelet removal. The result showed that wheat grain yield did not change; however, the concentration of Zn, iron (Fe), manganese (Mn), and protein in grain was significantly (p<0.05) increased by Zn application. At 90 mu mol l-1 Zn supply, grain Zn concentration reached a maximum of 100 mg kg-1; compared to the no Zn treatment, this represented 5.5 to 9.8-fold and 5.7 to 8.4-fold increase, for superior grain and inferior grain, respectively. With the increase in sucrose supply, grain weight, as well as the content of micronutrients and protein significantly (p<0.05) increased, while the concentrations of these significantly (p<0.05) decreased. The partial spikelet removal treatment, along with increasing single grain weight, also increased grain Zn concentration and grain Zn content by 24.0 to 33.4%, 4.1 to 30.8%, and 34.7 to 75.0%, respectively. The concentration and content of Fe, Mn, and protein in wheat grain also increased. These results indicated that Zn concentration in wheat grain was mainly restricted by the source, and the concentration of Zn, Fe, and protein may be increased simultaneously in wheat grain in certain source supply ranges.