Improving the concentration and bioavailability of zinc (Zn) in cereal grains is an important way to solve the problem of Zn deficiency in human body. The bioavailability of Zn is related to both its distribution and speciation in grains. In the current study, we examined the differences of Zn concentration, distribution, and speciation within grains among wheat cultivars with similar high grain yield but contrasting grain Zn concentration using synchrotron micro X-ray fluorescence (μ-XRF) and X-ray absorption near-edge structure (XANES). Results showed that compared to the low-Zn cultivar, the Zn concentration was 103, 50, 76, 33, and 64% higher in the crease region, aleurone layer, scutellum, embryonic axis, and endosperm of the high-Zn cultivar, respectively. Zinc mainly colocalized with phosphorus (P) in the aleurone layer and the scutellum, but less colocalization of Zn with P and a much lower concentration ratio of P/Zn were found in the high-Zn cultivar. Sulfur (S) is present in the form of scattered spots in the endosperm in accord with Zn, but the colocalization of Zn with S was predominant in the modified aleurone layer and the nucellar projection of the high-Zn cultivar. XANES results showed the lower proportion of Zn-phytate in the high-Zn cultivar. Findings indicated that it is possible to select the high-yield wheat cultivar with both high grain Zn concentration and high bioavailability, which provide a new perspective for genetic Zn biofortification.
Keywords: Zn biofortification; bioavailability; colocalization; distribution; wheat cultivars.