Selecting High Zinc Wheat Cultivars Increases Grain Zinc Bioavailability

Abstract

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.

Synchrotron X-ray Fluorescence Technique Identifies Contribution of Node Iron and Zinc Accumulations to the Grain of Wheat

“…To determine the concentrations of Fe and Zn in each part, ground samples (0.2500 g) were mixed with HNO 3 −H 2 O 2 in a microwave digester and then analyzed using an inductively coupled plasma mass spectrometer (iCAP Qc, Thermo Fisher, USA). 9,23 Synchrotron Micro-X-ray Fluorescence Imaging. Synchrotron micro-X-ray fluorescence (micro-XRF) technique was used to in situ detect elements of samples, and it had nondestructive feature, high resolution, and low element detection line.…”

“…The fresh samples were cut into 60 μm cross sections in a freezing slicer (HM525 NX, Thermo Fisher, China) and freeze-dried for 1 day in a lyophilizer (Freezone P1, Labconco, USA) before the intact slices underwent micro-XRF analysis as described previously. 23 The micro-XRF maps of Fe and Zn in every slice were collected at beamline 2-3 of Stanford Synchrotron Radiation Lightsource (SSRL, USA). In the beamline 2-3, the energy range was 4900−23,000 eV, the spot size was 2 × 2 μm, the flux was above 1 × 10 10 , and the elemental signal intensities of samples were collected by a multipleelement silicon detector at room temperature and pressure (https:// www-ssrl.slac.stanford.edu/content/beam-lines/bl2-3).…”

“…The standard curve was then used to transform the signal intensities of samples into elemental concentrations. 23,25,26 The collected micro-XRF intensities from the spectrum of all samples and standards were calculated and then corrected by the changed beam in the detection, and the background value was deducted in the process of plotting. The two-dimensional maps were analyzed by SMAK software 27 and OriginPro using elemental concentrations transformed from the collected signal intensities.…”

“…The dry weights of all plant parts were measured. To determine the concentrations of Fe and Zn in each part, ground samples (0.2500 g) were mixed with HNO 3 –H 2 O 2 in a microwave digester and then analyzed using an inductively coupled plasma mass spectrometer (iCAP Qc, Thermo Fisher, USA). , …”

“…Roots, first nodes, internodes, top nodes, and flag leaves at anthesis and grains at maturity of each cultivar were sampled in 2019. The fresh samples were cut into 60 μm cross sections in a freezing slicer (HM525 NX, Thermo Fisher, China) and freeze-dried for 1 day in a lyophilizer (Freezone P1, Labconco, USA) before the intact slices underwent micro-XRF analysis as described previously …”