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

Abstract

Increasing iron (Fe) and zinc (Zn) concentrations in crop grains with high yield is an effective measure to ensure food supply and alleviate mineral malnutrition in humans. Micronutrient concentrations in grains depend on not only their availability in soils but also their uptake in roots and translocation to shoots and grains. In this three-year field study, we investigated genotypic variation in Fe and Zn uptake and translocation within six wheat cultivars and examined in detail Fe and Zn distributions in various tissues of two cultivars with similar high yield but different grain Fe and Zn concentrations using synchrotron micro-X-ray fluorescence. Results revealed that root Fe and Zn concentrations were 11 and 44% greater in high-nutrient (HN) than in low-nutrient (LN) concentration cultivar. Although both cultivars accumulated similar amounts of Fe in shoots, HN cultivar had greater accumulation of Fe in grain and greater accumulation of Zn in both shoots and grain. Grain Zn concentration was positively correlated with shoot Zn accumulation, and grain Fe concentration was positively correlated with the ability to translocate Fe from leaves/stem to grains. In the first nodes of shoots, HN cultivar had 482% greater Fe and 36% greater Zn concentrations in the enlarged vascular bundle (EVB) than LN cultivar. In top nodes, HN cultivar had 225 and 116% greater Fe and Zn concentrations in the transit vascular bundle and 77 and 71% greater in the EVB when compared to LN cultivar. HN cultivar also had a greater ability to allocate Fe and Zn to the grain than LN cultivar. In conclusion, HN cultivar had greater capacity of Fe and Zn acquirement by roots and translocation and partitioning from shoots into grains. Screening wheat cultivars for larger Fe and Zn concentrations in shoot nodes could be a novel strategy for breeding crops with greater grain Fe and Zn concentrations.

Uptake and preferential partitioning of zinc in different wheat species

“…This indicated a retarded transportation of Zn in the node of CEW. Nodes are important sites for controlling Zn distribution in graminaceous plants (Guo et al., 2022; Yamaguchi et al., 2012; Yamaji & Ma, 2014). Genes expressed in rice nodes are important for grain Zn accumulation by controlling xylem unloading, phloem loading, and distribution of Zn to the developing tissues (Mu et al., 2021; Sasaki et al., 2015; Yamaji et al., 2013).…”

“…Genes expressed in rice nodes are important for grain Zn accumulation by controlling xylem unloading, phloem loading, and distribution of Zn to the developing tissues (Mu et al., 2021; Sasaki et al., 2015; Yamaji et al., 2013). In one study, high Zn cultivars had higher Zn concentration than low Zn cultivars in the enlarged vascular bundle (EVB) of the first nodes and EVB and the transit vascular bundle (TVB) of the top nodes in wheat (Guo et al., 2022). However, no significant difference was observed for Zn concentration in nodes between high and low Zn genotypes in our study.…”