New Insights to Zinc Biofortification of Wheat: Opportunities to Fine-tune Zinc Uptake, Remobilization and Grain Loading

Abstract

Wheat contains low grain zinc (Zn) due to its genetics and the physiochemical properties of the soil in which it is grown. Consequently, where wheat forms a major part of the human diet, bioavailable Zn is below dietary requirements. Understanding the regulation of genes responsible for cellular Zn-transport, particularly those responsible for the control of the biosynthesis pathway of nicotianamine, provides an opportunity to increase Zn loading into the grain. Decreasing the levels of phytic acid, an inhibitor of Zn absorption in humans, provides another opportunity to increase the bioavailability of grain Zn. Synchrotron X-ray fluorescence microscopy clearly demonstrated that the crease region of the wheat grain is a major bottleneck to Zn loading in the endosperm. Higher expression of Zn transporter families, particularly metal tolerance proteins and yellow stripe like transporter families in the aleurone layer are also likely to play a major role in determining grain Zn content. Finally, anatomical barriers in the vascular region at the base of the wheat grain are a major limitation to Zn loading. Modification of any of these traits through traditional plant breeding or gene editing provides an opportunity to increase the Zn concentration in wheat grain.

Formulation of zinc foliar sprays for wheat grain biofortification: a review of current applications and future perspectives

“…This is a particular challenge since studies should be conducted in vivo , to replicate the internal conditions of leaf, vascular tissue, and connecting tissue responsible for delivering nutrients to grain. Physiological studies should investigate the benefits of applying Zn-foliar nanoformulations in regard to overcoming the so-called ‘push-pull’ bottleneck processes identified in the wheat plant such as leaf and nodal accumulation ( Stanton et al., 2022 ); and Zn retranslocation and loading to edible parts of the grain - the endosperm ( Kamaral et al., 2020 ). For this reason, it is recommended that state-of-the-art technology in microscopy and combining more sophisticated approaches such as Zn isotope tracing and synchrotron-based technologies can be used to determine the localization and movement of nanoparticles and nanomaterials in crops ( Kopittke et al., 2018 ).…”