Comparative response of nanometric forms of Zn and Fe to promote crop biofortification

Micronutrient deficiency or malnutrition, particularly iron (Fe) and zinc (Zn), is a serious global health problem and represents a challenge for the agri-food sector. Crop biofortification has emerged as a strategy to increase the mineral content of the target organs. To improve and maximize biofortification, alternatives, such as nanotechnology (mainly nanoparticles), have been proposed and studied. The objective of this minireview was to highlight the responses of nanometric forms of Zn and Fe used in crop biofortification, which can guide the design and/or selection of the most appropriate form to efficiently promote the bioaccumulation of these nutrients. Studies have shown that Fe and Zn applied as nanoparticles (NPs), in different shapes (including spherical, irregular and wurtzite crystals), sizes and doses significantly influence their absorption, translocation rates and ion bioavailability in plants. Spherical NPs are the most common Fe (1-100 nm) and Zn (12-81 nm) nanoforms used. The supplementation routes include foliar application, drench and seed priming, with responses depending on the dose applied, which ranged from 20-500 mg L-1 for Fe NPs and 10-1000 mg L−1 for Zn NPs. Biofortification with Zn NPs increased the Zn content up to 230 % in wheat grains and 56.61 % in melon fruits. Similarly, Fe contents in cucumber fruits and rice grains increased by 71.37 % and 155.91 %, respectively, when Fe NPs were applied. Different forms of Fe and Zn NPs offer promising strategies to enhance the synthesis and accumulation of bioactive compounds as well as the accumulation of Fe and Zn in plants. However, their use in a wider range of crops requires further study.