Potential of microbes in the biofortification of Zn and Fe in dietary food grains. A review

Abstract

Micronutrients are essential factors for human health and integral for plant growth and development. Among the micronutrients, zinc (Zn) and iron (Fe) deficiency in dietary food are associated with malnutrition symptoms (hidden hunger), which can be overcome through biofortification. Different strategies, such as traditional and molecular plant breeding or application of chemical supplements along with fertilizers, have been employed to develop biofortified crop varieties with enhanced bioavailability of micronutrients. The use of microorganisms to help the crop plant in more efficient and effective uptake and translocation of Zn and Fe is a promising option that needs to be effectively integrated into agronomic or breeding approaches. However, this is less documented and forms the subject of our review. The major findings related to the mobilization of micronutrients by microorganisms highlighted the significance of (1) acidification of rhizospheric soil and (2) stimulation of secretion of phenolics. Plantmicrobe interaction studies illustrated novel inferences related to the (3) modifications in the root morphology and architecture, (4) reduction of phytic acid in food grains, and (5) upregulation of Zn/Fe transporters. For the biofortification of Zn and Fe, formulation(s) of such microbes (bacteria or fungi) can be explored as seed priming or soil dressing options. Using the modern tools of transcriptomics, metaproteomics, and genomics, the genes/proteins involved in their translocation within the plants of major crops can be identified and engineered for improving the efficacy of plant-microbe interactions. With micronutrient nutrition being of global concern, it is imperative that the synergies of scientists, policy makers, and educationists focus toward developing multipronged approaches that are environmentally sustainable, and integrating such microbial options into the mainframe of integrated farming practices in agriculture. This can lead to better quality and yields of produce, and innovative approaches in food processing can deliver cost-effective nutritious food for the undernourished populations.

Elucidating the source–sink relationships of zinc biofortification in wheat grains: A review

“…Binding of Cd 2+ , Pb 2+ , Ni 2+ , and Hg 2+ ions to thiol groups of proteins causes protein inactivation and denaturation of various enzymes, and thus has detrimental effects on plant growth and also Zn accumulation, particularly in soils contaminated with such heavy metals (Gupta et al., 2016). Regarding Zn‐Fe interactions, both metal ions have common transporter proteins required for their absorption by roots and transport to shoots (Gupta et al., 2016; Singh & Prasanna, 2020; Xue, Xia, et al, 2016). The concentrations of Zn and Fe in wheat grains were simultaneously increased by foliar Fe fertilization (Rakshit et al, 2016).…”

Green Synthesis of Zinc Oxide Nanoparticles: Fortification for Rice Grain Yield and Nutrients Uptake Enhancement

“…Moreover, in rice grains, genotype variation of the Zn element content is well established, because these grains are mostly categorized as a very poor source of Zn content. Otherwise, ZnSO 4 , with the appropriate dose, is a broadly traditional soil application that functions to intensify the amount of Zn in tissues and maximize both the growth and yields [ 10 , 11 ]. Preventing the problem of Zn binding [ 12 ] leads to the increased probability of obtaining nutrients, notably when a cultivable soil condition restricts root uptake [ 13 ].…”

Bacterial Endophytes of Spring Wheat Grains and the Potential to Acquire Fe, Cu, and Zn under Their Low Soil Bioavailability

“…[ 57 ]. The mechanisms promoting micronutrition that were specified by [ 58 ] include (1) organic acid secretion and proton extrusion; (2) indirect upregulation of Zn and Fe transporters; (3) secretion of phytohormone-like molecules, such as auxins (IAA), cytokinins, abscisic acid, brassinosteroids, ethylene, gibberellins, jasmonates, and strigolactones, as well as some specific amino acids [ 39 , 40 , 41 , 42 , 43 , 44 , 59 ]. As reported by White et al [ 60 ], the inoculation of plant roots with endophytes produces wheat endophytic biota, microbial siderophores, and other mechanisms that sequester micronutrients efficiently; furthermore, metals adhere to microbial cell walls inside the plant root.…”

“…However, the knowledge of the role of particular genera of endophytic bacteria in the microelement acquisition by wheat in field conditions is insufficient [ 51 , 53 , 58 , 61 ]. Data regarding endophytes inhabiting spring wheat grains are equally scarce.…”