Biofortification of Sweetcorn with Iodine: Interaction of Organic and Inorganic Forms of Iodine Combined with Vanadium

Around the world, maize cultivation is an essential part of food systems for humans and animals. Effective reactions against the occurrence of diseases related to the deficiency of elements in the human diet are related to the biofortification of plant species of broad importance, including maize. The enrichment of maize with iodine is difficult due to the poor transport of this element to the plant’s generative organs. In marine algae, vanadium is part of the structure of the enzyme iodine-dependent peroxidase (vHIPO) that catalyzes the uptake of cellular iodine (I) and its volatilization as I₂. The relationship between iodine and vanadium in higher plants, however, is not well-known. The aim of this research was to determine the effect of vanadium fertilization and the interactions of organic and inorganic iodine compounds with vanadium under soil application. In the pot experiment, NH₄VO₃ was applied to the soil in two doses of 0.1 and 1 μmol·dm⁻³ both separately and in combination, with the following iodine compounds: 5-iodosalicylic acid (5-ISA), 2-iodobenzoic acid (2-IBeA), potassium iodide (KI), and potassium iodate (KIO₃). The iodine compounds were also applied independently to vanadium, while in the control combination, fertilization was performed without I and V. Iodine compounds were applied with doses calculated using the molar mass of this element (i.e., 10 μmol·dm⁻³ I). The highest level of iodine accumulation in grains (regardless of fertilization with V) was obtained after the application of organic compounds 5ISA and 2IBeA. A lower dose of vanadium (0.1 μmol·dm⁻³) in combination with KI and KIO₃ increased the accumulation of iodine in leaves, roots, and grains compared to the combination without the additional application of vanadium. The combined application of vanadium in both doses with 2-IBeA most effectively stimulated the transport and accumulation of iodine to the maize grain. Under the combined application of 5-ISA and vanadium (10 μmol·dm⁻³), we observed the stimulating effect of this organic iodine compound on the accumulation of vanadium in the roots as well as the antagonistic effect of vanadium in combination with 5-ISA on the accumulation of iodine in the roots, leaves, and maize grain. Vanadium accumulated mainly in the roots, where the content of this element increased proportionally to its dose. The soil application of 5-ISA increased the total sugar content and vitamin C content in the grain.