Iodine Fortification Plant Screening Process and Accumulation inTomato Fruits and Potato Tubers

Iodine is an essential microelement for human health, and Recommended Daily Allowance (RDA) of such element should range from 40 to 200 µg day-1. Because of the low iodine contents in vegetables, cereals, and many other foods, Iodine Deficiency Disorder (IDD) is one of the most widespread nutrient deficiency diseases in the world. Therefore, investigations of iodine uptake in plants with the aim of their fortification can help reaching the important health and social objective of IDD elimination. This study was conducted to determine the effects of the absorption of iodine from two different chemical forms - potassium iodide (I-) vs. potassium iodate (IO-3) - in a wide range of wild and cultivated plant species. Pot plants were irrigated with different concentrations of I- or IO-3, namely 0.05% and 0.1% (w/v) I-, and 0.05%, 0.1%, 0.2% and 0.5% (w/v) IO-3. Inhibiting effects on plant growth were observed after adding these amounts of iodine to the irrigation water. Plants wereable to tolerate better the higher levels of iodine as IO-3 rather than I- in the root environment. Among cultivated species, barley (Hordeum vulgare L.) showed the lowest, and maize (Zea mays L.) together with tobacco (Nicotiana tabacum L.) the highest biomass reductions due to iodine toxicity. After the screening, cultivated tomato and potato resulted good targets for a fortification rate study among the species screened. When fed with 0.05% iodine salts, potato (Solanum tuberosum L.) tubers and tomato (Solanum lycopersicum L.) fruits absorbed iodine up to 272 and 527 µg/100 g FW from IO-3, and 1,875 and 3,900 µg/100 g FW from I-. These uptake levels were well above the RDA of 150µg day-1 for adults. Moreover, the agronomic efficiency of iodine accumulation of potato tubers and tomato fruits was calculated. Both plant organs showed greater accumulation efficiency for given unit of iodine from iodide than from iodate. This accumulation efficiency decreased in both potato tubers and tomato fruits at iodine concentrations higher than 0.05% for iodide, and at respectively 0.2% and 0.1% for iodate. On the basis of the uptake curve it was finally possible to calculate, although to be validated, the doses of supply in the irrigation water of iodine as iodate (0.028% for potato, and0.014% for tomato) as well as of iodide (0.004% for potato, and 0.002% for tomato), to reach the 150 µg day-1 RDA for adults in 100 g of such vegetables, to efficiently control IDD.