Abstract
Accumulation of iodine by potato (Solanum tuberosum L.) and carrot (Daucus carota L. var. sativus) plants cultivated on different soils (sand, sandy silt, and silt) using irrigation water containing iodine at concentrations of 0.1 and 0.5 mg/L was investigated. In the edible organs of potato and carrot control plants grown on sand, sandy silt, and silt soils, the iodine concentrations were 0.15, 0.17, and 0.20 mg/kg (potato) and 0.012, 0.012, and 0.013 mg/kg (carrot); after the treatment by applying 0.5 mg/L iodine dosage, the iodine concentrations were 0.21, 0.19, 0.27 mg/kg (potato) and 3.5, 3.7, 3.0 mg/kg (carrot), respectively. Although the iodine treatment had no significant effect on the biomass production of these plants, in potato tubers, it resulted in higher Fe and lower Mg and P concentrations, whereas no similar trend was observable in carrot roots. The accumulation of Mn, Cu, Zn, and B in the edible part of both plants was not influenced by the iodine treatment. The soil properties did not have a significant impact on biomass production under the same environmental conditions. The concentration and the distribution of iodine in both plants were slightly modified by the growing medium; however, the photosynthetic efficiency and the chlorophyll content index of potato plants cultivated in silt soil increased significantly. Potato plant was not suitable for biofortification with iodine, while considering the iodine concentration and the moisture content of carrot roots, it can be calculated that consuming 100 g fresh carrot would cover about 38% of the daily iodine intake requirement for an average adult person.
Highlights
Iodine is an essential micronutrient for human health, having a unique role in the regulation of metabolic processes such as synthesis of thyroid hormones, which are involved in the synthesis of sugars, nucleic acids, and proteins (Velasco et al, 2018)
The Fv/Fm changed in the range of 0.667–0.747, the soil type did not affect it (p > 0.089), and the iodine treatment had no significant effect on it (p > 0.36), independently from the soil type
The iodine treatment resulted in a marginally significant, positive effect on the chlorophyll content index (CCI) of potato cultivated on sand (p = 0.059) and silt soils (p = 0.065), while a moderate but non-significant reduction of CCI values was observed in the case of sandy silt soil (p > 0.50)
Summary
Iodine is an essential micronutrient for human health, having a unique role in the regulation of metabolic processes such as synthesis of thyroid hormones (triiodothyronine and thyroxine), which are involved in the synthesis of sugars, nucleic acids, and proteins (Velasco et al, 2018). On the basis of the literature data, the following statements can be summarized: (1) the major species of iodine like organic-iodine compounds, iodate (IO3−), and iodide (I−) ions in the soil and volatile iodine forms (molecular iodine and methyl iodide) in the atmosphere can be efficiently taken up by the roots and leaves (dominant); (2) due to the relatively large leaf surface in leafy vegetables (spinach, lettuce, cabbage, Chinese cabbage), iodine can be taken up more rapidly and effectively from the atmosphere; (3) iodine moves mainly by xylematic routes; the iodine concentration of a plant decreases from the root to the fruit, i.e., iodine is stored better in vegetative plant tissues than in fruits; the phloematic way has been reported for some plants, e.g., tomato, lettuce; (4) as compared to iodate, accumulation of iodide by the roots and translocation to the different upper parts (e.g., stem, leaf, fruit) are more efficient; and (5) over a certain iodine concentration (e.g., 1 mg/L in hydroponic solution or 25 mg/kg using fertilizer), toxic effect in plants can be observed, resulting in reduced biomass production
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