Effect of iodine species on biofortification of iodine in cabbage plants cultivated in hydroponic cultures

Abstract

Iodine is an essential trace element in the human diet because it is involved in the synthesis of thyroid hormones. Iodine deficiency affects over 2.2 billion people worldwide, making it a significant challenge to find plant-based sources of iodine that meet the recommended daily intake of this trace element. In this study, cabbage plants were cultivated in a hydroponic system containing iodine at concentrations ranging from 0.01 to 1.0 mg/L in the form of potassium iodide or potassium iodate. During the experiments, plant physiological parameters, biomass production, and concentration changes of iodine and selected microelements in different plant parts were investigated. In addition, the oxidation state of the accumulated iodine in root samples was determined. Results showed that iodine addition had no effect on photosynthetic efficiency and chlorophyll content. Iodide treatment did not considerably stimulate biomass production but iodate treatment increased it at concentrations less than 0.5 mg/L. Increasing iodine concentrations in the nutrient solutions increased iodine content in all plant parts; however, the iodide treatment was 2-7 times more efficient than the iodate treatment. It was concluded, that iodide addition was more favourable on the target element accumulation, however, it should be highlighted that application of this chemical form in nutrient solution decreased the concetrations of selected micoelement concentration comparing with the control plants. It was established that iodate was reduced to iodide during its uptake in cabbage roots, which means that independently from the oxidation number of iodine (+ 5, - 1) applied in the nutrient solutions, the reduced form of target element was transported to the aerial and edible tissues.

Figure 1

Mean dry mass of roots, stems, and leaves of cabbages cultivated in nutrient solutions containing KI (A) or KIO₃ (B) species. Data are presented as mean (n = 5) with error bars representing RSD%. *Significant (p < 0.05) differences from the control (linear regression).

Figure 2

Iodine concentration in plant parts of cabbages cultivated in nutrient solutions containing KI or KIO₃ species. Data are presented as mean and error bars represent RSD%. According to the linear regressions fitted on the log-transformed data, all treatments significantly increased the iodine concentration of all plant parts compared to the controls (p < 0.03).

Figure 3

I-K edge XANES spectra of KI and KIO₃ reference materials and cabbage roots cultivated in nutrient solutions containing KI or KIO₃ species.