Iodine biofortification of vegetable plants—An innovative method for iodine supplementation

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

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.

Curly Kale (Brassica oleracea var. Sabellica L.) Biofortified with 5,7-Diiodo-8-quinolinol: The Influence of Heat Treatment on Iodine Level, Macronutrient Composition and Antioxidant Content

Many disorders are a result of an inadequate supply of macronutrients and micronutrients in the diet. One such element is iodine. This study used curly kale (Brassica oleracea var. Sabellica L.) biofortified with the 5,7-diiodo-8-quinolinol iodine compound. The effect of the heat treatment on the chemical composition of the curly kale was studied. In addition, iodine bioavailability was evaluated in in vivo studies. Our investigation showed that iodine loss depends on the type of heat treatment as well as on the variety of kale. Curly kale biofortified with iodoquinoline had significantly higher iodine levels after thermal processing (steaming, blanching, boiling) than the vegetable biofortified with KIO3. Generally, steaming was the best thermal processing method, as it contributed to the lowest iodine loss in curly kale. The red variety of kale, 'Redbor F1', showed a better iodine stability during the heat treatment than the green variety, 'Oldenbor F1'. The thermal treatment also significantly affected the dry matter content and the basic chemical composition of the tested varieties of the 5,7-diI-8-Q biofortified kale. The steaming process caused a significant increase in total carbohydrates, fiber, protein and crude fat content ('Oldenbor F1', 'Redbor F1'), and antioxidant activity ('Oldenbor F1'). On the other hand, boiling caused a significant decrease, while steaming caused a significant increase, in protein and dry matter content ('Oldenbor F1', 'Redbor F1'). The blanching process caused the smallest significant decrease in ash compared to the other thermal processes used ('Oldenbor F1'). A feeding experiment using Wistar rats showed that iodine from the 5,7-diI-8-Q biofortified kale has a higher bioavailability than that from the AIN-93G diet. A number of promising results have been obtained, which could form the basis for further research.

A review of iodine in plants with biofortification: Uptake, accumulation, transportation, function, and toxicity

Iodine deficiency can cause thyroid disease, a serious health problem that has been affecting humans since several years. The biofortification of plants with iodine is an effective strategy for regulating iodine content in humans. In addition, radioiodine released into the atmosphere may contaminate terrestrial ecosystem along with dry or wet deposition and its accumulation in plants may cause exposure risks to humans via food chain. Recent progress in understanding the mechanisms related to iodine uptake, elementary speciation, dynamic transportation, nutritional role, and toxicity in plants is reviewed here. First, we introduced the iodine cycle in a marine-atmosphere-land system. The content and speciation of iodine in plants under natural conditions and biofortification backgrounds were also analyzed. We then discussed the mechanisms of iodine uptake and efflux by plants. The promotion or inhibition effects of iodine on plant growth were also investigated. Finally, the participation of radioiodine in plant growth and its safety risks along the food chain were evaluated. Furthermore, future challenges and opportunities for understanding the participation of iodine in plants have been outlined.

Role of different organic and inorganic amendments in the biofortification of iodine in Coriandrum sativum crop

Iodine deficiency disorder (IDDs) is one of the most prevailing and common health issues in mountainous communities. An effective way to control the prevalence and emergence of IDDs in remote areas is to use iodized salt. However, recent studies indicated that iodized salt is mostly lost during the cooking process. The current study of iodine biofortification differed from the previous studies in two main aspects: it involved exogenous organic iodine (OI), and inorganic iodine such as potassium iodide (KI), added in the amended soils, which previous studies did not consider. Moreover, the translocation, transformation, and distribution of iodine from soil to plants are poorly understood in amended soil. Thus, identifying an effective management option to enhance iodine (I) bioavailability in nutrient-deficient soils is currently a significant challenge. Therefore, a greenhouse study was conducted to investigate the effects of organic and inorganic soil amendments on the uptake of different iodine sources in coriander crops. Results showed that applying an inorganic iodine source significantly enhanced the iodine edible part of the crop compared to the control (p < 0.05). The application of soil amendments relatively improved iodine uptake by the coriander crop compared to the control. The highest iodine was found in crop tissues grown in wood ash-amended soil supplemented with KI (291.97 μg kg−1). The KI uptake was significantly higher than the OI (p < 0.05). Compared to OI, a higher translocation factor (0.96) and distribution coefficient (3.51) were found for plants treated with KI. Thus, this study indicates that a suitable soil amendment can be a better option for iodine biofortification and that it can serve as an alternative to iodized salt in preventing IDDs.

Iodine supplementation through its biofortification in Brassica species depending on the type of soil

Iodine is an essential microelement for humans and its deficiency leads to iodine deficiency disorder (IDD) which is a common problem faced by people in hilly areas. Biofortification of iodine is an option to overcome the IDD problem. Herein, we investigated the iodine uptake and accumulation in the edible portion of vegetables such as Brassica napus (BNP) and Brassica pekinensis (BPK) which were grown on two different soils such as sandy soil (SS) and silty loam soil (SLS) with different concentrations of iodine application (used in sodium iodide form) such as 0 ppm, 50 ppm, and 100 ppm. The concentration of iodine was determined by the oxidation of iodide, and nutrients were examined by double acid digestion. Different concentrations of iodine were noticed in silty loam and sandy soils, roots, and shoots of BNP and BPK, while the concentration follows the order: soils > roots > shoots. Iodine concentrations in the roots of BNP and BPK ranged from 46 to 223.7 μg/g which shows a strong correlation with other soil nutrients. Moreover, a large amount of iodine was lost due to the leaching. It is concluded that the biofortification of iodine increases its concentration in Brassica species. This work provides a reference for the iodine biofortification in plant species which will be helpful to control IDD.

Iodine Biofortification and Seaweed Extract-Based Biostimulant Supply Interactively Drive the Yield, Quality, and Functional Traits in Strawberry Fruits

The horticultural sector is seeking innovative and sustainable agronomic practices which could lead to enhanced yield and product quality. Currently, plant biofortification is recognized as a valuable technique to improve microelement concentrations in plant tissues. Among trace elements, iodine (I) is an essential microelement for human nutrition. Concomitantly, the application of biostimulants may improve overall plant production and quality traits. With the above background in mind, an experiment was designed with the aim of assessing the interactive impact of a seaweed extract-based biostimulant (SwE) (0 mL L^-1 (served as control) or 3 mL L^-1 (optimal dosage)) and 0, 100, 300, or 600 mg L^-1 I on the growth parameters, yield, fruit quality, minerals, and functional characteristics of the tunnel-grown "Savana" strawberry. SwE foliar application improved the plant growth-related traits, total and marketable yield, fruit color parameters, soluble solids content, nitrogen (N), potassium (K), and magnesium (Mg) fruit concentrations. Furthermore, an enhancement in the fruit dry matter content, ascorbic acid, and I concentration in fruits was detected when the SwE supply interacted with a mild I dose (100 or 300 mg L^-1). The research underlined that combining SwE application and I biofortification increased the strawberry yield and quality and enhanced the plant nutritional status variation, thereby, determining a boosted strawberry I tolerance.

Current Strategies for Selenium and Iodine Biofortification in Crop Plants

Selenium and iodine are essential trace elements for both humans and animals. Among other things, they have an essential role in thyroid function and the production of important hormones by the thyroid gland. Unfortunately, in many areas, soils are deficient in selenium and iodine, and their amount is insufficient to produce crops with adequate contents to cover the recommended daily intake; thus, deficiencies have an endemic character. With the introduction of iodized table salt in the food industry, the thyroid status of the population has improved, but several areas remain iodine deficient. Furthermore, due to the strong relationship between iodine and selenium in metabolic processes, selenium deficiency often compromises the desired positive impact of salt iodization efforts. Therefore, a considerable number of studies have looked for alternative methods for the simultaneous supplementation of selenium and iodine in foodstuff. In most cases, the subject of these studies is crops; recently, meat has also been a subject of interest. This paper reviews the most recent strategies in agriculture to fortify selenium and iodine in crop plants, their effect on the quality of the plant species used, and the potential impact of food processing on their stability in fortified crops.

Imaging of I, Re and Tc plant uptake on the single-cell scale using SIMS and rL-SNMS

In radioecological studies, there is a significant need for understanding the plant uptake of radionuclides on a cellular level. The present work applies mass spectrometry to image the radionuclide distribution within the cellular structures of plants at varying concentrations. In a first step, plants of Daucus carota and Pisum sativum labelled with iodine and rhenium were examined, at concentrations in the range of 10 mM. Cross sections of several plant parts were imaged by secondary ion mass spectrometry (SIMS) after cryogenation in order to preserve cell structure. In a second step, the distribution of ⁹⁹Tc in the two plant species was determined. For radiological reasons, a concentration three orders of magnitude lower was used, rendering measurements with SIMS impossible. Therefore, resonant laser secondary neutral mass spectrometry (rL-SNMS) was used for the first time to image ⁹⁹Tc with suppression of molecular isobaric interferences. The measurement of only about 10¹⁰ atoms of ⁹⁹Tc atoms is demonstrated and the distribution of ⁹⁹Tc within a single epidermal cell is imaged.

Records of iodine isotopes (129I, 127I) in the Barkol peat bog from northwest China and their sources, transport and preservation

The research on geochemical behaviors of iodine is significant for deep understanding of the source and distribution of iodine on the earth. However, as one of the most important sources, the ocean emissions and relative transport pathways of iodine, as well as the preservation after deposition are still not well known, especially in the arid areas of central Asia. A peat sediment core collected nearby Barkol Lake from northwest China was analyzed for iodine isotopes (¹²⁷I and ¹²⁹I). The observed high ¹²⁷I concentration in the top 2 cm indicated a significant accumulation of iodine in the surface oxic conditions due to the continuous sources of incompletely decomposed organic matter. Dissociation of iodine into pore waters occurred once the anoxic conditions established beneath the surface by a serial reduction reaction during the degradation of organic matter. The temporal variation of anthropogenic ¹²⁹I in the peat sediment recorded its sources and transport pathways. Besides the global fallout ¹²⁹I during late 1950s and early 1960s, the significantly increased air releases from the European nuclear fuel reprocessing plants during 1975-1997 and the increased marine discharges since 1990s contributed the major portion of ¹²⁹I in the peat core. The major transport pathway of ¹²⁹I from the Europe was through Westerlies following the re-emission of the marine discharged ¹²⁹I to the atmosphere, indicating a clearly ocean emitted iodine in the concerned central Asia.

Evidences for a Nutritional Role of Iodine in Plants

Little is known about the role of iodine in plant physiology. We evaluated the impact of low concentrations of iodine on the phenotype, transcriptome and proteome of Arabidopsis thaliana. Our experiments showed that removal of iodine from the nutrition solution compromises plant growth, and restoring it in micromolar concentrations is beneficial for biomass accumulation and leads to early flowering. In addition, iodine treatments specifically regulate the expression of several genes, mostly involved in the plant defence response, suggesting that iodine may protect against both biotic and abiotic stress. Finally, we demonstrated iodine organification in proteins. Our bioinformatic analysis of proteomic data revealed that iodinated proteins identified in the shoots are mainly associated with the chloroplast and are functionally involved in photosynthetic processes, whereas those in the roots mostly belong and/or are related to the action of various peroxidases. These results suggest the functional involvement of iodine in plant nutrition.

Agronomic iodine biofortification of leafy vegetables grown in Vertisols, Oxisols and Alfisols

Iodine deficiency disorders (IDD) in sub-Saharan African countries are related to low dietary I intake and generally combatted through salt iodisation. Agronomic biofortification of food crops may be an alternative approach. This study assessed the effectiveness of I biofortification of green vegetables (Brassica napus L and Amaranthus retroflexus L.) grown in tropical soils with contrasting chemistry and fertility. Application rates of 0, 5 and 10 kg ha^-1 I applied to foliage or soil were assessed. Leaves were harvested fortnightly for ~ 2 months after I application before a second crop was grown to assess the availability of residual soil I. A separate experiment was used to investigate storage of I within the plants. Iodine concentration and uptake in sequential harvests showed a sharp drop within 28 days of I application in all soil types for all I application levels and methods. This rapid decline likely reflects I fixation in the soil. Iodine biofortification increased I uptake and concentration in the vegetables to a level useful for increasing dietary I intake and could be a feasible way to reduce IDD in tropical regions. However, biofortification of green vegetables which are subject to multiple harvests requires repeated I applications.

Agronomic iodine biofortification of leafy vegetables grown in Vertisols, Oxisols and Alfisols

Iodine deficiency disorders (IDD) in sub-Saharan African countries are related to low dietary I intake and generally combatted through salt iodisation. Agronomic biofortification of food crops may be an alternative approach. This study assessed the effectiveness of I biofortification of green vegetables (Brassica napus L and Amaranthus retroflexus L.) grown in tropical soils with contrasting chemistry and fertility. Application rates of 0, 5 and 10 kg ha^-1 I applied to foliage or soil were assessed. Leaves were harvested fortnightly for ~ 2 months after I application before a second crop was grown to assess the availability of residual soil I. A separate experiment was used to investigate storage of I within the plants. Iodine concentration and uptake in sequential harvests showed a sharp drop within 28 days of I application in all soil types for all I application levels and methods. This rapid decline likely reflects I fixation in the soil. Iodine biofortification increased I uptake and concentration in the vegetables to a level useful for increasing dietary I intake and could be a feasible way to reduce IDD in tropical regions. However, biofortification of green vegetables which are subject to multiple harvests requires repeated I applications.

Joint Selenium-Iodine Supply and Arbuscular Mycorrhizal Fungi Inoculation Affect Yield and Quality of Chickpea Seeds and Residual Biomass

The essentiality of selenium (Se) and iodine (I) for the human organism and the relationship between these two trace elements in mammal metabolism highlight the importance of the joint Se–I biofortification to vegetable crops in the frame of sustainable farming management. A research study was carried out in southern Italy to determine the effects of the combined inoculation with arbuscular mycorrhizal fungi (AMF) and biofortification with Se and I on plant growth, seed yield, quality, and antioxidant and elemental status, as well as residual biomass chemical composition of chickpea grown in two different planting times (14 January and 28 February). The AMF application improved the intensity of I and Se accumulation both in single and joint supply of these elements, resulting in higher seed yield and number as well as dry weight, and was also beneficial for increasing the content of antioxidants, protein, and macro- and microelements. Earlier planting time resulted in higher values of seed yield, as well as Se, I, N, P, Ca, protein, and antioxidant levels. Se and I showed a synergistic effect, stimulating the accumulation of each other in chickpea seeds. The AMF inoculation elicited a higher protein and cellulose synthesis, as well as glucose production in the residual biomass, compared to the single iodine application and the untreated control. From the present research, it can be inferred that the plant biostimulation through the soil inoculation with AMF and the biofortification with Se and I, applied singly or jointly, proved to be effective sustainable farming tools for improving the chickpea seed yield and/or quality, as well as the residual biomass chemical composition for energy production or beneficial metabolite extraction.

Iodine Biofortification of Four Brassica Genotypes is Effective Already at Low Rates of Potassium Iodate

The use of iodine-biofortified vegetables may be a health alternative instead of iodine-biofortified salt for preventing iodine (I) deficiency and related human disorders. In this study, four Brassica genotypes (broccoli raab, curly kale, mizuna, red mustard) were hydroponically grown with three I-IO₃⁻ rates (0, 0.75 and 1.5 mg/L) to produce iodine-biofortified vegetables. Crop performances and quality traits were analyzed; iodine content was measured on raw, boiled, and steamed vegetables. The highest I rate generally increased I content in all Brassica genotypes, without plants toxicity effects in terms of reduced growth or morphological symptoms. After 21 day-iodine biofortification, the highest I content (49.5 µg/100 g Fresh Weight (FW)) was reached in broccoli raab shoots, while after 43 day-iodine biofortification, genotype differences were flattened and the highest I content (66 µg/100 g FW, on average) was obtained using 1.5 mg I-IO₃/L. Nitrate content (ranging from 1800 to 4575 mg/kg FW) was generally higher with 0.75 mg I-IO₃/L, although it depended on genotypes. Generally, boiling reduced iodine content, while steaming increased or left it unchanged, depending on genotypes. Applying low levels of I proved to be suitable, since it could contribute to the partial intake of the recommended dose of 150 µg/day: A serving size of 100 g may supply on average 24% of the recommended dose. Cooking method should be chosen in order to preserve and/or enhance the final I amount.

The bioaccessibility of iodine in the biofortified vegetables throughout cooking and simulated digestion

Biofortification of crops with exogenous iodine is a novel strategy to control iodine deficiency disorders (IDD). The bioaccessibility of iodine (BI) in the biofortified vegetables in the course of soaking, cooking and digestion, were examined. Under hydroponics, the concentration of iodine in leafstalks of the celery and pakchoi increased with increasing exogenous iodine concentration, 54.8-63.9% of the iodine absorbed by pakchoi was stored in the soluble cellular substance. Being soaked in water within 8 h, the iodine loss rate of the biofortified celery was 3.5-10.4% only. More than 80% of the iodine in the biofortified celery was retained after cooking under high temperature. The highest BI of the biofortified vegetables after digestion in simulated gastric and intestinal juice amounted to 74.08 and 68.28%, respectively. Factors influencing BI included pH, digestion duration, and liquid-to-solid ratio. The high BI of the biofortified vegetables provided a sound reference for the promotion of iodine biofortification as a tool to eliminate the IDD.

The Iodine Content in Urine, Faeces and Selected Organs of Rats Fed Lettuce Biofortified with Iodine Through Foliar Application

Iodine is an essential trace element for humans. Foliar application of micronutrients is successfully used in order to increase the concentration of essential elements in vegetables. The aim of this study was to evaluate the iodine absorption in the rat organism fed foliar biofortified lettuce. The presented study was consisted of the vegetative and animal experiment. In the vegetative experiment with lettuce, two combinations of foliar application were used: (1) control-without iodine application and (2) iodine application in the potassium iodide (KI) form. In the animal experiment, Wistar rats were divided to four groups, which received one of four diets: (1) C-control diet containing iodine in the KI form, (2) D-diet deficient in iodine, (3) D + BL-diet containing biofortified lettuce, and (4) D + CL-diet containing control lettuce (as the only source of iodine in diet, respectively). The diets contained 0.260, 0.060, 0.254 and 0.075 mg I/kg, respectively. In order to determine the iodine absorption in the rat organisms, the content of this trace element was measured in urine, faeces and in selected organs with the use of the ICP-OES technique. Foliar application of the KI increased the content of iodine in lettuce. The rats from the D + BL group excreted significantly less iodine in their urine and faeces and also accumulated more iodine in the organs than the rats from the C group. Iodine with biofortified lettuce was much bioavailable for rodents than iodine from control diet. Biofortified lettuce can be a source of iodine in a diet of human and can improve iodine nutrition.

Silicon biofortification of leafy vegetables and its bioaccessibility in the edible parts

BACKGROUND

The mineral silicon (Si) is an essential element for humans and a general component of the diet found mainly in plant-based foods. The aim of this study was to obtain Si biofortificated leafy vegetables (tatsoi, mizuna, purslane, basil, Swiss chard, and chicory) to use for the fresh-cut products (ready to use). For the production of biofortified plants, a floating system with 0, 50 and 100 mg L(-1) of Si in nutrient solution, was used. In addition, the assessment of bioaccessibility of biofortified plants, by in vitro gastro-digestion process, was performed.

RESULTS

The added silicon in nutrient solution did not influence yield and colour of vegetables but a species-related accumulation of Si (expressed as SiO2) was found: from 18 to 69 mg kg(-1) fresh weight (FW) in tatsoi, from 19 to 106 mg kg(-1) FW in mizuna, from 15 to 93 mg kg(-1) FW in purslane, from 41 to 294 mg kg(-1) FW in basil, from 17 to 76 mg kg(-1) FW in Swiss chard, and from 23 to 76 mg kg(-1) FW in chicory. The Si became bioaccessible in all species considered in a range from 23% (basil) to 64% (chicory).

CONCLUSION

The application of Si to the nutrient solution in the range of 50-100 mg L(-1) allows biofortification of leafy vegetables. In addition, the biofortified vegetables showed, on average, more bioaccessible Si, with respect to unbiofortified vegetables.

Use of Iodine to Biofortify and Promote Growth and Stress Tolerance in Crops

Iodine is not considered essential for land plants; however, in some aquatic plants, iodine plays a critical role in antioxidant metabolism. In humans, iodine is essential for the metabolism of the thyroid and for the development of cognitive abilities, and it is associated with lower risks of developing certain types of cancer. Therefore, great efforts are made to ensure the proper intake of iodine to the population, for example, the iodization of table salt. In the same way, as an alternative, the use of different iodine fertilization techniques to biofortify crops is considered an adequate iodine supply method. Hence, biofortification with iodine is an active area of research, with highly relevant results. The agricultural application of iodine to enhance growth, environmental adaptation, and stress tolerance in plants has not been well explored, although it may lead to the increased use of this element in agricultural practice and thus contribute to the biofortification of crops. This review systematically presents the results published on the application of iodine in agriculture, considering different environmental conditions and farming systems in various species and varying concentrations of the element, its chemical forms, and its application method. Some studies report beneficial effects of iodine, including better growth, and changes in the tolerance to stress and antioxidant capacity, while other studies report that the applications of iodine cause no response or even have adverse effects. We suggested different assumptions that attempt to explain these conflicting results, considering the possible interaction of iodine with other trace elements, as well as the different physicochemical and biogeochemical conditions that give rise to the distinct availability and the volatilization of the element.

Factors influencing real time internal structural visualization and dynamic process monitoring in plants using synchrotron-based phase contrast X-ray imaging

Minimally invasive investigation of plant parts (root, stem, leaves, and flower) has good potential to elucidate the dynamics of plant growth, morphology, physiology, and root-rhizosphere interactions. Laboratory based absorption X-ray imaging and computed tomography (CT) systems are extensively used for in situ feasibility studies of plants grown in natural and artificial soil. These techniques have challenges such as low contrast between soil pore space and roots, long X-ray imaging time, and low spatial resolution. In this study, the use of synchrotron (SR) based phase contrast X-ray imaging (PCI) has been demonstrated as a minimally invasive technique for imaging plants. Above ground plant parts and roots of 10 day old canola and wheat seedlings grown in sandy clay loam soil were successfully scanned and reconstructed. Results confirmed that SR-PCI can deliver good quality images to study dynamic and real time processes such as cavitation and water-refilling in plants. The advantages of SR-PCI, effect of X-ray energy, and effective pixel size to study plant samples have been demonstrated. The use of contrast agents to monitor physiological processes in plants was also investigated and discussed.