In marine algae, vanadium (V) regulates the cellular uptake of iodine (I) and its volatilization as I2, the processes catalyzed by vanadium-dependent haloperoxidases (vHPO). Relationships between I and vanadium V in higher plants, including crop plants, have not yet been described. Little is known about the possibility of the synthesis of plant-derived thyroid hormone analogs (PDTHA) in crop plants. The activity of vHPO in crop plants as well as the uptake and metabolism of iodosalicylates in lettuce have not yet been studied. This studyaimed to determine the effect of V on the uptake and accumulation of various forms of I, the metabolism of iodosalicylates and iodobenzoates and, finally, on the accumulation of T3 (triiodothyronine—as example of PDTHA) in plants. Lettuce (Lactuca sativa L. var. capitata ‘Melodion’ cv.) cultivation in a hydroponic NutrientFilm Technique (NFT) system was conducted with the introduction of 0 (control), 0.05, 0.1, 0.2, and 0.4 µM V doses of ammonium metavanadate (NH4VO3) in four independent experiments. No iodine treatment was applied in Experiment No. 1, while iodine compounds were applied at a dose of 10 µM (based on our own previous research) as KIO3, 5-iodosalicylic acid (5-ISA) and 3,5-diiodosalicylic acid (3,5-diISA) in Experiment Nos. 2, 3 and 4, respectively. When lettuce was grown at trace amount of I in the nutrient solution, increasing doses of V contributed to the increase of (a) I content in roots, (b) I uptake by whole lettuce plants (leaves + roots), and (c) vHPO activity in leaves (for doses 0.05–0.20 µM V). Vanadium was mainly found in roots where the content of this element increased proportionally to its dose. The content of V in leaves was not modified by V introduced into the nutrient solution. We found that5-ISA, 3,5-diISA and T3 were naturally synthesized in lettuce and its content increased when 5-ISA, 3,5-diISA were applied. Quantitative changes in the accumulation of organic metabolites (iodosalicylates and iodobenzoates) accumulation were observed, along with increased T3 synthesis, with its content in leaves exceeding the level of individual iodosalicylates and iodobenzoates. The content of T3 was not affected by V fertilization. It was concluded that iodosalicylates may participate in the biosynthesis pathway of T3—and probably of other PDTHA compounds.

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Iodine and vanadium are elements that are closely related to organisms in water environments. Iodine and vanadium are known as “beneficial elements” that stimulate the growth and development of higher plants. Iodine is an essential element for the synthesis of the thyroid hormones triiodothyronine and thyroxine in the human body, with vanadium also known to be involved in the synthesis of thyroid hormones. The cooperation of both elements in the human body and in algae presents a question regarding the impact of vanadium interaction on iodine uptake in higher plants. The absorption of iodine from seawater in algae is known to be more efficient in the presence of vanadium, with key role in this process played by the iodoperoxidase enzyme, with vanadium acting as a cofactor. The study of the nature of the absorption of iodine by higher plants, and in particular by crops such as corn, remains insufficiently studied. The aim of this study was to investigate the effect of vanadium on iodine uptake via vanadium-dependent iodoperoxidase (vHPO) activity in sweetcorn plants (Zea mays L. subsp. Mays Saccharata Group) “Złota Karłowa”. The experiment was carried out with organic and inorganic iodine compounds, namely potassium iodide (KI), potassium iodate (KIO3), 5-iodosalicylic acid (5-ISA), and 2-iodobenzoic acid (2-IBeA), each used in a dose of 10 μM. These compounds were applied with and without vanadium in the form of ammonium methavanadate (NH4VO3) at a dose of 0.1 μM. A double control was used, the first without iodine and vanadium and the second with vanadium but without iodine. Root length, root mass, and above-ground weight were significantly higher after iodine and vanadium compared to controls. Plants were collected at the five true leaf stage. vHPO activity level was much higher in the roots than in the leaves, but greater variation in the leaves was observed between treatments in terms of vHPO activity. Vanadium was shown to accumulate in the roots. The use of a relatively low dose of vanadium may have caused changes in the accumulation of this element in the aerial parts of the plant, leaves, and shoots. Fertilization with iodine and vanadium compounds decreased the accumulation of most minerals, macroelements, and microelements compared to controls. The obtained results of iodine accumulation in individual parts after applying iodine and vanadium fertilization testify to the stimulating effect of vanadium on iodine uptake and accumulation.

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.

The process of uptake and translocation of non-organic iodine (I) ions, I– and IO3–, has been relatively well-described in literature. The situation is different for low-molecular-weight organic aromatic I compounds, as data on their uptake or metabolic pathway is only fragmentary. The aim of this study was to determine the process of uptake, transport, and metabolism of I applied to lettuce plants by fertigation as KIO3, KIO3 + salicylic acid (KIO3+SA), and iodosalicylates, 5-iodosalicylic acid (5-ISA) and 3,5-diiodosalicylic acid (3,5-diISA), depending on whether additional fertilization with vanadium (V) was used. Each I compound was applied at a dose of 10 μM, SA at a dose of 10 μM, and V at a dose of 0.1 μM. Three independent 2-year-long experiments were carried out with lettuce; two with pot systems using a peat substrate and mineral soil and one with hydroponic lettuce. The effectiveness of I uptake and translocation from the roots to leaves was as follows: 5-ISA > 3,5-diISA > KIO3. Iodosalicylates, 5-ISA and 3,5-diISA, were naturally synthesized in plants, similarly to other organic iodine metabolites, i.e., iodotyrosine, as well as plant-derived thyroid hormone analogs (PDTHA), triiodothyronine (T3) and thyroxine (T4). T3 and T4 were synthesized in roots with the participation of endogenous and exogenous 5-ISA and 3,5-diISA and then transported to leaves. The level of plant enrichment in I was safe for consumers. Several genes were shown to perform physiological functions, i.e., per64-like, samdmt, msams5, and cipk6.

Iodine (I) and selenium (Se) are essential to human and animal development. There is a worldwide deficit of I and Se in the diet of humans, as well as in animals. It is advisable to enrich plants with these elements to ensure adequate uptake in animals and humans. The aim of this study was to determine the efficacy of the application of I and Se in the cultivation of carrot crops, to better understand the metabolic pathways and processes of I applied through foliar spray. Carrots were fertilized with 4-fold foliar applications of I and Se, which were applied as the liquid fertilizers “I + Se”, “Solo iodine” and “Solo selenium”, all containing an organic stabilizer, in two field trials. Foliar nutrient applications of I and Se were translocated by the plant for storage in the roots. The level of enriched I and Se in the roots was considered safe for the consumer. The Recommended Daily Allowance values for I and Se in the roots of 100 g of fresh carrots are 4.16% and 4.37%, respectively. Furthermore, I and Se accumulated in the roots to a level that was physiologically tolerated by carrot. Biofortification through foliar feeding did not impact negatively on the yield or quality of the carrot crop. Iodides applied via foliar application were the dominant form of I in the plant tissues and were included in the metabolic process of the synthesis of iodosalicylates, iodobenzoates, iodotyrosine (I-Tyr), and plant-derived thyroid hormone analogs. No synergistic or antagonistic interaction between I and Se, with respect to the effectiveness of biofortification in roots, was observed in any treatments. The molar ratio of I:Se in the roots after foliar application of both elements was approximately 1.6:1 and was similar to the control (1.35:1).

A human’s diet should be diverse and rich in vitamins, macro- and microelements essential for the proper functioning of the human body. Globally, a high percentage of the human population suffers from malnutrition, deficiencies of nutrients and vitamins also known as the problem of hidden hunger. This problem it is not only common in poor countries, but also occurs in developed countries. Iodine is a nutrient crucial for the proper functioning of the human and animal body. For plants, it is referred to as a beneficial element or even a microelement. The design of the biofortification experiment was determined on the basis of the interaction of iodine and vanadium (synergistic interaction in marine algae), where vanadium-dependent iodoperoxidase catalyzes apoplastic oxidation of iodine, resulting in high efficiency of iodine uptake and accumulation in brown algae (Laminaria digitate). Three independent experiments (Exp.) were carried out with the foliar application of vanadium (V) and iodine (I) compounds. The main differences between the experiments with the adapted proper corn biofortification method were the different application stage between the individual experiments, the application intervals and the dose of the iodine–vanadium compound. In each experiment, the accumulation of iodine and vanadium in the grain was several times lower than in the leaves. The combination iodine and vanadium significantly increased the accumulation of iodine in the grain in the case of applying V with inorganic iodine compounds, and a decrease in the accumulation of I after applying V with organic iodine compound —especially in Exp. No. 3. In grain, the highest content of I−, IO3− was in combination with the application of 2-iodobenzoic acid (products of its metabolism). In most of the tested combinations, vanadium stimulated the accumulation/synthesis of exogenous/endogenous 5-iodosalicylic acid (5ISA) and 2-iodobenzoic acid (2IBeA), respectively, and decreased the content of 2,3,5-triiodobenzoic acid (2,3,5-triIBeA) in leaves and grains. The tested compounds I and V and the combinations of their application had a diversified effect on the vitamin C content in the grains. Vanadium in the lower dose of 0.1 µM significantly increased the sugar content in the grain.

A two-year greenhouse study was conducted to assess the effects of the application of I (as KIO3), Se (as Na2SeO3), and salicylic acid (SA) in nutrient solutions on the chemical composition of six lettuce cultivars, i.e., two butterhead lettuces (BUTL), “Cud Voorburgu” and “Zimująca”; two iceberg lettuces (ICEL), “Maugli” and “Królowa lata”; and two Lactuca sativa L. var. crispa L. (REDL) cultivars, “Lollorossa” and “Redin”, grown in the NFT (nutrient film technique) system. The treatments were as follows: control, I+Se, I+Se+0.1 mg SA dm−3, I+Se+1.0 mg SA dm−3, and I+Se+10.0 mg SA dm−3. KIO3 was used at a dose of 5 mg I dm−3, while Na2SeO3 was used at 0.5 mg Se dm−3. The application of I+Se was a mild abiotic stress factor for the plants of the ICEL and REDL cultivars. In contrast, I+Se did not have a negative impact on the BUTLcultivars. The application of 1.0 mg SA dm−3 improved the biomass productivity in all cultivars compared with I+Se. In the majority of the cultivars, the applied combinations of I+Se and I+Se+SA resulted in a reduction in the nitrate(V) content that was beneficial to the consumer and increased levels of sugars, phenols, phenylpropanoids, flavonols, and anthocyanins. In addition, an increase in ascorbic acid content was observed, but only in the BUTL cultivars and REDL “Redin”. The application of I, Se, and SA had upward or downward effects on the concentrations of N, K, P, Ca, Mg, S, Na, B, Cu, Fe, Mn, Mo, and Zn in the leaves.