Transcriptomic and metabolic studies on the role of inorganic and organic iodine compounds in lettuce plants.

Iodine (I) is considered a beneficial element or even micronutrient for plants. The aim of this study was to determine the molecular and physiological processes of uptake, transport, and metabolism of I applied to lettuce plants. KIO3, KIO3 + salicylic acid, 5-iodosalicylic acid and 3,5-diiodosalicylic acid were applied. RNA-sequencing was executed using 18 cDNA libraries constructed separately for leaves and roots from KIO3, SA and control plants. De novo transcriptome assembly generated 1937.76 million sequence reads resulting in 27,163 transcripts with N50 of 1638 bp. 329 differentially expressed genes (DEGs) in roots were detected after application of KIO3, out of which 252 genes were up-regulated, and 77 were down-regulated. In leaves, 9 genes revealed differential expression pattern. DEGs analysis indicated its involvement in such metabolic pathways and processes as: chloride transmembrane transport, phenylpropanoid metabolism, positive regulation of defense response and leaf abscission, and also ubiquinone and other terpenoid-quinone biosynthesis, protein processing in endoplasmic reticulum, circadian rhythm including flowering induction as well as a putative PDTHA (i.e. Plant Derived Thyroid Hormone Analogs) metabolic pathway. qRT-PCR of selected genes suggested their participation in the transport and metabolism of iodine compounds, biosynthesis of primary and secondary metabolites, PDTHA pathway and flowering induction.

Iodine biofortification through expression of HMT, SAMT and S3H genes in Solanum lycopersicum L.

The uptake process and physiological reaction of plants to aromatic iodine compounds have not yet been documented. The aim of this research was to compare uptake by tomato plants of KI and KIO3, as well as of organic iodine compounds - 5-ISA (5-iodosalicylic acid), 3,5-diISA (3,5-diiodosalicylic acid), 2-IBeA (2-iodobenzoic acid), 4-IBeA (4-iodobenzoic acid) and 2,3,5-triIBeA (2,3,5-triiodobenzoic acid). Only 2,3,5-triIBeA had a negative influence on plant development. All organic iodine compounds were taken up by roots and transported to leaves and fruits. Among all the compounds applied, the most efficiently transferred iodine was 2-IBeA - to fruits, and 4-IBeA - to leaves. The order of iodine accumulation in fruit cell compartments was as follows: organelles > cell walls > soluble portions of cells; for leaf and root cells, it was: organelles > cell walls or soluble portions, depending on the compound applied. The compounds studied influence iodine metabolism through expression of the HMT gene which encodes halide ion methyltransferase in leaves and roots. Also, their influence on modification of the activity of the SAMT and S3H genes that encode salicylic acid carboxyl methyltransferase and salicylic acid 3-hydroxylase was established. It was discovered that exogenously applied 5-ISA, 3,5-diISA, 2-IBeA and 4-IBeA are genuinely (endogenously) synthesised in tomato plants; to date, this has not been described for the tomato, nor for any other species of higher plant.

Biofortification of Six Varieties of Lettuce (Lactuca sativa L.) With Iodine and Selenium in Combination With the Application of Salicylic Acid.

The agrotechnical methods of biofortification of plants, i.e., enriching them in iodine (I) and selenium (Se) could be effective methods to enrich food products in these elements. The advantage of agrotechnical methods of biofortification is the incorporation of elements in organic compounds in plants; therefore, they have better health-promoting properties than pure technical salts. Two-year studies were conducted in a greenhouse with hydroponic cultivation of three botanical varieties of lettuce in an NFT (nutrient film technique) system: two cultivars butterhead lettuces (abb. BUTL) 'Cud Voorburgu' and 'Zimujaca,' two cultivars iceberg lettuces (abb. ICEL) 'Maugli' and 'Królowa lata' (all this four cultivars are classified as Lactuca sativa L. var. capitata) as well two cultivars Lactuca sativa L. var. crispa L. cultivars (abb. REDL) 'Lollo rossa' and 'Redin' having little red leaves. The study included the application of I (as KIO3), Se (as Na2SeO3), and SA into the nutrient solution. The tested treatments were as follows: (1) control, (2) I+Se, (3) I+Se+0.1 mg SA dm-3, (4) I+Se+1.0 mg SA dm-3, and (5) I+Se+10.0 mg SA dm-3. KIO3 was used at a dose of 5 mg I dm-3, while Na2SeO3 was 0.5 mg Se dm-3. Regardless of the kind of the applied compound, the highest biomass of heads was produced by the REDL 'Redin' variety. Furthermore, this variety, as the only one in six varieties tested, reacted with the decrease in yield to the application of I+Se and I+Se+three concentrations of SA. In the heads of all cultivars, the level of I accumulation was 10-30 times higher than of Se. The level of I accumulation formed the following order: REDL 'Lollo rossa' > REDL 'Redin' = BUTL 'Cud Voorburgu' > BUTL 'Zimujaca' > ICEL 'Maugli' > ICEL 'Królowa lata'. The order of Se content in leaves was as follows: REDL 'Redin' = BUTL 'Cud Voorburgu' > REDL 'Lollo rossa' > ICEL 'Maugli' > BUTL 'Zimujaca' > ICEL 'Królowa lata'. The obtained results indicate that the introduction of SA to the nutrient solutions in hydroponic systems may allow an improve the effectiveness of - biofortification.

Organic iodine supply affects tomato plants differently than inorganic iodine.

Iodine is a beneficial element for humans but very lowly represented in our diet. Iodine-enriched vegetables could boost the iodine content in the food chain. Despite being a beneficial element for plants, little is known about the effect of different iodine forms on plant growth. This work analyses the effect of uptake of mineral (KI) and organoiodine (5-iodosalicylic acid, 5-ISA; 3,5-diiodosalicylic acid, 3,5-di-ISA; 2-iodobenzoic acid, 2-IBeA; 4-iodobenzoic acid, 4-IBeA) compounds on tomato plants at an early stage of vegetative growth. As many organoiodine compounds are derived from salicylic (SA) and benzoic acids (BeA), treatments with I, SA and BeA in various treatments were realized and the influence of tested compounds on plant growth was analyzed. Iodine content was measured, as well as expression of key genes involved in I and SA metabolism. Organoiodine compounds accumulated mainly in roots whereas iodine accumulated in the upper parts when given as KI. The shoot system had 5, 12 and 25 times higher iodine content after KI treatment than after 4-IBeA, 5-ISA and 2-IBeA, or 3,5-diISA treatments, respectively. A toxic effect on plants was observed only for 3,5-diISA and 4-IBeA. The expression levels of a gene related to iodine metabolism (HMT, halide ion methylotransferase), a gene responsible for SA methylation in leaves (SAMT) and a gene related to SA catabolism (S3H, salicylic acid 3-hydroxylase) were modified differently depending on the iodine source. Overall, our data point out to a difference in plant uptake, transport of iodine in tomato plants based on the form of iodine compound.

Iodine and Selenium Biofortification with Additional Application of Salicylic Acid Affects Yield, Selected Molecular Parameters and Chemical Composition of Lettuce Plants (Lactuca sativa L. var. capitata).

Iodine (I) and selenium (Se) are included in the group of beneficial elements. They both play important roles in humans and other animals, particularly in the regulation of thyroid functioning. A substantial percentage of people around the world suffer from health disorders related to the deficiency of these elements in the diet. Salicylic acid (SA) is a compound similar to phytohormones and is known to improve the efficiency of I biofortification of plants. The influence of SA on Se enrichment of plants has not, however, been recognized together with its effect on simultaneous application of I and Se to plants. Two-year studies (2014-2015) were conducted in a greenhouse with hydroponic cultivation of lettuce in an NFT (nutrient film technique) system. They included the application of I (as KIO3), Se (as Na2SeO3) and SA into the nutrient solution. KIO3 was used at a dose of 5 mg I⋅dm-3 (i.e., 39.4 µM I), while Na2SeO3 was 0.5 mg Se⋅dm-3 (i.e., 6.3 µM Se). SA was introduced at three doses: 0.1, 1.0, and 10.0 mg⋅dm-3 nutrient solutions, equivalent to 0.724, 7.24, and 72.4 µM SA, respectively. The tested combinations were as follows: (1) control, (2) I + Se, (3) I + Se + 0.1 mg SA⋅dm-3, (4) I + Se + 1.0 mg SA⋅dm-3 and (5) I + Se + 10.0 mg SA⋅dm-3. The applied treatments had no significant impact on lettuce biomass (leaves and roots). Depending on the dose, a diverse influence of SA was noted with respect to the efficiency of I and Se biofortification; chemical composition of leaves; and mineral nutrition of lettuce plants, including the content of macro- and microelements and selenocysteine methyltransferase (SMT) gene expression. SA application at all tested doses comparably increased the level of selenomethionine (SeMet) and decreased the content of SA in leaves.