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.