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.