Improvement in fruit yield and tolerance to salinity of tomato plants fertigated with micronutrient amounts of iodine.

Iodine is an essential micronutrient for humans, but its role in plant physiology was debated for nearly a century. Recently its functional involvement in plant nutrition and stress-protection collected the first experimental evidence. This study wanted to examine in depth the involvement of iodine in tomato plant nutrition, also evaluating its potential on salt stress tolerance. To this end, iodine was administered at dosages effective for micronutrients to plants grown in different experimental systems (growth chamber and greenhouse), alone or in presence of a mild-moderate NaCl-salinity stress. Plant vegetative fitness, fruit yield and quality, biochemical parameters and transcriptional activity of selected stress-responsive genes were evaluated. In unstressed plants, iodine increased plant growth and fruit yield, as well as some fruit qualitative parameters. In presence of salt stress, iodine mitigated some of the negative effects observed, according to the iodine/NaCl concentrations used. Some fruit parameters and the expressions of the stress marker genes analyzed were affected by the treatments, explaining, at least in part, the increased plant tolerance to the salinity. This study thus reconfirms the functional involvement of iodine in plant nutrition and offers evidence towards the use of minute amounts of it as a beneficial nutrient for crop production.

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.

Fate and Bioaccessibility of Iodine in Food Prepared from Agronomically Biofortified Wheat and Rice and Impact of Cofertilization with Zinc and Selenium.

Enrichment of food crops with iodine is an option to alleviate dietary deficiencies. Therefore, foliar iodine fertilizer was applied on wheat and rice, in the presence and absence of the other micronutrients zinc and selenium. This treatment increased the concentration of iodine, as well as zinc and selenium, in the staple grains. Subsequently, potential iodine losses during preparation of foodstuffs with the enriched grains were studied. Oven-heating did not affect the iodine content in bread. Extraction of bran from flour lowered the iodine in white bread compared to wholegrain bread, but it was still markedly higher compared to the control. During subsequent in vitro gastrointestinal digestion, a higher percentage of iodine was released from foods based on extracted flour (82-92%) compared to wholegrain foods (50-76%). The foliar fertilization of wheat was found to be adequate to alleviate iodine deficiency in a population with a moderate to high intake of bread.