Iodine: an emerging biostimulant of growth and stress responses in plants

Background The growth and productivity of plants are largely dependent on the availability of various mineral nutrients, of which some are required at relatively higher concentrations and are termed as macronutrients, while others are required in low amounts and are termed as micronutrients. Both macro- and micro-nutrients are considered as essential elements as their deficiency can result in severe growth defects in plants. Moreover, some of the recent studies have highlighted the role of even non-essential elements in plants. Iodine is one such non-essential element that, at low concentrations, exhibits positive effects on plant growth. Scope In this review, we discuss the effects of iodine on plants including its uptake and transportation, and the current understanding of the pathways responsible for its functioning as a biostimulant. Moreover, we provide evidence that supports the role of iodine as a biostimulant of growth and stress responses in plants. Conclusion Iodine, in the range of 0.20 to 10 µM, has been documented to regulate the (1) expression of various genes, and (2) activity and structure of various proteins by protein iodination to improve biomass production and defense responses in plants. Further, a growing body of evidence also suggests a role of iodine in the maintenance of ROS homeostasis in plants under normal as well as challenging environmental conditions.