Iodate and iodide effects on iodine uptake and partitioning in rice (Oryza sativa L.) grown in solution culture

Abstract

In the Xinjiang province of western China, conventional methods of iodine (I) supplementation (i.e, goiter pills and iodinated salt) used to mitigate I deficiencies were ineffectual. However, the recent addition of KIO₃ to irrigation waters has proven effective. This study was conducted to determine the effects of I form and concentration on rice (Oryza sativa L.) growth, I partitioning within the plant, and ultimately to assist in establishing guidelines for incorporating I into the human food chain. We compared IO₃ ⁻ vs. I⁻ in order to determine how these chemical species differ in their biological effects. Rice was grown in 48 L aerated tubs containing nutrient solution and IO₃ ⁻ or I⁻ at 0, 1, 10, or 100 μM concentrations (approximately 0, 0.1, 1, and 10 mg kg⁻¹ I). The IO₃ ⁻ at 1 and 10 μM had no effect on biomass yields, and the 100 μM treatment had a small negative effect. The I⁻ at 10 and 100 μM was detrimental to biomass yields. The IO₃ ⁻ treatments had more I partitioning to the roots (56%) on average than did the I⁻ treatments (36%), suggesting differences in uptake or translocation between I forms. The data support the theory that IO₃ ⁻ is electrochemically or biologically reduced to I⁻ prior to plant uptake. None of the treatments provided sufficient I in the seed to meet human dietary requirements. The I concentration found in straw at 100 μM IO₃ ⁻ was several times greater than seed, and could provide an indirect source of dietary I via livestock feeding on the straw.