Mechanism of Iodine Uptake by Cabbage: Effects of Iodine Species and Where It is Stored

Abstract

Iodine-enhanced vegetable has been proven to be an effective way to reduce iodine deficiency disorders in many regions. However, the knowledge about what mechanisms control plant uptake of iodine and where iodine is stored in plants is still very limited. A series of controlled experiments, including solution culture, pot planting, and field experiments were carried out to investigate the uptake mechanism of iodine in different forms. A new methodology for observing the iodine distribution within the plant tissues, based on AgI precipitation reaction and transmission electron microscope techniques, has been developed and successfully applied to Chinese cabbage. Results show that iodine uptake by Chinese cabbage was more effective when iodine was in the form of IO(3) (-) than in the form of I(-) if the concentration was low (<0.5 mg L(-1)), but the trend was opposite if iodine concentration was 0.5 mg L(-1) or higher. The uptake was more sensitive to metabolism inhibitor in lower concentration of iodine, which implies that the uptake mechanism transits from active to passive as the iodine concentration increases, especially when the iodine is in the form of IO(3) (-). The inorganic iodine fertilizer provided a quicker supply for plant uptake, but the higher level of iodine was toxic to plant growth. The organic iodine fertilizer (seaweed composite) provided a more sustainable iodine supply for plants. Most of the iodine uptake by the cabbage is intercepted and stored in the fibrins in the root while the iodine that is transported to the above-ground portion (shoots and leaves) is selectively stored in the chloroplasts.

Rice (Oryza sativa L.) roots have iodate reduction activity in response to iodine

“…In soil solutions, the major chemical species of soluble iodine are generally thought to be I − under flooded conditions (Muramatsu et al, 1989; Yuita, 1992) and IO − 3 under non-flooded conditions (Yuita, 1992). At similar concentrations, I − appears to be more phytotoxic than IO − 3 (Umaly and Poel, 1971; Mackowiak and Grossl, 1999; Zhu et al, 2003; Weng et al, 2008a). Böszörményi and Cseh (1960) suggested that IO − 3 is reduced to I − electrochemically before uptake by wheat roots.…”

Use of Iodine to Biofortify and Promote Growth and Stress Tolerance in Crops

“…However, throughout the years it has been shown that this technique alone is insufficient to ensure the total requirement of iodine (de Benoist et al, 2008), partly because the iodine of table salt is unstable and is subject to many losses by volatilization (Mottiar and Altosaar, 2011). In this regard, the consumption of iodine in organic forms such as seaweed and biofortified foods and yeast, is considered more appropriate (Funahashi et al, 2001; Weng et al, 2008a; Kopeć et al, 2015) because those organic sources are more stable than inorganic ones.…”

Metabolic engineering of the iodine content in Arabidopsis

“…Plants can absorb iodine from the soil and it is assumed that in root cells iodine fluxes across membranes through putative H + /halide transporters and anion channels7. However, the molecular identities of such transporters have not yet been established78. Once inside the plant, a xylematic flux of iodine seems to be predominant46910, although a phloematic route for this element has been recently observed in tomato11.…”