New Aspects of Uptake and Metabolism of Non-organic and Organic Iodine Compounds-The Role of Vanadium and Plant-Derived Thyroid Hormone Analogs in Lettuce.

Sylwester Smoleń,Małgorzata Czernicka,Marlena Grzanka,Maria Halka,Peter Kováčik,Aneta Koronowicz,Iwona Kowalska,Dariusz Grzebelus,Kinga Kȩska,Łukasz Skoczylas,Joanna Pitala

doi:10.3389/fpls.2021.653168

Sylwester Smoleń, Małgorzata Czernicka + Show 9 more

Open Access

https://doi.org/10.3389/fpls.2021.653168

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Abstract

The process of uptake and translocation of non-organic iodine (I) ions, I– and IO3–, has been relatively well-described in literature. The situation is different for low-molecular-weight organic aromatic I compounds, as data on their uptake or metabolic pathway is only fragmentary. The aim of this study was to determine the process of uptake, transport, and metabolism of I applied to lettuce plants by fertigation as KIO3, KIO3 + salicylic acid (KIO3+SA), and iodosalicylates, 5-iodosalicylic acid (5-ISA) and 3,5-diiodosalicylic acid (3,5-diISA), depending on whether additional fertilization with vanadium (V) was used. Each I compound was applied at a dose of 10 μM, SA at a dose of 10 μM, and V at a dose of 0.1 μM. Three independent 2-year-long experiments were carried out with lettuce; two with pot systems using a peat substrate and mineral soil and one with hydroponic lettuce. The effectiveness of I uptake and translocation from the roots to leaves was as follows: 5-ISA > 3,5-diISA > KIO3. Iodosalicylates, 5-ISA and 3,5-diISA, were naturally synthesized in plants, similarly to other organic iodine metabolites, i.e., iodotyrosine, as well as plant-derived thyroid hormone analogs (PDTHA), triiodothyronine (T3) and thyroxine (T4). T3 and T4 were synthesized in roots with the participation of endogenous and exogenous 5-ISA and 3,5-diISA and then transported to leaves. The level of plant enrichment in I was safe for consumers. Several genes were shown to perform physiological functions, i.e., per64-like, samdmt, msams5, and cipk6.

Highlights

Iodine in PlantsIodine (I) is a beneficial element for plants and studies have determine the effectiveness of iodide (I−) or iodate (IO3−) uptake by plants through roots or leaves and their potential translocation (Medrano-Macías et al, 2016; Antonyak et al, 2018)
In this experiment, combined fertilization with V and KIO3, KIO3 + salicylic acid (KIO3+salicylic acid (SA)), 5-iodosalicylic acid (5-ISA), and 3,5-diISA had no effect on the weight of roots and heads of lettuce, compared with the application of these compounds without V
Based on the results of a study by Smolenet al. (2017) and the reduced lettuce biomass shown in this study (Experiment 1), we presume that the threshold of transition from harmful to toxic I activity in lettuce is somewhere between the dose of 8.0 μM and 10.0 μM of I applied as 5-ISA

Summary

Introduction

Iodine (I) is a beneficial element for plants and studies have determine the effectiveness of iodide (I−) or iodate (IO3−) uptake by plants through roots or leaves (upon foliar application) and their potential translocation (Medrano-Macías et al, 2016; Antonyak et al, 2018). The effectiveness of I ion accumulation has been determined for a number of species of plants. The majority of the studies have been performed in the context of I biofortification of plants. They were conducted with the aim to prepare an I deficiency prevention program, other than through the consumption of kitchen salt based on plant enrichment with I (White and Broadley, 2009). There was research devoted to the I uptake mechanism (Kato et al, 2013; Humphrey et al, 2019)

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