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; Iwona Kowalska; Kinga Kȩska; Maria Halka; Dariusz Grzebelus; Marlena Grzanka; Łukasz Skoczylas; Joanna Pitala; Aneta Koronowicz; Peter Kováčik

doi:10.3389/fpls.2021.653168

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

Front Plant Sci. 2021 Apr 16:12:653168. doi: 10.3389/fpls.2021.653168. eCollection 2021.

Affiliations

¹ Department of Plant Biology and Biotechnology, Faculty of Biotechnology and Horticulture, University of Agriculture in Krakow, Kraków, Poland.
² Department of Plant Product Technology and Nutrition Hygiene, Faculty of Food Technology, University of Agriculture in Krakow, Kraków, Poland.
³ Laboratory of Mass Spectrometry, Faculty of Biotechnology and Horticulture, University of Agriculture in Krakow, Kraków, Poland.
⁴ Department of Human Nutrition and Dietetics, Faculty of Food Technology, University of Agriculture in Krakow, Kraków, Poland.
⁵ Department of Agrochemistry and Plant Nutrition, Slovak University of Agriculture in Nitra, Nitra, Slovakia.

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.

Keywords: 3; 5-diiodosalicylic acid; 5-iodosalicylic acid; CBL-interacting serine/threonine-protein kinase 6; plant-derived thyroid hormone analogs; vHPO.