Synchrotron X-rays elucidate the intracellular storage of the iodide and bromide antioxidant system in the kelp Laminaria digitata.

Frithjof C Küpper, Mijovilovich Ana, Peter Cloetens, Peter M H Kroneck, Matthew Newville, Antonio Lanzirotti, Eric P Miller, Martin C Feiters, Wolfram Meyer-Klaucke, Christos Katsaros, Hendrik Küpper, Carl J Carrano

Journal: Journal of the Royal Society, Interface 2026;23(238):

PMID: 42089323

View on PubMed

Abstract

The kelp Laminaria digitata uses iodide as a unique inorganic antioxidant to protect its surface and apoplastic space, with implications for atmospheric and marine chemistry as well as regional climatic processes. However, until now, significant open questions have remained regarding the cellular localization and processes involved. Here, using cutting-edge, synchrotron-based micro-X-ray fluorescence (µXRF) nanoprobe tomography with strontium (II) as a biomarker for algal cell walls, complemented by micro-X-ray absorption near-edge structure (μXANES) and scanning imaging, we unambiguously show that iodide is stored in intracellular vesicles of cortical cells. In contrast, bromide is mostly accumulated in the vacuoles of meristoderm cells. Upon oxidative stress, it is mobilized by a hitherto-uncharacterized anion transporter different from the well-known eukaryotic chloride channels. This study offers the first evidence of tissue localization for the formation of I2 or an organic iodine compound as a minor component in the cortical cell layer, as demonstrated using µXANES.

Address: School of Biological Sciences, University of Aberdeen, AberdeenAB24 3UU, UK.; Department of Chemistry and Biochemistry, San Diego State University, San Diego, CA, USA.; Oceanography Center, University of Cyprus, 1 Panepistimiou Av., 2109 Aglandjia, Nicosia, Cyprus.; Department of Plant Biophysics and Biochemistry, Biology Centre, Czech Academy of Sciences, Institute of Plant Molecular Biology, České Budějovice, Czech Republic.; Experiments Division, ESRF, Grenoble, France.; Department of Biology, University of Konstanz, Konstanz, Germany.; Consortium for Advanced Radiation Sources, University of Chicago, Argonne, IL, USA.; Center for Advanced Radiation Sources, University of Chicago, Chicago, IL, USA.; Department of Chemistry and Biochemistry, San Diego State University, San Diego, CA, USA.; Department of Organic Chemistry, Radboud University Nijmegen, Nijmegen, The Netherlands.; DESY , Hamburg, Germany.; National and Kapodistrian University of Athens , Athens, Attica, Greece.; Department of Plant Biophysics and Biochemistry, Biology Centre, Czech Academy of Sciences, Institute of Plant Molecular Biology, České Budějovice, Czech Republic.; Department of Experimental Plant Biology, Faculty of Science, University of South Bohemia, České Budějovice, Czech Republic.

DOI: 10.1098/rsif.2025.0358

MeSH Terms: Laminaria, Iodides, Antioxidants, Synchrotrons, Bromides, Oxidative Stress, Edible Seaweeds