  Citation: Plachno, B.J.; Kapusta, M.; Stolarczyk, P.; ´ Swi ˛ atek, P. Arabinogalactan Proteins in the Digestive Glands of Dionaea muscipula J.Ellis Traps. Cells 2022, 11, 586. https://doi.org/10.3390/ cells11030586 Academic Editors: Christophe Dunand and Elisabeth Jamet Received: 28 December 2021 Accepted: 6 February 2022 Published: 8 February 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). cells Article Arabinogalactan Proteins in the Digestive Glands of Dionaea muscipula J.Ellis Traps Bartosz J. Plachno 1, * , Malgorzata Kapusta 2 , Piotr Stolarczyk 3 and Piotr ´ Swi ˛ atek 4 1 Department of Plant Cytology and Embryology, Institute of Botany, Faculty of Biology, Jagiellonian University in Kraków, 9 Gronostajowa St., 30-387 Kraków, Poland 2 Department of Plant Cytology and Embryology, Faculty of Biology, University of Gda´ nsk, 59 Wita Stwosza St., 80-308 Gda ´ nsk, Poland; malgorzata.kapusta@ug.edu.pl 3 Department of Botany, Physiology and Plant Protection, Faculty of Biotechnology and Horticulture, University of Agriculture in Kraków, 29 Listopada 54 Ave., 31-425 Kraków, Poland; piotr.stolarczyk@urk.edu.pl 4 Institute of Biology, Biotechnology and Environmental Protection, Faculty of Natural Sciences, University of Silesia in Katowice, 9 Bankowa St., 40-007 Katowice, Poland; piotr.swiatek@us.edu.pl * Correspondence: bartosz.plachno@uj.edu.pl; Tel.: +48-12-664-60-39 Abstract: The arabinogalactan proteins (AGP) play important roles in plant growth and develop- mental processes. However, to the best of our knowledge, there is no information on the spatial distribution of AGP in the plant organs and tissues of carnivorous plants during their carnivorous cycle. The Dionaea muscipula trap forms an “external stomach” and is equipped with an effective digestive-absorbing system. Because its digestive glands are composed of specialized cells, the hypothesis that their cell walls are also very specialized in terms of their composition (AGP) com- pared to the cell wall of the trap epidermal and parenchyma cells was tested. Another aim of this study was to determine whether there is a spatio-temporal distribution of the AGP in the digestive glands during the secretory cycle of D. muscipula. Antibodies that act against AGPs, including JIM8, JIM13 and JIM14, were used. The localization of the examined compounds was determined using immunohistochemistry techniques and immunogold labeling. In both the un-fed and fed traps, there was an accumulation of AGP in the cell walls of the gland secretory cells. The epitope, which is recognized by JIM14, was a useful marker of the digestive glands. The secretory cells of the D. muscipula digestive glands are transfer cells and an accumulation of specific AGP was at the site where the cell wall labyrinth occurred. Immunogold labeling confirmed an occurrence of AGP in the cell wall ingrowths. There were differences in the AGP occurrence (labeled with JIM8 and JIM13) in the cell walls of the gland secretory cells between the unfed and fed traps. Keywords: carnivorous plants; cell wall; Droseraceae; transfer cells; wall labyrinth; wall ingrowths; Venus flytrap 1. Introduction Dionaea muscipula J.Ellis (Venus flytrap) is a carnivorous plant that creates active traps that are modified leaves and that are used to attract, capture and digest invertebrates, mainly insects, but also spiders [1–3]. Dionaea was called the “miraculum naturae” by Linnaeus [2] and ‘the most wonderful plant in the world’ by Charles Darwin [4]. Its traps have very sensitive mechanoreceptors and perform very rapid thigmonastic movements [5,6], which is why it has become one of the most common carnivorous plants and a true icon of carnivory in the plant kingdom (it has been used in pop culture, e.g., in the American drama television series “True Blood” and in the anime television series “Maya the Honey Bee”). Since Charles Darwin’s observations, the Venus flytrap D. muscipula has been a marvelous research model for studying carnivory in plants. Because of the various processes that occur in the traps (reception of the stimuli needed to close the trap, trap movement, electric signal Cells 2022, 11, 586. https://doi.org/10.3390/cells11030586 https://www.mdpi.com/journal/cells