title: Arabinogalactan protein-rich cell walls, paramural deposits and ergastic globules define the hyaline bodies of rhinanthoid Orobanchaceae haustoria.
abstract: OBJECTIVE
  Parasitic plants obtain nutrients from their hosts through organs called haustoria. The hyaline body is a specialized parenchymatous tissue occupying the central parts of haustoria in many Orobanchaceae species. The structure and functions of hyaline bodies are poorly understood despite their apparent necessity for the proper functioning of haustoria. Reported here is a cell wall-focused immunohistochemical study of the hyaline bodies of three species from the ecologically important clade of rhinanthoid Orobanchaceae.
  
  
  METHODS
  Haustoria collected from laboratory-grown and field-collected plants of Rhinanthus minor, Odontites vernus and Melampyrum pratense attached to various hosts were immunolabelled for cell wall matrix glycans and glycoproteins using specific monoclonal antibodies (mAbs).
  
  
  RESULTS
  Hyaline body cell wall architecture differed from that of the surrounding parenchyma in all species investigated. Enrichment in arabinogalactan protein (AGP) epitopes labelled with mAbs LM2, JIM8, JIM13, JIM14 and CCRC-M7 was prominent and coincided with reduced labelling of de-esterified homogalacturonan with mAbs JIM5, LM18 and LM19. Furthermore, paramural bodies, intercellular deposits and globular ergastic bodies composed of pectins, xyloglucans, extensins and AGPs were common. In Rhinanthus they were particularly abundant in pairings with legume hosts. Hyaline body cells were not in direct contact with haustorial xylem, which was surrounded by a single layer of paratracheal parenchyma with thickened cell walls abutting the xylem.
  
  
  CONCLUSIONS
  The distinctive anatomy and cell wall architecture indicate hyaline body specialization. Altered proportions of AGPs and pectins may affect the mechanical properties of hyaline body cell walls. This and the association with a transfer-like type of paratracheal parenchyma suggest a role in nutrient translocation. Organelle-rich protoplasts and the presence of exceptionally profuse intra- and intercellular wall materials when attached to a nitrogen-fixing host suggest subsequent processing and transient storage of nutrients. AGPs might therefore be implicated in nutrient transfer and metabolism in haustoria.
authors.affiliation: Botany and Plant Science and Ryan Institute for Environmental, Marine and Energy Research, School of Natural Sciences, National University of Ireland Galway, Galway, Ireland Department of Arctic and Marine Biology, Naturfagbygget, The Arctic University of Norway, 9037 Tromsø, Norway pielach.anna@gmail.com.
authors.forename: Anna
authors.initials: A
authors.lastname: Pielach
authors.affiliation: Botany and Plant Science and Ryan Institute for Environmental, Marine and Energy Research, School of Natural Sciences, National University of Ireland Galway, Galway, Ireland Department of Biology, Research Group Pteridology, Ghent University, Ghent, Belgium.
authors.forename: Olivier
authors.initials: O
authors.lastname: Leroux
authors.affiliation: Department of Biology and Skidmore Microscopy Imaging Center, Skidmore College, Saratoga Springs, NY 12866, USA.
authors.forename: David S
authors.initials: DS
authors.lastname: Domozych
authors.affiliation: Centre for Plant Sciences, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, UK.
authors.forename: J Paul
authors.initials: JP
authors.lastname: Knox
authors.affiliation: Botany and Plant Science and Ryan Institute for Environmental, Marine and Energy Research, School of Natural Sciences, National University of Ireland Galway, Galway, Ireland.
authors.forename: Zoë A
authors.initials: ZA
authors.lastname: Popper
mesh_terms: D000911:Antibodies, Monoclonal; D002473:Cell Wall / Q000737:chemistry* / Q000378:metabolism; D000939:Epitopes; D004951:Esterification; D005936:Glucans / Q000276:immunology / Q000378:metabolism; D006023:Glycoproteins / Q000378:metabolism; D007150:Immunohistochemistry; D009088:Mucoproteins / Q000276:immunology / Q000378:metabolism*; D031670:Orobanchaceae / Q000737:chemistry / Q000166:cytology* / Q000378:metabolism; D010368:Pectins / Q000276:immunology / Q000378:metabolism*; D010940:Plant Proteins / Q000276:immunology / Q000378:metabolism; D011134:Polysaccharides / Q000276:immunology / Q000378:metabolism; D014990:Xylans / Q000276:immunology / Q000378:metabolism; D052584:Xylem / Q000737:chemistry / Q000166:cytology / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; D005936:Glucans; D006023:Glycoproteins; D009088:Mucoproteins; D010940:Plant Proteins; D011134:Polysaccharides; D014990:Xylans; C006619:arabinogalactan proteins; C029353:xyloglucan; D010368:Pectins; C003181:polygalacturonic acid
keywords: AGPs; Haustorium; Melampyrum pratense; Odontites vernus; Rhinanthus minor; arabinogalactan proteins; cell wall; globular ergastic body; hemiparasite; hyaline body; immunocytochemistry; paramural body; parasitic plant; rhinanthoid Orobanchaceae