title: Holoparasitic Rafflesiaceae possess the most reduced endophytes and yet give rise to the world's largest flowers.
abstract: OBJECTIVE
  Species in the holoparasitic plant family Rafflesiaceae exhibit one of the most highly modified vegetative bodies in flowering plants. Apart from the flower shoot and associated bracts, the parasite is a mycelium-like endophyte living inside their grapevine hosts. This study provides a comprehensive treatment of the endophytic vegetative body for all three genera of Rafflesiaceae (Rafflesia, Rhizanthes and Sapria), and reports on the cytology and development of the endophyte, including its structural connection to the host, shedding light on the poorly understood nature of this symbiosis.
  
  
  METHODS
  Serial sectioning and staining with non-specific dyes, periodic-Schiff's reagent and aniline blue were employed in order to characterize the structure of the endophyte across a phylogenetically diverse sampling.
  
  
  RESULTS
  A previously identified difference in the nuclear size between Rafflesiaceae endophytes and their hosts was used to investigate the morphology and development of the endophytic body. The endophytes generally comprise uniseriate filaments oriented radially within the host root. The emergence of the parasite from the host during floral development is arrested in some cases by an apparent host response, but otherwise vegetative growth does not appear to elicit suppression by the host.
  
  
  CONCLUSIONS
  Rafflesiaceae produce greatly reduced and modified vegetative bodies even when compared with the other holoparasitic angiosperms once grouped with Rafflesiaceae, which possess some vegetative differentiation. Based on previous studies of seeds together with these findings, it is concluded that the endophyte probably develops directly from a proembryo, and not from an embryo proper. Similarly, the flowering shoot arises directly from the undifferentiated endophyte. These filaments produce a protocorm in which a shoot apex originates endogenously by formation of a secondary morphological surface. This degree of modification to the vegetative body is exceptional within angiosperms and warrants additional investigation. Furthermore, the study highlights a mechanical isolation mechanism by which the host may defend itself from the parasite.
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University Herbaria, Cambridge, MA 02138, USA.
authors.forename: Lachezar A
authors.initials: LA
authors.lastname: Nikolov
authors.affiliation: The Kampong, National Tropical Botanical Garden, 4013 Douglas Road, Miami, FL 33133, USA.
authors.forename: P B
authors.initials: PB
authors.lastname: Tomlinson
authors.affiliation: Rimba Ilmu Botanic Garden, Institute of Biological Sciences, University of Malaya, 50603 Kuala Lumpur, Malaysia and.
authors.forename: Sugumaran
authors.initials: S
authors.lastname: Manickam
authors.affiliation: Institute of Systematic Botany, University of Zurich, Zollikerstrasse 107, CH-8008 Zurich, Switzerland.
authors.forename: Peter K
authors.initials: PK
authors.lastname: Endress
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University Herbaria, Cambridge, MA 02138, USA.
authors.forename: Elena M
authors.initials: EM
authors.lastname: Kramer
authors.affiliation: Department of Organismic and Evolutionary Biology, Harvard University Herbaria, Cambridge, MA 02138, USA cdavis@oeb.harvard.edu.
authors.forename: Charles C
authors.initials: CC
authors.lastname: Davis
mesh_terms: D060026:Endophytes / Q000166:cytology / Q000502:physiology*; D035264:Flowers / Q000033:anatomy & histology*; D019684:Magnoliopsida / Q000033:anatomy & histology* / Q000382:microbiology*; D018517:Plant Roots / Q000033:anatomy & histology / Q000382:microbiology; D018520:Plant Shoots / Q000382:microbiology
keywords: Comparative morphology; Rafflesia; Rafflesiaceae; Rhizanthes; Sapria; Tetrastigma; endophyte; gigantism; heterochrony; holoparasitism; host–parasite relationship; proembryo