title: Anatomically and morphologically unique dark septate endophytic association in the roots of the Mediterranean endemic seagrass Posidonia oceanica.
abstract: Roots of terrestrial plants host a wide spectrum of soil fungi that form various parasitic, neutral and mutualistic associations. A similar trend is evident in freshwater aquatic plants and plants inhabiting salt marshes or mangroves. Marine vascular plants (seagrasses), by contrast, seem to lack specific root-fungus symbioses. We examined roots of two Mediterranean seagrasses, Posidonia oceanica and Cymodocea nodosa, in the northwestern Mediterranean Sea for fungal colonization using light and scanning and transmission electron microscopy. We found that P. oceanica, but not C. nodosa, is regularly associated with melanized septate hyphae in a manner resembling colonization by the ubiquitous dark septate endophytes (DSE) in roots of most terrestrial plants. P. oceanica roots were found to be colonized by sparse dematiaceous running hyphae as well as dense parenchymatous nets/hyphal sheaths on the root surface, intracellular melanized microsclerotia and occasionally also intra- and intercellular hyphae. The colonization was most prominent in the thick-walled hypodermis of the thinnest healthy looking roots, and the mycobiont seemed to colonize both living and dead host cells. Dark septate hyphae infrequently occurred also inside rhizodermal cells, but never colonized vascular tissues. The biological significance of this overlooked marine symbiosis remains unknown, but its morphology, extent, distribution across the NW Mediterranean Sea and absence in C. nodosa indicate an intriguing relationship between the dominant Mediterranean seagrass and its dark septate root mycobionts.
authors.affiliation: Department of Mycorrhizal Symbioses, Institute of Botany ASCR, Průhonice, Czech Republic. vohnik@ibot.cas.cz.|Department of Experimental Plant Biology, Faculty of Science, Charles University in Prague, Prague, Czech Republic. vohnik@ibot.cas.cz.
authors.forename: Martin
authors.initials: M
authors.lastname: Vohník
authors.affiliation: Department of Mycorrhizal Symbioses, Institute of Botany ASCR, Průhonice, Czech Republic.|Department of Experimental Plant Biology, Faculty of Science, Charles University in Prague, Prague, Czech Republic.
authors.forename: Ondřej
authors.initials: O
authors.lastname: Borovec
authors.affiliation: Department of Ecology, Agronomy and Aquaculture, University of Zadar, Zadar, Croatia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Župan
authors.affiliation: Department of Technical and Combat Sports and Martial Arts, Faculty of Physical Education and Sport, Charles University in Prague, Prague, Czech Republic.
authors.forename: David
authors.initials: D
authors.lastname: Vondrášek
authors.affiliation: Department of Zoology and Fisheries, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences, Prague, Czech Republic.
authors.forename: Miloslav
authors.initials: M
authors.lastname: Petrtýl
authors.affiliation: Department of Mycorrhizal Symbioses, Institute of Botany ASCR, Průhonice, Czech Republic.
authors.forename: Radka
authors.initials: R
authors.lastname: Sudová
mesh_terms: D035961:Alismatales / Q000382:microbiology*; D060026:Endophytes / Q000254:growth & development*; D008522:Mediterranean Sea; D046529:Microscopy, Electron, Transmission; D038821:Mycorrhizae / Q000254:growth & development / Q000302:isolation & purification; D018517:Plant Roots / Q000382:microbiology; D013559:Symbiosis
keywords: Cymodocea nodosa; Dark septate endophytes; Marine vascular plants; Mediterranean Sea; Posidonia oceanica; Seagrasses