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Abstract Detail

Paleobotanical Section

Klymiuk, Ashley [1], Krings, Michael [2].

Trauma in the fossil record: dictyosporic conidia in an extinct fern may illustrate phenotypic response associated with Nox-dependent ROS production.

Rhizomes of the extinct semi-aquatic fern Dennstaedtiopsis aerenchymata Arnold et Lyman are anatomically preserved within the Princeton Chert locality of British Columbia, Canada. The locality comprises ~49 anastomosing layers of silicified peat interbedded with sub-bituminous coal, and has been K-Ar dated to ~48.7 Ma (Eocene, latest Ypresian to earliest Lutetian). In the course of ongoing paleomycological investigations, we examined several different rhizomes from the informally designated Layer #24. Samples were thin sectioned (100–200 μm) and photomicrographed through a succession of focal planes; composite focal-stacked images were compiled with Helicon Focus v5.3.7. The rhizomes exhibit degradation of the epidermis and cortex, as well as post-mortem penetration by small rootlets or rhizomes of other plants. Fungal hyphae occur throughout all rhizomes; moreover, in two separate rhizomes, two of the penetrating rootlets are circumferentially surrounded by dense assemblages of conspicuous fungal body fossils, which have not been detected elsewhere in D. aerenchymata. These comprise >100 dematiaceous, obovate muriform dictyospores, typically composed of 8–12 cells, which appear inflated, owing to constriction by transverse and longitudinal septa. Mature conidia are 10–15 μm diam, while immature specimens are 3–5 μm and less pigmented. Septation becomes increasingly oblique and more irregular as conidia mature. Conidia are produced basipetally from hyaline or slightly pigmented conidiogenous cells, which are either integrated and micronematous, or percurrent. Basal cells of some mature conidia are widely truncated, probably resultant from schizolytic secession at the septum separating the conidium and conidiogenous cell. Developmental and morphological data suggest affinities within Dothideomycetes (Ascomycota, Pezizomycotina). The exclusive occurrence of the conidia in a discrete zone around small rootlets penetrating the D. aerenchymata rhizomes strongly suggests that the formation of these conidia is linked with the intrusion of extraneous rootlets into the rhizomes. Recent research has shown that mycelial trauma in an extant sordariomycete, Trichoderma atroviride, triggers NADPH oxidase (Nox) production of reactive oxygen species (ROS), and this oxidative stress in turn induces conidiation. It is possible to envision that the intruding rootlets mechanically disrupted the assimilative mycelium of a fungal saprotroph thriving in the degrading D. aerenchymata rhizomes, and that this mycelial trauma triggered conidiation, perhaps via similar mechanisms as described for extant T. atroviride.

Broader Impacts:

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1 - University of Kansas, Ecology & Evolutionary Biology, Haworth Hall, 1200 Sunnyside Ave, Lawrence, KS, 66045, USA
2 - Bayerische Staatssammlung Für Paläontologie Und Ge, Richard-Wagner Strasse 10, Munich, N/A, D-80333, Germany

Princeton Chert

Presentation Type: Oral Paper:Papers for Sections
Session: 16
Location: Melrose/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 10:45 AM
Number: 16010
Abstract ID:315
Candidate for Awards:Isabel Cookson Award

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