Taylor, Thomas N. , Krings, Michael , Kerp, Hans , Hass, Hagen , Dotzler, Nora .
Land plant/cyanobacterial associations in the Early Devonian Rhynie chert.
ASSOCIATIONS of cyanobacteria with land plants are relatively restricted today, but occur in most major lineages of plants. In most of these symbioses, the primary benefit to the plant is fixed nitrogen originating from N2-fixation of the cyanobacteri; the cyanobacterium gains access to a stable environment and a wider nutrient source available from the host. Although the fossil record of cyanobacteria is extensive, associations with land plants are practically absent. As a result, the origin and evolution of land plant/cyanobacterial associations remains unknown. The Early Devonian Rhynie chert, an in situ silicified hot springs dominated by ephemeral fresh water pools, hosts a diverse assemblage of exquisitely preserved land plants, animals, algae, and various microorganisms. Recent studies have shown that the Rhynie chert land plant Aglaophyton major is variously associated with filamentous cyanobacteria. Aggregaions of cyanobacterial filaments are present on the surface of A. major axes, especially in areas where the axes that show tissue disruption and may have exuded some kind of wound secretion. Other filamentous cyanobacteria occupy spaces in the walls of partially degraded sporangia. Still others live as endophytes in the prostrate mycorrhizal axes of A. major. These cyanobacteria enter the axes through the stomatal pores and initially colonize the substomatal chambers. They colonize the axes through the outer cortical tissues and mycorrhizal arbuscule-zone by growing through the intercellular system. Near the arbuscule-zone, some filaments penetrate cortical cells, and appear to represent intracellular endophytes. Within cortical cells, the filaments form characteristic coils. This association represents the earliest fossil evidence of endophytic cyanobacteria in land plants. Although we are uncertain as to the role of the cyanobacteria in this symbiosis, it is hypothesized that they provided some benefit to the plant, perhaps regarding nitrogen fixation. A second hypothesis views the cyanobacteria as aiding in the establishment of the mycorrhiza.
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1 - University of Kansas, Department of Ecology & Evolutionary Biology, Natural History Museum and Biodiversity Research Center, 1200 Sunnyside Avenue, Lawrence, Kansas, 66045-7534, USA
2 - Bayerische Staatssammlung Für Paläontologie und Geologie, Richard-Wagner Strasse 10, Munich, D-80333, Germany
3 - Westfälische Wilhelms-Universität Münster, Forschungsstelle für Paläobotanik, Hindenburgplatz 57, Münster, D-48143, Germany
4 - Bayerische Staatssammlung Für Paläontologie und Geologie, Richard-Wagner Strasse 10, Munich, 80333, Germany
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 31st, 2006
Time: 8:45 AM