Graham, Linda , Trest, Marie , Cook, Martha , Taylor, Wilson , Lewis, Louise , Wellman, Charles .
Acetolysis as a screen for degradation-resistant algal and fungal structures.
The fossil remains of early land plants often occur as degradation-resistant bits and pieces, and acetolysis of modern bryophytes has revealed the occurrence of chemically-resistant cells and tissues that can be compared with such microfossils. Past studies demonstrated that acetolysis generates remains consistent with those obtained by decay experiments, and that acetolysis does not generate artifactual remains by polymerizing lipids.We investigated the possibility that acetolysis can likewise be applied to modern fungi and algae with the goal of identifying structures that can be compared to enigmatic remains in the fossil record, to test hypotheses of microfossil identity. Acetolysis was accomplished by standard procedures that include boiling organic samples in a mixture of acetic anhydride and concentrated sulfuric acid for at least half an hour. Acid- and water-washed remains were evaluated with the use of bright-field and fluorescence microscopy, crossed-polarizers, and SEM, plus TEM in selected cases. We investigated the acetolysis-resistance of: 1) diverse representatives of modern fungi, 2) modern cladophoraleans and xanthophyceans, 3) diverse cyanobacterial structural types, and 4) communities of algae cultured from sediments collected from the littoral of water bodies located in extreme terrestrial environments. Results from the fungal survey include observations that the branched, non-septate hyphae of glomaleans stain densely at the TEM level and were acetolysis-resistant, an observation having implications for concepts of land colonization by plants and the interpretation of certain macrofossils as well as microfossils. Zygosporangia and sporangiospores of Mucor bacilliformis survived acetolysis. The large sporangiophores of Phycomyces survived as tubes of varying diameter (some containing hyphal material), and sporangiospore walls (sometimes within intact sporangia at the tips) and hyphae were also observed among remains of this genus. Other resistant fungal structures included conidiophores, phialides (conidiogenous cells), conidia, and cleistothecial walls of Eurotium (=Aspergillis) chevalieri. Dense-walled septate hyphae, typical flask-shaped perithecia, ascospores,and ascus walls of Sordaria fimicola survived. Fungal remains consistently appeared golden to deep brown in bright field view. Acetolysis results from cladophoraleans and xanthophyceans allow inferences to be made regarding certain fossils whose classifications have been controversial. Acetolysis results were also used to evaluate the impact of environmental conditions and cell wall chemistry on degradation resistance by freshwater green algae such as Oedogonium and Closterium for which paleoanalogs (Paleooedogonium and Paleoclosterium) are known from the fossil record. A database of images representing such acetolysis remains is proposed to aid the interpretation of ancient microfossils.
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1 - University Of Wisconsin, Botany Dept, 211 Birge Hall, 430 Lincoln Drive, Madison, WI, 53706, USA
2 - University of Wisconsin, Botany, 430 Lincoln Drive, Madison, WI, 53706, USA
3 - Illinois State University, Department Of Biological Sciences, CAMPUS BOX 4120, NORMAL, IL, 61790-4120, USA
4 - UNIVERSITY OF WISCONSIN - EAU CLAIRE, DEPT OF BIOLOGY-PHILLIPS HALL, 105 Garfield Avenue, P.O. Box 4004, EAU CLAIRE, WI, 54702-4004, USA
5 - University Of Connecticut, Department Of Ecology & Evolutionary Biology, 75 North Eagleville Rd, Unit 43, Storrs, CT, 06269-3043, USA
6 - Sheffield University, Department of Animal and Plant Sciences, Sheffield, S10 2TN, UK
Presentation Type: Oral Paper:Papers for Sections
Location: Union A/Hyatt
Date: Wednesday, July 11th, 2012
Time: 1:30 PM