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- All Subjects: Plant Biology
- Creators: Farmer, Jack
Description
Some cyanobacteria, referred to as boring or euendolithic, are capable of excavating tunnels into calcareous substrates, both mineral and biogenic. The erosive activity of these cyanobacteria results in the destruction of coastal limestones and dead corals, the reworking of carbonate sands, and the cementation of microbialites. They thus link the biological and mineral parts of the global carbon cycle directly. They are also relevant for marine aquaculture as pests of mollusk populations. In spite of their importance, the mechanism by which these cyanobacteria bore remains unknown. In fact, boring by phototrophs is geochemically paradoxical, in that they should promote precipitation of carbonates, not dissolution. To approach this paradox experimentally, I developed an empirical model based on a newly isolated euendolith, which I characterized physiologically, ultrastructurally and phylogenetically (Mastigocoleus testarum BC008); it bores on pure calcite in the laboratory under controlled conditions. Mechanistic hypotheses suggesting the aid of accompanying heterotrophic bacteria, or the spatial/temporal separation of photosynthesis and boring could be readily rejected. Real-time Ca2+ mapping by laser scanning confocal microscopy of boring BC008 cells showed that boring resulted in undersaturation at the boring front and supersaturation in and around boreholes. This is consistent with a process of uptake of Ca2+ from the boring front, trans-cellular mobilization, and extrusion at the distal end of the filaments (borehole entrance). Ca2+ disequilibrium could be inhibited by ceasing illumination, preventing ATP generation, and, more specifically, by blocking P-type Ca2+ ATPase transporters. This demonstrates that BC008 bores by promoting calcite dissolution locally at the boring front through Ca2+ uptake, an unprecedented capacity among living organisms. Parallel studies using mixed microbial assemblages of euendoliths boring into Caribbean, Mediterranean, North and South Pacific marine carbonates, demonstrate that the mechanism operating in BC008 is widespread, but perhaps not universal.
ContributorsRamírez-Reinat, Edgardo L (Author) / Garcia-Pichel, Ferran (Thesis advisor) / Chandler, Douglas (Committee member) / Farmer, Jack (Committee member) / Neuer, Susanne (Committee member) / Arizona State University (Publisher)
Created2010
Description
The Juglandaceae (walnuts, hickories, pecans) has one of the best-documented fossil records in the Northern Hemisphere. The oldest modern genus, Cyclocarya, today restricted to China, first appears in the late Paleocene (57 ma) of North Dakota, USA. Unlike walnuts and pecans that produce edible fruits dispersed by mammals, Cyclocarya fruits are small nutlets surrounded by a prominent circular wing, and are thought to be wind- or water-dispersed. The current study provides the first evidence that fossil fruits were different from modern forms in the number and organization of their attachment to reproductive branches, and in their anatomical structure. Unlike the modern genus that bears separate pistillate and staminate flowers the fossil fruits had attached pollen-bearing structures. Unisexual pollen catkins are also present, suggesting the fossil Cyclocarya may have differed from its modern relative in this feature. Like several other plants from the late Paleocene Almont/Beicegel Creek floras, Cyclocarya shows a mosaic combination of characters not seen in their modern counterparts. Fossils were collected from the field, and examined for specimens exposed on the weathered rock surface. Specimens from Almont were photographed with reflected light, while those from Beicegel Creek cut into slabs and prepared by etching the rock matrix in 49% hydrofluoric and re-embedding the exposed plant material in cellulose acetate and acetone to make "peels". Selected specimens are cut out, mounted on microscope slides, and studied with light microscopy. These fossil fruits were studied because they are the earliest fossil evidence of Cyclocarya. They are exceptionally preserved and thus provide critical structural evidence for changes in that occurred during the evolution of plants within this lineage. Because Cyclocarya fruits are winged, they might be assumed to be wind-dispersed. Their radial symmetry does not have the aerodynamic qualities typical of wind-dispersed fruits, and may have been dispersed by water.
ContributorsTaylor, Malcom DeWitt (Author) / Pigg, Kathleen B (Thesis advisor) / Wojciechowski, Martin F (Committee member) / Devore, Melanie L (Committee member) / Farmer, Jack (Committee member) / Gill, Anthony (Committee member) / Arizona State University (Publisher)
Created2010