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Abstract Coccolithophores fix organic carbon and produce calcite plates (coccoliths) that ballast organic matter and facilitate carbon export. Photosynthesis consumes carbon dioxide, while calcification produces it, raising questions about whether coccolithophores are a net sink or source of carbon. We characterized the physiology of calcified and noncalcified (“naked”) phenotypes ofEmiliania huxleyi(CCMP374) and investigated the relationship between calcification and photosynthesis across a gradient of light (25–2000 μmol photons m−2 s−1) spanning the euphotic zone. Growth and photophysiological parameters increased with light until reaching a mid‐light (150 μmol photons m−2 s−1) maximum for both phenotypes. Calcified cells were characterized by enhanced photophysiology and less photoinhibition. Further, enhanced bicarbonate transport in calcified cells led to higher rates of particulate organic carbon fixation and growth compared to naked cells at mid‐light to high light (150–2000 μmol photons m−2 s−1). Coccolith production was similarly high at mid and high light, but the rate of coccolith shedding was >3‐fold lower at high‐light (1.2 vs. 0.35 coccoliths cell−1 h−1). The cellular mechanims(s) of this differential shedding remain unknown and underly light‐related controls on coccosphere maintenance. Our data suggest coccoliths shade cells at high light and that enhanced bicarbonate transport associated with calcification increases internal carbon supplies available for organic carbon fixation.
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The Effect of cytoskeleton inhibitors on coccolith morphology in Coccolithus braarudii and Scyphosphaera apsteinii
The calcite platelets of coccolithophores (Haptophyta), the coccoliths, are among the most elaborate biomineral structures. How these unicellular algae accomplish the complex morphogenesis of coccoliths is still largely unknown. It has long been proposed that the cytoskeleton plays a central role in shaping the growing coccoliths. Previous studies have indicated that disruption of the microtubule network led to defects in coccolith morphogenesis inEmiliania huxleyiandCoccolithus braarudii. Disruption of the actin network also led to defects in coccolith morphology inE. huxleyi, but its impact on coccolith morphology inC. braarudiiwas unclear, as coccolith secretion was largely inhibited under the conditions used. A more detailed examination of the role of actin and microtubule networks is therefore required to address the wider role of the cytoskeleton in coccolith morphogenesis. In this study, we have examined coccolith morphology inC. braarudiiandScyphosphaera apsteiniifollowing treatment with the microtubule inhibitors vinblastine and colchicine (S. apsteiniionly) and the actin inhibitor cytochalasin B. We found that all cytoskeleton inhibitors induced coccolith malformations, strongly suggesting that both microtubules and actin filaments are instrumental in morphogenesis. By demonstrating the requirement for the microtubule and actin networks in coccolith morphogenesis in diverse species, our results suggest that both of these cytoskeletal elements are likely to play conserved roles in defining coccolith morphology.
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- Award ID(s):
- 1638838
- PAR ID:
- 10387565
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Phycology
- Volume:
- 59
- Issue:
- 1
- ISSN:
- 0022-3646
- Page Range / eLocation ID:
- p. 87-96
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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