Microtubule disassembly enhances reversible cytochalasin-dependent disruption of actin bundles in characean internodes |
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Authors: | I Foissner G O Wasteneys |
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Institution: | 1. Institut für Pflanzenphysiologie, Universit?t Salzburg, Hellbrunnerstrasse 34, A-5020, Salzburg, Austria 2. Plant Cell Biology Group, Research School of Biological Sciences, Australian National University, Canberra
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Abstract: | Summary Parallel bundles of actin filaments at the cortex-endoplasm interface provide tracks for myosin-generated cytoplasmic streaming
in characean internodes. These bundles resist disassembly or structural modification when exposed to 10 μM cytochalasin D
(CD) even though this concentration of CD rapidly (within minutes) but reversibly arrests streaming. Unexpectedly, we discovered
that prolonged treatment with lower concentrations of CD could partially disassemble the subcortical actin bundles. Actin
bundles became discontinuous following one- to several-day treatment with concentrations (6 μM) that reduced but did not arrest
streaming, and the residual fragments mostly remained parallel to the chloroplast files. When microtubules were concurrently
disassembled with tubulin-specific drugs, however, low CD concentrations (2.5–3 μM) completely arrested bulk streaming, disrupted
the largely 2-dimensional actin bundle array and caused the formation of a coarse, thick-meshed actin network that extended
from the cortex to the endoplasm. Despite such massive reconstruction, drug removal enabled cells to recover continuous parallel
bundles and streaming. Recovery was possible if both or just one of the drugs were removed. In recovered cells, the streaming
pattern frequently redeveloped in new directions that did not follow the chloroplast files, and later, chloroplast files readjusted
to the new polarity established by the actin bundles. This first report on the complete and reversible disassembly of characean
actin bundles provides new insights into the mechanism of actin bundle assembly and organization and supports the idea of
indirect interactions between actin filaments and microtubules. |
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Keywords: | Actin bundles Actin-microtubule interactions Characeae Cytochalasin D Microtubule depolymerization |
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