Dynamic rearrangements of transvacuolar strands in BY-2 cells imply a role of myosin in remodeling the plant actin cytoskeleton
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Plant cells typically contain a large central vacuole that confines the cytoplasm and organelles to the periphery of the cell and the vicinity of the nucleus. These two domains are often connected by transvacuolar strands (TVS), thin tubular structures that traverse the vacuole. The TVS are thought to act as important transport routes for the distribution of organelles and metabolites, and also to play a role in the positioning of the nucleus. Most TVS depend on internal actin filaments for their existence, and rearrangements of TVS can therefore indicate modifications in the actin cytoskeleton. In this study we describe time-lapse observations of tobacco BY-2 suspension-cultured cells that document the dynamic behavior of TVS. The TVS formed, branched, and collapsed, and their attachment points in the nuclear or cortical cytoplasm, as well as on other TVS, moved around. These dynamic rearrangements were inhibited within 5 min by the myosin inhibitor 2,3-butanedione monoxime (BDM). In particular, the movements of TVS attachment points and the variations in TVS length were significantly reduced in the presence of the drug. Similarly, movements of the nucleus were reduced by two thirds in BDM-treated cells. The number of TVS, together with the number of attachment and branch points, also dropped during BDM treatment. All effects of BDM on TVS dynamics were reversible upon removal of the drug. These results suggest a role for myosin motors in the rearrangement of TVS, which is likely to occur through their interaction with actin filaments.
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Movie S2. Time-lapse movie showing the inhibitory effect of BDM on TVS dynamics. Same cell as in S1. Individual DIC images were captured at 30 s intervals. Time points are shown on the lower left; black numbers indicate regular MS medium, white numbers indicate the presence of 40 mM BDM. File format and size: Quicktime, 1.6 MB.
Movie S4. Time-lapse movie showing the inhibitory effect of BDM on TVS dynamics. Same cell as in S3. Individual DIC images were captured at 30 s intervals. Time points are shown on the lower left; black numbers indicate regular MS medium, white numbers indicate the presence of 40 mM BDM. File format and size: Quicktime, 2 MB.