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A, B
The ultrastructure of cytokinetic defects was analyzed by transmission electron microscopy of 5‐day‐old root tip meristems. Images shown are from three roots (wild type) and seven roots (pi4kβ1 pi4kβ2 double mutant). In wild‐type controls (A), vesicles fused at the cell division plane to give rise to the tubular network (TN) of a nascent cell plate. White arrowheads, fused vesicles at the division plane. n = 8 cells. In the pi4kβ1 pi4kβ2 double mutant (B), vesicles were delivered to the cell division plane at a similar stage as wild type but did not fuse. The nuclei of both wild‐type and double mutant cells were at telophase or interphase, as judged by the presence of decondensed chromatin and a nuclear envelope. At this stage, failed cell plate formation was never seen in wild type (A). Black arrowheads, unfused vesicles. n = 6 cells.
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C
Unfused vesicles clustered around a cell wall stub (arrow). White arrowheads, light vesicles; black arrowheads, dark vesicles; black arrow, cell wall stub. n = 8 cells.
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D
No cross‐wall was seen in this cell with two nuclei. n = 6 cells.
Data information: Insets, overviews; dashed boxes, areas of magnification. n, nucleus; ne, nuclear envelope. Scale bars in magnified figures, 2 μm; in insets, 1 μm.
