MICROTUBULE REORGANIZATION DURING THE CELL-CYCLE IN SYNCHRONIZED BY-2 TOBACCO SUSPENSIONS

Tobacco BY-2 suspension cultures were synchronized with aphidicolin in order to assess the relationship between microtubules (MTs), microfilaments (MFs), and the nuclear envelope (NE) at different stages of the cell cycle. Using immunofluorescence techniques, ordered MT arrays were found in the cortex in G1; few MTs are evident deeper in the cytoplasm or near the nucleus. However, MTs radiate from the surface of the nucleus during S and G2 as the interphase cortical array is replaced by the preprophase band. Perinuclear fluorescence is also visible at the end of cytokinesis but does not overlap with new ordered cortical arrays early in G1. When isolated nuclei are examined, associated MTs are again evident in S and G2, but not in G1. Microfilaments are colocalized with the MTs in the radiating arrays, as ascertained by dual staining of cells with rhodamine phalloidin. Propyzamide treatment leads to the loss of MTs at all stages, while cytoplasmic and perinuclear MF networks persist. Conversely, cytochalasin D disrupts MFs, including those radiating from the nucleus during S and G2, without any apparent effect on MTs. The results cast doubt on a proposed role for the NE in the generation of cortical MTs in plants. A universal role for MFs in the deployment of MTs is also in question.