Fate of nascent microtubules organized at the M/G(1) interface, as visualized by synchronized tobacco BY-2 cells stably expressing GFP-tubulin: Time-sequence observations of the reorganization of cortical microtubules in living plant cells

Transgenic (BY) under bar -2 cells stably expressing a (G) under bar FP (gr een fluorescent protein)-(t) under bar ubulin fusion protein (BY-GT16) were subcultured in a modified Linsmaier and Skoog medium. The BY-GT16 cells co uld be synchronized by aphidicolin and the dynamics of their microtubules ( MTs) were monitored by the confocal laser scanning microscopy (CLSM), We ha ve succeeded in investigating the mode of reorganization of cortical MTs at the M/G(1) interface. The cortical MTs were initially organized in the per inuclear regions and then they elongated to reach the cell cortex, forming the bright spots there. Subsequently, the first cortical MTs rapidly elonga ted from the spots and they were oriented parallel to the long axis towards the distal end of the cells. Around the time when the tips of the parallel MTs reached the distal end, the formation of transverse cortical MTs follo wed in the cortex near the division site, as we had previously suggested [H asezawa and Nagata (1991) Bet. Acta 104: 206, Nagata et al, (1994) Planta 1 93: 567], It was confirmed in independent observations that the appearance of the parallel MTs was followed by the appearance of the transverse MTs in each cell. We found that the transverse MTs spread through the whole cell cortex within about 20-30 min, while the parallel MTs disappeared. The sign ificance of these observations on the mode of cortical MT organization is d iscussed.