Abstract
In green plant cells, microtubules run along the plasma membrane to form an interphase cortical array. To address mechanism of cortical microtubule formation, we analyzed assembly of microtubules on isolated plasma membrane ghosts in vitro. When cytoplasmic extract with rhodamine-tubulin was added onto the ghosts isolated from protoplasts of tobacco BY-2 cells, newly assembled microtubules were detected on ghosts. Upon the addition of cytoplasmic extract, the number of γ-tubulin spots on the cortical microtubules greatly increased and microtubules elongated from the spots. Antibodies against γ-tubulin inhibited the microtubule formation. The formation was also inhibited by removal of cortical microtubules before addition of the extract. We hypothesize that cytoplasmic γ-tubulin binds onto cortical microtubules, and new cortical microtubules initiate from γ-tubulin on the microtubules in vivo. To examine the hypothesis, analyses of microtubule organization in γ-tubulin silenced Nicotiana benthamiana are in progress.
