Abstract
The mechanism of the gravitropic bending was studied in azuki bean epicotyl. It is well known that orientation of cortical microtubule (cMT) changes during the bending. However, we reported that the change of cMT orientation was not caused by gravity situation, but by bending. In the present study, we analyzed the change of extensibility of epicotyl upon gravi-stimulation. We measured cell wall extensibility in the bending part for gravitropism. The extensibility of the lower side was higher than that of the upper side in epicotyl bending upward. After an epicotyl was fixed to a hard metal rod to prevent bending, gravi-stimulation was applied. It was found that the extensibility of lower part was increased, although bending did not occur. Thus, it is concluded that increase in extensibility of lower part is induced via a process other than cortical microtubules at least in the early step of gravi-response.
